Would a BFD help? what does it do?? [Archive] - Audio & Video Forums

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bjornb17
02-11-2005, 09:25 AM
Hi,

I've stumbled across a couple threads which describe BFDs, and how they help with subwoofer response. What exactly do they do and how do they work?

I have a Velodyne CHT-12 which does a great job. i think the 25Hz response is at -3db or so. would a BFD help and what could i expect of it? I like deep bass a lot. i have my crossover for my subwoofer set at 40hz since my mains can go deeper than that, and i love the impact of the low tones.

My room size is 11x14 (i know, kind of small for a subwoofer like that). any help would be appreciated. Thanks!

Sir Terrence the Terrible
02-11-2005, 10:05 AM
Hi,

I've stumbled across a couple threads which describe BFDs, and how they help with subwoofer response. What exactly do they do and how do they work?

I have a Velodyne CHT-12 which does a great job. i think the 25Hz response is at -3db or so. would a BFD help and what could i expect of it? I like deep bass a lot. i have my crossover for my subwoofer set at 40hz since my mains can go deeper than that, and i love the impact of the low tones.

My room size is 11x14 (i know, kind of small for a subwoofer like that). any help would be appreciated. Thanks!

The BFD is made for live reinforcement rigs. It is designed to automatically, and digitally control any feedback coming through the microphone speaker loop in live conditions. It, by way of it's precise boost and cut filters, just happens to be handy for controlling modes and nodes in small rooms via the subwoofers output.

All rooms introduce peaks and valleys when speakers are placed in them. Depending on where they are placed, it will excite the peaks, or emphasize the valleys. The BFD allows you to dial in precisely the peak amplitude(mode) and the width(frequencies effected), and introduce a cut in amplitude to that peak(via the subwoofer output), which smoothes the overall output and frequency response of the speakers(most likely sub). At this point you set the balance of the subwoofer to the main speakers. This is the most effective, and accurate way to setup a sub once it's optimum position has been found in the room.
You will most likely have to turn up the sub, because you are now balancing the sub to the mains with a flatter frequency response than you had before.

If you have a subwoofer in your system, the BFD is a must have. In all of the years I have been installing and tuning high end music and theater systems, I have never met the perfect room/speaker balance. Every room has a resonance point, and if you place you sub anywhere near a corner, that resonant point will be fully or partially excited.


What the BFD can do for a systems overall balance is pretty amazing, and it's cheap too!

Woochifer
02-11-2005, 12:52 PM
In addition to what Terrence already said (I also use a BFD, which stands for Behringer Feedback Destroyer, and have had tremendous results using it as well), I think that for your setup, you should first head down to Radio Shack and grab a SPL meter. Use the SPL meter to take some in-room response measurements using test tones. Since you only have the subwoofer taking over at 40 Hz, then you might not need to do the kind of room correction that the BFD does since the subwoofer works within a much narrower range than with the more widely used 80 Hz crossover point.

After taking the measurements, look and see if you can find any huge peaks in the response curve. If you see something at about +6 db or higher, then you might want to consider using a parametric EQ like the BFD to correct that. The net effect of the BFD will depend on how severe your room problems are. The typical improvement with a BFD hooked up is more accurate, even, and full bass.

Keep in mind that these peaks are created by your room, and these room interactions also affect the main speakers. In most cases, main speakers are positioned somewhere along the front wall and not right in the corners. That type of positioning is usually best for the imaging, but it also has the least bass reinforcement. The main speakers are also susceptible to room effects, so you should take an in room measurement with them as well. If you find that the bass response is uneven, then you might want to raise the crossover point to 60 or 80 Hz. By redirecting the lows to the subwoofer, it gives you the flexibility to place the sub where the bass sounds fullest and most even, and it allows you to use the BFD to do the room corrections. With the main speakers, you don't have an easy way to do those kinds of room corrections without compromising the best location for the highs and mids.

Another note on the BFD, it was originally designed for pro audio use, but it has grown in popularity with home theater users because it also happens to be the lowest priced parametric equalizer on the market. But, because it was designed for pro audio rigs, and intended to be used for feedback reduction, the instructions suck for the parametric EQ function. Also, the BFD is not very intuitive to use. I suggest you go over to Sonny Parker's BFD setup site for all the info you need on how to setup the BFD. It also has downloads for test tones and the correction charts for the Radio Shack SPL meter (which uses a mic that's less sensitive in the lower bass).

http://www.snapbug.ws/bfd.htm