# EQ'ing my new IB



## PeteD (Sep 9, 2006)

First post here, but have been lurking for some time. Great forum!

I have played with REW with some manual imported readings and I greatly enjoy the interactive adjustments that can be made to the response curves. Truly a fun and useful program.

Anyway, my BFD should arrive tomorrow. I am not configured to use REW to test my response, yet, but I am going to do some manual measurements and generate some filters to enter manually (for fun and to get my IB to a listenable state), while I finish acquiring the components (sound card, cables, etc.) and climb the learning curve of the program. Anyway, it sounds like manual entry will be with me for the foreseeable future because of the Midi issue with the new BFDs. I am sure there will be many more along the way, but my first questions relate to the general procedure for sub EQ'ing. Let me know if I have the general procedure right.

1. Measure response with BFD in chain (necessary?) and the subwoofer plugged in, other speakers not. During this, the anticiapted bass management settings for the receiver will be active. i.e. I will have my crossover for the mains set at 80Hz and my crossover for my surrounds set at 100 Hz. I assume this will limit the amount of EQ I will generated above my crossover, if it is not engaged during sub testing.
2 Correct my measurements with the .cal file provided on this site for my SPL meter (4050).
3. Import my corrected data into REW, checking off that I used "C weighting", which I did.
4 Set up REW as indicated in the help file, including loading my desired house curve and selecting the BFD as my EQ.
5. Find peaks and then manually tweak and adjust these peaks (I have done this already with preliminary measurements).
6. Enter the filters into my BFD.
7. Measure the response again, with only the sub active still (?). If looks good, continue on. If not, adjust filters in REW again.
8. Plug in one (both?) of front mains and measure response of main and sub together. Adjust filters, as necessary to correct peak or dip at crossover (maybe adjust crossover frequency?) Use readings to adjust SPL of sub and main speaker to achieve similar response, generating smooth curve across frequency plot.

Any corrections or tips on things I may be missing would be greatly appreciated. Of course, I will post curves as I generate and tweak them.

Link for my IB project, if interested:
http://tinyurl.com/yd4fzd
I have already used the REW to generate filters (all cuts) that really helped my curve. Hopefully they will translate to reality. I will be performing 1 Hz measurements from 10 through 100 at least to tweak my response better than 1/6 octave. Painful, yes. Worth it, I hope so!

Thanks,
Pete


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## brucek (Apr 11, 2006)

> 1. Measure response with BFD in chain (necessary?) and the subwoofer plugged in, other speakers not. During this, the anticiapted bass management settings for the receiver will be active. i.e. I will have my crossover for the mains set at 80Hz and my crossover for my surrounds set at 100 Hz. I assume this will limit the amount of EQ I will generated above my crossover, if it is not engaged during sub testing.


You don't really need the BFD in the chain, but why not have it there. Simply select the bypass mode. Since you're doing this manually it would be nice not to disturb your receiver/sub levels before and after filter entry, so you can do a proper comparison on the effectiveness of the filters with a before and after plot. That would be hard to do without the BFD in the chain.
The surrounds have no effect here. We equalize the sub first, and then add the mains only in stereo mode to check the crossover interaction.



> 8. Plug in one (both?) of front mains and measure response of main and sub together. Adjust filters, as necessary to correct peak or dip at crossover (maybe adjust crossover frequency?) Use readings to adjust SPL of sub and main speaker to achieve similar response, generating smooth curve across frequency plot.


I would use both mains, some use one. Feed the receiver from REW with a Y-splitter to the AUX or CD input and you'll have both mains.
The crossover is usually determined by the quality of the mains (usually 80Hz). They've got to be really good to select 60Hz...



> I will be performing 1 Hz measurements from 10 through 100 at least to tweak my response better than 1/6 octave. Painful, yes.


I did it for years. Not so bad. But once you see it all take place in a matter of seconds when you get REW finally working, it will make you weep... :duh: 

brucek


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## PeteD (Sep 9, 2006)

brucek said:


> The surrounds have no effect here. We equalize the sub first, and then add the mains only in stereo mode to check the crossover interactionbrucek


Should I send full signal to the sub during initial calibration measurements? i.e. If I use cross over at 80Hz, will I trim some potential LFE response. I saw in the BFD guide Sonnie talking about LFE having 120Hz content.

Thanks for the feedback,
Pete


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## brucek (Apr 11, 2006)

> Should I send full signal to the sub during initial calibration measurements?


No, just set and use the crossover you'll normally use and then equalize.

Yeah, the LFE does indeed extend out to 120Hz in the Dolby spec, but my understanding is that the sound engineers roll that off themselves to integrate it more smoothly into the standard 80Hz LPF (low pass filter) crossover provided by all home processors. The actual spec'd information when given to the sound engineer goes all the way to 120Hz and then is digitally cut off. This would be horrible to listen to if sent to a sub, so I guess it's their creativity to roll it off (and a smart move).

Since the 'small setting' redirected bass is normally rolled off from 80Hz (when that's the crossover you choose) at 24dB per octave, I suspect that the LFE channel is given similar roll off characteristics. At 24dB per octave, the amount of signal left at 120hZ is very, very weak. (see the graph above of the perfect sub).

Myself, I wouldn't be concerned about any differences in setup because of the LFE channel.

brucek


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## PeteD (Sep 9, 2006)

If my mains are crossed over at 80Hz and my other surrounds are crossed at 100Hz, what should I use for my "cutoff" in REW?

I did some quick and dirty EQ with my BFD using some old full scale measurements (no crossover) to get the feel of using it and got some pretty good results for my first attempt.


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## brucek (Apr 11, 2006)

> If my mains are crossed over at 80Hz and my other surrounds are crossed at 100Hz, what should I use for my "cutoff" in REW?


Yeah, that's a good question. I would use the mains crossover of 80Hz, since you'll be in the stereo mode when you equalize. I don't really know any other way to do it.

I've thought about this myself, since I have my mains and surrounds crossed at 60Hz and my center and rear back crossed at 80Hz. 

I use an REW target of 60Hz since I equalize with my processor in stereo mode, that's the crossover used for that mode with the two mains. But once I have filtered with my sub only and then added my mains to check the interaction, I also turn on 6 channel stereo to see how it looks with the mixed crossovers. Seems fine....

brucek


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## PeteD (Sep 9, 2006)

I have noticed that the plot of my manually measured data looks different than in the Excel sheet when imported into REW, with C-weighting checked as "Yes". My imported values have already been corrected, but are higher when imported into REW. Is this because of the "C" weighting?

My curve slopes off in the Excel spreadsheet, but looks more level in REW. Is REW more accurate for some reason beyond the SPL meter correction factors? Do the SPL correction factors in the Excel sheet take the "C" weighting into account?

Here is my plot in Excel:









Here are these very same numbers from Excel plotted in REW versus my house curve:









Obviously, things look better in REW, which makes sense, since I created the filters in REW. Why the difference? Am I doing something wrong?

How does my curve look for sub only? I plan to tweak 25 Hz up a few dB...


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## brucek (Apr 11, 2006)

> I have noticed that the plot of my manually measured data looks different than in the Excel sheet when imported into REW


Yes, because if you're importing Radio Shack meter readings that you have already compensated for in the Excel chart and then subsequently apply C-Weighting in REW, the results will be incorrect.
Say no to C-weighting when you import Excel compensated readings. In fact that's the only way to do it, because if you had imported raw RS meter readings, C-Weight in REW wouldn't have been accurate because REW doesn't apply the calibration data.



> Why the difference? Am I doing something wrong?


The main reason is writen above, but also notice that you have altered the vertical axis of the Excel graph. It should be from 45dB to 105dB to match REW. Also in the horizontal axis of REW you're using 15Hz to 200Hz, where the Excel graph is from 10Hz to 160Hz. You're comparing apples and oranges.

Make the change to the C-weight problem and make your graph axis the same and your graphs will be identical.



> How does my curve look for sub only?


Perfect. You're done. 

brucek


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## PeteD (Sep 9, 2006)

OK, good point about the aixs. That does exaggerate things. The different actual values is what really threw me off. Plus the values were not off by the SPL correction values, so I figured something else was going on.

I will redo my filters, not applying C-weighting on import, because I have double corrected my values to generate my filters.

So, in the future, if collecting real time readings through REW, I must use the correct cal file for my SPL meter - so that REW corrects them properly?

I will post updated graphs after I redo my filters with the correct data.

Thanks!
Pete


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## brucek (Apr 11, 2006)

> So, in the future, if collecting real time readings through REW, I must use the correct cal file for my SPL meter - so that REW corrects them properly?


Yeah, when using REW to take a measurement, you need the correct calibration file installed and you also need the C-weight box checked to take care of any compensation that is outside the area covered by the calibration file (i.e. above 100Hz). The calibration files only go to about 100Hz, since after that the RS meters are fairly close to the C-Weight standard.

brucek


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## PeteD (Sep 9, 2006)

OK. I have almost EQ'd my sub to my mains. However, my amp is maxed out and my BFD lights up the red lights up sporadically (input level) at a reasonable loud listening volume for me on "Darla Taps the Glass". I will usually listen at lower levels, but I would like to be able to crank it up to this level or a little higher every once in a while. I could use a just a few more dBs for my sub level, but I don't want to clip the BFD. My receiver sub output level is at "0" on a -10 to 10 scale.

If I switch the level on the BFD from -10 to +4, does that give me a little more headroom? Or am I not thinking straight?

I am some very large cuts in the upper frequencies because of the large hump in my un EQ'd IB response. Maybe this is why I need more juice compared to people with standard subs?

Thanks,
Pete


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## Wayne A. Pflughaupt (Apr 13, 2006)

> If I switch the level on the BFD from -10 to +4, does that give me a little more headroom? Or am I not thinking straight?


No, that’s going to make the clipping worse. The best thing to do is just reduce the sub output at the receiver.

Regards,
Wayne


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## PeteD (Sep 9, 2006)

Really? Isn't it the output level.

My amp is not clipping at all, it is just turned all the way up. I think I worded my last post in a confusing manner, leading you to think my amp was clipping. Of course, I am assuming that the operating level on the BFD has nothing to do with the clipping of the BFD based on the input level.

I really need more sub output, but if I do it at the receiver, then my BFD will clip. I think this is an IB thing...

Thanks for the feedback Wayne.

Pete


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## Wayne A. Pflughaupt (Apr 13, 2006)

No, I’m pretty sure I understood – the BFD is clipping (red lights).

I did overlook that your amp is maxed out, so I understand the problem. I guess you’ll just have to live with the BFD hitting red. 

Regards,
Wayne


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## brucek (Apr 11, 2006)

> If I switch the level on the BFD from -10 to +4, does that give me a little more headroom?


Well, it certainly will allow you more headroom in the BFD, because it changes the operating level to +4dBu. Will you be able to supply a strong enough signal in this mode though?

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

> Well, it certainly will allow you more headroom in the BFD, because it changes the operating level to +4dBu. Will you be able to supply a strong enough signal in this mode though?


Ouch – got that backwards, didn’t I? :duh: 

I had the same problem, the meters hitting red to often so I switched to the + 4 setting, and haven’t had any problems getting good readings. If the sub level is set to 0 on a –10 to +10 scale, there shouldn’t be any problem getting the level up enough, especially if it’s too hot now with the –10 setting.

Regards,
Wayne A. Pflughaupt


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## PeteD (Sep 9, 2006)

brucek said:


> Well, it certainly will allow you more headroom in the BFD, because it changes the operating level to +4dBu. Will you be able to supply a strong enough signal in this mode though?


I am not sure. Obviously, I have up to +10dB of range on my sub out. Also, I could dial the mains and other speakers back by up to 10dB. This would result in a signal up to 20dB stronger at a given volume.

I have a concern with this. What happens when listening at quiet SPLs. Do you lose bass entirely if the bass content is low level? I don't think this makes sense at all. It must an issue of whether my receiver can kick out the higher line level signal during heavy bass scenes, right? I have an H/K AVR235. My loud listening level for me is -20dB on a -80 to 10dB scale. H/K's tend to have decent power supplies, so I suspect it is up to the task...

Any concern with standard guitar cable style interconnects at this higher operating level?

I suppose a level shifter for after the BFD is another option?

I guess I will have to do some testing...

Thanks,
Pete


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## brucek (Apr 11, 2006)

The operating level switches are there to match the BFD to either consumer or Pro equipment. These two equipment types tend to output (and receive) levels within a defined range.

If you discover that your receiver outputs levels that exceed the standard -10dBV operating range on the BFD, and as a result causes consistent clipping, then you have a couple options.

Option 1: Reduce the receiver subwoofer output level trim until the BFD doesn't clip (at the loudest listening levels). Then adjust the subwoofer amplifier level until it matches your other speakers. If the sub amp isn't receiving enough level (a possibility with a Pro amp), then you would need to boost the signal with a level shifter or line amp.

Option 2: Change the operating range of the BFD to +4dBu. This is a fair jump in level. The maximum input level in the -10dBV range is +2dBV (1.25vRMS), while the maximum input level in the +4dBu range is +16dBu (4.89vRMS). 
If the input level from the receiver supports this higher range by its ability to supply signals near maximum, then a reduction in the gain of the subwoofer amplifier brings the balance between the sub and mains output SPL levels back into check. 
But, if the receiver only marginally provides an output that exceeds the -10dBV levels, then the resolution and overall signal to noise level will suffer. You want to take advantage of as many bits as possible. The bit resolution defines the dynamic range of the system and so the signal to noise ratio is maximized by using as much of the dynamic range as possible. If the range from your weakest signal to the strongest signal was only half the required maximum input level, you would be robbing yourself of dynamic range and subsequently decreasing (worsening) your signal to noise level. You may in fact find this acceptable though. Anyone who uses gain in a BFD filter already accepts the results of this loss of dynamic range and S/N decrease. Filters with gain are directly subtracted from the dynamic range and S/N ratio. You can be the judge whether it affects the overall sound.



> Any concern with standard guitar cable style interconnects at this higher operating level?


No concern at all.

brucek


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## Ayreonaut (Apr 26, 2006)

My Denon AVR-1905 sub-out level is pretty high. With the Denon sub-out set to its minimum at -12 dB and the BFD input set to -10 dBV, the BFD input was clipping on reference level DTS material like "The Haunting." Setting the BFD input to +4 dBu allowed me to increase the Denon's sub-out to -2 dB. That helped the Denon's signal-to-noise ratio too.


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## brucek (Apr 11, 2006)

> That helped the Denon's signal-to-noise ratio too


Can you explain this statement a bit further?

brucek


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## Ayreonaut (Apr 26, 2006)

There is more to choosing the crossover than the LF capability of your mains. My mains have strong output below 60 Hz and I was using a 60 Hz crossover. But I determined that the in-room response of my mains had a hump between 90-130 Hz. Setting my crossover up to 80 Hz attenuated this by a few dB, and the system sounds much better.


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## Ayreonaut (Apr 26, 2006)

brucek said:


> Can you explain this statement a bit further?
> 
> brucek


Sure. My Denon's noise floor is constant from the lowest volume to the highest. I was able to turn up the subwoofer pre-out level from -12 dB to -2 dB, which did not increase the noise level. I then decreased the amp's gain -10 dB. Thus I reduced the audile noise by -10 dB. (I eliminated audible noise altogether by using a BFD filter to simulate a low-pass.)


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## brucek (Apr 11, 2006)

> Thus I reduced the audile noise by -10 dB


Good stuff.



> There is more to choosing the crossover than the LF capability of your mains


Yeah, it's a good point. Since the only real control we have is with the sub frequencies via the BFD, it may be a better choice to choose the 80hz crossover if you need equalization in that area, even though the mains are quite capable of a lower cross.

brucek


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## PeteD (Sep 9, 2006)

Ayreonaut said:


> I eliminated audible noise altogether by using a BFD filter to simulate a low-pass.


Very interesting Ayrenaut. I have tried the +4 setting. At the same sub channel and amp settings there is no increase in output. However, the BFD does not even come close to clipping at loud volumes, allowing me to increase my sub channel output (or decrease my mains) and still have headroom to spare. I do detect increased audible noise, though.

What filter did you use to eliminate the elevated noise floor?

Thanks,
Pete


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## brucek (Apr 11, 2006)

> I have tried the +4 setting. At the same sub channel and amp settings there is no increase in output.


That's expected, there shouldn't be any change. You didn't increase the level, you changed the operating range.



> However, the BFD does not even come close to clipping at loud volumes


Then you're not getting enough level to the BFD.



> I do detect increased audible noise, though


Also expected.

Option 1 outlined above is your preferred route....

brucek


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## PeteD (Sep 9, 2006)

I used Ayreonaut's trick of raising my sub channel output by 10dB and lowering my pro-amp level by 10dB. The receiver has a much lower noise floor. Also, I turned down all speakers by 5dB, which gives me an added +5dB for my sub relative to my mains.

The noise is much less, but audible enough to be undesirable - I have a low tolerance for noise.

Regarding the low level fed to the BFD, how will this manifest itself as a negative? Lost information, or poor sound. i.e. If it still sounds good, don't worry about it?

Also, the confusing part of this issue for me is that even if the BFD is close to clipping during the depth charges on U-571, what about all of the other scenes when it is not close to clipping, even on the -10dB setting. Is this undesirable for the quality of the lower intensity bass scenes? I suppose, you just want to make the best of the situation and send it as much signal as possible in all situations without clipping right during the bass heavy scenes, right?

What does the line level shifter do to the noise floor? Are they fairly "quiet"? If they are quiet, I think you are on the money with this one.

Thanks,
Pete


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## Guest (Nov 7, 2006)

Interestingly, with my BFD FBQ2496, even with my Anthem processor sub volume at max, it never comes close to clipping for me either.

THM


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## Ayreonaut (Apr 26, 2006)

PeteD said:


> What filter did you use to eliminate the elevated noise floor?


1.00 kHz, -30 dB, 120/60 octaves. All of the low level hum that I was hearing was wiped out. This setting was also useful to help shape my house curve. You can adjust the frequency and gain a bit to hit your own target levels.


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## brucek (Apr 11, 2006)

> Regarding the low level fed to the BFD, how will this manifest itself as a negative? Lost information, or poor sound. i.e. If it still sounds good, don't worry about it?


The short answer is _"If it still sounds good, don't worry about it?_.
The bit resolution defines the dynamic range of the system and so the signal to noise ratio is maximized by using as much of the dynamic range as possible. If the range from your weakest signal to the strongest signal was only half the required maximum input level, you would be robbing yourself of dynamic range and subsequently decreasing (worsening) your signal to noise ratio. 

The BFD1124 is a 24bit device. This means the device theoretically can resolve 16777216 discrete voltage steps (translates to ~=147db). Well, that's the theory, but another 1124 spec is that the noise unweighted is >94dB. That's a little better than 15 bits of resolution. So about 9 bits (of the 24 bits) are lost in the noise. That leaves ~15 bits to define the input voltage levels or a possibility of 32768 voltage steps as long as I supply the input with a full scale signal. A signal that is at half the maximum input level (as an example) would have its softest signals (that would normally be greater than the noise floor), lost in the noise. If you maximize the input, so that at least your loudest signal reaches the maximum allowed, it gives you the best chance for optimum resolution. 

If you switch to the +4dBu setting and only use half it, you will have signals that would have passed the noise floor using the -10dBV setting, that now are lost. You already have observed that you now hear the noise. I guess you can filter it, but it's not really the most elegant solution when you have an alternative. 

You have a consumer level receiver. It would be best to use a consumer level operating range with the BFD. Adjust the trim of your sub out of the receiver to accomplish a proper input level to the BFD. Then modify the level of the BFD output to satisfy the sub amp if necessary.



> What does the line level shifter do to the noise floor? Are they fairly "quiet"?


I would expect this level shifter to be fairly quiet since its passive with a transformer, but I have no experience with it. If your sub amp expects pro level, then I think it's probably necessary.

brucek


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## PeteD (Sep 9, 2006)

Thanks brucek. After my experimentation last night and hearing the noise floor, I think that is my best option. I did try Ayreonaut's filter with no success on the noise floor.

I am hopeful the line level shifter will be quieter, since it is a device designed specifically for this purpose and the operating level shift on the BFD is just one part of another device that only costs slight more than the line level shifter does.

In addition, even if the noise floor is not improved at all (which I hope it is, of course), I will be using the BFD more effectively and passing a better signal on to my sub amp, as you describe.

Sounds like it is worth a shot!

Pete


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## PeteD (Sep 9, 2006)

Ayreonaut said:


> 1.00 kHz, -30 dB, 120/60 octaves. All of the low level hum that I was hearing was wiped out. This setting was also useful to help shape my house curve. You can adjust the frequency and gain a bit to hit your own target levels.


Thanks. I tried that, but it didn't help. I think I am going the line level shifter route in the long term.


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## Ayreonaut (Apr 26, 2006)

A few questions:

1. Is the noise very low frequency or higher?
2. Do you have a balanced connection between the BFD and the amp?
3. Are you sure its not ground loop hum?


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## PeteD (Sep 9, 2006)

A few answers:

1. Noise sounds high, but no filter frequency from 1Kz and above (tried them all) with 120/60 bandwith at -48dB gain made any difference. It is quite audible, but only measured 54dB nearfield, so it must be high.

2. I have a 1/4 mono (guitar cable) between my BFD and amp. I believe this is unbalanced.

3. Don't think it is ground loop. I am using a cheater on the BFD, which eliminated the ground loop that I did have. This noise happens because my amp is turned all the way up and only with the BFD in +4 operating level. If I crank my amp back to 2/3 turned up, noise is barely audible. That doesn't solve the headroom problem that I am trying to conquer by using the +4 level in the first place, though.

Pete


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## Ayreonaut (Apr 26, 2006)

I highly recommend trying a balaced connection between the BFD and amp. This cut out a lot of noise in my system.


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## PeteD (Sep 9, 2006)

This is an area of confusion for me. Do you mean an XLR connection, or can I use a stereo 1/4" jack?

Thanks,
Pete


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## Ayreonaut (Apr 26, 2006)

XLR and 1/4" Tip-Ring-Sleeve (stereo) are both balanced connections. I used 1/4" TRS.


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## brucek (Apr 11, 2006)

> I have a 1/4 mono (guitar cable) between my BFD and amp. I believe this is unbalanced.


Correct. But, if the sub amp you're using allows balanced input, then use 1/4" TRS connectors as Ayreonaut recommends.

brucek


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## PeteD (Sep 9, 2006)

I did try a TRS 1/4" cable tonight...no improvement in noise floor - it sounds exactly the same.

Hopefully, it is not just the amp, since it is turned up all of the way. But, if the line level shifter is quiet, I should be able to turn down the amp enough to keep the noise floor down.


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## PeteD (Sep 9, 2006)

So, I finally generated a house curve in my sub response and tried to integrate the sub with the main speakers. Here is what I got. I think it is pretty good, now I just need to solve the headroom issue... I am going to wait until I get REW up and running before tweaking my curve further. BTW, the response at 10Hz comes back up to the level at 25Hz, so I have some good output down low. If only we could tweak down there...


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## Ayreonaut (Apr 26, 2006)

PeteD said:


> Hopefully, it is not just the amp, since it is turned up all of the way.


What does the noise floor sound like with the receiver disconected? 
What does it sound like with the BFD disonnected? 
You might be able to figure out which component is generating the noise.


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## PeteD (Sep 9, 2006)

Good thought. The noise is really only an issue when the amp is fed the +4 signal from the BFD. At -10, the noise is negligible. So maybe that means it is the BFD. I am not sure what the other options will tell me.

The amp by itself is quiet.

I could connect the receiver directly, but I don't see how it could be noisier that with the BFD in-line and the operating level at -10. Maybe I am missing something here...

My real question is whether the line level shifter will raise the noise floor, also. Only one way to find out...

However, the good thing is I can still enjoy my IB at lower listening levels at the -10 setting on the BFD.


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## brucek (Apr 11, 2006)

> The amp by itself is quiet.


I looked, but couldn't find the type of amp you have? Could you tell us what model of amp it is?

brucek


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## PeteD (Sep 9, 2006)

Nady XA-900


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## brucek (Apr 11, 2006)

Ahhh, and do you have the mode set to Parallel, Bridged or Stereo?


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## PeteD (Sep 9, 2006)

I currently have it set to parallel with 2 woofers (4 ohm woofers, single voice coil) on each channel, wired in series for an 8-ohm load.

I also tried to get more headroom by bridging (switch set to bridged and woofers all wired to channel A) all woofers into a 4-ohm load and also by running each channel as a 2-ohm load (switch set to parallel). I got no increase in output, actually slightly less (2 dB) bridged and exactly the same with either 8-ohm or 2-ohm loads per channel. I think this is becuase the amp volume controls are really attenuators, so they can only pass what the input signal is at their maximum volume? Seems a little weird to me though.

Maybe something is going on here, but I am confident (but I would never guarrantee it) that I wired everything as described above during my testing (I double checked all the connections and used the crutchfield wiring diagrams).

Pete


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## brucek (Apr 11, 2006)

> I currently have it set to parallel with 2 woofers


That seems reasonable.

I downloaded your manual and see that even though this is a "pro amp" it is using consumer level input range.

It reads that the maximum input level is 1.15vRMS. Well that's about exactly the maximum input / output level of the BFD when set to the -10dBV consumer level setting.

So, I'm a bit confused. Can you go over again what the problem is exactly......

brucek


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## PeteD (Sep 9, 2006)

The problem boils down to my BFD almost clipping when I play a movie scene (Darla Taps the Glass in Finding Nemo) at a pretty loud, but not ridiculous level. With the house curve that I plotted above, I have the sub at +5dB, which is going to cut further into my headroom.

Part of the reason for this is undoubtedly that I have some significant cuts (quite a few cuts from 30 to 80 Hz). See my raw curve below to see what I am cutting.










The nearfield (dark blue line) is characteristic of an IB. However, I am lacking room gain due to the shape of my room, so I have cut my curve down to generate my house curve.

Oddly enough though, when I crank up the test tones (no BFD), I get the following response at high SPLs (yes, I wore hearing protection). The yellow line is actual levels, the magenta is overlayed to cross my nearfield response at 50Hz. Needless to say, the room is getting pressurized at these levels and everything is vibrating.










Now, as I am thinking about this, I realize that I have used no boost filters.

Maybe I should use some boost on the BFD down low instead? This would then decrease the amplitude of my signal sent to the BFD (reducing clipping), and pass some of the workload onto my amp! I think I could be onto something, helped by your question. Maybe like may rules, the "no boost" rule is meant to be broken sometimes?

What do you think?

Thanks,
Pete


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## brucek (Apr 11, 2006)

> Maybe I should use some boost on the BFD down low instead? This would then decrease the amplitude of my signal sent to the BFD (reducing clipping), and pass some of the workload onto my amp! I think I could be onto something, helped by your question. Maybe like may rules, the "no boost" rule is meant to be broken sometimes?


MY feeling is that you should set the input level to the BFD to show Yellow LED's at your loudest level by using the trim adjust on the processors subwoofer output. Then, adjust the BFD filters for the desired output voltage curve to send to your subwoofer amplifier.

Then adjust the subwoofer amplifiers gain to match and balance the sub to the rest of the system. If there isn't enough voltage from the BFD to accomplish this, then amplify the signal (with a level shifter).

This will reveal the best resolution and S/N ratio.....

brucek


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## PeteD (Sep 9, 2006)

Will boosting the low end instead of just cutting the high level help my headroom?


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## brucek (Apr 11, 2006)

> Will boosting the low end instead of just cutting the high level help my headroom?


If the input level to the BFD is set properly, you would not be able to use *any* boost or you would clip the output. Anyone that uses boost has an input level that isn't optimum.

Look at it this way. If I send a 30Hz sine wave to the BFD and set its input level so that the yellow LED is on full and the RED clipping LED is just about to come on, how much gain can I apply to a 30Hz filter?

The answer is zero, of course. Any gain would cause clipping.

So, let's say I decide I want a 30Hz filter with +15dB gain. I will have to turn down the input level to the BFD by -15dB. But when I do that, I don't just reduce the level of the 30Hz signal, I reduce *all* frequencies going to the BFD by -15dB, because the input level is not frequency specific, it's wholesale.

So for the sake of a single 30Hz filter of +15dB, I have drastically reduced my dynamic range and signal to noise ratio. Do you see why I continue to admonish everyone who use these large plus gain filters?

Leave the input level at maximum and cut. Then amplify the output of the BFD if necessary (and it usually isn't ever necessary).

brucek


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## PeteD (Sep 9, 2006)

That makes perfect sense. I was thinking in term of that one scene, which I know has some serious content in the area of my cuts. If I did use low boost, I would destroy my sub if I watched War of the Worlds or something with a ton of really low content.

I have basically done what you suggest here already and I am at the point of purchasing the line level shifter:

"MY feeling is that you should set the input level to the BFD to show Yellow LED's at your loudest level by using the trim adjust on the processors subwoofer output. Then, adjust the BFD filters for the desired output voltage curve to send to your subwoofer amplifier.

Then adjust the subwoofer amplifiers gain to match and balance the sub to the rest of the system. If there isn't enough voltage from the BFD to accomplish this, then amplify the signal (with a level shifter)."

Given the realtively low line voltage requirement of the Nady XA900, will the line level shifter cause any problems?

Thanks,
Pete


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## brucek (Apr 11, 2006)

> Given the realtively low line voltage requirement of the Nady XA900, will the line level shifter cause any problems?


You're apparently not feeding it a maximum signal now, so it definitely needs some amplification to bring it higher. You will simply use the input level control of the Nady to set the perfect amount of input..

brucek


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## PeteD (Sep 9, 2006)

OK, so my Ebtech line level shifter arrived and boy does this thing raise the noise floor significantly - much more than operating the BFD in +4 mode (and after calibrating the sub level for both with my mains). To top it off, it only gives me 9dB additional output, so I don't think it can work for me.

So, I went back to the +4 operating level on the BFD and maxed my sub out on my processor to +10, and pulled all of the the other speakers down to -10dB. The net effect is that the noise floor is reduced because I scan can turn my pro-amp down 15dB. The good news is that at these levels, my BFD lights up the red LED (for a split second) on the "Darla Taps the Glass" scene. So I think my BFD is happy.

The only question I have is whether I can do anything about the "static" or noise - not sure how best to describe it - nearfield by my sub. It is now not measurable (less than 50 dB) inside my IB manifold, but you can hear it there. I also have some static from my mains at reference volume. I am pretty sure it is not ground-loop (or at least not strong one), but I suppose I will remove some connections and lift the ground (temporarily) on my components to see if the noise improves. All of this noise I would call barely audible at my seating position. Maybe this is normal?

Am I doing the audio equivalent of staring at the pixels from close range on my television? I am not sure how to judge my noise floor - I just now it is worse now operating the BFD at +4 than it was at -10. Of course, I don't want to watch my movies at a listening level of 64dB!

Is there anything (besides upgrading components) that I can do to reduce noise - eg. filters, in-path noise reduction devices (I am making stuff up now). Maybe there is a better option than the BFD? i.e. Something that can take and pass a stronger signal but with less noise. I realize I am asking too much of a $100 equalizer at this point, but if I spent $250, could I conquer this problem?

Thanks,
Pete


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## brucek (Apr 11, 2006)

> The only question I have is whether I can do anything about the "static" or noise


Static? I don't really understand what the noise is. Do you mean hiss, or hum, or crackle? Can you better describe it? It has to be low frequency because you have a limited response from the sub. A sub doesn't pass traditional hiss that would be heard from a mains speaker.



> I also have some static from my mains at reference volume.


But the BFD isn't in that chain, so is there another source of this problem? Does the mains "static" sound like the "static" noise you describe coming from the sub?



> Maybe there is a better option than the BFD? i.e. Something that can take and pass a stronger signal but with less noise. I realize I am asking too much of a $100 equalizer at this point,


I use a BFD and I can turn my volume on my processor full up and there is not a sound coming out of my sub, so it isn't a matter of the $100 device not being up for the challenge.

brucek


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## PeteD (Sep 9, 2006)

The noise sounds like what you hear when an amp is cranked up really loud, but no signal is sent to it - like a DJ's speakers between songs. I am not sure what to call it. Static with a little crackling maybe?

Yes, both static noises sound the same, but again my receiver/processor is turned up louder now, with the speaker and sub settings as they are. But maybe I have some other minor ground loop thing going on here. I think I need to disconnect other devices from my receiver and/or lift some grounds temporarily, to see if I can make the noise go away.

Can you check to see if you get some noise at the +4 operating level (with no signal) and your amp cranked up? The static at -10 is basically non-existent on my system, but quite pronounced when the +4 operating button is activated.

Thanks,
Pete


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## brucek (Apr 11, 2006)

> Can you check to see if you get some noise at the +4 operating level (with no signal) and your amp cranked up? The static at -10 is basically non-existent on my system, but quite pronounced when the +4 operating button is activated.


I have two systems, one expensive and one cheap.

The expensive one at full processor volume with no input signal produces zero noise and hum in both -10dbV and +4dBu switch positions at the subwoofer. This is using both my ear and spl meter to test.

But, the cheap system at full processor volume with no input signal produces ~54dbSPL hum in the -10dbV with the meter pressed against the subwoofer cloth. It produces ~58dBSPL hum in the +4dBu position under the same conditions.

This tells me the source of the noise is from the processor and is suitably raised and lowered by the BFD depending on the operating range selected. When there is no noise sent to the BFD (as in the case of the expensive processor), then nothing happens in either switch position.

This is exactly as I would have expected. The noise from a BFD is noise floor hiss and would be detectable in a mains system where the speakers can amplify that range. But a subwoofer doesn't pass this hiss and is the reason why a BFD is **** suitable for a subwoofer.

If you have noise from your subwoofer, it ain't coming from the BFD. Could be ground loop, or something else.

brucek


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## PeteD (Sep 9, 2006)

brucek said:


> But, the cheap system at full processor volume with no input signal produces ~54dbSPL hum in the -10dbV with the meter pressed against the subwoofer cloth. It produces ~58dBSPL hum in the +4dBu position under the same conditions.
> 
> This is exactly as I would have expected. The noise from a BFD is noise floor hiss and would be detectable in a mains system where the speakers can amplify that range. But a subwoofer doesn't pass this hiss and is the reason why a BFD is **** suitable for a subwoofer.
> 
> If you have noise from your subwoofer, it ain't coming from the BFD. Could be ground loop, or something else.


Thanks a bunch. I really appreciate you taking the time to do that.

I have a cheap system - H/K AVR 235, was less than $500 The one I don't get is the noise generated in your sub using the cheap system means the sub is passing that hiss, right? And it is coming from the main amplifier or receiver, which I suppose mine is also. 

I think hiss (after doing more reading on-line) does best describe my noise.

Also, since my noise varies with amplification, I don't think it is ground loop, but rather cheap (relatively) amps.

How much is an "expensive system", where one can expect to avoid that hiss? i.e. How does one know they won't get the hiss? Probably having more power to allow operation in the low to middle portion of its range helps, also.

Pete


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## Ayreonaut (Apr 26, 2006)

PeteD said:


> I did try Ayreonaut's filter with no success on the noise floor.


 If the hiss is from the receiver, and it is above the subwoofer frequencies, then that filter would have had a significant impact.

I can't remember if you tried this already, but have you connected the reciever to the amp directly? Does the hiss remain?


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## brucek (Apr 11, 2006)

> the noise generated in your sub using the cheap system means the sub is passing that hiss, right?


No, it's passing hum. There's a big difference in the sound of hiss and hum.



> I think hiss (after doing more reading on-line) does best describe my noise.


Again, I'm confused. How can a subwoofer hiss when it's only capable of passing up to ~150Hz ?

You could try some cheaters (only as a test) to eliminate ground loop. Also remove any cable or satellite as a test. I suspect an inexpensive receiver is the culprit though.

brucek


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## PeteD (Sep 9, 2006)

OK, for the record, I am probably the most tone deaf person on the planet. I enjoy music, but I have no clue what I am actually hearing in terms of tones.

I think I am the one who is confused. If hum vs hiss sounds like the difference between humming with your mouth closed and hissing through your teeth, then it is a hum.

I feel like when I am trying to describe that noise my car is making to my mechanic...

Ayreonat, I can't remember exactly what the receiver to the amp sounded like. I will check that again. I think it was pretty quiet, but I did not have each of them turned up as much as I do now.

I also suspect amplifier noise from my receiver and pro-amp. I did have ground loop when I first hooked up my BFD and that (even to me) is easy to recognize. The current "hum" does not seem the same to me. I will do some more testing.


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## PeteD (Sep 9, 2006)

brucek said:


> If the input level to the BFD is set properly, you would not be able to use *any* boost or you would clip the output. Anyone that uses boost has an input level that isn't optimum.
> 
> Look at it this way. If I send a 30Hz sine wave to the BFD and set its input level so that the yellow LED is on full and the RED clipping LED is just about to come on, how much gain can I apply to a 30Hz filter?
> 
> ...


Hi brucek:

I have been rethinking this, and I am not sure that the above is true with the multiple frequency sound that we send to our BFDs. 

In your example, you are correct, but we are not setting our BFD level based on one frequency of input - we are using a test scene with mulitple frequencies being input. Obviously, we could not boost that one frequency without clipping.

In my case (simplifying for this hypothetical argument), say that I am cutting 15 dB off of the frequencies from 40 to 100Hz. These are now not in my output, but still contribute to clipping in my input on the BFD. If I reduce the cut from 40 to 100 Hz down to 10 dB and boost frequencies from 10 to 40 Hz by 5 dB, I will gain more headroom on my input (which is my problem) and I don't see why that would clip my output, since I still "mostly cutting my input".

If you look at some of my raw response curves, I am cutting huge amounts of response with my BFD. I will provide my filter settings later so you can see them. I am thinking that I can lower my noise floor by having my BFD output signal strength be closer to my input strength. Right now my relative output is so weak, that I have the sub at +10 on my receiver, I am running the BFD at +4, and my pro amp is cranked most of the way up.

Doesn't one just need to cut the total signal more than they boost the total signal to prevent clipping of the output, to keep BFD happy? If one only cuts, then the output signal will never approach the strength of the input signal. More specifically, I am using large cuts of the frequencies that are causing my clipping when I use "Darla" to do this, so my output is definitely not close to clipping in this case.

In a way, the way we set the input level seems kind of flawed, because we don't know what frequencies are causing the almost clipping (they may be ones we are cutting). I realize that we are probably doing the best we can do in that regard...

Thanks,
Pete


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## brucek (Apr 11, 2006)

> In your example, you are correct, but we are not setting our BFD level based on one frequency of input - we are using a test scene with multiple frequencies being input. Obviously, we could not boost that one frequency without clipping.


Many people have a problem accepting sine waves as a test signal, using the argument that they are listening to music and not a sinusoid. True, but the fact is that you are able to mathematically Fourier any signal into its fundamental and primitive components. Any complex, stochastic signal can be decomposed and represented by a bunch of sinusoidal waves. So the sine wave is commonly accepted as a representative test signal.



> If one only cuts, then the output signal will never approach the strength of the input signal.


That's correct. The rationale being that if you had a peak at 50Hz for example (which is caused by a resonance at that frequency in the room), then reducing the level of 50hz with a cut filter would reduce the voltage feeding the sub amp and then the room would re-boost that 50Hz signal to match the SPL level of the level of the other frequencies.

Remember that the voltage feeding the BFD is perfectly flat (other than it falls off above the crossover). Music, tones, pink noise, whatever, all have a flat maximum level feeding the BFD set by your volume control and trimmed by the small channel adjustments provided. You want this level to be the highest possible feeding the BFD. That's a simple fact and there's no disputing it. If we feed a maximum signal to the BFD, then any gain at any frequency (before the crossover) will cause clipping if the input level is at a maximum. That's another absolute that can't be disputed.

So, if you understand that, and want to boost some frequency by +15db, then the input level of all frequencies will have to be 15dB lower than maximum feeding the BFD. If it still sounds good to you, then that's what you should do.....



> In a way, the way we set the input level seems kind of flawed, because we don't know what frequencies are causing the almost clipping


As I said, the signal feeding the BFD enjoys the same maximum level for *all frequencies* below the crossover.

Pictorially in green, this is the input level waveform feeding the BFD for all frequencies. Notice that there are no peaks or dips or clips. It's what happens after, that causes those problems...












brucek


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## PeteD (Sep 9, 2006)

OK, let me back up for a minute and make sure I understand what makes the BFD clip it inputs signal. Is it:

1. The total strength of the signal that is sent to the BFD, or
2. The strongest signal at a given frequency (or even frequency interval), or
3. None of the above

I was thinking it was number 1, such that a signal sent the the BFD shaped like a triangle with its tip at 30 Hz and a level of 120 dB (when reaching the sub) would be just as likely as a signal shaped like the curve in your last post, with a maximum level of 90 dB, to clip the BFD - if the area under each curve that was sent through the BFD was the same.

Is it the total area under the curve that determines clipping, or is it frequency specific? I was thinking it was total area, but I think your post above suggests otherwise...

Thanks,
Pete

Edit: Here are my filter settings BTW:
Equaliser: DSP1124P
Sub
Cutoff 80Hz
Target level: 69.3dB
Filter 1: ON PA Fc 51.3Hz Gain -21.0dB BW/60 24.0
Filter 2: ON PA Fc 28.2Hz Gain -5.0dB BW/60 9.0
Filter 3: ON PA Fc 22.0Hz Gain -8.0dB BW/60 9.0
Filter 4: ON PA Fc 80.0Hz Gain -32.0dB BW/60 30.0
Filter 5: ON PA Fc 99.0Hz Gain -11.0dB BW/60 8.0
Filter 6: ON PA Fc 125.0Hz Gain -16.0dB BW/60 11.0
Filter 7: ON PA Fc 36.2Hz Gain -4.0dB BW/60 5.0
Filter 8: ON PA Fc 146.0Hz Gain -17.0dB BW/60 24.0
Filter 9: ON None
Filter 10: ON None
Filter 11: ON None
Filter 12: ON None


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## brucek (Apr 11, 2006)

You're making this more complex than it is. When the RMS voltage level at the input is greater than +2dBV, then the BFD will clip its input. You can tell when the red LED flashes when it's clipping. It shouldn't happen very often.

Set the BFD's LED's to monitor input level (by selecting total bypass) and adjust the volume on your receiver to your loudest level you'll likely listen too and ensure the input doesn't clip too much. If it does, then adjust the receivers subwoofer trim.

Then set your filters and monitor the BFD's output LED's and ensure it doesn't clip too much. If it does, you probably added too much filter gain. If you did, either turn down the gain (recommended) or turn down the trim input (not recommended).

brucek

edit: why are you using such huge filters ?


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## PeteD (Sep 9, 2006)

Is the RMS voltage equal to the area under the curve of the signal sent to the BFD?

When I set my BFD input to almost clipping (flashing red occassionally in by-pass mode) and then engage my filters and look at the output: I get 3 green bars.

_Wouldn't boosting frequencies in the BFD only cause potential clipping of the output signal - not the input signal??? _ I am very far from clipping there on this movie scene (3 green bars).

I am using such huge filters because of my response curve. The short answer is my room gain stinks at lower volumes, but I can get those lower frequencies to happen. Here is a lower volume listening level curve:










Here are the raw data:
10	62.29
12.5	67
16	75.3
18	73.7
20	79.25
22	84
25	81.65
28	86.25
31.5	83.85
36	90.27
40	86.98
45	94.63
50	99.46
56	98.48
63	96.59
71	95.77
80	98.86
89	93.91
100	93.82
111	85.73
125	89.73
142.5	77.73
160	67.73

The room gain comes around at very high SPLs (yes I wore earplugs) - unfiltered response:









The blue line is the nearfield response of my IB and the yellow line is the response at those actual SPLs.

Below is my corrected response, using the filters in my previous post (for the sub only):









I would be in great shape except that because of the huge cuts that I am using, my BFD output signal is weak. As a result, I need to send an even stronger signal to my BFD and operate at +4. Also, I need to turn the amp up more to intregate with my mains because operating at +4 does not increase BFD output, just acceptable input signal. As a result of all of this, I have a high noise floor - 54dB by the sub.

I was thinking that do something more like these filters below would enable me to have a stronger output signal so I could turn my amp down a little. I think that these filters should have no effect on my input clipping (see question above) and will not result in my output clipping, since I am not close right now. Thus my questions about what makes the BFD clip and if boost in the BFD can only clip the output.
Equaliser: DSP1124P
Sub
Cutoff 80Hz
Target level: 85.0dB
Filter 1: ON PA Fc 51.3Hz Gain -22.0dB BW/60 32.0
Filter 2: ON PA Fc 20.0Hz Gain 8.0dB BW/60 120.0
Filter 3: ON PA Fc 100.0Hz Gain -8.0dB BW/60 7.0
Filter 4: ON PA Fc 80.0Hz Gain -16.0dB BW/60 13.0
Filter 5: ON PA Fc 36.2Hz Gain -1.0dB BW/60 4.0
Filter 6: ON PA Fc 40.5Hz Gain 3.0dB BW/60 4.0
Filter 7: ON PA Fc 28.2Hz Gain -1.0dB BW/60 4.0
Filter 8: ON PA Fc 22.0Hz Gain -3.0dB BW/60 6.0
Filter 9: ON PA Fc 128.5Hz Gain -27.0dB BW/60 16.0
Filter 10: ON None
Filter 11: ON None
Filter 12: ON None

Note that some of my 8dB boost is actually cut above 20Hz by the filters there.

Here is the "Darla" spectrograph - very hot, but mostly above 20Hz:









So, it seems to me if I boost outside of the maximum below 20Hz (assuming boost can clip the input - which I don't think is correct) that it still should not clip the BFD input level because this scene is hottest around 30Hz . This is the reason for my questions regarding input versus output clipping.

Of course if I watch a movie with tons of hot 15 to 20Hz content, I may clip the output (assuming the input to BFD can't be clipped with boost) on these scenes (which are hot at 15 to 20Hz) at the same volume I used to set the BFD level using Darla, which is not so hot down low....right? Of course, I think those movies will be fewer and farther between. Maybe "War of the Worlds"...

If the total area under the curve is what clips the input, then as long as one uses cuts that create more area than the boosts that are used, it seems that the output should not clip if the input doesn't. Unless, everything is frequency specific - which I dont understand, yet.

Thanks and sorry for the long post - hopefully you understand what I am getting at...

Pete


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## brucek (Apr 11, 2006)

Why does your raw signal appear to not have any crossover low pass filter applied to it?










bruce


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## PeteD (Sep 9, 2006)

Hmmm, not sure. I am quite sure I had the crossover set, though. I suspect it is either something funky about IBs in general, my woofers (stiff suspension) specifically, or the location of/room design where my sub is. However, when I intergrated with my mains - I get a good result in terms of following my desired curve:









I think I have a better way to ask the meat of my question. Please see the graph below:










Please assume that the green line (similar to your previous post) is the maximum signal that the BFD can take before it almost clips the input. [dB on Y-axis and Frequency on X-axis] Now, assume that the movie I am watching generates the red curve (disregard filters for the moment - assume that I watch my movie in bypass mode)..._If the area of A is less than or equal to the area of B, does my BFD input clip?_

Thanks,
Pete


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## brucek (Apr 11, 2006)

Thanks for posting those filters. 
I think if you look at the graph below of your filters (in green) you'll see why your voltage output of the BFD is so low. You really have introduced a lot of cut. Way too much.You have something wrong with your raw output of the sub. 

It really appears that you have no crossover engaged. If you do, then the amount of room gain you're getting at mid to upper bass frequencies is huge. 

If you do indeed have the crossover enabled in the crossover, then try and reduce it to 60Hz and lets see another raw measurement. I know they're annoying to do manually, but you need to get your raw unfiltered sub into better shape.










brucek


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## brucek (Apr 11, 2006)

we cross posted.........


> assume that I watch my movie in bypass mode)...If the area of A is less than or equal to the area of B, does my BFD input clip?


Your BFD would clip the input of the waveform shown.. because your feeding it a signal greater than the maximum input signal. The input would have to be turned down until the maximum input signal *at any frequency was below +2dBV*.

brucek


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## PeteD (Sep 9, 2006)

I agree with your crossover comment and I realize I have way too much cut. That is my problem. Good thought about the 60 Hz crossover. I will try that (along with 80 Hz cross again) and do some more measurements.

OK, so given that the exceedance at any given frequency causes the clip, please see the graphic below:








If the green line is the max signal our BFD can take (in theory as from my last post), what happens when I use a movie with the red line frequency response in the above graph to set my BFD? This seems problematic to me. If this movie has exceessive dynamic range and one very high peak at a given frequency, It will clip the BFD...

Yet, many other scenes in movies with a smoother response well below the curve will not be using the full processing capability of the BFD (why we set the level high in the first place). i.e. With my BFD set to almost clip at "Darla", many other scenes from this movie with audible and enjoyable bass content result in 1 green light of input (by-pass mode).

So, to get to the point. Why not turn down the input level and use some boost, since the only time we are using the full capability of the BFD is when those thunderous scenes are playing. The rest of the time (99% of the average movie) we are "less than optimal" anyway. I understand the desire to optimize the response - I am not suggesting dialing the BFD input down needlessly. But in my case (barring a crossover solution to be discovered), why not dial it down some and use boost? If the sound will be degraded, aren't we already degrading the sound during 99% of the movie when the input is lower than almost clipping? It seems like we are pushing for the best sound quality for the few seconds (which I understand as long as the output is OK and other factors like elevated noise floor don't come into play), but if having lower input during the rest of the movie is so awful, that suggests that only the loud dynamic scenes will sound good. See what I mean?

EDIT: I found some more of your thoughts on this issue in this post and others in this thread:
http://tinyurl.com/yal5fk

Thanks for your patience and sharing your knowledge.

Pete


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## brucek (Apr 11, 2006)

> Why not turn down the input level and use some boost, since the only time we are using the full capability of the BFD is when those thunderous scenes are playing


I will try and attack this from another angle. 

The BFD is a digital device that accepts analog signals at its input and produces analog signals at its output. A fact.

The BFD digitizes the analog signals, passes them through a DSP, and then undigitizes those signals. The best signal to noise ratio, distortion and dynamic range are enjoyed when the analog signal at the BFD's input (when at its highest expected level) is at a maximum allowed to avoid clipping. A fact. 

The maximum input level is +2dBV. The maximum output level is +2dBV. A fact.

The analog signal sent to the BFD is stochastic and non-deterministic and as such can be represented by sinusoidal signals at all frequencies of interest. That is to say, as an example, I may send the BFD several movie selections where at *any* frequency there may be +2dBV signal feeding the BFD at the highest expected volume selected on your receiver. We don't just play one movie with a loud noise at one frequency forever. We must assume the input will receive maximum input level for all frequencies at some time.
The concern is not about the level of specific frequencies entering the BFD - assume all frequencies entering the BFD are at one time or the other at a maximum level. The concern for specific frequencies are a matter of how the speaker reacts with the room and what frequency specific voltage modifications must be made to the subwoofer input to compensate. 

An example.

Assume the speaker / room interaction causes +15dB peaks at 20, 30, 40, 50, 60 Hz.

You have the option of:

1) Setting the input level of the BFD at maximum and cutting the areas at the peaks. *This results in the output of the BFD being at +2dBV for those areas between the peak frequencies.*

2) Setting the BFD input level of the BFD down -15dB and boosting the areas between the peaks. *This results in the output of the BFD being at +2dBV for those areas between the peak frequencies.*

The output signal level of the BFD is identical for both scenarios and will be for all scenarios. The #2 option results in a worse noise floor, less meaningful bits sent to the DSP for processing, and worse dynamic range.

Which option do you choose? You've indicated you prefer #2.

brucek


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## PeteD (Sep 9, 2006)

That all makes sense.

My only counter-argument would be that maybe the other components in my system produce more noise right now than the BFD would if I use some boost. In other words, maybe boosting the BFD output somewhat, which I think would allow me to lower my receiver volume (which is way up there right now at -10 dB on a -80 to +10 dB scale), and lower my sub amp volume, will result in my overall system (receiver - BFD - proamp) having less noise.

Possible?

I don't know if this is true, but I guess I will try it and see how things sound. Also, I will look at a 60Hz crossover and check my 80Hz crossover numbers.

OT - I heard that the 1124 is now discontinued (though there are many left in the supply chain). Here's hoping to an alternative with the same flexibility and nice price that incorporates an independant output level control and/or better dynamic range and/or anti-clipping technology...

Edit - Maybe I should just get a bigger amp like an EP2500 for my sub...

Thanks,
Pete


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## brucek (Apr 11, 2006)

> Also, I will look at a 60Hz crossover and check my 80Hz crossover numbers.


Yeah, you should really look into this and figure out why your raw measurement appears to not have a low pass filter applied to it from the reciever.



> which is way up there right now at -10 dB on a -80 to +10 dB scale


Your receiver actually allows that much trim adjustment on the subwoofer output? What kind of receiver is it?



> Possible?


I would say no. Your problem really seems to come down to the massive amount of filtering you're doing because your raw measurement is wacky for some reason. No amount of messing around with input levels to the BFD will correct that problem.

brucek


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## PeteD (Sep 9, 2006)

brucek said:


> Your receiver actually allows that much trim adjustment on the subwoofer output? What kind of receiver is it?


That is the master volume. I have run the sub at +10, and the mains as low as -10, to allow me to turn down the pro-amp. H/K AVR235.


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## brucek (Apr 11, 2006)

> I have run the sub at +10, and the mains as low as -10, to allow me to turn down the pro-amp. H/K AVR235.


Yeah, I wish I could help you more, but I guess we'd be going in circles. Fact is, the H/K AVR235 is a standard consumer item that outputs standard levels from the pre-out jacks and should easily satisfy the BFD input levels. That level should be fine for your sub amp that we already looked at, but could be increased with the line amp you bought if needed.

There's just something not right, and I really have no clue what it is...... you need to do some more investigation. Could be as simple as a bad cable.

brucek


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## PeteD (Sep 9, 2006)

I will start back at new raw measurements of the sub only using crossovers of 60 and 80Hz and post those when I have them.

I appreciate your help.

Pete


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## PeteD (Sep 9, 2006)

OK, I have two pieces of information. This curve is correct for my sub only crossed at 80 Hz. Actually, the curve is exactly the same for 100 Hz crossover also, which seems a little strange to me:









I will post a 60 Hz cross tomorrow, but I quickly tested that it will draw it down at the higher frequencies.

One question I have is can I get away with a 60 Hz crossover? Here is the response of my mains by themselves. The response falls away quickly below 45 Hz.


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## brucek (Apr 11, 2006)

> One question I have is can I get away with a 60 Hz crossover?


With the amount of gain you must be getting from the room (evidenced by that raw sub graph), I can't see that you'd have any trouble.



> Actually, the curve is exactly the same for 100 Hz crossover also, which seems a little strange to me:


Yeah, seems strange to me to. I'd sure like to see the 60Hz raw graph (and the 40Hz too)...

brucek


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## PeteD (Sep 9, 2006)

Actually, something weird may be going on with my receiver - I may reset the whole processor and start over. The sub is getting signals based on the crossover of my rear surrounds in a certain mode, when it should be getting them from the front - I have checked the manual and settings many times and the OSD looks a little funky - doesn't quite match the manual.

Do you take the readings in stereo mode (with sub enabled) or in a surround mode?

Also, when doing manual readings, does it matter if I determine the master volume setting (scale in dB) to bring a certain frequency to a given decibal level (i.e. how much power to reach 75 dB) or leave the master volume in one spot and take actual dB readings of the room. I have done both with the same results, but I want to make sure I am doing things right.

Which method does REW use?

A potential "fly in the ointment" of using a lower crossover (i.e. 60Hz):
What do I do with my surrounds/center? They need support below 100Hz. If I cal the sub with 60Hz crossover with my mains in stereo, but feed the sub up to 100Hz material from my center and four surrounds, won't I create a huge hump in my surround mode response and maybe clip the BFD? I realize this is a problem for everyone, but I was bascially using the BFD as part of my crossover before to tame the response from 60 to 100Hz. No perfect answer, I guess...

Thanks,
Pete


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## brucek (Apr 11, 2006)

> Do you take the readings in stereo mode (with sub enabled) or in a surround mode?


Stereo.



> Also, when doing manual readings, does it matter if I determine the master volume setting (scale in dB) to bring a certain frequency to a given decibal level (i.e. how much power to reach 75 dB) or leave the master volume in one spot and take actual dB readings of the room. I have done both with the same results, but I want to make sure I am doing things right.


Best to set the master volume to bring a certain frequency to a 75dB level using the SPL meter (with correction), and then leave the volume there for the entire set of measurements.

You can pick any frequency you want for that initial setting, but you may have to redo the whole thing if you picked a frequency that was a peak. I think you get what I mean..



> Which method does REW use?


REW sets the initial level with a type of pink noise. No big deal. If you're not using REW (and you should), then using a single frequency or a selection of a couple frequencies to get the starting master volume level is fine. Just don't touch the volume once you start measuring. If you do, start over.



> What do I do with my surrounds/center? They need support below 100Hz.


Not much you can do there. I'm actually more interested in seeing the 60Hz and 40Hz raw setting graph just to try and establish what the **** is wrong with your system.......

brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

> One question I have is can I get away with a 60 Hz crossover?


 The speakers I used to use were rated down to 28 Hz or so, and I had trouble with them bottoming out with movies when I tried to use a 60 Hz crossover (which I thought would be adequate, since it was an octave above my rated extension).

So, it ultimately depends on your speakers, although – as brucek observed – if your output is that good, you might be fine.



> A potential "fly in the ointment" of using a lower crossover (i.e. 60Hz):
> What do I do with my surrounds/center? They need support below 100Hz. If I cal the sub with 60Hz crossover with my mains in stereo, but feed the sub up to 100Hz material from my center and four surrounds, won't I create a huge hump in my surround mode response and maybe clip the BFD? I realize this is a problem for everyone, but I was bascially using the BFD as part of my crossover before to tame the response from 60 to 100Hz. No perfect answer, I guess...


 I suggest an outboard crossover added to the sub chain. That way you could set your sub’s crossover separately from the rest of the system. You can get something like a Rane AC 22 pretty cheap on eBay.

Regards,
Wayne


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## PeteD (Sep 9, 2006)

brucek said:


> I'm actually more interested in seeing the 60Hz and 40Hz raw setting graph just to try and establish what the **** is wrong with your system......


Well here is my new raw plot showing four crossovers, with my system running in stereo, sub engaged. Front speakers were not plugged in. The squiggle in the 60 HZ response that does not match the others may be a mistake...

Does this look like the receiver is crossing appropriately? I would expect more of a drop-off with the lower crossovers. Could room resonances be boosting the response that much? I was able to intergrate with my mains during my inital effort and get a generally flat line up through 160 Hz...

Now my room has a tile on concrete floor with just an area rug, so it is definitely on the "bright" side. Maybe that explains part of the response?











Wayne, regarding the external crossover, I have independent bass management in the receivers for each set of speakers (assuming it is working correctly). I am not sure what an external crossover would gain. Maybe an additional equalizer for the other channels to then intergrate each set of speakers with the sub would work...

Maybe it is not really a large issue with HT (movies) because they may send the low stuff up front or to the sub realizing people have small surrounds, in general?

Thanks,
Pete


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## brucek (Apr 11, 2006)

> Does this look like the receiver is crossing appropriately?


No. 

I don't think it looks like it should. 

Below is what it should look like in a perfect world. I'm using the same scaling that you are so we can compare apples to apples. Something is not right.

Look at the 40Hz crossover trace at 80Hz measured on both graphs. Mine is at about 50dB. Yours is at about 87dB???????









brucek


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## Wayne A. Pflughaupt (Apr 13, 2006)

Hi Pete,



> Wayne, regarding the external crossover, I have independent bass management in the receivers for each set of speakers (assuming it is working correctly). I am not sure what an external crossover would gain.


 Well, you mentioned you were concerned about the effect it would have on your surround speakers if you dialed your receiver’s crossover down to 60 or 40 Hz (assuming it doesn’t have the ability to use separate high and low pass filters, which is pretty unusual). If you use an outboard crossover, inserted between the receiver and the sub amp (i.e., the same way the BFD is connected), you could leave the receiver’s crossover set at 100 Hz. Then you could adjust the outboard crossover for whatever frequency the sub needed, and it would have no effect on the surround speakers. Make sense?



> Does this look like the receiver is crossing appropriately? I would expect more of a drop-off with the lower crossovers.


 I agree with brucek, it certainly looks suspicious. Take a look at the 80 Hz marking on the graph. If the crossover is working correctly, and assuming it is 24 dB/octave, there should be a 24 dB difference between the “40 Hz Cross” and the “80 Hz Cross” line at the 80 Hz mark. As you can see, the 40 Hz line is reading at about 76 dB, and the 80 Hz is at 92, which is only a 6-dB difference. I don’t know what the rated slope of your receiver is, but it appears to be functioning at a mere 6 dB/octave.

Of course, it doesn’t help that your subwoofer’s response is kinda backwards from what we’re used to seeing, with exaggerated output in the upper frequencies. Since your output at 80 Hz is about 18 dB higher than output at 20 Hz, about the best you can hope for with a 24 dB/octave low pass filter is to flatten your upper-end rise. At that point, adding another crossover filter from an outboard crossover would get the slope looking more like what brucek’s picture shows.

Aside from all that, judging from what I see in the previous pages of this thread, it looks like you’ve applied so many cutting filters, so severely, trying to combat that upper end rise, that you’ve EQ’d yourself into a “black hole.” Naturally, this was done in the interest of maximizing the BFD’s S/N ratio, which of course is desirable. But cutting so much that the output level is really low also exacts a noise penalty. This is because you have to turn up your amplifier’s gain to compensate for the weak signal. Well, a high gain/weak signal combination is a known recipe for high residual noise, is it not?

For instance, you indicated back at post #65 that the best reading you can get on your BFD’s output meter is –20 dB. Assuming the meter is accurate, and that your Nady’s S/N spec of 100 dB is also accurate, this means you've sucked your amp’s S/N ratio down to 80 dB, which is significantly lower than the best the BFD is capable of. When you added the Ebtech, all you did was boost an already noisy signal – an increase from 1.25 vRMS to 4.89 vRMS. What’s that, an additional 400% loss in S/N?

Simply put, there is no advantage in maximizing the S/N ratio of one component – the BFD in this case – at the expense of the rest of the signal chain. After all, the S/N ratio of the system as a whole _will never be higher than the component operating with the lowest S/N._

I think your best course of action would be to install an outboard crossover that can hopefully tame your sub’s excessive upper-frequency output. Then you can use the equalizer for its intended function, equalizing response, instead of forcing it to operate as a defacto low pass filter.

Before you go that route, though, you might try brucek’s innovative house curve filter trick, as explained in Part 1 of my house curve thread. Basically, it’s using a steep, wide filter set a couple of octaves above the subwoofer’s range, with a deep cut. 

That should probably flatten out your sub’s response to the point that you could then use other filters to smooth response. At that point I would use a combination of boosting and cutting filters and try to get the BFD’s output matching the input, or close to it. Sure, it will cost you some S/N at the BFD. But if that means you get enough output from it so that your amp can adequately drive the subs, then the S/N ratio of the complete signal chain has improved enough to compensate.

Regards,
Wayne


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## PeteD (Sep 9, 2006)

OK. I agree the receiver crossover doesn't look right. I suppose the best way to see exactly what the receiver is doing would be to take direct reading of the output, instead of measuring my in-room response.

Now, maybe I am being really dense about the crossover, but let's assume the receiver's crossovers are working correctly and talk about setup in general. I can cross my mains at 60Hz, my center and surrounds at 80Hz and my rear surrounds at 100Hz, if I like. If I put another crossover between the receiver and the BFD, I am applying a crossover again. Can't I just adjust the receiver crossovers differently to get the desired response? It seems like to address the issue I was looking at, which is calibrating the BFD for a crossover response of the mains at 60 Hz for example, but then sending 100Hz crossover material from the surrounds, I would need another equalizer to adjust peaks in the response as a result of the additional input from 80 to 100Hz. Alternatively, as Wayne mentioned, why not use the BFD as a filter above the crossover and make my own crossover?

Going forward, I think I am going to use the BFD to tame my output above the crossover, which is evidently what I did the first time I equalized my response and integrated with my mains:










It seems to work really well, except for the output issue. I was concerned that I might make the output issue worse by using the BFD as my crossover, but I don't think that is true. Specifically, since my biggest peak of in-room response is at 80Hz, which would not go away, even with a proper 80Hz crossover, it is this peak that controls my degree of cutting and thus my S/N ratio that will be generated (I think). Especially since my mains will be contributing also at this frequency. I do not want crossover my mains lower than this because my surrounds will be crossed at 100Hz and I want to keep them close, plus I don't think they are up for the task. 

After doing some further reading at the Cult of IB, I have discovered that boosting down low is not very unusual with an IB. (I doubt that too many people not running an IB drop their target line down to their reponse at 10 or 15Hz and cut from there - this is exactly what I did the first time around.) It seems to take some power to get the frequencies less than 20Hz to get up to snuff, but it can be done (room gain does take care of this for many people). The key is to not boost more than you cut and not apply boost to a room mode, which won't respond. In fact, I think from reading some other posts, that boosting maybe +10dB at 20Hz with a 120/60 width (and toning down my output to the BFD by 10dB) will allow me to even out my input and output levels on the BFD. This will require some cuts above 20Hz, therby eliminating some of the boost, anyway.

I realize this will degrade my S/N ratio for the BFD specifically, but once I can run the BFD back at an operating level of -10dB, the noise in my system becomes inaudible. The reason for my running at +4 was obviously that I had to crank up the input to the BFD to get enough out the back side. The additional negative to my configuration has been the introduction of noise in my mains and surrounds from having my receiver cranked up so loud, since the mains have to be cut back relative to the sub.

I will develop multiple filter settings in REW, by tweaking the target line up in 5dB increments and creating filters using boost as needed to get to the target line. Then I will play high output test scenes at listening levels and check the input and output to the BFD to get them close to the same. Admittedly, I will then have to keep my BFD input in the green bars for safety sake, but I think it is the best compromise, given my current situation. It will be a few days, but I will report back how things work and the noise observed for others who my find themselves in my situation.

Thanks for the feedback brucek and Wayne!

Pete


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## Chrisbee (Apr 20, 2006)

I haven't read the whole thread (yet) but why is there no black line in your REW graphs to show the correction file has been applied to whichever SPL meter or microphone you are using? 

I see your blue target curve but no black correction curve to indicate you are compensating for the bass roll off in your measurement device.


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## brucek (Apr 11, 2006)

Pete, I really question whether your crossover in the receiver is working.

Examine the 40Hz trace on your graph and my target graph. With a 40Hz crossover you produce 100Hz signal at 80dBSPL. The level should be ~43dBSPL. Do you think that the room is boosting 37dB, or is the response of your sub really, really bad below 50Hz?

Recheck your crossover setup in the receiver using the BFD as test equipment.

You can use the input LED monitor on the BFD to test roughly if the crossover is correct. Shut off all speakers and sub and set the BFD LED's to monitor input (flashing green light). 
Set the crossover to 40Hz. 
Send a fixed sine wave tone at 20Hz from REW and adjust receiver volume to turn on the yellow LED. Then change the frequency to 30Hz, 40Hz, 50Hz, 60Hz, 70Hz, 80Hz, 90Hz, 100Hz. 
The output begin to drop over those settings. 
You can try and predict the drop by using REW with a 40Hz target on the screen and use the frequency follows cursor feature. i.e the level should drop over -20dB from 60Hz to 120Hz in the LED's....


brucek


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## PeteD (Sep 9, 2006)

Hey Chrisbee - I am still in the dark ages - manual measurements imported after correction factors applied in Excel.

Thanks brucek. I agree with you and was planning to do this, as I read Wayne had done in the Chrisbee boost thread. I think you are correct:

40Hz Crossover:
40 -3dB
50 -6dB
60 -6dB
70 -10dB
80 -10dB
90 -15dB
100 -15dB
110 -15dB
120 -20dB
130 -20dB
140 -20dB

80Hz Crossover:
40 -3dB
50 -3dB
60 -3dB
70 -3dB
80 -6dB
90 -6dB
100 -6dB
110 -6dB
120 -6dB
130 -10dB
140 -10dB
150 -10dB
160 -10dB
170 -15dB
180 -15dB
190 -15dB
200 -15dB
210 -15dB
220 -20dB

Thankfully, I still have 6 months of warranty. I just hope the HK-authorized repair people believe me.

Just out of curiosity, are there various degrees of rolloff for crossovers (and do they have names), or is their one standard?

Thanks - never would have had a clue about this without this forum.

Pete


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## brucek (Apr 11, 2006)

> Just out of curiosity, are there various degrees of rolloff for crossovers (and do they have names), or is their one standard?


The THX recommended low pass rolloff for a subwoofer is -24dB/octave and is called a 4th order rolloff. This is the target rolloff that REW uses for the subwoofer.

Most (if not all) receivers/processors comply with this crossover rolloff. 

Mains are usually rolled off at high pass of -12dB/octave (2nd order) and combined with their natural rolloff of -12dB/octave, hopefully this provides the best crossover transition between them and the sub.

Granted this is all very crude measurements, but when I take your figures posted and scale/normalize them to 75dB for a comparison to the normal targets of 40Hz and 80Hz I get the graphs shown below. It shows the rolloffs are fairly equal irregardless of the crossover setting. 

It would appear your subwoofer crossover is likely -12db/octave 2nd order. I get this value approximately when I extend your graph slope out a few octaves to get an idea of the slope.

Check your manual and see if they specify your low pass (LPF) crossover slope at -12dB/octave or 2nd order. If so, then it isn't a fault, it's just poor design................. who knows. Anyway, I think we can see what your problems is.....

40Hz crossover target compared to Petes measured rolloff.









80Hz crossover target compared to Petes measured rolloff.








brucek


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## PeteD (Sep 9, 2006)

brucek said:


> It would appear your subwoofer crossover is likely -12db/octave 2nd order. I get this value approximately when I extend your graph slope out a few octaves to get an idea of the slope.


Wow, brucek. You are good!

I confirmed with tech support that I have a -12db/octave sub crossover roll-off. My receiver is functioning as intended.

Anyway, I guess I am left with dialing down via the BFD or an external crossover...

Any other thoughts or implications?

I take it that my recevier rolls the mains off more rapidly to compensate, right? Oddly (to me), when I used REW and dialed my BFD into an -24dB/octave crossover, it integrated well with my mains.


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## brucek (Apr 11, 2006)

> I take it that my recevier rolls the mains off more rapidly to compensate, right? Oddly (to me), when I used REW and dialed my BFD into an -24dB/octave crossover, it integrated well with my mains..


I suggest your mains are likely 2nd order and so when you forced the subwoofer into a -24dB/octave with the BFD, then everything worked fine. 

Unfortunately, the combination of:

* the bottom end of your IB likely needing some boost.
* gain in the room likely boosting the 50-100Hz area.
* a poorly designed crossover slope in the receiver.

and you end up with having to use so much cutting down of the sub signal above 50Hz that the gain required at the sub amplifier adds a lot of unwanted noise...

Don't really know what to suggest other than playing around with filters to get the best result possible. Being armed with the knowledge of what the problem is might help in that regard.... :scratchhead: 

brucek


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## DrWho (Sep 27, 2006)

I fear being yet another cook in the kitchen, but it's quite apparent that your IB is rolling off at 12dB/octave below 40Hz.

How big exactly is the rear air chamber for your drivers? And how far away is every boundary in the rear air chamber? And what is the final size of the mouth exiting into the room? I have a feeling that your implementation is emulating a lossy 4th order bandpass.

And the "roomgain" you think you're noticing seems more inline with an increase in voice coil temperature (as the coil gets hot, the resistance in the motor increases, causing a reduction in the output where the impedance is low).

Combine that with a room induced peak around 50Hz or so and I can accurately predict the final response that you're actually measuring...Once I get over 10 posts I can provide an image for you


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## DrWho (Sep 27, 2006)

so here's a rough prediction of just one random acoustical issue around 60Hz:








And then this one is showing the effects of voice coil temperature (ignoring the increase in SPL to make it an easier comparison):








These are of course illustrations of predictions, but I tried to make the predictions as accurate to your situation as possible. So in a way, it looks as if everything is behaving as it should. However, it is incredibly interesting that you aren't showing any standing waves with your measurement - you are taking readings of test tones with an SPL Meter? You really should invest in a calibrated mic and then run some sweeps. It will show you a lot more of what is going on, in a lot less time - surely your time is worth at least something


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## PeteD (Sep 9, 2006)

DrWho said:


> I fear being yet another cook in the kitchen, but it's quite apparent that your IB is rolling off at 12dB/octave below 40Hz.
> 
> How big exactly is the rear air chamber for your drivers? And how far away is every boundary in the rear air chamber? And what is the final size of the mouth exiting into the room? I have a feeling that your implementation is emulating a lossy 4th order bandpass.
> 
> ...


The rear chamber is over 1000 cubic feet. Three of the four woofers have 6 feet or more of space behind them. The other is less than 1 foot from a boundary

The IB opening is 16 inches by 30 inches, minus a stud in the middle, or about 90% of my total Sd.

The roomgain occurred only at high volumes. I have a "L" shaped room with stairs up off the short leg of the "L". I think the bass goes up the stairs at the back of the room. The door at the top rattles at 16Hz and the low end output is decreased with the door open.

The AE IB-15 drivers that I have used very stiff coated spiders that have been discussed at the Cult forum. I suspect that the stiff suspension and lossy room are the culprits.


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## PeteD (Sep 9, 2006)

DrWho said:


> However, it is incredibly interesting that you aren't showing any standing waves with your measurement - you are taking readings of test tones with an SPL Meter? You really should invest in a calibrated mic and then run some sweeps. It will show you a lot more of what is going on, in a lot less time - surely your time is worth at least something


Yep, still using the SPL. Right now it is a balance between the money for the sound card, mic, etc. and the learning curve of running the sweeps, versus the 5 to 10 minutes to do it manually. I will get there eventually.


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