Taming/Damping Electrostat Backwave

I have thought of building a large sealed cabinet onto the back of a set of E-stat's or Planars just to see what it would do. While i think that the backwave contributes to the "space" and "air" that you can get out of a set of these speakers, i also think that it creates a whole batch of problems on its' own. Sean
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The back wall reflection of E-stats is very important. For one it comprises probably 35% of the total sound that you hear (in the panel frequency range). Secondly, the back wall reflection is short in terms of timing. You can calculate this by taking the distance (ft) from the panel to the back wall and dividing it by 1130 ft/sec. So let's say you have 6 feet from the back wall. The reflection will arrive at the listener approximately 20 milliseconds after the first wave. Since this is less than 35 milliseconds your ear/brain integrates this up as part of the original signal and it's probably 50% or so lower in db from the original signal. This ads to the ambiance and spaciousness. If you eliminate this reflection you will probably not have enough high and mid frequency energy and the speakers will likely sound rather dull and the sound stage will collapse, but if you have 2 extra mattresses in the house and some down and wool blankets--there's a pretty easy experiment you could try.
So you probably wonder why did the speakers sound bad when they were close to the back wall. The panels are curved and when they are two close they may have focused at near a point on the back wall, creating a very strong point of reflection that might have had near the energy of the first wave that reached you. This would do two things: throw the speakers out of balance with too much high frequency energy, and 2 while the reverberation time is okay, the second point source with nearly as much energy would not be okay. It would mean rather than your ear perceiving ambiance, it would hear notes that were not clearly defined because of two signals near the same strength.

SL3 likes having its back wave diffused rather than absorbed. It also needs a lot of room behind. If you don’t have that much room, SL3 is not the right speaker. You won’t be able to achieve good results by damping the back wave.

The best way to diffuse the back wave is to install some professional diffusers. But they are expensive. If you want something cheaper, you can use plants, either real ones or fake ones will do.

Rives notes an important point about the SL3s -- their curved surface is like a part of a cylinder, the focal area is really a near-vertical line where the axis of the cylinder would be. Consider putting an effective mid-high frequency absorber like ASC Tube Traps at the focal area. Good luck.

Jamesswei's and Sidssp's sugestions are good ones from my experience with the old CLS's and the old Monoliths. I have owned 3 pair of Maggies as well and they benifit from the same thing. They all like space behind them. The fact that they don't have a cabinet is part of why they sound the way they do,no cabinet resonences to deal with. I have a friend who has Sound Labs and the sound is difficult when things get loud. His room is too hard and reflective. When you put on an acoustic jazz trio the potential is revealed. I have used the tube traps with sucess myself and they alow for some tuning where the results with permenent difusers are harder to predict. If you don't like the sound with the trap just rotate it or move it around until you do.

Sean, you might remember Harold Beveridge did exactly what you are proposing, and also went as far as using a bizare JBL style lens in front of the stat panel to control dispersion. I remember that they could sound quite nice but never heard them in a controlled situation. It always seemed to me like it was an approach that added some of the problems associated with box speakers.

I remember the old Dayton Wrights, the Koss electro stats, I had a boss with double KLH 9's, I also sold Quads and Acoustats at different times, they all have an aluring quality, you just need to acomodate their needs with some space around them and some room treatment. I had to go back to dynamic speakers from a stand point of practicality. Good luck and don't give up, you will be rewarded when you get 'em set up well.

Here is a horror story for Quad fans. I ran across some people while working in a HiFi shop who had inherited some speakers the knew nothing about. After talking with them I determined that they were Quad 57's. They told me about how they liked to watch the light show of sparks inside the speakers when the turned them up REAL loud. It about made me cry!