Home Theater Library


Sound Isolation Versus Acoustics

Posted by on 11:05 pm in Home Theater Acoustics, Home Theater Audio, Home Theater Design, Home Theater Soundproofing | 0 comments

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...

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DIY Super Chunk Corner Bass Traps

Posted by on 4:34 pm in DIY Home Theater Projects, Home Theater Acoustics, Home Theater Audio | 0 comments

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...

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Room Mode Calculator

Posted by on 5:04 pm in Home Theater Acoustics, Home Theater Design | 2 comments

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...

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Home Theater Seating Guide

Posted by on 4:01 pm in Home Theater Design, Home Theater Seating | 0 comments

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...

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Home Theater Projection Screens

Posted by on 5:09 pm in Home Theater Design, Home Theater Projection Screens | 0 comments

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...

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Home Theater Viewing Angle

Posted by on 4:55 pm in Home Theater Design | 0 comments

So you’re getting ready to enjoy the awesomeness that is a big old projection screen in your home theater, which is excellent. There is nothing like the lights going down, and your show starting up on your screen. Of course, while you are designing your theater, there are many screen related questions like, What should the viewing distance be for my seats? What kind of screen should I get? And, what are viewing angles anyway? The shortest answer is this image below, the viewing angle is shown on this picture: On a high level, this is how ‘wide’ the image is to your eyes, when you are watching the screen. But, you want more than that, and you should. A properly designed home theater will take into account the viewing angle – and not just put the largest possible screen that can fit onto the wall. To explain this more, we need to discuss something called Field-of-view. Field-of-view is basically the visual area you can see, when your eyes are fixed on a point (meaning, you are not looking around at things, you are staring at one point). The more of your field-of-view that is taken up by your screen, the more immersive the image will be. While you can technically see nearly 180 degrees, from left to right, you can’t really see that large of an angle with any clarity or with any resolution. What you see on your far peripheral vision is very hard for your brain to concentrate on, so instead you focus on what is in front of you. You want your screen to be inside that comfortable field of view, and you want a viewing angle that will give you the amount of immersion that you desire. Now, even though that level of immersion is a personal preference, there are some standards to work with . The Society of Motion Picture and Television Engineers (SMPTE) define the ideal viewing angle at 30 degrees or more. THX defines the ideal viewing angle at 40 degrees or more. Now that 40 degree or more number, that THX recommends, is based on a 16×9 Screen Ratio. However, since more and more home theaters are using a 2.39:1 ratio for their screen, we really need to discuss that ratio more than the big screen TV ratio. The THX recommendation for a cinemascope (2.39:1) screen is that the farthest seat, in the center of the theater, has a viewing angle of 36 degrees. So in your theater, you are likely going to want to have a minimum viewing angle of 36 degrees. To add onto this discussion is the issue of image resolution. As the resolution of displays keeps increasing, the comfortable viewing angle will also increase. This means that with a higher resolution display, such as a 4K display, you can comfortably enjoy a larger viewing angle that you can with an old 480p display. With this increase in resolution, with the use of CinemaScope ratio screens, many theater owners are creating theaters with 60 to 70 degree viewing angles, or even higher. There is no perfect answer here, there is no ‘exact’ viewing angle that you should use in your theater. As a general rule though you will, most likely, end up with a viewing angle that...

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Home Theater Viewing Distance

Posted by on 4:55 pm in Home Theater Design | 1 comment

Once you have decided to have a home theater, nothing will stop you! During your journey of creating your home theater, there are lots of decisions you have to make (which is a common theme of the home theater process). This includes lots about your screen – learning about viewing angles, screen choices, and how far away should your seats be from your screen. In a prior post, we talked about viewing angles, and here we’ll get into where your seats go, and how you can figure out the correct viewing distances for your theater. There are some formulas to figure out the recommended viewing angle limitations, but keep in mind that your own personal preference matters as well. Don’t focus solely on the math of these basic formulas, at the expense of ignoring what you personally like. In other words, do you like to sit closer to a screen, and have that ‘bigger’ feel, or do you like to sit farther away from the screen? That matters as well, it isn’t just about the math. But, It Is Easy Math! OK, so onto the basic math here. Don’t worry, it isn’t going to be hard! We’ll go through the main two formulas, starting with the SMPTE recommendation and then the THX recommendation. The Society of Motion Picture and Television Engineers (SMPTE) define the farthest viewing angle at 30 degrees. To use this formula, and to create your viewing distance, you take the Screen Diagonal (in inches) divided by 0.6. The answer (also in inches) to that is your viewing distance, at a 30 degree viewing angle. Let’s work through a common example, using a screen diagonal of 120 inches. 120 divided by 0.6 equals 200. 200 inches, divided by 12 is 16 feet, 8 inches. This means that, when following the SMPTE recommendation, your eyes should be 16 feet 8 inches away from a screen that is 120 inches diagonal, at the farthest seating position. Now the THX recommendation ends up with you closer to the screen, and provides a more immersive experience. This originates from THX being for the commercial movie theater market, where the bigger screen experience is preferred. The basic formula is the same, you start with your Screen Diagonal (in inches) size and you divide it. However, with the THX recommendation, you divide by 0.84, and your answer (in inches) is your viewing distance. Let’s work through the same common example, a screen diagonal of 120 inches. 120 divided by 0.84 equals 143 (excluding the fractional remainder).  143 inches, divided by 12 is 11 feet, 11 inches, so just under 12 feet, and this would be the farthest recommended seating location. You can see that with the SMPTE viewing angle, the seating is 16′ 8″ from the screen, and with the THX viewing angle, the seating is 11′ 11″ from the screen, that is already a pretty large range of where you should put your seats, so clearly there is room for flexibility here. In interviews with THX, the discussion of an ‘ideal viewing angle’ comes up, and it is right around 50 degrees, on a scope screen, so if you are looking for a good starting point, you can begin there. Forget Angles, Let’s Just Go With Height The other way of calculating...

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Home Theater Subwoofer Placement

Posted by on 4:50 pm in Home Theater Audio, Home Theater Design | 0 comments

When it comes to home theater, most owners really want to bring the bass, they want powerful, clean, and strong bass. This requires subwoofers, there is no way around it. You can have excellent main speakers, but if you really want the boom, you need a subwoofer, and – if possible – more than one. The subwoofer is a critical element of your home theater. Interestingly, there isn’t nearly as much audio coming out of this speaker as you might think; if you were to mute all your speakers except for your subwoofer you might be surprised at how little comes out of that speaker, compared to all the others. However, what does come from your subwoofer is so extremely important to your overall sound and enjoyment of your home theater. Without a great subwoofer, you can miss entire sections of the soundtrack, and even lose out on important parts of the movie’s story. Subwoofer placement is a little bit more of an art than the rest of your speaker placement. While there are guidelines that we will discuss, there aren’t quite the same set-in-stone angles and recommendations as there are with the rest of your speakers. One of the main reasons for this is because subwoofer frequencies are not directional, meaning you shouldn’t be able to detect where the bass is coming from in the room, the low frequencies should ‘seem’ to be everywhere. Another reason that there is no single recommendation to use is that the performance of the subwoofer is tied to the size of the room (meaning the actual dimensions and air volume of the room), the room impacts the sound of the subwoofer dramatically. In other words, the exact same subwoofer will perform quite differently in a room that is 10′ wide x 12′ long x 8′ tall compared to a room that is 16′ wide x 22′ long x 10′ high. To add to this issue, where you are in a room also impacts what you hear from the subwoofer, this means that as you move around the room, the audible level of the subwoofer will seem to change, even if there has been no change in volume at the source. At the most basic level, if you just want the most bass, go ahead and stick the subwoofer in the corner of your room. Putting the subwoofer there will ‘enhance’ the apparent sound level coming from the subwoofer, to some of the seating location in your room. The downside here is that other seats will have far less bass – the performance of the subwoofer will not seem even throughout your room. This is why corners are not the most ideal location for a subwoofer in your theater. Yes, you can create what sounds like an increase in bass level, but the performance is so uneven throughout your theater that the bass level from one row to another (and from the left seat to the right seat) can be drastically different. When you take it out of the corner, that ‘enhancement’ will seem to diminish and the sound level will also seem to diminish. However, you will have a more even performance throughout your room. So what you should do is put on some music, or a movie scene, that you know...

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