Woodpin

BFD or LT for sealed sub EQ?

I havent found a thread that deals with the issue of wether to use a Behringer Feedback Destroyer or a Linkwitz Transform circuit to flatten the response of a sealed subwoofer down to 20 hz or so (my target). I understand that the LT circuit surgically sets the response of the driver to whatever frequency your target is, assuming ideal conditions, but the BFD is easily programed to compensate for any environment or placement quickly. Is the choice motivated by cost, or is there a good reason to choose one over the other regardless of cost? Perhaps incorporating both is the best answer. Any thoughts?

Thanks,

Woody

Robert_J

Re: BFD or LT for sealed sub EQ?

Two different pieces of equipment used for two different things. A BFD is used to pull down peaks in the frequency response caused by your room. It can be used to pull up valleys but if they are truely room modes, then there is very littly you can do.

An LT circuit is used to make a sealed sub with an Fb of A hz and Qtc B sound like a sub with an Fb of X and a Qtc of Y. It does nothing to flatten the response. Remember that boosting the low end eats up amp power and driver excursion quickly. Make sure both are up to the task.

-Robert

David_P

Re: BFD or LT for sealed sub EQ?

A BFD (or more flexibly, a DEQ2496) will do SOME of what a LT can do, but not all.

LT allows you to modify system Q, and increase low end extension (lower Fb).
E.g., you can build a sealed system, size it such that it is power-limited (e.g. volume is small enough that the power you're applying cannot bottom the driver(s)), then modify system Q to get the sound quality you want (e.g. lower Q from .8 to .5), then add extension (lower Fb from say 35hz to 20hz).

All can be done, at the same time, with a LT cct.

A DEQ2496 can give you the extension bit of it... in essence you build a wide filter centered at 300-400hz with a 10-15 db cut. This has the effect of boosting the bottom end. By upping the input, or amp output, you end up creating greater lowend extension.

The real advantage of a BFD or DEQ 2496 comes from being able to equalize your room... you'll want one JUST for that, trust me.

if you look at my sub project, you can see how I ended up using both a LT and a BFD

http://www.hometheaterforum.com/htf/...d.php?t=245726

David

Woodpin

Re: BFD or LT for sealed sub EQ?

Thanks, guys,

I had an idea that I would ultimately need both. My sub has around 27 mm one way travel and I don't intend to over drive it. Just want to hit low C on pipe organ passages with authority as well as demanding movie soundtracks.

Woody

MaRtIn^dB

Re: BFD or LT for sealed sub EQ?

Quote:

Originally Posted by Woodpin Thanks, guys, I had an idea that I would ultimately need both. My sub has around 27 mm one way travel and I don't intend to over drive it. Just want to hit low C on pipe organ passages with authority as well as demanding movie soundtracks. Woody

squash the BFD...you can't set the filters wide enough...however the Behringer FBQ2496 or the DEQ that was mentioned can dig up the bottom without the need for a Bassis, which btw, is a nifty piece of architecture...the way i did it was to set two filters...one at 20 Hz (10 octaves wide/ + 7 dB) and the second at 130 Hz (5 octaves wide/ -9 dB)

These shelving filters overlap and work together to form a smooth linear curve while also keeping group delay in check...because the 130 Hz has less width, the gain from the 20 Hz filter is largely kept intact in the final analysis...

You mention pipe organ music...what size driver are you using?...if it's sealed, then you should probably look at a 15". Good luck, martin

2x15" TC Sounds .45Q sealed
M. Boutte HT
3x15" @ 10 Hz