One thing I often see happen is the confusion between sound isolation and acoustics. In this home theater library entry, I’ll explain these two important issues to getting great sound in your theater.
While these two issues are absolutely related, they are, in fact, separate elements of your home theater.
On a high level, Sound Isolation is simply the techniques to manage the amount of sound that enters, or leaves, a home theater; while Acoustics are the techniques to manage what the sound inside your theater actually sounds like.
You could have a home theater with outstanding Sound Isolation, where virtually no sound “leaks” into the theater, from outside (and where virtually no sound “leaks” out of the theater) while at the same time having that same home theater sound horrible inside, due to poor (or lacking) acoustics inside the theater.
On the flipside, you could have a home theater with excellent acoustics inside, but the theater sound is quite loud outside the room, due to poor (or lacking) sound isolation in the home theater.
Sound Isolation is a combination of techniques, designed to limit the sound that leaves the theater and limit the sound that enters the theater. And both sides of that equation are important, by the way…
Often people mention to me that they do not care if sound is heard outside the theater, but keep in mind that if sound can easily leave the theater, then sound can easily enter the theater. All home theater owners should take sound isolation into consideration, during their design process.
So your sound isolation system combines four key techniques, and together they limit the sound vibrations from transmitting through the walls and through the ceiling of your home theater (and if you take it to the next level, yes also through the floor of your theater).
These four sound isolation techniques are Mass, Absorption, Decoupling, and Damping.
1.0 Mass – If you make your walls heavier, it is harder for that wall to move, which means it is harder for that wall to transmit sound through to the other side.
2.0 Absorption – When you beat on a hollow drum it will make more sound than when you beat on a drum what was filled with sand. The same principle applies to your theater walls. When you fill those walls with insulation it cuts down some on the sound that is transmitted through to the other side.
3.0 Decoupling – If you can create a ‘gap’ between two surfaces, it makes it harder for the sound to ‘jump’ from one surface to another, which decreases the amount of sound that can be transmitted from one surface through to the other side.
4.0 Damping – If you are able to use some material to minimize the amount of vibration, in the wall, to start with, then you will have a much more successful overall sound isolation system. One great product (and one that we are fans of here) is called Green Glue. This damping material makes it so the wall itself vibrates less, which makes it harder for sound to be transmitted through to the other side.
So all four of these techniques are used together in your sound isolation system, and you will notice that none of them are designed to address the actual sound that is inside your home theater, that is where acoustics comes into play.
Now that you have a nice quite home theater, where you cannot hear any outside noise coming in, and you can play your system loud without disturbing the family, it is time to take care of the acoustics inside the room.
Before you think that this might not be needed, consider that if you created all concrete theater, buried underground, you sure would have impressive sound isolation. However, inside that bunker you would have horrible acoustics – sound would be bouncing all over the place.
While acoustics can seem like magic, it is rooted in science. However, you do not need a science degree to understand the core concepts. Just like there are four main issues to Sound Isolation, there are some main concepts to Acoustics.
These issues are Reflection Points, Absorption, Diffusion, and Bass Traps.
1.0 Reflections – In your theater, sound is bouncing all over the place, every surface will bounce sound. If you hear the same sound more than once (meaning directly from the speakers and then a moment later you hear the same sound reflected off a wall) that makes your sound much less clear. So you want to control the reflections in your theater.
2.0 Absorption – The main way to control these reflections is through absorption panels. These are panels that you place at obvious reflection points, like between your front speakers and your seating area, to ‘absorb’ that reflected sound.
3.0 Diffusion – If you were to cover your entire room in absorption, the room would sound ‘dead’, meaning there are no reflections and it will not sound life-like at all. So instead of only using absorption panels, you also use diffusion panels. These are panels that are designed to bounce sound around, but not directly back at the listening position.
4.0 Bass Traps – In your theater, bass is quite often a problem. It is too loud in some places, not loud enough in others, and almost always really loud in the corners. So in the corners you install bass traps, which are like large absorption panels, large enough to ‘trap’ the massive low frequency waves.
Yes these two aspects of your home theater work together, it is hard to have great acoustics in a room, when you can hear every truck drive by, every dog barking outside, every time the furnace turns on – and on the other side is your underground concrete bunker will have outstanding isolation, but sound horrible without acoustics.
In your home theater’s design, you should be planning on both aspects being part of your plan.
Design a sound isolation system, that is right for you (not everyone will be able to follow every technique) and design an acoustic plan, that is right for you (not everyone will be able to follow every technique here either).
At the end of the day, you want a home theater that sounds great. You want a home theater that lives up to your expectations, and one of the best ways to get there is to have address both issues – Sound Isolation and Acoustics.
If you want to learn how to put these concepts into action, check out The Ultimate Course on Designing and Building Your Dream Home Theater.