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.              ...

Home Theater Subwoofer Placement

in Home Theater Audio, Home Theater Design

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 and love really well. Let that section repeat, and while it does, move the subwoofer away from the corner. Move it towards the center of the room a foot, move it towards the seating position a foot, and so on. There is no exact answer to this, again due to the fact that the room dimensions have such an impact on performance. At each position, sit in your seats and listen. Close your eyes and just listen. You should be able to hear an obvious audio difference as you move the subwoofer around in your room. If you are open to trying it, there is a fun method called the Subwoofer Crawl. The Subwoofer Crawl is pretty simple in concept, and is actually an effective method, for the average person in their home theater, for finding the best subwoofer location. To perform a Subwoofer Crawl, what you do is place the subwoofer in your seating location, so you might have to move your seat to do this. The sub is temporarily placed in that seat’s place. After the sub is in your seating location, go ahead and play your music or movie scene. The, drop down onto your knees and crawl around the walls, the entire perimeter, of your theater. While you are crawling, listen to the bass level. You will hear that some parts of your crawl have strong bass, some have weak bass, and some have even bass. When you are at a location that has even bass, that is a location where you would put your subwoofer. If you add another subwoofer, you then are dealing with placement of multiple subwoofers, which is a separate (although related) project in your theater. Adding that second subwoofer will not remove any of your room’s standing waves, the nulls, or the peaks (those are based on the math of the room). However, adding a second subwoofer can create a more even level of bass throughout the room, which means more of your theater’s seats will experience the exact same level of bass performance. So if you can, go ahead and...

Home Theater Speaker Placement

in Home Theater Audio, Home Theater Design

You want a great home theater? Then you have to have your room right, and you need to have your speakers in the right location. If you buy some awesome speakers, but you put them in the wrong places in your room, those awesome speakers won’t sound nearly as awesome as they could. In this article, we’ll go through the best practices in setting up your home theater speakers. As an important note, please keep in mind that loudspeaker manufacturers will have specific guidelines for their products, so always follow what the manufacturer specifies. One other note, all the discussions you read tend to be about the single seated position. I’ll be using the same concept here, but realize that the farther away from that ideal seated position, the more out of ‘alignment’ your audio will be. That is where audio calibration comes into play, your audio performance does not stop with where you position your speakers. OK, so let’s get started… Center Channel Placement Your center channel is the workhorse of your home theater speakers, and the placement of this speaker is critical. This speaker is where the vast majority of dialogue is located, and the true ‘center’ of the audio you hear while you are listening to your system. Ideally, the tweeter(s) of your center channel should be horizontally aligned with the tweeters of your front left and right speakers. If you cannot place the tweeters on the exact same height, then you should have the tweeter(s) of the center channel within 12 inches of the tweeters on the left and right speakers. In terms of where to put the speaker, you should have your center channel positioned directly in the middle of your display. Doing so, gives you three options, one is to place this speaker above your screen, the second is to place the speaker below your screen, and the third option is to place the speaker centered directly behind your screen. There are pros and cons to both above and below the screen. When the speaker is below the screen, the tweeter is more likely within that 12 inch range of your left and right speakers, however if you have multiple rows in your theater, then the viewers in the front row are likely going to block the audio from reaching the subsequent rows. When you place your center channel above the screen, a downside is that there is a large difference between the tweeter height of your left and right speakers with your center channel. You can angle it down towards the audience, however you might still pickup that the speaker is well above your left and right speakers. So your best option is to place your center channel speaker directly behind the screen, with the tweeters aligned in a straight line. Of course, if you make the choice to have your center channel directly behind your screen, you will have to be using an Acoustically Transparent screen surface, so that your audio can come right through from the center of the screen. Regardless of your vertical position choice, the center channel speaker is considered 0 degrees from the listening position, meaning it is exactly centered on that seat. Front Left and Right Speakers While your center channel is the workhorse, the other two speakers that make up your front sound stage are your front left and right speakers. These two speakers are, obviously, placed on the left and the right of your center channel. There really isn’t an exact distance apart for these two speakers, rather the distance between them is based on where your seating is positioned. You should try to have the tweeter of this speaker in line with the ear height of your listening position, and (as mentioned) your center channel should have the same tweet height. This keeps the audio that is moving from left to right, smooth and on the same plane. These two speakers should be in a range that is anywhere between 22 degrees and 30 degrees from the listening position. With an acoustically transparent screen, this can often place the front left and right speakers behind the screen, so keep that in mind when you are planning your room.   Side Surround Speakers Your center channel, your front left, and your front right speaker all make up a single soundstage, with audio moving smoothly from one speaker to the other, and with you able to easily follow that movement. When it comes to your surround speakers, your placement is designed so that the entire surround sound audio blends into an envelope around the side, and rear, of the listening position. While the audio engineer might create sounds that are coming from specific speakers, in general, your surround sound is diffused, and you shouldn’t be able to easily pick out what sound is coming from what speaker. These speakers are placed anywhere between 90 degrees and 110 degrees from the listening position. And, where you want your front soundstage speakers to have the tweeter at ear height, with your surrounds you do not. Your surround sound speakers should be above ear height, if your room allows it they should be two to three feet higher than the ear height of the listening position. Remember the idea here is to create an immersive sound field, not point the speakers directly at the ears of the listeners....

Home Theater Multiple Subwoofer Placement

in Home Theater Audio, Home Theater Design

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

Standing Waves, Peaks, and Nulls

in Home Theater Acoustics, Home Theater Audio

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