What subwoofers keep up with Quad ESL 57 ?

The room is the dominant factor at bass frequencies. Not to say that different subs don't sound different, but the peak-and-dip pattern imposed by the room is quite audible, as is the progressive boundary reinforcement ("room gain") at low frequencies that makes a "flat anechoic" sub sound boomy and slow, and a sub that rolls off high and gradually sound tight and fast. The ear actually has very poor time-domain resolution at low frequencies, so the subjective impression of "slowness" is really a frequency response issue; in studies where group delay was digitally separated from frequency response, group delay proved to be barely audible on test tones and inaudible on music. On the other hand, frequency response anomalies were readiliy audible if they spanned a large enough portion of the spectrum (which happens routinely in the bass region).

Dipoles have been shown to have smoother in-room bass than monopoles, so this makes matching a pair of dipole main speakers with a single monopole sub often frustrating. The ear can often hear the discrepancy between the smooth upper bass of the pair of dipoles in contrast with the lumpy middle and lower bass from the sub. Using two subs helps a great deal, as each sub will interact with the room's bass modes differently, and the two dissimilar peak-and-dip patterns will smoothe one another out. I advocate taking that one step further and using four small subs... preferrably, small subs that are tuned to take room gain into account.

I know it seems highly counter-intuitive to use a lot of subs when your goal is quality instead of quantity, but this is the best way to get the room to work with you instead of against you. And the elephant in the room is... the room. The multisub approach is effective at extending the smoothness inherent in a good dipole like the Quad 57 down into the low bass region.

Imo, ime, ymmv, etc.

Duke
dealer/manufacturer

Hi Bob,

I don't recall how wide a "critical band" is in the bass region, sorry. My impression is that it's less than 1/3 octave wide.

For those who wonder what I'm talking about, the ear/brain system "averages out" narrow-band peaks and dips across what's called a "critical band", which is approximately 1/3 octave wide over much of the spectrum. So in other words if we have offsetting peaks and dips within 1/3 octave of one another, the ear tends not to hear either one. If we just have a peak, then the ear will hear it, though if it's a narrow peak it looks worse to the eye than it sounds to the ear.

In the bass region, the room-induced peaks and dips are inherently too far apart for the ear/brain system to average them out, and as a result they are audible and objectionable. Higher up we still have numerous peaks and dips from room interaction, but they are so close together (and delayed by so many wavelengths) that they are relatively benign, even though they may look awful on an unsmoothed in-room frequency response curve.

Tieing back in to the multisub concept, each sub will produce a different peak-and-dip pattern so the sum ends up not only averaging out considerably, but the remaining peaks and dips are more numerous and thus closer together - giving the ear/brain system's smoothing mechanism a better chance to work in to our benefit. As a result, the subjective benefit of a multisub system is often greater than one would expect from merely eyeballing the in-room frequency response curves.

It's not necessary to use identical subs like in the system I build; in fact if the subs aren't designed with room gain in mind, we're probably better off with some of the subs extending deeper in the bass than others. The basic principle can be employed without spending megabucks.

Duke