I find that damping room reflections is necessary in order to maximize the imaging and staging abilities of a home audio reproduction system, as well as to eliminate spurious brightness and grunge from the reproduction. The subjective magnitude of the improvements which such damping can provide are very substantial, easily audible to even the most casual listener as an improvement. To an audiophile, they are the proverbial "night and day" improvement.
But how do you know what part of room surfaces to damp? Audiophiles are more wary of "overdamping" their listening rooms than the should be. But I think that the procedure described here will assure that the room will not sound "too dead" to most listeners, at least once one gets used to the sound of hearing the space actually recorded, as opposed to the constant overlay of spurious spatiousness caused by undamped room reflections.
The procedure described here relies on the assumption that sound travels in straight lines and reflects off room surfaces much the way light reflects off a mirror--a specular reflection in which the angle of incidence equals the angle of reflection. While this assumption is not literally true, my years of experimentation and listening convinces me that it is a close enough approximation to be useful.
One way to find the specular, mirror-like reflection points on room surfaces without test equipment is to use a small flat mirror. I use one which is about 4" x 6". It has a cardboard backing to make it a bit less fragile while still keeping it thin and light-weight. I move it around flat against the room surfaces. I use two small strips of blue painter's tape to attach the mirror very temporarily flat against walls and ceiling surfaces. No tape is needed for the floor surface, obviously.
Damp with acoustical foam or dense fiberglass any spot on walls, ceiling, or floor where, when sitting in the listening seat, you can see any part of either speaker reflected in the mirror. I find it helpful to mark the spots on the room surface where the reflection of any part of the speaker begins and ends--a reflective outline of the speaker, in other words.
I find that foam or fiberglass thicknesses of 3" or more are necessary for best results. While you might think that you only have to damp the areas where you can see the actual mid and treble drivers, I find more damping as described above provides more imaging stability and also allows a bit of movement of the listener within the listening area without getting into a brighter sounding position. One reason for this is that sound waves don't really move in straight lines or bounce as coherently off room surfaces as light rays bounce off a mirror; the specular reflection assumption is not strictly true.
That will take care of first reflections. If you also want to deal with second reflections, put pieces of contrasting tape or something else easy to see on the room surfaces where you can see the speaker reflections and then move the mirror around some more, damping the additional spots where you now see the contrasting tape.
Then use a "clap" track to test the results. Track 4 of the Sheffield/XLO Test and Burn-In CD is such a track. First listen to the track with headphones, to hear what this track should sound like with absolutely no room echo. Then listen to it through your speakers. It should sound a bit more reverberant than through headphones because you haven't killed all room reverb by damping the first and second reflections, but there should be no slap echos or long reverberant tails. If you hear problem echos, experiment with additional damping to see what room surface is causing the echo.
But how do you know what part of room surfaces to damp? Audiophiles are more wary of "overdamping" their listening rooms than the should be. But I think that the procedure described here will assure that the room will not sound "too dead" to most listeners, at least once one gets used to the sound of hearing the space actually recorded, as opposed to the constant overlay of spurious spatiousness caused by undamped room reflections.
The procedure described here relies on the assumption that sound travels in straight lines and reflects off room surfaces much the way light reflects off a mirror--a specular reflection in which the angle of incidence equals the angle of reflection. While this assumption is not literally true, my years of experimentation and listening convinces me that it is a close enough approximation to be useful.
One way to find the specular, mirror-like reflection points on room surfaces without test equipment is to use a small flat mirror. I use one which is about 4" x 6". It has a cardboard backing to make it a bit less fragile while still keeping it thin and light-weight. I move it around flat against the room surfaces. I use two small strips of blue painter's tape to attach the mirror very temporarily flat against walls and ceiling surfaces. No tape is needed for the floor surface, obviously.
Damp with acoustical foam or dense fiberglass any spot on walls, ceiling, or floor where, when sitting in the listening seat, you can see any part of either speaker reflected in the mirror. I find it helpful to mark the spots on the room surface where the reflection of any part of the speaker begins and ends--a reflective outline of the speaker, in other words.
I find that foam or fiberglass thicknesses of 3" or more are necessary for best results. While you might think that you only have to damp the areas where you can see the actual mid and treble drivers, I find more damping as described above provides more imaging stability and also allows a bit of movement of the listener within the listening area without getting into a brighter sounding position. One reason for this is that sound waves don't really move in straight lines or bounce as coherently off room surfaces as light rays bounce off a mirror; the specular reflection assumption is not strictly true.
That will take care of first reflections. If you also want to deal with second reflections, put pieces of contrasting tape or something else easy to see on the room surfaces where you can see the speaker reflections and then move the mirror around some more, damping the additional spots where you now see the contrasting tape.
Then use a "clap" track to test the results. Track 4 of the Sheffield/XLO Test and Burn-In CD is such a track. First listen to the track with headphones, to hear what this track should sound like with absolutely no room echo. Then listen to it through your speakers. It should sound a bit more reverberant than through headphones because you haven't killed all room reverb by damping the first and second reflections, but there should be no slap echos or long reverberant tails. If you hear problem echos, experiment with additional damping to see what room surface is causing the echo.