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.

I agree with Bosso's post for the mid and upper frequencies but not for the sub frequencies. The post describes how you hear the direct sound first then the reflected sound. This holds true except for the sub which may have the speaker not pointed directly at you (like the LFM-1) so all that you get would be reflected sound. I don't currently us any EQ but in the past I have used it for attenuation only which did seem to help.

Whether the the sub fires front or down, there is still a direct radiated wave that hits you before the room-affected wave.

When you attenuate a frequency band that is peaked because of a room mode, you attenuate the direct radiated wave.

This allows the room affected wave to dominate what you hear, as the direct radiated wave is attenuated well below listening level.

So, what you hear at listening level is delayed by the distance disparity of the the sub placement vs. the mains, by the DSP of the PEQ and by the room mode.

You may play a ruler flat line, but what you're hearing is grossly time-smeared (which doesn't show up in the graph) in relation to the rest of the speakers, which changes the kick drum from a 'tock' to a 'thhwock'

If you draw a circle around the LP so that every point on that circle is equidistant to the LP with the mains, and use that line as the possible placement options for the sub (+/-) 1 or 2 feet, you have the start of accurate sub integration.

If you then chart the mains without the sub, so that you can determine the in-room slope of their roll-off, after the HP filter, then shut the mains off and do the same for the sub, you can tweak the slopes to resemble a proper crossover...that's step #2.

Tweaking the phase comes next, to fine tune time arrival to your ears of the sub + mains.

This is followed by level calibration, at the crossover point. If the sub and mains aren't exactly the same volume at the crossover point...there goes your entire 2 octaves of crossover region.

Many times, IMO, a dip and/or a peak are mistaken for room modes, when in fact, they are mismatched crossover slopes and badly out of phase sub/mains in the crossover region (which stretches from 30ish to 200 Hz. Run several graphs with the only difference being a 20 degree change in phase of the sub each graph and see how wide a bandwidth is affected).

I believe this because I'm +/-3dB from 15-30 Hz., and +/- 2dB from 30 to 200 Hz., with NO EQ. And, I assure you that my room isn't some magic size and shape.

Maybe I was lucky, but it sure sounds good, and that's always convincing evidence.

>> 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. <<

Yes! This is what "corner" loading is all about. But because the walls of the corner are relatively close to the sub, there still isn't much delay between the initial signal, and at least the 1st reflections. Especially considered wrt to the wavelengths involved.

>> You may play a ruler flat line, but what you're hearing is grossly time-smeared... <<

Yes, but this is why I adjust phase *after* setting up the eq. To regain time alignment.

Plus, I'm only attenuating the single peak by about 5 dB. Not a humungous amount, all things considered.

>> If you draw a circle around the LP so that every point on that circle is equidistant to the LP with the mains ... <<

"LP" stands for ... ??

LP = Listening Position I believe.

KCB,

I've always felt that you have a good handle on sub tweaks. 5dB boost is acceptable, IMO, when using a PEQ.

Do you still use Vandersteen sub(s)? It would be cool to hear your setup someday.

LP=listening position..sorry.

This reminds me...DB asked, in the original question, if changing the distances of the satellite speakers would compensate for the delay. The answer is no. The delays are based on the farthest distance being 0 delay. Since there's no subwoofer distance setting, there's nothing you can do to compensate for a subwoofer being farther away from the listening position (physically or virtually), which it almost always is with a corner placement and/or when using outboard DSP equipment.

This is something the next-gen pre/pro should definitely have that the 950 (and many pre/pro/receivers) doesn't.

I need to think on this some more. The nature of bass waves is highly interdependent and I don't believe the direct wave from our little subwoofers dominates what we hear, Soundhound's system notwithstanding. The drivers are simply too small to support waves that are 20 to 30 ft in length without help.

I'm sure I don't have any crossover problems in my room and the position of the subs is fixed. Nonetheless, I'm going to run the tests that Bosso suggests and see what the charts look like.

Thanks for the answer on the delay settings in the 950.

BoB- (I always really learn stuff from you and SH...)

>> If you draw a circle around the LP so that every point on that circle is equidistant to the LP with the mains, and use that line as the possible placement options for the sub (+/-) 1 or 2 feet, you have the start of accurate sub integration. <<

But, and this is why I have become so fanatical about phase *and* time alignment, this does not compensate for the phase delay introduce by the LPF (= low pass filter) of the pre/pro. Plus, this distance might result in nasty room interactions depending one where those equidistant points falls wrt the room boundaries.

Yes, still have the Vandersteen V2W. (Good memory!) I have been looking at the SVS PB2+, but I just can't get past how big and heavy it is. But ... it has flat freq response to 11 Hz. (I've measured mine, and I'm flat to 21 Hz, down 6 dB at 20 Hz.)

One of the reasons I mention stuff like this thread contains is, I remember debating the merits of SH's stereo subs in a thread (or 2, or 3), using logic and accumulated knowledge.

When I actually TRIED the setup, using the appropriate source material, per SH's suggestions, guess what...it worked, as advertised (and thanks to SH for his long-suffering at my expense).

Some of what gets posted is mistaken thought, some is pure gold. Nothing ventured, nothing gained.