Is this thing on? Sorry, I had a glitch with my password.

I had this BFD hanging around and I wanted to see what benefits it could provide after reading how HT enthusiasts are using it as a parametric eq over on hometheaterforum. I put it in the signal path for my sub feed. I have two M&K VX-100s which are 8” down-firing subs, really compact. I hooked my PC up to the 950 with a coax digital cable for tone generation and used TrueRTA for measurements. With three adjustments, I pulled down two peaks. I also tried to fill in a null knowing full well it wouldn't work. I think it was this null that caused problems. It was about a 10 dB null at 55 and again at 110 and boosting the 55 had the expected effect of boosting 110 (and probably 165 and 220 as well). I then made the mistake of trying a DVD-A (Toy Matinee). All my speaker cals were based on the 950 DACs and DSP as were these frequency measurements, so when I switched to the 6 CH Direct, I was already out of phase. My sub placement always minimized the Outlaw 6 CH phase deal that Kevin brought to light some time ago, meaning flipping the phase switch made little difference. However, with the BFD in the chain it was very obvious that something was wrong, at least while playing Toy Matinee. This disc has significant midrange signal in the sub channel.

The 950 employs a low pass filter at 120 Hz. However, the effect I heard was in the lower mids, not the bass. The attack of the bass, bass drum and lower register of the piano was way off. The fundamentals were fine but the overtones that give the instruments their character weren’t happening. When I flipped the phase switch on the subs, it got better but not as good as it was before. I then pulled the 55 Hz boost out and it mitigated the effect some more. My thought is that the boost aggravated the low mid range that the sub was getting and the reported delay in the BFD was inducing a transient or early reflection effect that was audible in these higher frequencies. I didn’t spend a lot of time on it because I simply didn’t like it.

The bass, however, wasn't too bad at all. My subs are not capable of directly producing low bass. I think this is the case for a lot of people. It seems to me that most subs are engineered to rely on room response. In your average sized room, the room response is unavoidable so why not use it. For this reason, I think using eq to make the subs "play the room" is a useful tool to cover the symptoms as Soundhound describes them. Correcting the “problem” is really not an option for me until I decide to build a dedicated room with the correct dimensions and carefully select new equipment.

I measured my room response with pink noise, a quick sweep and a long sweep. The bass was much improved at the listening position with the BFD online, cutting down the peaks and not trying to fill in the nulls. So, until I convince my wife that the two 18” bass bins in the garage would be a nice addition to our family room, I may try to do more eq adjustments. I don’t have much hope that this will work for multichannel music but I think it’ll be fine for movies.

Finally, one problem I had with the dissertation that Bosso posted is that I think the argument starts to fall apart in the bass range. When you are talking about sounds with long wavelengths, all the subject hears is reflections and reverberations if they are standing or sitting too close to the loudspeaker. Also, wouldn’t the “perfect” speaker have to have a very large bass driver in order to produce 20 Hz anechoically? And, I’m pretty sure that what the subject hears or doesn’t hear in the bass range will be based in part on where he or she is with respect to wavelength. I’m sure this is a gross oversimplification of the physics, but for example, if my math is correct, the subject at 9 feet is sitting at a null for roughly 60 Hz and 120 Hz, so unless those frequencies are reinforced somehow by room response, they’ll be lost or significantly reduced.