# Do I need a BFD?



## Danothemano (Jul 5, 2008)

I've taken some measurements and I have some pretty nasty dips and peaks. The big peak is about 10dB more than the curve. I was pondering whether I should get a BFD so I can try and smooth some of these things out. I've tried moving the subwoofer around, but that only made the peak worse.

I've been a little disappointed with the low bass from my sonosub, but I think that is because I am turning it the level down so the 40-60hz range wasn't so boomy and loud. So what do y'all think?


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## brucek (Apr 11, 2006)

> because I am turning it the level down so the 40-60hz range wasn't so boomy and loud


Yep, that's exactly what you're doing. 

You do need to address the peak from 35-55Hz.

brucek


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## Danothemano (Jul 5, 2008)

So with the BFD I've read I could connect it to my E-MU 0404 with MIDI and just send the filter corrections straight to the BFD and that's it? I don't need to have the midi cable connected after I send it over?


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## brucek (Apr 11, 2006)

Yeah, you can send the filters with a midi cable (or enter them manually).

The midi cable is only for loading the filters - that's it.

brucek


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## Danothemano (Jul 5, 2008)

Anywhere I can get a BFD1124 cheaper than $100? Hopefully this is the last thing I have to buy for a while. This is a pretty expensive hobby, but worth it.


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## brucek (Apr 11, 2006)

e-bay............


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## Otto (May 18, 2006)

Right here, sir. Let's go $75 shipped...


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## Danothemano (Jul 5, 2008)

I don't need a MIDI to USB right? Just a straight up MIDI to MIDI cable?


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## Otto (May 18, 2006)

Danothemano said:


> I don't need a MIDI to USB right? Just a straight up MIDI to MIDI cable?


Depends. You don't actually need the MIDI cable at all, if you don't mind entering the filter values by hand. It's not that hard, but the MIDI connection does streamline things a bit. Still, the BFD will be 100% functional for EQing your sub with or without the MIDI connection. 

If your PC (it was on my sound card as a game port or something) has a MIDI output, you'll need a MIDI cable with the MIDI connectors on one end and the game port thing on the other end. I'm not sure if there's a common PC output that would just take a MIDI to MIDI cable. I admit that I'm not terribly familiar with MIDI.

If your PC doesn't have any type of MIDI output, then the easiest way is to just get the USB to MIDI cable.


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## brucek (Apr 11, 2006)

> E-MU 0404 with MIDI


Since you have a soundcard with a midi, then you need a midi to midi.

brucek


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## Danothemano (Jul 5, 2008)

And how would I transfer all of the settings over? Also, how does this look compared to my old graph. These are the settings I would likely apply.


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## brucek (Apr 11, 2006)

> And how would I transfer all of the settings over?


Read and become familiar with the REW HELP files. 

Here is the page to read.

brucek


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## Danothemano (Jul 5, 2008)

Got my BFD setup today. Wow. I really cannot thank you guys enough. I sent my filters across with an MIDI cable without a hitch. First movie I had to plop in was Black Hawk down. I went straight to the "Irene" scene. I could literally feel the helicopter as it was taking off. Before, I could barely feel it at all. The people in the other room said that the ceiling fan was vibrating.

I really cannot wait to watch other movies and re-watch some with the BFD installed. I have no idea why I didn't do it sooner.


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## Eric D (Feb 9, 2009)

This thread should almost be a clinical study - your first graph was so good and the measurement showed such a clear hump that would be easy to treat that even I knew how much you were going to love the results.

Happy for you! I still remember when I first eq'd a sub and got rid of a hump like that. Doing eq right is as good as getting the sub in the first place, isn't it. 

enjoy!


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## jschaefer7406 (Feb 5, 2009)

Hello all,

I have the same problem (needing to lower the overall sub volume to avoid "boominess"). I am hoping to have that deep bass back into my music and movies as well. Received the BFD today, now just waiting on the MIDI cable...

Joe


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## joz (Jul 14, 2008)

Getting back to the OP.
Do you need BFD??

Ummm,yes you do..at least something that does EQ.
I'm sure atm your bass may sound a bit FAT and slow.
With eq although it may sound leaner it'll be more accurate.
By that you should hear is the individual bass notes rather then the usual boom boom!
What the EQ wil do is reduce the doubling up of certain bass frequencies (floor bounce)
that bloats the sound..

Don't worry you're not alone here,most systems need some EQ ( they just don't know it yet)!

PS still an EQ newbie here, finding his way!


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## Danothemano (Jul 5, 2008)

joz said:


> Getting back to the OP.
> Do you need BFD??
> 
> Ummm,yes you do..at least something that does EQ.
> ...


I already bought one and posted about it above. It is really amazing what just a simple EQ can do.


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## Eric D (Feb 9, 2009)

And just to pile on to the OPs response, see just above where his words were: "I have no idea why I didn't do it sooner."

For those of you thinking about it, ask around for someone near you who's done it, and ask for a demonstration of what the difference is like. IMO it can be as much difference as getting the sub in the first place. And also IMO it's far better to get an adequate sub and eq it than it is to get a great sub that doesnt' respond well in the room.

I used to do figure out the adjustments using frequency sweeps from Avia. Had to watch the SPL meter and try to track the SPL to the frequency on the screen in real time - it usually took several runs to try to get close to the peak level and the frequency, much less the width. Long, slow and boring. Then after attempting an adjustment, repeat that whole process. :thud: But I had Wow! moments of bass clarity even with that technique that made it all worthwhile.

Using REW and getting good accurate visual data has made it MUCH easier even if I had to do my own ciphering and then remeasure. But also being able to let the program figure out placement of the filters, and/or simulating my own, and having it show a visual prediction the results, so that all I have to do is match the settings on my PEQ. :yay:

Anyway, that's my 2 cents. Hope Dano doesn't mind me jumping on his bandwagon.

enjoy!


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## Danothemano (Jul 5, 2008)

Not at all. What movie should I try next? Cloverfield?


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## salvasol (Oct 31, 2006)

Danothemano said:


> Not at all. What movie should I try next? Cloverfield?


War of the World
Transformers
U-571
Master and Commander
King Kong

Just to start...:bigsmile:

You can also read question #9 ....* here  *


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## bcharlow (Dec 23, 2008)

You will really find the BFD useful and you'll love the results. 

I found mine for under $60 delivered by bidding on eBay. They come up frequently, so set a search filter to alert you.

Frankly, this is the best money I've spent in years on my stereo! I cannot believe how well a simple EQ unit for sub (only for sub, not for mains) can make the sub integrate properly in a difficult room.

Try it and be amazed at the results.

FYI, I use mine only for music, strictly a 2 channel guy. If you're after HT use for BOOM BOOM in movies, I'm not sure EQing a sub is really very important.


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## Rambo4 (Jan 25, 2008)

Would it be preferrable to go with just the Audyssey EQ with a receiver, like say a Denon 2808CI, first and then introduce the BFD? Or would that be a case of too many cooks?


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## Eric D (Feb 9, 2009)

bcharlow said:


> .... If you're after HT use for BOOM BOOM in movies, I'm not sure EQing a sub is really very important.


Oh yeah it is! Without it, all you often hear is the typical 40-70 Hz freq hump from the walls and floor/ceiling. You can get it nice and loud, and you would be probably happy if you didn't know what you were missing. But once you get a nice clean low effect that is so visceral, there's no going back! :flex: It does help bring peace to my house, as I don't have to turn up the movie so loud to get some impressive BOOMs.

P.S. I also love what eq'ing does for music.


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## Eric D (Feb 9, 2009)

Rambo4 said:


> Would it be preferrable to go with just the Audyssey EQ with a receiver, like say a Denon 2808CI, first and then introduce the BFD? Or would that be a case of too many cooks?


I haven't done it (older receiver still), but from what I understand it is a great idea to do both. I don't remember the order in which you want to do them though - that info should be around here somewhere.


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## Rambo4 (Jan 25, 2008)

Thanks Eric, I'll check a few more threads. It is likely best to do both, the less is more philosophy is encouraged in the Two channel audio world for music in my experience, but dealing with deep bass down to 20Hz and room resonance goes out of that realm and worth experimenting.


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## bcharlow (Dec 23, 2008)

Sorry, not a clue.


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## fredk (May 14, 2008)

> FYI, I use mine only for music, strictly a 2 channel guy.


I wonder if everybody's room responds differently to EQ? I applied a huge 16db cut at 52Hz to tame a peak. I was expecting to hear a big difference for music, but found it hard to tell the difference with most material. 

The most notable difference is that the kick drum is quieter; almost a bit recessed compared to before. I havn't done an on/off comparison with pipe organ music yet.

For HT, there is a definite difference. I can actually feel some of the lfe now. I live in a concrete formed apartment so I figure this is a big acomplishment.


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## bcharlow (Dec 23, 2008)

My apologies. Wasn't meaning to insult HT users. Just meant that so many are looking for the dinosaur footsteps, and the quality vs. quantity issue wasn't the point in that genre. Obviously, better quality sound is better quality sound; if in you can better replicate what we hear in the real world with our reproductions, it has to sound better to any discriminating ear! 

I'm just making the point that I'm not listening loud (average 72db) at all and listening for a particular range of sound (not really much below 28 Hz in music at all).


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## bcharlow (Dec 23, 2008)

That's the whole point of EQ: Everybody's room responds differently. So how you set your EQ is equally idiosyncratic and your results are too.

If you set it correctly and completely and IF the musical recording has the detail in it (that's a big if with a lot of stuff in the LF), then you will start to recognize that you will hear differences that are significant and appreciable (in the full sense of that word). 

To my ears synthesized sound is very obvious almost always, and especially synthesized LF tracks. Too much pop and rock is exactly that for drums, for example, so you'll never get realistic sounding drums in my book (I was a percussionist in younger days), nor realistic bass. Sure you can get and love electric bass, but it doesn't have the same nuances (has its own) as acoustic bass. 

But to top it all off, for decades recording engineers appear to have deliberately suppressed or neglected the bass instruments, deeming them too loud and unimportant compared to the other instruments. So the acoustic bass or the drums were recorded at an unnaturally low level of SPL and fidelity/clarity, farther from the mikes. You can hear this in lots of stuff recorded from 1950s through early 70s, for example, and you'll know because those instruments are lower, less distinct, and the sound is laughable when they try to turn up the volume slightly for their solos. 

From such recordings as the above 2 groups, you'll never get good LF fidelity in my book. But you can do better than boominess still with EQ.

On AA, RBNG taught me that there are often 3-4 bass peaks worth taming in the average sub in the average room. I bothered to work with all of them and the results are decidedly much much better.

Here's the kicker: We don't hear much in the classical sense below about 32Hz, we feel it more. So how well our ears distinguish the nuances might vary considerably with physiology, room response and how our ears are attuned to select differences for our preferences.


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## fredk (May 14, 2008)

> But you can do better than boominess still with EQ


I am not so sure about that. EQ can reduce peaks, but it does nothing to treat that which creates those peaks, so the ringing stays. I have EQd peaks at 22Hz, 34Hz, and 52Hz. That has reduced the ringing by about 200ms, but it still dosn't hit the noise floor until between 500 and 600ms. I am sure that is still quite audible. Definately an improvement though.


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## Bailman (Nov 21, 2006)

fredk said:


> I am not so sure about that. EQ can reduce peaks, but it does nothing to treat that which creates those peaks, so the ringing stays. I have EQd peaks at 22Hz, 34Hz, and 52Hz. That has reduced the ringing by about 200ms, but it still dosn't hit the noise floor until between 500 and 600ms. I am sure that is still quite audible. Definately an improvement though.



The author of REW :hail: , JohnM, claims he has not only reduced peaks but also reduced ringing through the use of the BFD and REW. I am still in the process of rereading this thread which although is a review of the DSpeaker Anti-Mode 8033, it addresses ringing.

http://www.hometheatershack.com/forums/bfd-forum/11699-testing-dspeaker-anti-mode-8033-a.html

I have never used REW and I am not using my BFD at this point having MultEQ XT. I am not so happy with what has happened to my low end compared to a RS SPL Meter and BFD. It seems from a quick review of this thread that using a few different graphs provided by REW you can in fact knock down ringing.

Now if only I wasn't a procrastinator.


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## brucek (Apr 11, 2006)

> EQ can reduce peaks, but it does nothing to treat that which creates those peaks, so the ringing stays


Not true. The filters in the BFD operate both in the frequency and the time domain, just as a modal resonance does. If the gain and bandwidth of a filter are carefully matched to a resonant peak, then both the excess amplitude and the excess decay time will be nullified. This is exactly what REW attempts to do in its filter matching of peaks.

brucek


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## dachness (Feb 17, 2009)

Hello,

I was wondering if any one could confirm that a BFD will help to improve the signal from a receiver to a pro amp?

I understand that often times receivers output isn't high enough for pro amps. 

Daniel


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

fredk said:


> I am not so sure about that. EQ can reduce peaks, but it does nothing to treat that which creates those peaks, so the ringing stays. I have EQd peaks at 22Hz, 34Hz, and 52Hz. That has reduced the ringing by about 200ms, but it still dosn't hit the noise floor until between 500 and 600ms. I am sure that is still quite audible. Definately an improvement though.


With a properly tweaked filter that's well matched to a room mode, you can expect to see ringing reduced. However at best it will only be brought back in line with the prevailing rate of decay in the room. With many rooms you can expect to see ringing increase the lower in the frequency spectrum you go. 

Keep in mind that not all peaks in response are room modes - you won't see an improvement in ringing in those, although it will definitely sound better to get them back in line with the rest of the response curve.

Regards,
Wayne


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

dachness said:


> Hello,
> 
> I was wondering if any one could confirm that a BFD will help to improve the signal from a receiver to a pro amp?
> 
> I understand that often times receivers output isn't high enough for pro amps.


The BFD is not designed to operate as a line driver. Boosted filters will indeed increase the BFD's signal output, but only in the frequency range of the boost. If you want to boost overall signal level, an inexpensive "project mixer" like the Behringer 802 will do the trick.

Regards,
Wayne


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## fredk (May 14, 2008)

> The filters in the BFD operate both in the frequency and the time domain, just as a modal resonance does.


You lost me on this. I guess I am not entirely clear what 'time domain' means.



> However at best it will only be brought back in line with the prevailing rate of decay in the room.


This is what I was trying to get at. You cannot change the rate of decay with EQ. You need (a lot of) absorbtion to keep those sound waves from bouncing back and forth.


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

fredk said:


> This is what I was trying to get at. You cannot change the rate of decay with EQ. You need (a lot of) absorbtion to keep those sound waves from bouncing back and forth.


 You are basically correct: Absorption is the best method for improving the rate of decay in a room. However, equalizers do introduce phase changes, so in that sense they do have a time domain element. That’s not necessarily a bad thing - as Rane's Exposing Equalizer Mythology article explains, “Amplitude, phase and time are all inextricably mixed by the physics of sound. One does not exist without the others.”

As John M explaines in this post, a room mode will exhibit a slower rate of decay compared to the rest of the frequency spectrum. Take a look at this waterfall graph of a 42 Hz mode:










Note that spacing between the mode’s slices are _closer together_ than the areas to each side of it. That shows the mode is decaying at a slower rate than the other areas, and indeed at the 200 ms point it has not decayed nearly as much as the rest of the frequency spectrum has. 

If we apply an EQ filter matched for that mode, it will of course have little or no decay element because it’s electronic, whereas the mode is acoustic. Nevertheless, when we apply the filter, we’ve robbed the mode of energy and essentially defeated it. The signal now decays at a rate more typical of other frequencies. So the equalizer doesn't necessarily _operate_ on the time domain (as say, a digital delay device would), but it does _affect_ the time domain.

You can see the effect with this waterfall. It has a parametric filter cut several dB applied to the same 42 Hz mode. The signal was level-matched after the fact, bringing the 42 Hz region back up to the same SPL level it was at before the filter cut was applied. As you can see, the spacing between the slices at the mode’s frequency center are now about the same as those adjacent to the mode. IOW, the mode’s rate of decay is much improved and brought back in line with the prevailing rate in the room.










Anyway, hope some of this makes sense...

Regards,
Wayne


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## JohnM (Apr 11, 2006)

Wayne A. Pflughaupt said:


> So the equalizer doesn't necessarily _operate_ on the time domain (as say, a digital delay device would), but it does _affect_ the time domain.


Nice illustrative plots, Wayne. I would like to correct one misconception though: equalisers do operate in the time domain, indeed it would be more correct to say that by far the majority of equalisers _only_ operate in the time domain, the filter maths is fed the sequence of samples in time of the input signal and calculates new time samples for the output. We are so used to being shown the frequency response effects of EQ filters it is easy to forget that they nearly all operate directly on the signal time sequence. 

The decay times of filters are not insignificant. For example, a -9dB filter at 42Hz with a bandwidth of 4/60ths of an octave (using DSP1124P settings) has a 60dB decay time (analogous to RT60) of 312ms. It would counter the effects of a mode at that frequency whose 60dB decay time was 879ms, however, so an 879ms decay is turned into a 312ms decay and at the same time the level is reduced by 9dB. A filter with 9dB of _gain_ at 42Hz would have an effect very like a modal resonance itself, the 60dB decay time would be 879ms. That is why narrow boost filters are usually a very bad idea.


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

Thanks John, great info! :T

Regards,
Wayne


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## brucek (Apr 11, 2006)

> You lost me on this. I guess I am not entirely clear what 'time domain' means.


An example may help.

If I feed REW directly through a BFD (line-out of soundcard to a BFD and then back to line-in of the soundcard) and turn on a single filter, you can see how both the amplitude and the time domains are affected in the resulting waterfall plot of the filter shown below. 

Note how the decay carries on in the time axis of the plot. 

In fact, this also represents what a modal resonance looks like. It creates excess amplitude (in the frequency domain) due to the modes gain, and excess decay (in the time domain) due to the modes decay.


*Waterfall plot plot of a BFD using a single filter of (40Hz, Gain +15dB, BW 10)*









So, you can also imagine that if I created a BFD filter with a cut and bandwidth that closely matched a room modes amplitude and bandwidth, then I would eliminate the resonance at the measurement position.

That last statement is important, because no one is saying that an equalizer changes a room mode. It simply removes the modes effect *at the listening / measurement position*. And what more can we ask for of an equalizer other than to make our listening position correct. We can't expect it to change the entire room, and it doesn't. That's where treatment is your best bet. But there's often a limit what treatment can do, so we add EQ to correct the listening position.

I was once challenged by Wayne to prove that filters operate in the time domain in the real world, so I did a little experiment to prove it here. You can make your own decision on the results..........

brucek


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