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Re: Room treatment and electrostatic speakers.

Posted by Duke (D) on February 24, 2002 at 12:26:36

In Reply to: Room treatment and electrostatic speakers. posted by Tekunda on February 24, 2002 at 08:17:23:

Greetings, O mighty Tekunda!

Mind if I take a shot at your questions?

The general principle with reflections is, you don't want powerful, distinct early reflections. Whether to diffuse or absorb the energy that would otherwise be reflected depends on your room's acoustic characteristics - we'll come back to that later.

First we need to consider the radiation pattern of the speakers in question.

With tall electrostats, which approximate line sources, you don't have significant reflections off of the floor and ceilings. With shorter ones (like Quads), those can still be an issue.

If your electrostats have a flat panel, then they will be much less susceptible to sidewall reflections that normal speakers because they will be quite directional at high frequencies. Examples include most Acoustats and the InnerSound speakers. Martin Logans radiate into a 30 degree arc, and so are more likely to have sidewall reflections going on. Sound Labs have a radiation pattern of from 60 to 90 degrees wide, depending on the model, so the sidewall is much more likely to come into play.

A strong, distinct first sidewall reflection can smear the left-right imaging. An imbalance in this early reflection can pull the image over to one side or the other.

My room is fairly well damped, so I use fake ficus trees to diffuse that first sidewall reflection. Absorption would work better in a brighter room. When I was experimenting, I made four big, six foot by two foot wooden -frame panels of Sonex that I could move around and lean up against the wall. Based on my experiments, I hung some moderately heavy drapes in a few places, but the fake ficus trees sounded better at the reflection points.

In any event, unless you have a fair amount of room behind the speakers, you may want to experiment with either diffusing or absorbing the backwave (depending on whether your room is adequately damped or not). You especially want to intercept the portion of the two backwaves that would bounce off the wall and then straight to your listening position, in kind of a W-shaped pattern, as this reflection can ruin the soundstage depth. In a well damped room the Sallie could be too much absorption, but in a fairly reverberant room it can greatly help both the imaging and the tonal balance.

You asked about treating the wall behind the listener. If that wall is fairly far behind you, then you probably don't need to worry about it. If that wall is pretty close, and if it's bare, I would advise against absorption. If warranted, use absoption elsewhere in the room to get the tonal balance right, but I suggest diffusion behind the listening position. Maybe it's just me, but absorption behind my head gives a thickness or deadness to the sound that I don't like. It's like I can hear that it's there, and that bugs me.

Now, there's a reason why, in general, you want to use diffusion rather than absorption if you can get away with it. The ears tend to find a well-energized, diffuse reverberant field subjectively pleasing (like what you get in a good concert hall). Also, the ears like for the reverberant field to have the same general tonal balance as the direct sound - this is conducive to good timbre and long-term listening enjoyment. On the other hand, imaging and clarity are better if there is relatively little reverberant energy. There is a tradeoff relationship between precise imaging and rich ambience, in the concert hall as well as in the home. So, individual preference comes into play a bit here. Personally I like a rich and lush sound field, hence my inclination towards wide-pattern electrostats.

You can check on the "voicing" of the rooms in your house by having someone talk continuously as you follow them from room to room. Simply listen to the tonal character of their voice. This will give you a feel for the acoustic signature of different rooms, which will be useful in deciding what to do in your listening room.

The best sounding room I've heard in many a home is at my mom's house. She has a weakness for old furniture, and the walls of this room (roughly 16 by 18 feet) are completely lined with dressers, bookcases, armoirs, and tables with lamps on them. There's a rug on the floor and a few stuffed chairs in the room, and my step-father's stereo. No dedicated acoustic treatment. But the timbre in the room is especially rich and pleasing. Now if only I could convince her and my step-father that speaker placement matters! Oh well.

Best of luck to you in your endeavors!

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