Comparison of various subwoofers for 2 channel audio

Hi drbond, thanks for the question...

This servo sub replaced 2 $900ea Paradigm "Cube" -  10" subwoofers in this small dedicated studio:  Rythmik L12 - sealed HT sub (rythmikaudio.com)

Texas to Maine was $629 delivered.  This upgrade was months ago and I am still startled on occasion by its speed, depth (room responds slightly to 20Hz test tone!) and superb musicality overall...improving all frequencies...yes, research the importance of an accurate deep bass foundation in audio. 

A long-time friend who made his first visit from Massachusetts recently was appropriately wowed.  He has focused on subwoofers and their design for decades, including DIY.  More info can be found in my posts.  The choice for the Rythmik came after much research and the advice of two channel, seasoned, music lovers.  Mare on the topic can be found in my posts.  Onwards!          More Peace         Pin            (bold print for old eyes)

@drbond Yes is was. I had to add another set of input terminals too the back plate. Dr West was kind enough to send me an identical set. The holes had to be right on. All crossover components were removed leaving the two transformers, the bias supply and the output terminal block. Primary resistors were added to the high frequency transformers.

Initial results sucked. The bass transformer is way less efficient than the treble transformer and the Atma-Spheres have less gain than your typical SS amp including the Bricasti M25 I am using to drive the high frequency transformer.

Then because of the dipole nature of the Sound Labs the DEQX was having a terrible time getting measurements, comb filtering like crazy. I must have tried 100 different set ups. I realized that the only way I was going to get this to work was by blocking the rear wave almost entirely and adding about 12 dB of gain to the Atma-Spheres. I built two of Dr West's SALLIEs (Sound Attenuation for Low Levels of Interference Effects) except mine are 24" wide instead of 12" and 7 feet tall. I will have a picture of them on my virtual system page shortly. I purchased a unit that converts single ended signals to balanced signals based on a older op amp, set for unity gain. I substituted a Burr Brown op amp and raised the feedback resistor by a factor of 4 which will give me 12 dB of gain. I have a set of Burson op amps coming. These are the highest quality available but very expensive. I wanted to make sure this was going to work before spending that kind of money. 

The bass control on your sound labs cuts or increases the volume of the bass transformer and functions from 500 Hz down. By lowering the bass you are taking the punch out of the music. Unless you are going to get a two way crossover I firmly believe you are better off without subwoofers. Adding more of them is simply going to increase coloration in the low end. The MAJOR benefit with your speakers is lowering distortion and increasing head room by removing 100 hz down from them. This is more important than the added bass. If you are every up in the Boston area I will prove it to you. 

You are stuck in old school thinking, like late 70's old school thinking. You have a great system, but as it is it is extremely inaccurate. The amplitude curves for the individual channels are way different, up to 10 dB in places and anything but reasonably flat, think roller coaster. Get a USB  measurement microphone and computer program and measure it. I promise it will set your hair on fire. The benefits of digital signal processing far outweigh any detrimental effects which with the best equipment are completely inaudible. 

@mijostyn 

Yes, in the theoretical world, adding a passive HPF around 80 Hz would decrease distortion in the rest of the sound frequency for the electrostatic speakers, but the distortion is so low in the electrostatic speakers, that I'm not sure that it would be worth it, although, in the interest of experimentation, I should try it.  However, my next sonic experiment will be adding 2 more subwoofers to create a swarm. . .afterwards, I may look at creating a passive HPF using Duelund capacitors and a resistor in parallel, but that's another project.  (And there's no way am I going to get wrapped up into bi-amping the speakers, although I commend you for your industriousness.) 

@drbond  Yes please, you should. That will be a 60 dB/oct filter which is very slow. You might want to try setting the HPF to 100 Hz and the sub LPF at 80 Hz. I spent years with Acoustats, RH Labs Subwoofers and the Dahlquist LP1. To set the HPF you were given an assortment of caps and the formula for determining the 3 dB down point given your amp's input impedance. I tried every combination you can think of. It was a very euphonic system and anything but accurate. Getting subwoofers to disappear running up to 80 or 100 Hz is not easy. Most have enough coloration to stick out like a sore thumb especially if you have very uncolored loudspeakers. 

I too am running an ESL system: 2 Quad 2905's and 2 Quad 2805's perpendicular to the 29's (all modified). I am running an isobaric sub with a 50 Hz cutoff, but frankly it doesn't do very much. Almost all of the bass augmentation comes from Magnepan DWM bass panels, powered by big Brystons (a 7BSST3 per DWM). The 7B's are potent, fast, and clean enough to drive the DWM's flawlessly - overkill, really.

The DWM bass panels use the latest push-pull technology favoured for the big panels. They are very fast - basically indistinguishable from ESL's at 500Hz, an octave above middle C. The stock crossover is at 200Hz, but it's easy to bypass that and do it right with an electronic crossover. The DWM's are fairly flat to 2 Kz and still produce a decent signal at 5KHz, so they are ideal for mid-to-upper bass augmentation in the critical region of 40-300 Hz.

I like them very much. YMMV