Sound Isolation Versus Acoustics

in Home Theater Acoustics, Home Theater Audio, Home Theater Design, Home Theater Soundproofing

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 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. Acoustics 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...

DIY Super Chunk Corner Bass Traps

in DIY Home Theater Projects, Home Theater Acoustics, Home Theater Audio

OK so you have your home theater, and you have your incredible subwoofers in your home theater. But, something isn’t right, something doesn’t sound right. The bass is not even, the sound is not clear, your theater does not sound the way you thought it would sound. Well, you forgot your bass traps, didn’t you? Don’t worry if you did, it is very common for theater owners to skip the bass traps in their theater – but they regret it later. And if they don’t yet, when they go to visit a theater that has bass traps and acoustic panels (panels will be discussed in a separate article), they quickly realize what is missing. It is time for you to add some bass traps. And, quite often, the easiest ones to make also have an immediate impact, the Super Chunk Corner Bass Traps.  So we’ll go over how to build your own corner bass traps, it won’t take you very long and it won’t cost very much. So let’s get started. The idea is simple. You are going to fill up the front corners of your home theater, from floor to ceiling, with a material that will ‘absorb’ the bass that builds in the room. Now technically nothing “traps” bass, rather it slows down the reflection of those low frequencies, so to speak, so that they become much weaker in the room. There are several kinds of bass traps, and there are several implementations for bass traps. The kind that is most common as a DIY project is the Corner Bass Trap, so that is what we will focus on here. Corner bass traps, as the name suggest, go in the corners of your home theater. The single most common location for these traps is to place them vertically in the front of your room, usually behind the screenwall. Therefore, you would have a vertical corner bass trap along the front left and the front right corners of your theater. If you have the option, you can also place them vertically along the rear corners (although that is harder for most theater owners, due to seating placement, door placement, equipment placement, and so on. Lastly, you could place them along the horizontal corners of the room, where the walls meet the ceiling – meaning you could have bass traps all the way around your room on that upper ‘corner’, but most theater owners do not go to that level. So we will keep our focus then on the common vertical front corner bass traps. It is recommended that virtually all home theaters have bass traps in these front corner locations. You can use mineral wool panels, each two inches thick, or you can use OC730 fiberglass insulation, which is also two inches thick. If you are looking at insulation, or other panels, and you find them as four inches thick, that is fine as well – less cutting for you! These bass traps, the Super Chunk corner bass traps are actually quite easy to make, which is why this is an excellent DIY project. You start out with a sheet of rigid fiberglass (or the mentioned mineral wool), which often comes in 4 foot by 8 foot sheets, or 4 foot squares. Lay down the insulation and cut it down into two foot by two foot squares, and then cut each square diagonally, to create a pair of triangles from each square. Next, you simply stack these triangles on top of one another, in the corner of your theater, from the floor to the ceiling. You don’t need to ‘overstuff’ them into place, meaning there is no need to hold the stack down and squeeze in more triangles. Just enough to fit so that the stack is in place. The images below are from a theater called, The Bacon Race home theater, which is one of the theaters featured in The Ultimate Course on Designing and Building Your Dream Home Theater. You can see a few angles of this Super Chunk Corner Bass Trap as it is installed into this home theater.              ...

Room Mode Calculator

in Home Theater Acoustics, Home Theater Design

When you are designing and building your home theater, and you want to go beyond just a basic room, you will need to take your room modes into consideration. Room modes (at a high level) are frequencies that reflect between parallel surfaces, and the low frequencies tend to be the ones that cause the trouble in your home theater. You can learn more about Room Modes here. There are several different calculators out there, but the one that we use here, is ModeCalc, created by Ethan Winer and available from his site: RealTraps. Ethan also includes a nice Help section built into his calculator, so you will easily be able to use this for your room. Using a calculator like this allows you to enter the dimensions of your room, and then the calculator will generate the modes of the room. Knowing the room modes will then allow you to design your acoustics plan, or even adjust a dimension (if you have the ability to move a wall/ceiling in your room). From another article, you know that building a room that is a perfect cube (See Home Theater Dimensions) is not a good plan, and the reason is Room Modes. That cube will mean that you have the same frequency resonating in all three dimensions, so when anything is played at that frequency, it will sound like it has been amplified and “lengthened” compared to all other sounds. So go download the calculator, and use the results to bring your home theater’s acoustic performance up to the next level. (Screenshot of ModeCalc from...

Standing Waves, Peaks, and Nulls

in Home Theater Acoustics, Home Theater Audio

Coming Soon! In the meantime, check out the free downloads below…

Home Theater Acoustics

in Home Theater Acoustics