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RE: Effectively killing all reflections from one surface…

Posted by David Aiken (A) on May 10, 2008 at 06:07:58

In Reply to: RE: Effectively killing all reflections from one surface… posted by KlausR. on May 10, 2008 at 01:06:21:

1- Granted your point that sound in small rooms is directional, you've eliminated one direction from which reflections can come. You have not added contra-lateral and rear reflections, you've subtracted vertical reflections. I didn't say that this was necessarily bad. I said it wasn't something I would like to do without some thought and perhaps experimentation because it's not the normal reflection situation in a room. Finally, since you refer to research about the noticeability of the addition of horizontal reflections it's worth noting that I was not talking about a possible adverse affect of adding reflections in the horizontal plane. I was talking about a possible adverse affect of removing reflections in the vertical plane, a point you didn't address when you trotted out your references.

2- "I doubt that the ceiling has an effect on horizontal modes: modes are generated by the superposition of a wave and its reflection, and the ceiling does not affect the reflections off the walls."

You're right about the superposition of the wave and reflection, but modes are strongest at the boundaries of the opposing room surfaces, ie in the corners formed by 2 adjacent surfaces. Horizontal modes are usually treated by placing bass traps in the vertical wall/wall corners, but the horizontal wall/ceiling and wall/floor corners are also involved as they form the other 2 boundaries of any each wall in the pair of opposing walls. You've got treatment covering the 4 wall/ceiling corners and that will have an effect on horizontal modes because those corners are involved with them as well as with the floor/ceiling modes.


3- "Try a living room with brick ‘n mortar walls, tiled floor, no carpet and rugs, plasterboard ceiling, you have intelligibility problems right away, such a room is extremely unpleasant, treatment is absolutely necessary, such a room IS broken."

I never said that it was not a problem room. I asked what makes you believe that others don't also have problem rooms. My living room area where my home theatre system is set up has a ceramic tiled cement slab floor, plasterboard walls as opposed to your brick and mortar, but with lots of large window and glass sliding door areas, the plasterboard ceiling, a kitchen nook at one end, openings into hallways and other areas, glass display shelves with a ceramics collection and a number of large frames with original prints framed under glass, and an 8' ceiling height. It probably isn't much better than yours acoustically. Others have such rooms as well, including me in that particular room which is not the room I chose for my audio system for obvious reasons though it too is far from perfect for other reasons. More rooms in normal houses are far from perfect than you seem to think.

4- "I’m not discussing whether you or Ethan like or don’t like the results of your treatments, I’m giving a different advice and I present a different view on these issues, based on scientific/psychoacoustic data."

And you routinely present that advice while not mentioning the fact that you've got acoustic treatment in your room which contains more absorption than people like me are suggesting that others add when we make our recommendations. You say that reflections aren't a problem but your reverberations which you've gone to so much trouble to treat are reflections. Whether or not you choose to admit it, you're virtually eliminated 2 of your first reflections. You say that you don't need to worry about room modes and that your room has only 1 minor modal problem but you've treated half of the wall boundaries and are getting the benefit of bass trapping there whether or not you installed your ceiling treatment for that purpose so your vaunted "only 1 modal problem in my room" is not due to the fact that modal problems are as minimal as you often infer but because you've got more treatment in your room reducing modal behaviour than I routinely recommend. You present advice on a "do as I say, don't do as I do" basis and you never mention the benefits you are obtaining from acoustic treatment when you give advice.




David Aiken

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