Home Theater Acoustics 101

When customers visit us to discuss building a custom home theater room in their house, they usually focus on details like the screen size, the surround sound system, the theater seating, or the popcorn machine. While all of these things are important, none of them are as important as room acoustics.

Why Room Acoustics Matters

Let’s take a step away from home theater for a minute and talk about something that more people have experience with -- a kitchen remodel. You may be inclined to think about the appliances and all of the great features, the color of the cabinets, and the granite countertops. You’re thinking about it as if it were a picture in a magazine. While the aesthetic is certainly important, the fact of the matter is that people tend to spend more time in the kitchen than anywhere else in the home. While the design is fun, the function is at least equally important. What looks good and what works well aren’t always the same thing. Of course, finding a balance is ideal, but if you have a beautiful kitchen that nobody wants to cook in or hang out in, what's the point?

This same concept also works for home theaters. A room may look like a theater, but if you can’t comfortably sit down and immerse yourself in a film for hours -- if you can’t pick up on the subtle emotional qualities in the actors voices while at the same time fully appreciating that Michael Bay-like action scene, you’re not really getting the experience you’re looking for.

A theater that has addressed any acoustical issues enables the movies to be far more involving. They draw you in, and you connect to them in an entirely different way. That, my friends, is what a great home theater experience is all about; escaping from the stress of our work lives and immersing yourself in another world for a couple of hours. It’s great therapy!

Achieving this kind of great sound really comes down to two primary things:

  1. A well thought out speaker plan for your room.
  2. Making sure the acoustic signature of your room enhances the experience instead of totally destroying the sound your great speakers are reproducing.

Today we will be focusing on acoustics and acoustic treatments.

Acoustics is All About Minimizing Reflections

Getting great acoustics comes down to one simple concept: controlling reflections. As you probably know, sound covers a pretty broad spectrum from the lowest low bass rumbles of an explosion to that sparkling high hat or tinkling of glass. The critical human voice falls in the middle.

As the low bass tone from your speakers or subwoofer(s) bounce around the room, depending on the room’s dimensions, those tones will build up in certain areas of the room and cause two problems. Some low tones will be totally canceled out by the reflections and you’ll hear very little bass, yet other tones will get more pronounced and overwhelm other frequencies. These are called modes.

Rooms with equal dimensions tend to have more problematic modes. Also, as a general rule of them, the smaller the room, the more issues you will have. Higher frequencies can also reflect, bouncing around your room and making it very difficult to understand the details in a movie.

Taming the Lower Frequency Reflections

If you have ever noticed that in one spot of your room you can hear lots of bass and in another spot you can barely hear deep bass, you are experiencing how low frequency reflections can be an issue. Let’s look at some options to make your room ideal.

Room Dimensions

If you are lucky enough to be building your home theater room from scratch or have some flexibility in the room dimensions, having a more rectangular shaped room is best. The Golden Ratio (1:1.6:2.56) is actually a perfect way to go, with the first number being the height of the room and the other two being the length and width. Of course, if you are working with Audio Advice on your home theater design, we will work with you to find the ideal room dimensions for your unique situation.

If your room is like many family rooms we see in modern homes, you may have many openings and it will be pretty far from a standard rectangle. While your initial reaction might be that this is a bad thing, depending on the shape and dimensions, it could actually work out in your favor (at least when it comes to lower frequencies). Parallel walls can sometimes create problematic bass nodes.

Try Multiple Subs

Having more than one subwoofer in a room will do wonders to minimize bass modes. When you have the energy coming from different places in the room, the modes tend to smooth out. Two is better than and four is even better than two. Doing something like this will give you and your guests even bass response in most seating positions in your theater room.

Room Equalization/Correction Technology

A few models of subwoofers come with a microphone kit for room correction. A typical room correction system involves placing the microphone in the primary or several of the seating positions. The system then plays some test tones and finds the peaks and valleys.

While it’s nearly impossible to bring up the dips, these systems can do a good job of bringing down the peaks, providing a more even bass response. The JL Audio Fathom series of subs are a great choice for a sub with room equalization built in. MartinLogan also has what they call their Perfect Bass Kit that you can use in conjunction with several of their subwoofers (and now speakers) to help your sound tremendously. Even one of the oldest names in performance audio, Vandersteen Audio, offers correction technology in some of their speakers. Their system is more manual, requiring some test gear, but it works amazingly well to smooth out the bass in a room.

If you already have your speakers and are shopping for a new home theater receiver or processor, the Anthem receivers with Anthem Room Correction are another great choice. These are great sounding home theater receivers with built-in room correction. And at the top end of the scale, the home theater processors from DataSat can not be beaten for their DIRAC room correction circuitry.


Anthem Room Correction (ARC)

Trap the Bass

One other solution to bass modes is the use of acoustic treatments called “bass traps”. These are typically placed in the corners of your room. Bass traps have to be pretty large in size in order to trap the low bass note reflections. There are some mixed opinions in the audio community on their use. Used with discretion, they can be a great choice, but be mindful that while they can capture lower frequencies and reduce modes, they may also drastically reduce the bass impact.

As you can see, this part of the equation has many variables. At Audio Advice, our team of expert will walk the room and do conduct some tests before making recommendations on how to minimize your bass modes. While we certainly enjoy the aesthetics and design of a beautiful theater, we love getting caught up in details like this when helping you design your new room.

Taming Higher Frequency Reflections

If you’ve ever been in an empty room with nothing but sheetrock walls, you know what upper frequency reflections sound like -- it’s got almost an echo chamber effect. If you want to be able to experience the subtleties and emotion in voices like the worlds best actors can portray, controlling these reflections is essential.

Think Soft

There are many choices for helping to reduce high-frequency reflections. Think soft! Of course, in a home theater, this usually means acoustic treatments and acoustic panels. While this article is specifically focused on acoustics for dedicated home theaters, we realize that many of you may have more of an open concept media room. In this case, acoustic panels may not pass the decorator (or Mom) test.

What we’re really trying to do is eliminate the chance of sound bouncing off of walls and windows and reflecting back at us, competing with other sounds. The best rule of thumb is to think soft! Large houseplants (it doesn’t matter if they’re fake or real), heavy curtains, area rugs, tapestries, and other wall hangings may make a huge difference.

A dedicated home theater room for movies, sports, and TV will have the most options for acoustic treatments. This can range from some basic absorptive wall panels spread out on your wall, to a full blown acoustic treatment package hidden behind a custom stretched fabric system that covers all of the wall surfaces. In a perfect world, the acoustic treatments of the room disappear into the aesthetic and allow your carefully selected home theater equipment to really shine.

Artnovion Andes acoustic treatments

Don’t Go Overboard

An important point to note is that some reflections are actually important. It’s really about finding balance and eliminating the modes more than deadening all sound. If you completely cover your room to the point that it can only absorb sound, you will wind up with a theater that lacks a sense of dynamics. The most well-design theaters will find the perfect balance between absorptive, reflective, and dispersing panels, strategically placed around the room.

If you are trying to get the most bang for the buck, placing a few absorptive panels around the room is probably your best bet. A good rule of thumb for this method is to calculate the total surface area of your two side walls and get acoustic panels that will fill up about 35-40% of that area. So for a wall 9’ tall by 18’ long, four panels 30” wide and 6’ high will do the trick. You can greatly improve a room that is just painted sheetrock by doing this for the two side walls, back walls, and either side of the screen with a few panels.

Cabinet Trickery for the Important Center Channel Speaker

The center channel speaker is perhaps the most important speaker in a surround sound system. This is where the majority of the dialogue comes from. Ideally, you would want your center channel on a dedicated stand, away from other surfaces so that the only thing coming through are the pure sounds of the speaker.

Of course, in the real world, this is rarely what happens. Often times we come into existing home theater only to find the critically important center channel relegated to a cabinet to hide it. While the designers or cabinet maker may have the best intentions, a lack of experience or attention to detail in this area means that most center channels in cabinets just don’t sound very good. The issue comes down to the resonance produced by the wooden cabinet. Certain frequencies will cause the cabinet to add some of its own coloration to the sound, often making voices sound muffled as if actors were talking with their hands cupped in front of their mouth.

We’re purists here at Audio Advice, so we will usually recommend having the center channel unencumbered. At the same time, we realize that for many of you, it just has to be in a cabinet. Luckily, in our two decades installing home theaters, we’ve picked up a few tricks along the way -- and we just happen to have one to address this very problem.

First, find some of those little stick-on rubber feet at your local hardware store. Put those on the bottom of the center channel to help isolate it from the wooden shelf. If your center speaker is down pretty low in relation to your ears, you can use this to stack up a couple of the feet in the front in order to tip it slightly up and aim it more at your ears.

From there, find the crossover setting for the center channel in your home theater receiver menu. It is probably set for 80hz. Put on a movie with some people who have deep voices and listen to a couple of minutes of dialog. Now try raising the crossover to 90, 100, or even 120hz. As you do this, you should notice less resonance as you are removing deeper bass from your center channel and thus preventing the wooden bookcase or cabinet from resonating. Feel free to play around, but don’t go higher than 120hz.

Acoustics is Just One Piece of the Puzzle

While understanding the basics of acoustics and these tips are important, the fact of the matter is that getting acoustics perfect is really a science. Working with a provider that has years of experience and all of the tools to properly plan your home theater is the only real way to ensure you’re getting the best sound possible in your room.

If you have or are planning to make a serious investment in the home theater gear in your room, we highly recommend a full acoustic plan. At Audio Advice we can be a big help with choosing design and products. We design and install acoustic treatment from Cinematech, Kinetics, Auralex, and Artnovion.

But even then, the acoustics and acoustic treatments themselves are only one piece of the puzzle. Understanding sight lines, choosing a screen size, picking your theater furniture, choosing your equipment, and making sure everything is properly installed and calibrated are also important elements that bring a custom theater to life.

If you’re in Raleigh, Charlotte, or surrounding areas of North Carolina, the Audio Advice team would love to help design, install, and calibrate your home theater. If you’re interested in learning more or have any questions, please contact us or visit one of our world-class showrooms.