Which is better for a DBA (Swarm); powered subs or unpowered?

Ieales wrote:

" DBA proponents are not charlatans, but neither are they correct as the the ability it to produce time coherent bass. "

Arrival time coherence in the bass region is not critical, but decay time coherence in the bass region is.

The ear is incapable of even registering the presence of bass energy from less than one wavelength. And the ear is incapable of registering pitch from less than several wavelengths. This from a Journal of the Audio Engineering Society paper which I no longer have access to.

So the ear simply does not have enough time-domain resolution in the bass region to detect arrival time differences of a few milliseconds.

So let’s look at the decay times. The longer a sound lasts, the louder it is perceived to be. So bass frequencies which take longer to decay sound louder.

Also, since speakers + room = a "minimum phase" system at low frequencies (according to both Floyd Toole and Earl Geddes), when we know the frequency response, we know the time-domain response. Thus is it the peaks which take longer to decay into inaudibility. This implies that the frequency response is particularly important at low frequencies.

Which indeed turns out to be the case. If we examine a set of equal-loudness curves, we see that they bunch up south of 100 Hz, such that a 6 dB change at 50 Hz is perceptually comparable to a 10 dB change at 1 kHz. This in turn implies that improvements in the frequency response in the bass region pay subjectively large dividends.

In other words I believe that a good distributed multi-sub system addresses the issue that matters the most to the ears; namely, the in-room frequency response.

Ieales again: "By FAT I mean that unless time correction is implemented the separate sub signals will arrive spread over several milliseconds...

"IMO, it’s as unlistenable as MP3...

At RMAF 2017 we displayed using a distributed multi-sub system in one of the standard (small) hotel rooms. An industry veteran cable manufacturer, with several decades of experience, handed us his thumb drive and asked us to play a recording of Fanfare for the Common Man. When it was over, he told us that was the most natural rendition of the tympani he had ever heard in any room at any audio show. He said it sounded just like what he heard when he went to a concert.

(Incidentally in my experience the term "fat" is normally associated with a frequency response peak and its attendant long decay time, so it IS a time-domain issue - but applicable to the DECAY behavior, not the ARRIVAL TIME behavior.  Our ears cannot react fast enough to hear "fat" in the arrival of bass energy).  

So I’m going to go out on a limb and claim that Ieales’ statement that a distributed multisub system is "as unlistenable as MP3" is an exaggeration. If he wishes to prioritize arrival time that is fine with me, we have a difference of opinion on that subject.

Duke

@cleeds wrote: "The price for that smooth, even, neutral bass is that your bass will be monophonic."

This is a misconception probably arising from the fact that the "regular" configuration for my price-conscious Swarm system only uses a single channel of amplification, and from my statements that true stereo bass is quite rare (which is controversial and has been disputed). For a few hundred dollars more, some Swarm users have added a second amplifier, though imo the most significant advantage of the second amplifier is that it gives you the option of introducing a 90 degree phase difference between the subs on the left-hand-ish side of the room and the subs on the right-hand-ish-side of the room. This can be done whether the signals going to the left and right amps are mono or stereo.

As others have noted, even if you do have mono bass, you never hear it as "mono bass". The localization cues are essentially all north of the subwoofer region, though spatial (hall size / envelopment / immersion) cues can be present in true stereo bass. The left-right 90-degree-phase-difference thing is a technique for synthesizing this sense of immersion in a large acoustic space; credit to David Griesinger for the idea, which does not depend on the recording having stereo information down in the subwoofer region. Nor in my experience does it result in a same-for-all-recordings acoustic signature; if anything, imo it unmasks more of the differences in spatial "feel" from one recording to the next.

@lewinskih01 wrote: "Would the ability to time-adjust each of the 4 subs improve sound? Like Toole described in his Sound Reproduction?"

My recollection is that Toole was referring to a Harmon subwoofer integrator processor which optimized the gain, frequency response, lowpass filter, phase, delay, and equalization based on in-room measurements. I assume it does what they claim.

Earl Geddes used to offer essentially the same services to his customers. He had them make measurements of each of their subs and then used a proprietary algorithm to calculate the settings for a Behringer processor. My understanding is that he could get in-room smoothness from three thusly equalized subs comparable to what he could get from four conventional subs. Since I’m no Earl Geddes, I still use four subs. (I have never claimed and hopefully never implied that the Swarm is "the ultimate" way to do the distributed multisub thing.)

If I had the choice between having the ability to time-adjust each sub and not, I’d choose to have it just to maximize my options... but wouldn’t want to trade off anything else that matters to get it. The arrival time differences in a normal size listening room are small enough that they are below the ear’s detection threshold at low frequencies, but it still might be beneficial.

I don’t have any experience with time alignment of subs, but do have some indirect experience with time mis-alignment:

One of my most-experienced-in-very-high-end customers has three of his Swarm subs spread around the room (with one in a front corner) and the fourth is right smack behind his listening chair (on an isolation pad). This essentially maximizes the arrival time differences, yet he finds it to be the best-sounding configuration.

So based on the information I have at this time, I would prioritize good in-room smoothness over arrival-time-alignment, but it would be interesting to try having both.

Duke

@m-db asked: "Wasn’t Dr. Floyd Toole adamant regarding cables lack of any measurable difference hence no sonic effect in the audio chain?"

I vaguely recall something like that. (My own experience with cables, which includes conducting a blind listening test, is otherwise.)

But imo it would be a mistake to dismiss Toole’s expertise in loudspeakers, acoustics, and psychoacoustics over a disagreement with him about cables.

@m-db: "Did Earl Geddes design for Behringer (processor) or simply use their processor?"

He simply used their processor. 

My understanding is that the concept came long before any of the specific pieces of the puzzle. 

Duke