# Pre-BFD jitters (questions).....:)



## Vader (Jul 8, 2006)

A couple of pre-BFD questions (OK, four):

1) After reading the BFD manual and the Guide here, am I correct in that I set the input level coming from the AVR via the speaker trim settings, then calibrate the SPL via the sub's gain?

2) I am running dual subs (not co-located), so do I need to hook each up to a different channel on the BFD (ie. both L and R) or can I simply run out of one channel and use a splitter? Does it make any difference to REW that there are dual subs when it assigns the filters? Do I need to set the filters for each sub independently?

3) When determining the house curve and dialing in phase, can I use the sine wave tones and freqency sweeps generated by REW? I have read that a sub can be damaged by playing loud pure sine tones. How loud is too loud? I'm nervous about inadvertantly damaging my drivers by doing something wrong...

4) Since I am only interested in the PEQ functionality, is there something I need to do to disable the rest of the stuff (feedback filters, etc)?

I'm sure I will have more as I get more into it... Thanx, everybody!


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## brucek (Apr 11, 2006)

> am I correct in that I set the input level coming from the AVR via the speaker trim settings


Yes........... since there is no real standard line level specification for all processors and receivers, it's necessary to make sure that the level feeding the BFD doesn't clip when you are listening at the loudest level you would use when watching a movie.

We set the trim output for the subwoofer by monitoring the input level of the BFD using its LED's. Once that's set, it's best not to touch it. So, if you need more or less level from your sub after that point, then use the subwoofer own amplifier volume control.

If you find that once that trim is set and you add any gain to your BFD filters, you may need to turn down the input level to the BFD a little. When the BFD filters are in place the LED's monitor the BFD's output level.....



> I am running dual subs (not co-located), so do I need to hook each up to a different channel on the BFD (ie. both L and R) or can I simply run out of one channel and use a splitter?


That's up to you. If you split the input and run separate lines to each sub, it allows for the possibility of two sets of different filters (may be needed)....



> can I use the sine wave tones and frequency sweeps generated by REW? I have read that a sub can be damaged by playing loud pure sine tones. How loud is loud? I'm nervous about inadvertently damaging my drivers by doing something wrong...


Use the standard sweeps up to 200Hz and add the mains (after the BFD is equalized) and then set the phase for the best transition at the crossover.



> Since I am only interested in the PEQ functionality, is there something I need to do to disable the rest of the stuff (feedback filters, etc)?


Yep. Pick the program slot you want to use and turn all the filters to 'OF' and then add filters as needed.
A lot of people use program 5 to remind them its the slot for 5.1 equalization. Use any of the slots you want though, but once you turn the BFD on for the first time, go to that program slot and turn all the filters off....

brucek


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## Sonnie (Apr 11, 2006)

1. Yes, set the input while the BFD is in Bypass mode using your sub pre-out adjustment in your AVR. Then level match the sub to your mains using your sub amp volume control.

2. I have three subs, two in each front corner and the Behemoth in the back of the room. The same filters are used for all three subs... it works beautifully. I did not have to use a separate set of filters for each sub. Actually I believe it would be impossible to try and use separate filters for each sub and then when combined have a respectable response. Try it and you will see what I mean. Simply measure all subs and then filter all of them with one set of filters.

3. Not really an issue with REW since it is a sweep. I ran somewhere around 60-70 sweeps from 2Hz to 200Hz when I was calibrating the CM-140... never an issue.

4. Not really. If you are going to use an 1124P then you could go through all the other presets and turn them to "OF" for off so that if you inadvertently changed to another preset it would not affect your response. However, the chances of that happening are pretty slim, and you'd most likely notice it. 

EDIT: Looks like brucek and were typing at the same time... he's obviously a little faster than me. While he suggest preset 5, you might also consider preset 10, which a lot of people use and will hold in memory if the power is lost for some reason.


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## Vader (Jul 8, 2006)

Bruce,

What is the recommended volume for the sine wave tones and sweeps, so that I don't damage the drivers?


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## Otto (May 18, 2006)

Vader said:


> A couple of pre-BFD questions (OK, three):
> 
> 1) After reading the BFD manual and the Guide here, am I correct in that I set the input level coming from the AVR via the speaker trim settings, then calibrate the SPL via the sub's gain?


Yep, you want to keep the input level to the BFD pretty constant, especially as you approach potentiall clipping the input to the BFD. I still tweak the sub output via my preamp from time to time, depending on program material (usually only 1 or 2 dB)



> 2) I am running dual subs (not co-located), so do I need to hook each up to a different channel on the BFD (ie. both L and R) or can I simply run out of one channel and use a splitter? Does it make any difference to REW that there are dual subs when it assigns the filters? Do I need to set the filters for each sub independently?


When I was running multiple non-co-located subs, I used one input the the BFD, and split it to the various subs. With that setup, I only had one set of filters, of course. You could do it the other way (each sub gets its own filter bank), but it will be more problematic to get the two subs to integrate nicely. Really, you want a good response at your listening position, and allowing REW to handle your multiple subs as one is probably the easiest way to go.



> 3) When determining the house curve and dialing in phase, can I use the sine wave tones and freqency sweeps generated by REW? I have read that a sub can be damaged by playing loud pure sine tones. How loud is too loud? I'm nervous about inadvertantly damaging my drivers by doing something wrong...


Yeah, you will use REW's sweep for house curve and phase setup. I don't use pure tones much for those diagnostics, and I'm not sure they will get you much -- perhaps they would be more relevant in the phase setup, but you can also do that with the normal sweeps. 

Don't worry about damaging your drivers unless you, at some point, turn the volume way up. Once your volume levels are set for the sweeps and such, they should also be OK for pure tones. If you're worried about it, just make a note of your current volume setting, turn it way down, and increase slowly. You'll be fine...



> 4) Since I am only interested in the PEQ functionality, is there something I need to do to disable the rest of the stuff (feedback filters, etc)?


Nope, REW will do it for you. Once you go into PEQ mode, the feedback destroyer mode is turned off (this is a per-filter setting, and it's easy to do -- it's right in REW, which should do it automatically).

Go for it!


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## Sonnie (Apr 11, 2006)

And some type faster than others... lol... we are all over it this morning... huh?


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## Vader (Jul 8, 2006)

That's why I love this place! Thanx, all!


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## Otto (May 18, 2006)

Sonnie said:


> And some type faster than others... lol... we are all over it this morning... huh?


You guys must have had a head start!


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## Sonnie (Apr 11, 2006)

I was using short hand, not sure what brucek was doing... I think he has a secretary typing for him... :huh:


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## allredp (Feb 7, 2007)

Hey Vader, 

I've just completed my first REW BFD setup and I couldn't be more happy with the results! :rubeyes: 

My room was really ruining some of the HZ in my LFE--now the 4 filters I added have toasted the "one note" boom I was having. Neither my M&K sealed nor my ported SVS were able to get out of the trap! 

Enter REW and the BFD... :bigsmile: 

brucek has been a champ at helping me through the steep learning curve (at least for a super-low tech like me). Looks like you're in good shape instructions-wise. 

Are you using a laptop or an HTPC?

I'm anxious to see some graphs and hear your impressions!

-- Phil


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## Vader (Jul 8, 2006)

Phil,

My computer is just an ordinary desktop PC in another room, to which I ran a couple of RCA audio cables (the longest Rat Shack had) in order to take measurements. I am looking forward to hearing what this thing (the BFD) can do for me, especially since I think the sound is pretty awesome right now!

A few more questions (told ya... and I don't even have the BFD yet - this weekend, hopefully):


> Yeah, you will use REW's sweep for house curve and phase setup.


1) From what I have gleaned from the house curve write-ups by Bruce and Wayne, the simplest way to determine my curve is to play a pure tone at 30Hz, then one at 80Hz (my XO) and adjust until I perceive them to be at the same volume. How would you use a sweep?

2) When entering the house curve data in REW, does it automatically adjust the filters for it, or is there something else I need to do?

3) Can anybody suggest a good bass-heavy sequence to set the input level? Given that there is a tremendous amount of variation between the sound level of different DVDs (ie. I cannot listen to Underworld at higher than -18dB, but Batman Begins weighs in at -10dB), does this mean that I need to reset the BFD input level for each film (That's crazy, I know...)

4) I leave my subs on auto-on. Will I get a loud "pop" when the BFD is turned on, or would you guys recommend that I leave the BFD on 24/7?

Thanks!


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## Otto (May 18, 2006)

Hi there...



> 1) From what I have gleaned from the house curve write-ups by Bruce and Wayne, the simplest way to determine my curve is to play a pure tone at 30Hz, then one at 80Hz (my XO) and adjust until I perceive them to be at the same volume. How would you use a sweep?


I've never done that myself, but I would imagine that's a valid path. Once you figure out your point at 30 and 80, though, you will enter them into a .txt file. Really, you can enter as many points as you want for your curve, but I think I have just two points -- one at 20 and one at 60. Whatever you determine them to be, once the file is created and loaded into REW, it will create a _target_ curve for you. That's where the sweep comes in. REW will sweep and then adjust filters to attain the target curve (whether it's your house curve, a flat curve, whatever).



> 2) When entering the house curve data in REW, does it automatically adjust the filters for it, or is there something else I need to do?


Yep, like above, whatever target you indicate is what REW is shooting for.



> 3) Can anybody suggest a good bass-heavy sequence to set the input level? Given that there is a tremendous amount of variation between the sound level of different DVDs (ie. I cannot listen to Underworld at higher than -18dB, but Batman Begins weighs in at -10dB), does this mean that I need to reset the BFD input level for each film (That's crazy, I know...)


I don't specifically adjust for different movies, but I defintiely allow myself some tweakability in the sub out on my pre/pro if I feel like it. Some sources are just mixed fatter or thinner in the bass department, and I like to try to keep it even to my ear (I usually only adjust by a couple dB either way). IIRC, I've tested with WOTW's emerging pod scenes and Finding Nemo's "Darla Tapping" sequence. Mine's set up to be pretty loud before I clip the input, and I've never had a problem with it (as far as I know -- the BFD's LEDs are set up to monitor the output level when things are operating; you have to specifically go into "monitor input levels mode" if you want to see input level -- and then your filters are not engaged (I think)). Anyway, once you get it in the ballpark, you can tweak it a little at both ends if you need to. That is, if you find you're clipping the input, you can turn down the level _feeding _the BFD (most likely the sub out on your receiver/pre/pro), and then turn _up _your sub amp a little to compensate.



> 4) I leave my subs on auto-on. Will I get a loud "pop" when the BFD is turned on, or would you guys recommend that I leave the BFD on 24/7?


I leave the BFD on 24/7, and I think a lot of other people do as well. Your subs being on auto-on should be OK either way. If you want to turn the BFD on only when you are using it, just do so before the subs kick on. I get the thump (and it can be quite a thump!) about 50/50.


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## Vader (Jul 8, 2006)

Ok, here are my preliminary results with the Galaxy 140 meter (no BFD yet):









I determined the room curve by listening to a pure sine wave tone at 80 Hz (70 dB), then a second at 32 Hz, which I perceived to be at the same volume at 70dB (80Hz was 70dB, 32 was was bumped to nearly 83dB...?). When this curve was applied, most of my FR was below the target...?!? So, I adjusted the curve (cheating, I know) to the best fit against my FR, then listened again to both tones. Even then, I could see them as being the same volume. I do not claim to have golden ears, so it was pretty much a toss-up. The final curve is 80.0Hz=0.0dB; 32.0Hz=3.0dB. Does this sound in the ballpark for a 3200 ft^3 room? My next question is, do I really need a BFD (would the sonic differences be significant; I mean "boomy, muddy car sub vs. clean, tight home sub" kind of significant). I love the sound as is (if I don't know what's on the other side of the fence...), the FR does not have any huge peaks or nulls that I can see, and the improvement over my original placement (BIG null at 42 Hz) is huge. What do you guys think?

EDIT: Now I'm confused. I was just playing around with the filters in REW, and it did not find all the peaks (to my eyes, the above FR has them at 20.9Hz, 25Hz, and a larger one at 46 Hz). REW only found the 20.9...?!? What am I missing?


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## Otto (May 18, 2006)

> When this curve was applied, most of my FR was below the target...?!?


Did you use "set target level" in REW (under the "Target Settings" box)? That attempts to determine the average value of your signal over the sweep range and then sets your target accordingly. Sometimes I find it shoots a little high (i.e., my measured FR is below the target).



> So, I adjusted the curve (cheating, I know) to the best fit against my FR, then listened again to both tones.


Well, I'm not sure if it's cheating... :bigsmile:, but I'm not sure it's going to do you much good either. You want to fit your FR to your target, not the other way around. But that's OK for now. 

If you have enough headroom and amp power, I might suggest that you increase your sub output so that your measurements are mostly above the target (or simply lower the target in REW -- that's also in the "Target Settings" box as "Target Level"; just reduce that number and it will drop your entire target curve.). Then, when/if you apply filtering via BFD, you should be able to easily quash your peaks to hit the target level. 



> Even then, I could see them as being the same volume. I do not claim to have golden ears, so it was pretty much a toss-up. The final curve is 80.0Hz=0.0dB; 32.0Hz=3.0dB. Does this sound in the ballpark for a 3200 ft^3 room?


Sure, that _could_ be fine, depending on your room, system, preferences, etc. 



> My next question is, do I really need a BFD?


I would agree that you have a very good response as is, and I'm sure lots of people will suggest you implement no EQ. Personally, I'd probably go for it anyway just because I'd like to see what could be done, and I like to play with stuff like the BFD. It's up to you at this point...



> EDIT: Now I'm confused. I was just playing around with the filters in REW, and it did not find all the peaks (to my eyes, the above FR has them at 20.9Hz, 25Hz, and a larger one at 46 Hz). REW only found the 20.9...?!? What am I missing?


I think JohnM has discussed the peak-finding algorithm around here somewhere, and he indicated that it does indeed not find all peaks like we humans think it should. Once you get going, it's pretty easy to target those manually if you don't like the way REW is calculating the filters for you.


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## brucek (Apr 11, 2006)

> I was just playing around with the filters in REW, and it did not find all the peaks


REW looks for peaks that it considers to be modal resonances. These have very specific characteristics. 

There's no problem with adding your own filters though, but be sure to press Optimise PK Gain & Q and Adjust PK Gains buttons to get REW to adjust them.

You can force REW to consider more of your response by simply lowering the target level with its associated thumbwheel (as Otto pointed out already) after you've taken a measurement. Then do a find peaks again etc to see if it will come up with new filter suggestions. 

It's not too necessary in your case since you've really just got a small peak around 46Hz. Manually tweak it in REW and then enter the filter and remeasure.

brucek


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## Vader (Jul 8, 2006)

> Did you use "set target level" in REW (under the "Target Settings" box)?


Yup. It just occured to me that I applied the house curve _after_ I did the sweep. Is the only thing REW does with the curve data is adjust the target, or does it in some way affect how the measurement itself is arrived at?

After playing around with last night's data in REW, applying three filters (one automatically found, two manually entered) and lowering the target level, here is the response I came up with (all filters were to _lower_ peaks, not raise them):







As a physicist (by training, anyway), I know that theoretical and real world results are rarely similar. How far away from these results am I likely to be (I have this mental image of Shrek saying "far, far away...":bigsmile ?


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## Otto (May 18, 2006)

Vader said:


> Is the only thing REW does with the curve data is adjust the target, or does it in some way affect how the measurement itself is arrived at?


Yeah, all this house curve business is just a way to modify your target. The measurement, peak finding and filter generating is all the same.



> After playing around with last night's data in REW, applying three filters (one automatically found, two manually entered) and lowering the target level, here is the response I came up with (all filters were to _lower_ peaks, not raise them):


Looks pretty good.



> How far away from these results am I likely to be


You should be able to get quite close. After the initial pass by REW, you may need to enter a few filters by hand and tweak a little, but I've generally been able to get very good results with the REW/BFD combo.


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## brucek (Apr 11, 2006)

> How far away from these results am I likely to be


If you only add cut, then they're extremely close.


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## Vader (Jul 8, 2006)

Well, I re-did my house curve completely by ear (as it is supposed to be - no cheating...), re-ran the sweep, and played around with the filters. Here is my final graph (theoretical). I think I am gonna get the BFD just because this looks so **** pretty!







In the process of taking the room curve, I neglected to turn on the C-Weighting on the Galaxy meter, and as a consequence the 32Hz and 80Hz tones were actually much hotter than the 70dB (80Hz) and 82dB (32Hz) I read them to be (by about 20dB from what I can figure). Both were running for a minute or two as I took readings, but it does not appear to have done any damage to the drivers that I can hear (thankfully!). I re-did the curve properly, and came up with a House curve of about 12 dB between 32 and 80 Hz empirically. Thanks guys for all your advice and help!


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## Vader (Jul 8, 2006)

Update: I almost pulled the trigger on a 1124DSP, but then ran across a thread at HTF where Sonnie mentioned the _possibility_ of Behringer developing a PEQ specifically for HT applications. Given that I do not have any "peaks" to deal with, and my sound is quite good and balanced (relatively speaking), I'm gonna hold off for a bit. I am gonna re-tune my babies down to 16Hz tonight - I figure that after relocating them, I lost about 3dB off the AVR trim (so, for almost a year they were operating at 3dB above where they should have been, with no problem), and retuning to 16Hz only adds about 1.5-2dB to the calibration..... Besides, taking the tune down will naturally help the minor hump I have in the 20-28Hz band... Thanks, everybody!


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## Otto (May 18, 2006)

Heh, if you're waiting for a new product from Behringer, don't. You are correct in that your FR isn't that bad. But I wouldn't expect anything better than the BFD for some time (from Behringer or anyone else). And for the price tag (<$100), it can't be beat!


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## Vader (Jul 8, 2006)

True. Hopeful thinking, I suppose (I have an inate talent for buying something, right before it's successor comes out).....


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## Vader (Jul 8, 2006)

OK,

I just got the BFD today, and I hooked everything up. Now the real questions begin...

EDIT: Ya know.... I had several questions, each of which I answered my self with a little reading (again) of the manual and the BFD guide here on the shack. The only quetsion I have been unable to find an answer for is whether I need to worry about the 1.4 firmware upgrade. The date stamp on my unit is 0701, but I cannot find any version numbers. I do not intend on using the MIDI functionality, just the PEQ stuff (manually set)...

That's all for now, but once I really get to playing this weekend, I'm sure I will have more. Thanks, all!


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## brucek (Apr 11, 2006)

> The date stamp on my unit is 0701, but I cannot find any version numbers


Fully power down the unit, press and hold the *Filter Select* button and power up.... The version number will be in the BFD display while you're holding the button down.

brucek


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## Vader (Jul 8, 2006)

Thanks Bruce!

It is already at 1.4 (Whew!). Guess I got one of the very last before they were discontinued! After playing some more with filter settings (the manual is less than crystal clear - to me, at least, I am starting to get a feel for this thing)...


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