Home Theater Design e-Guide:
Sound Absorption -- The Path to Acoustical Paradise
Sound Absorption Overview
In an earlier article posted on our site, we discussed concepts around soundproofing/noise control. Now we're turning our attention to sound absorption, which represents the other side of the equation in your acoustics strategy for your home theater room. Where soundproofing deals with keeping sound from going out of the room or coming in, absorbption pertains to addressing the reflective properties of sound. This should be an important element of your home theater design concept unless you're trying to create a conundrum of echoes and distorted sound to later solve in your media room.
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Understanding Sound Behavior
Before we dive into the techniques/strategies for sound asbsorption and lineup of products offered in this arena, we think it's important to briefly discuss the behavior of sound. At the very least, this should give you a general idea of how sound innately responds within any environment.By virtue, all "matter" absorbs sound -- it's just that some do a better job than others. Typically, the more density the matter has the less sound it absorbs and the more it reflects. Likewise, the less density the matter has the more sound it absorbs and the less it reflects. Building materials also have these properties, so by default you're getting some level of sound absorption from the general construction of your home theater room. Acoustical materials are designed to better absorb sound emanating from a source and further add to the absorptive properties of the room.
When sound waves come into contact with matter, it can either reflect or "bounce" off of the surface or it can be diffused and transmitted through the matter. The illustration below provides you a visual representation of how sound behaves, using an wall and an acoustic panel as the basis. Ultimately, your acoustics strategy hinges upon how effectively you can keep sound from bouncing off of the surface and how well you can diffuse it.
Acoustic Design Strategies
FurnitureOften overlooked as a part of one's home theater design strategy, selection of furniture within your home theater room is extremely important if you want to properly manage sound absorption. Furniture made from wood or glass will cause increased reflection of sound in your home theater. If you desire to have a piece of furniture such as a coffee table in your home theater, you may want to consider using a blanket, tapestry, or some other fabric as part of the interior's decoration to help mitigate reflection issues. Other items such as storage cabinets, media towers, bookcases, etc. are OK to incorporate into your design -- but if at all possible, try to keep them housed elsewhere.
Window Treatments
Not only do windows represent a source of light (which is something we try to minimize to be able to replicate the movie going experience), but they also are a source of reflection and sound loss. If windows are part of your home theater design, we recommend using window treatments to help with sound absorption. Sheers or other thin fabrics won't do as well as other more dense, fibrous fabrics. Those that have the extra backing to help diffuse light are good choices, and they help you to address a couple of items (sound, light) at once.
Surface Finishes
Believe it or not, the surface finish of your walls can have an impact on sound absorption. Smooth painted surfaces, which are the most common finish, reflect sound more than a textured wall. It's difficult to recommend going with a textured wall, however, because of the inherent problems with fixing future wall imperfections, additional effort required to paint such a surface, an aesthetic appeal.
Wall Construction
It's actually perfectly acceptable for you to get a little fancy with the contruction of your walls in your home theater. To put it simply, a home theater that's in the shape of a box is going to have more issues with the reflection of sound than one that has some offsets built into its construction. It's not very costly to incorporate recessed (what is the opposite of recessed?) areas to help enhance the sound in your room, in addition to giving it a more unique aesthetic appeal.
Glass -- The Pain in the...Well, You Know!
While it's extremely difficult to avoid using glass altogether in your home theater, it's still important to note that it also has very strong reflective properties. Tables, poster frames, windows, and art, among other things, all contribute to sound bouncing around in your home theater. Believe it or not, you can actually purchase acoustic glass, but it's not pratical from a cost or aesthetic perspective for conventional home theaters.
The main thing to take away here is to avoid incorporating items constructed of glass within your home theater room.
Acoustic Panels
Acoustic panels are probably the most common products used to address sound absorption in home theaters today. Panels are effective at mitigating sound absorption issues and for the price (whether DIY or purchased), they contribute nicely to a cost effective strategy.
They are typically made out of a fairly simple set of materials: fiberglass and fabric. They can be had for relatively inexpensive prices (as cheap as $40-$50 each), but you may want to consider making these on your own. They can be bought in many different sizes, shapes, colors, and patterns to suit the tastes of virtually any individual. Custom styles obviously will cost you more. 2' x 4' panels are probably the most common size you'll see on the market. Additionally, they can be bought/made in varying thickness, usually 1"-2".
Ceiling Tiles
Acoustic ceiling tiles are also offered that aren't much different than your ordinary drop ceiling tile. The also aren't much different in composition from acoustic panels. They too are often constructed of fiberglass, fiberglass/gypsum composites, and even particle board with veneer, among other things. Since you'll need a lot of these to cover the ceiling in even the smallest of home theaters, they can quickly add up to a lot of money. A dozen of these things can run you upwards of $300-$400. Ceiling tiles can also be bought of varying thickness, usually 1"-2".
Traps
Again, bass traps are not much different than acoustical panels, but they are designed for a somewhat different purpose. Bass traps are specifically designed to be low frequency sound absorbers, which typical acoustical panels are not engineered to handle effectively. These are really expensive to buy, but can be made yourself for considerably cheaper. They're also pretty large -- and since real estate is typically of concern to all of us building home theaters, they aren't all that practical, not to mention their overall lack of aesthetic appeal.
Sound Absorption → Design Guide
