Acoustic Treatment For Your Home Theater

Acoustic treatment can be a significant upgrade to the sound of a home theater system. The fewer the furnishings your room has the more the sound will benefit from some type of sound absorption or diffusion materials. One simple way to test this is to speak in the room. If you can clearly hear your voice echo from your normal viewing position some level of treatment will be advantageous. Clapping your hands and listening for an echo is another test that can be used.

Two different types of products can be used to improve this. The first is absorption. This is anything that absorbs sound and will only reflect part of it back from the surface into the room. Materials that will do this are porous and bulky like heavy drapes, books and sound absorption panels. Second is diffusion. This is anything that will scatter the sound that impacts its surface. This will make the absorption material in the room more effective and further reduce strong echos from occurring.

When planning how to improve your room the first place to start is to estimate how many absorption panels you would need. I would use the ATS Acoustics calculator for this. A link to it is here. The recommendations from this site are very reasonable for the typical dedicated theater room. I would add 1 panel to their recommendation for every 3 seats if your seating is leather and none if it is microfiber. If your room has plush furnishings, book cases or the like you should reduce the number of panels proportional to the surface area of those features in your room. Diffusion can also be added. Optimally you would have an equal surface area of diffusion to absorption. The cost to benefit ratio of diffusion compared to absorption is low so some people add none or less than they do of absorption. Examples of where to purchase these products are ATS Acoustics and Auralex. It should be noted that the values they calculate for RT60 at various frequencies are not very close to what the room will really measure. This file shows a comparison of their calculator to what the room is actually doing. If you really want to design a room with accurate acoustics relative to a standard it is best to take measurements and design the treatments to fit or use a more accurate method of calculation.

Locating your acoustic panels properly is important if you want to get the performance improvement they can provide. One key factor is to locate the panels so they impact the sound that will be reflected in the path to your ears. One example of what not to do is to place all of the treatment very low in the room below ear level. The improvement this will have on sound quality will be minimal. I find that seats near a back wall need to have treatment directly behind the seats to prevent the rear reflection from smearing the sound from the front. Diffusion can be alternated with absorption on opposite walls so each diffuser is across from an absorber. It is important to treat at least one of each parallel wall and preferably both. Each absorber and diffuser on a wall should be located so it is not obstructed by furniture and the bottom of an absorber on a wall is at least as low as the lowest ear height. If you are going to place treatment on the ceiling it is best located in front of the primary seating location. The ceiling treatment is most effective if the floors are not carpeted or if the distance from the center or main speakers to the listener is more than about 1.5 times the ceiling height. Placing treatment such that it prevents the surround speakers from scattering sound around the room is not recommended. Experimenting with temporarily locating panels in various locations while listening to dialog and music is always a good idea.

Fastening the panels securely to the wall is very important. Having a panel vibrate and make sound is trading off one problem for another. I personally prefer the mounting method that ATS recommends here. Their mounting brackets can be purchased separately from their panels and allow the panels to be removed after installation. Gluing lighter panels to the wall is also an option. Mounting systems that use a simple wire hanger system tend to vibrate and make annoying sounds.

If the appearance of these panels is not desirable in your room. Heavy drapery, tapestries, acoustic ceiling tile, plush furniture, book cases, and stretched fabric walls can substitute for these systems.

W. Jeff Meier

ISF and THX Certified Home Theater Consultant

16 Comments
Corey

Adding room treatments was the best investment that I made to my HT setup. Electronic upgrades can’t correct the problems with a room.

W. Jeff Meier

Corey:

Adding room treatments was the best investment that I made to my HT setup. Electronic upgrades can’t correct the problems with a room.

Very true. The belief that electronics will fix a poor room are false.

Corey

Do room treatments, I guess bass traps in particular, prevent room gain? Also, is room gain something that’s good to have? I guess to me room gain means what the room is adding to the sound which I think is not what you would really want because you are not hearing the natural sound from your system.

W. Jeff Meier

One of the negatives of adding absorption is it will reduce room gain. It will not eliminate it. The more absorption the more power required. The level of treatment suggested here will not add dramatically to the power required for the same SPL level.

Room gain is a good thing. The mix studio room sound is part of what you should be trying to reproduce. This adds a character to the sound and greatly reduces the power required.

I do not find bass traps to be easy to apply. Adding enough bass traps to reduce room modes as some attempt will result in severly over treating the room above 500 Hz. These effects can be seen in waterfall charts and acoustic simulations. Multiple subwoofers are a better solution for these rooms.

Corey

Thanks for the clarification. It sounds like the mix studio expects each room to have a certain amount of room gain. I have heard the norm is between 2 and 4.

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Great read! You might want to follow up on this topic…

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I’m glad you said that..

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