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...

Home Theater Seating Guide

in Home Theater Design, Home Theater Seating

You’re ready to build your home theater. Awesome! You know you are going to have a massive screen, an amazing projector, incredible sound, controlled lighting, and then you realize you need to also figure out where you and your guests are going to sit. So you start to look into home theater seating, and pretty quickly it becomes clear that you have tons of choices, and the prices can get out of control very fast. Want to spend a few thousand dollars per seat? No problem, you can do that very easily in a home theater. In this library entry, we’ll talk about the basics of home theater seating, and you need to get this right. After all, you might be sitting in that seat for long movie marathons and for years and years… How Big Is Your Room? Where you will likely start is considering how much room you have to work with, literally. Meaning, how big is your room? How wide is your theater room? How deep is your theater room? You have to know this basic information to even start the process of determining what seats you will have in your theater. Don’t forget that when you are considering your room size, you need to be thinking about the interior finished dimensions. Lots of rooms have several inches of acoustic treatment, or other finishes, on the ‘inside’ of the room, so you can easily end up with a room that is 6 inches smaller than you might have first thought. Inside the room, you also need to consider that you have to have space around the sides, essentially aisles. Not all theaters will have an aisle on either side of the seating, one aisle on one side is also very common, but that ‘space’ needs to be planned out. You don’t need the width of a regular hallway, meaning you do not have to have three feet of space as an aisle next to your seats. However, you do need enough room to get by without squeezing between the seat and the wall. Likewise, you also need to plan for the space between the rows. Now this will be greatly impacted by your actual seating choice. In other words if you use non-recliners you need far less space between the rows than if you have full sized reclining seats. As a side note, also keep in mind the dimensions leading into your theater. The size of the doorways, hallways, windows, and so on… It is not unheard of for people to purchase seating for their home theater room, only to find out the seats are too large to make it down a stairway, hallway, through a doorway, or around a corner. How Many People? In addition to knowing how big your room is, you also need to think about how many people you want to have seated in your theater. The options for seating 12 people are not the same as the options for seating 6 people, in the same sized room. When you are thinking about how many people, it is pretty common for folks planning a theater to overestimate the number of people. You should not build/design your theater for the maximum number of people that you think might be there someday. Planning a theater to seat 16 people for the once per year Super Bowl party is not the best way to plan a theater. You should plan the seats for what you are expecting will be your normal use. If the room can support 16 people, using more traditional non-recliners, but 99.9% of the time you are using the theater it will be just you and one other person, it doesn’t make sense to fit 16 seats in there. It makes much more sense to build the theater around you and that other person, and allow for additional seats (even folding seats) to be brought in during those rare times you need more capacity. You’ll enjoy your theater much more with seating that is really designed for your primary use first. Seating Styles When it comes to the styles of seating for your theater, the choices are really as wide and varied as any other place you have seating. Some owners use couches, some use sectionals, some even use over-sized beanbags. That is all based on your own design and style choice. There are some main styles of home theater seats however, and one of these styles is what the majority of theater owners will select. Traditional Theater Seating When people think of these seats, they tend to think small, cramped, and uncomfortable, but that is really incorrect these days. Traditional theater seating has come a long way over the years, and today you can find very comfortable seats in this style. If you have a bit less space, or you really do want to have lots of seats in your theater, then you should give serious consideration to this style of seat. They are less expensive than the home theater recliners, and have evolved quite a bit. Home Theater Recliners Full-sized home theater recliners are currently the most popular type of seat in the home theater. These are similar to a stand-alone reclining chair, only for the theater they are manufactured to be put together in rows, sharing the armrest space between the seats. With recliners, you need to make sure...

Home Theater Projection Screens

in Home Theater Design, Home Theater Projection Screens

So your big TV might be nice, but when you are ready to really step up to all that a home theater can be, you need a projector and a screen. A screen that is measured in feet, not inches! When it comes time to pick a screen, you have lots of choices. At the higher end, you have fully motorized screens with masking to provide you multiple aspect ratios. At the lower end you have manual pull-down screens. Screen Size Screen size is a hotly debated issue in the world of home theater. There are two main groups of thought on this subject. One is that you should try to get the best possible image for your space, even if it means the screen is smaller than your neighbors. The other is that you should try to get the biggest possible screen to maximize your theater and make your neighbors envious! The choice is yours, no one other than you can decide this issue; it must be what you are comfortable with and what your goals are in your theater. For many folks, the way to determine the screen size is to go to your local movie theater. Find your favorite seat. Then, take some time and estimate the screen size, and the distance you picked from the screen. Often the ceiling tiles in the theater will be 2×4 feet, so you can count the tiles to estimate your seating preference. You might find that you like to sit at 1x or 2x the screen width. Knowing your personal preference, you can then take that home and determine your ideal seating distance for the screen width you will use. You normally want the screen to sit so that the audience isn’t looking down, so your screen will sit higher on the wall than you might first expect. If you have one to two rows of seats, your screen will likely end up 24 inches from the floor of the theater. If you have many rows, do not be surprised if the bottom of the screen ends up several feet from the floor of the theater. Generally, you want the center of the screen to be no more than 15 degrees higher than the eye-level of the viewer, with the top of the screen no greater than 35 degrees higher than the eye-level of the viewer. Later in this course you will see a section that discusses viewing angles in relation to seat risers. Many projector manuals also include a chart that shows screen height calculations. There are two related articles, in the Home Theater Learning Library, about screens and viewing. Check them out here:  Home Theater Viewing Angles and Home Theater Viewing Distance Screen Material When it comes to the actual screen material itself there are several more issues to consider. The primary two of these are screen gain and viewing angle. You should account for both of these when choosing your screen. The screen gain, as you will read in a moment, is related to the brightness of your projector. This means you should make your projector and screen decisions together. A single screen will react differently for two different projectors, one brighter than the other, so keep this in mind. Every screen these days has a listed ‘gain’, and can range from low gain to high gain screens. Most of the screens that are white and used in the home theater have a gain of between 1.0 and 1.3. Screens that are gray in color tend to have lower gains, including numbers lower than 1.0, although it is not unheard of for a gray screen to have a gain higher than 1.0. The gain of the screen is measured by noting the reflectivity of the screen material. The measurement is in comparison to the amount of light that is reflected from a pure white board. A screen with a 1.0 gain has the same reflectivity as the white board, while a screen that has a 1.5 gain reflects 50% more light than the white board. Screens that are lower and have a gain of .80 reflect 80% of the light of the white board. These gains above 1.0 are not to imply that light is “added”, only that by using technology in manufacturing, more light is reflected to the viewing position than would normally occur. If you shine a flashlight against a flat white wall, light will be reflected in all angles, even the ceiling and floor. Imagine now that the wall were created so that some of the light that would normally reflect to the ceiling and floor is now reflected towards you, it would seem that there is an increase in the actual light. The measurement itself is taken at the brightest point on the screen, which is usually the center of the screen and perpendicular to the projection source. This is the peak gain of the screen. As you move to the side of center, you may reach a point where the brightness of the screen lowers. The distance you move with the picture remaining bright is the viewing angle of the screen. When you move beyond this point, the picture will continue to get dimmer as you move further and further to the side. While it might seem that you should pick a high gain screen to get the brightest image possible,...