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'Stealth' Acoustics

Posted by David Aiken (A) on March 17, 2005 at 16:25:53

In Reply to: Room Treatment Discussion and Advice posted by davidspeed@shaw.ca on March 17, 2005 at 09:34:15:

You say you've already got the speakers away from the walls. Good - get them as far away as practical because that increases the length of the early reflection paths relative to the direct path from the speakers to you. This reduces the level of the early reflections relative to that of the direct signal and helps make the direct signal more dominant which helps take the room out of your perceptions to a great degree.

Next, add some absorption. Thick curtains on the windows helps, even if they're just bunched up and hanging at the sides of the windows. If they'e going to have to be like that, see if you can use sheers behind the main curtains and keep the sheers covering the window - you will be able to see through them but not as well as through the open window. It's also possible to get heavy, noise-absorbing liners for curtains which are intended to block sound from outside. They do a good job of absorbing sound inside the room also and they're invisible behind the main curtains so they have very high WAF due to invisibility. If curtains are permitted, the liners won't be a problem.

What do you have on the walls? Instead of framed pictures under glass, look at things like soft fabric wall coverings (tapestries, fancy quilts, or the like) or large bookcase areas full of books if you're into reading. I have 8 square metres of bookcase in my room and 24 linear metres of shelves in them. Books make good absorbers and books of different sizes can also act as diffusors to a degree. You can also increase the amount of absorption that books offer by pulling them forward towards the front of the shelf so that there's a space behind the books between them and the wall or bookcase back. Exosing that edge of the book rather than pushing it right up against the wall/bookcase back offers a very large increase in absorptive area. If you want pictures, consider paintings on canvas or similar and try lining the back of the painting with polyester batting out of sight where it can't be seen. Try making sure you have whatever you use for absorption covering the early reflection points in particular because it will be most effective there.

Bass traps are a problem because they're usually visible and not overly attractive. They also work best in corners and they're so large that they'll be far too visible anywhere else so go for the corners or forget them. There are some things you can try. You could consider the triangular foam wedge style of bass trap and get the foam in a colour that matches either the walls or the curtains so it appears much less obvious, or you could hide the wedges by placing a tall bookcase diagonally or display shelving across the corner in front of the wedges leaving a small gap on each side. If you have a bookcase or shelving across the corner, you could even use that to conceal normal the tube trap or panel trap style of bass traps. While it would be nice to do all 4 corners, aim for 2 - either the 2 behind the speakers or the 2 behind you.

It's hard to do anything in the way of attractive or invisible ceiling treatments but a thicker floor rug may help, as would a larger rug if it doesn't go wall to wall. Several small rugs would also work if they are placed strategically.

Try and keep the areas around the speakers and listening position relatively clear. If you have things close to the speakers try and make them absorptive - soft furnishings with foam or similar fills and fabric rather than leather covering - rather than reflective. Try to avoid having coffee tables or anything hard and reflective between you and the speakers - side tables beside the listening chairs/sofa can be a reasonable alternative.

While it isn't an acoustics tip, if you can afford it you should consider a good rack which isolates your components from floor borne vibration. Grand Prix Audio, Finite Element, and HRS all make racks which seem to be very effective and which are quite attractive though each has it's own style. You should be able to find one which fits in well with the rest of the room's decor. My Grand Prix Audio Monaco matches quite well with my chaisse which is a copy of the famous Le Corbusier one, my reproduction Eileen Grey side table, and the Italian reading lamp I have. The Finite Elemente and HRS designs may work better with more traditional room styles.

That's about my standard list of stealth treatments that aren't going to be noticed. You may well not be able to implement all but implement as many as you can and you should notice an improvement - a big one if you can do the lot. And remember that where you put things can be as important as what you do. You should be able to get some absorption in the room and placing it at the early reflection points is the best place to put it. If you can't place it at the existing reflection points, it may even be worth while moving the speakers and listening position slightly to change the location of the reflection points and ensure that they coincide with the placement of absorption.

David Aiken

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