BFD delay question....

Whadyasay

Hello All,

I'll be integrating a Behringer Fedback Destroyer into my system. After reading through the setup guide at http://www.snapbug.ws/bfd.htm , I was wondering if those of you using this with their subs have had any issues with the apparent 1 millisecond processing delay of the BFD...which I guess equates to having your sub an extra foot away from your listening position? I can set delay/speaker distance for DVD movies through my Denon AVR 2805, but I have no way to do this for SACD playback...not on the direct 7.1 input of the 2805 (which I don't use), the Sony TA-P9000ES 5.1 analog preamp I do use, or in the Denon 2200 player itself (it only has it for DVD-A playback). It's suggested that you set your sub distance for an extra foot to compensate...but seeing that all my regular speakers are about an equal 8' away from me, and the front of my SVS PB10-ISD extends about 5-6" farther out than the plane of my front mains, should this even be an issue?

gatemplin

l wouldn't worry about it. I've never noticed a problem with delay myself.

Whadyasay

Here are the results with the BFD (pink) versus the original measurements (blue). The stuff that's going on above about 75Hz is most likely due to room modes reacting to my mains, so I'll have to deal with them via room treatment down the road. A big house curve set at around 366Hz, -18dB, 120/60 BW helped get that nice slope in the upper 60's-80's. Got some more fiddling to do.

scottnbnj

Originally posted by Whadyasay
... should this even be an issue?

i'm still trying to get a handle on what exactly bfd does.

i mean, i understand that peaks are caused by reflections and that those reflections arrive some milliseconds later than the direct sound depending on the length of their path to the listening position or test equipment.

and, i understand that if you lower a peak with a conventional equalizer, you lower direct output at that frequency, but also keep the reflections relative to it. where the sum of the direct sound *plus* reflections get closer to a flat response with a continuous tone or pink noise. for sounds that attack and recede quickly, you get a dip in direct response at the corrected frequency that lingers as reflections arrive later.

does the bfd correct or account for this?

does anyone know whether this is what the delay is about? and whether moving the sub closer (or correcting with speaker distance processing), in conjunction with bfd processing, is a partial correction for the delay caused by reflections? if so, that would be pretty cool.

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gatemplin

Originally posted by Whadyasay
Got some more fiddling to do.

I've been changing my filters for at least a year now. Lots of fun. I tried a house curve for a long time but ditched it and now run it flat. You're off to a good start, and have clearly done your homework.

does the bfd correct or account for this?

No. It's just a plain parametric equalizer. We cant tell what is direct or reflected. We just measure response at the listening position and decrease the peaks to achieve a flat response.

does anyone know whether this is what the delay is about?

It's due to the signal processing in the BFD. It's really irrelevant in most cases.

Whadyasay

Yeah...I did some more. What I'm going to do is burn a CD of the actual 1/6 octave (istead of the 5Hz intervals I was using) test tones and go again. Also want to mess around more with bandwidth, and then ssee how a house curve will affect things again. Delay isn't an issue because my PB10-ISD has continuously variable phase adjustment, so I just find the right setting after everything's done. The only peak I can't really get rid of is at around 98Hz, as well as the dipi at 112Hz, which is really not coming from the sub, but the mains and room (tried it with the sub off), so I'll have to think about room treatment. It has definitely helped things, though. I don't get that annoying crunchiness when large bass rumbles come up on DVD's...like the sub over the edge in Nemo or the opening battle in LOTR Fellowship. Running bass lines in music are also much more even.

gatemplin

That looks good. Don't worry too much about the nulls. The only way to get rid of them is to move the couch, move the sub or build traps. Dont boost them, but I'm sure you already know that.

For phase, I use a test tone at the crossover frequency and rotate the phase dial until it reads loudest on the meter.

Whadyasay

That's what I did too...ended up at about 10 o'clock, with 7 o'clock being 0 degrees.