Best setup for two subwoofers.

In answer to Soix, I am running a LH and RH sub but I believe the signal is basically mono. I don't think this is important because at these sort of frequencies the bass notes are not directional

Answering Dbphd, my setub is as follows:

2 subs, crossing to Open baffles containing four aluminium/magnesium midrange drivers per speaker and a ribbon tweeter (d'appolito array)

0-100Hz both subs, 48db LR crossover on subs, 60db LR crossover on mains (this gives symmetrical slopes on the filter)

100hz-3100hz 48db Linear crossover to ribbon tweeters

Calibrated, corrected, aligned, eq'd measure basically flat 16hz to 20khz in room

For most recordings this blend of crossover slopes gives a 'faultlessly' smooth performance and I never notice the slightest hint of a dip or boom in the sound, even in the bass region. Music is extremely realistic sounding, has great timing and the most dynamic response I could possibly want. Transients are simply stunning, fast, tight and deep which I guess comes from the speed of the open midrange (uncoloured by cabinets 100hz up) and the fact that all drivers only receive the optimum frequencies they are calibrated for

As the DEQX has four profiles, switchable by remote, two also use 72db LR crossovers between subs and mains with the benefit that bass is even tighter and faster when certain recordings benefit. The flip side is that this is also slightly leaner in the mid bass area of the crossover, very pleasing on a slightly muddy recording. Steeper slopes mean speakers only receive the specific frequencies specified and DEQX is smart enough to handle the time delays and phasing in the crossover seamlessly.

I tried crossovers to the ribbons with slopes from 48db all the way up to 'brick wall' 300db but the steepest required phase inversion at the crossover to avoid very slight ringing. I have settled on a 48db slope as being the most natural sounding and chose 3100hz as the point where both frequency plots were completely in phase and both driver types had similarly flat responses either side of the crossover.

I would say that achieving exactly what I wanted has taken about 5 months of continuous tweaking. I finally arrived at this back in early June and have changed nothing since. I genuinely have nothing more to change, it's as close to live music as I have heard (better than the majority because it is so clean)- I spend a lot of time at gigs and concerts.

Drewan77,

Is my understanding that the speakers are mounted on a baffle of sufficient size that front-rear cancellation is handled without an enclosure correct?

The answer I was alluding to in my previous post was the answer you gave to Soix, i.e., very LF are essentially not directional. Two subs are used to smooth LF sound field, not to provide stereo information.

db

Yes that is correct, the baffle is made from 25mm thick zebrano bamboo, a very dense material which seems acoustically dead. The subs are not directional, as you say

FWIW,

My own experience would suggest a few things, all of which have already been mentioned, but none of which may be clear from the debate:

If you lack bass management software in your system, an array of four optimally placed subs is likely to provide significantly smoother bass response at your listening position than an optimally placed single or dual subwoofer set-up. If you DO use bass management, the delta in performance between more subs and fewer subs at your primary listening position is likely to be smaller. IME (and I did try a decidedly poorly controlled A/B comparison at one point), a single (or pair of) bass managed sub(s) may well provide smoother response than a quad array of non-managed subs at the primary listening position.

However, you may still have smoother response over a large listening area with a "non-managed" quad subwoofer array vs a pair of managed subs - since bass management software IME optimizes response in a smallish window. As to optimal placement of such a quad array, you're on your own. Expert opinion seems to vary, so - if you end up with four subs - you should probably experiment with both in-corner and non-corner subwoofer placement to determine which sounds better.

As a practical matter, for a 2 channel, music only system, bass management software is still rare. In this case a quad array is likely to be the better choice. Once you introduce bass management software, the incremental value of additional subs is less dramatic. Of course, everyone has their own particular sweet spot on the curve of diminishing returns.

Since you're using an HT system, it's likely that you already have bass management software. If that is the case, the primary advantage of adding additional subs is the incremental gain in clean output capability at any given frequency. Even the best subwoofers' distortion increases dramatically with SPL at very low frequencies (tho the best models offer mighty impressive performance in this regard). A single monster - like the 1812 - may provide more than enough output for you. Still, two 1812s will get you more. So, in this respect, (assuming the use of identical subwoofers) more subs are better than fewer subs. But IMO, the real question here is.... overkill. How much clean output capability do you really need?

Well...,

How loud do you listen?
How big is your room?
How deep is the is the lowest frequency you care about reproducing cleanly?

IME, I'd say that a pair of high quality, high output 12" subs (SVS, Rythmik, HSU, etc) probably does the trick for most listeners in most HT rooms that have bass management systems. However, it's just not possible to say with certainty that it will be enough for you. You can always start there and add more if the need arises.

Good Luck,

Marty