Improve the Sound in Your Home Theatre

Improve the Sound in Your Home Theatre: Hot tips that every home theatre system can benefit from!

It doesn’t matter whether you spend two thousand or fifty thousand dollars on your home theatre – if your gear isn’t positioned and configured properly – you’re not enjoying the full potential of your home theatre. Before throwing in the towel and getting new gear, try the basic (and free!) sound improving tips described below. You may be pleasantly surprised at just how much better your existing setup can sound. It’s not always about bigger and more powerful equipment – it’s just as important how you use it. Besides the quality of the gear, three other factors have a major influence on the sound in your home theatre: The placement of the speakers, room acoustics and the configuration of your A/V receiver.

Centre Channel

I am frequently asked to recommend a replacement centre channel speaker by people who are unhappy with the performance of their current centre channel. My first question is always whether they are using a centre channel that matches the rest of their speakers. And more often than not, the centre speaker is from the same manufacturer and matching line of speakers. Could it be that many speaker manufacturers can make great left and right speakers, yet not be able to make a decent centre speaker? No!

It’s more likely that the centre channel isn’t placed or positioned to deliver optimal sound. Ideally, the tweeters of the centre channel should be horizontally aligned with the tweeters in the main left and right speakers. This is usually only possible if your centre channel is behind an acoustically transparent projection screen. In practice, your centre channel is likely above or below your television set. If this is the case, position the centre channel as close to the bottom or the top of the TV as possible. The further away the centre channel tweeter is from tweeter levels of the left and right speakers, the less accurate the imaging of your centre channel will be. The intelligibility of the audio will also be compromised by the sound reflecting off the floor or ceiling. The closer your centre channel is to either one, the muddier the audio will get.

Even if the TV isn’t exactly centred between the left and right speakers, keep the centre channel in the middle of your display. Most of the dialogue in movies comes out of the centre channel, so you want it anchored in the middle of your screen.

If your centre channel is on a shelf inside a wall unit, or even a shelf of a TV stand, pull the speaker out a little bit. Also pull out any speaker that’s inside a bookcase. If your speakers are inside a box, the soundtrack will sound like it’s coming out of a box. All they need is a little breathing room, just enough for the baffles to stick out about quarter-of-an-inch past the edge of the shelf. You might be amazed at how much the sound will open up by doing so.

Finally, make sure the centre channel is pointed at the listening position. It’s not doing much good aimed at your knees or above your head. Some centre speakers have a downward slope on the top surface. Flipping it up side down will angle the speaker up. You can also use small rubber feet to angle the speaker. If your speaker is below the TV and you want to angle it upwards, simply put rubber feet along the front under the speaker cabinet.

Front Speakers

The main left and right speakers are pretty straight forward to place. Ideally you want each one to be the same distance from the edges of the display. When you are sitting directly in front of the centre channel, the left and right speaker should be 22 to 30 degrees away from it (from your seating position). They should also be in the same plane with the each other and the centre channel. Again, if they are in a wall unit or a bookshelf, pull them out a little.

The distance between the speaker and the wall behind it (and the wall to its side) has a major impact on the bass and the soundstage. The closer the speaker is placed to the back or the side wall, the more reinforced the bass will sound. The speaker’s proximity to the walls will affect the quality and the amount of bass. Pulling a speaker away from the back wall will increase the depth of the soundstage. However pulling it out too far may deteriorate the soundstage focus. Experimenting with these distances and finding the right balance is the key to getting desirable sound from the front channels. Ideally the speakers should be at least a foot away from the back and side walls. Of course, this may not always be achievable because of the room size or layout. Finally, the distance to the back wall and side wall should not be equal.

The distance between the left and right speakers will influence the width of the soundstage. The bigger the distance between the speakers, the wider the soundstage will sound.

Aiming the speakers toward the listening spot, called a toe-in, also has a major impact on the soundstage and the centre image. A large soundstage can be achieved with no toe-in but the centre image may not be very focused. More toe-in will produce a focused centre image but reduce the soundstage width. Some speaker manufacturers specify a recommended amount of toe-in for their speakers in the manual. Otherwise, experiment with different amounts of toe-in to achieve best results.

Surround Speakers

The surround speakers should be a couple of feet above your listening position. Directly to the left and right will also work, although you may want to move them back, up to 20 degrees behind your listening position. In movie soundtracks the surround speakers carry mostly ambient sound and directionality isn’t nearly as crucial as the centre channel. That being said, the dispersion characteristics of your speakers may require you to point them towards the listening position. Using dipole speakers as surrounds will generally produce a more enveloping sound stage.

6.1 and 7.1 Systems

In a 6.1 channel system, the sole rear speaker should be positioned directly behind the listening position, at approximately the same height as the left and right surround speakers. The addition of a rear speaker means that your surround speakers no longer have to be rearwards of the listening position. It’s recommended that the surround speakers be placed directly to each side of the listener, with the rear speaker the same distance behind the listener that the surrounds are to either side. If you are running a 7.1 system, there are two schools of thought as to rear speaker positioning. One is to place the rear surround speakers several feet apart, in order to more evenly disperse sound throughout the listening room. The other is to have the rear speakers fairly close, less than a foot or two apart, so as to give a solid anchor to the rear soundstage during flybys and the like. For example, if a character in a movie is walking behind the viewer, you’d want to hear their footsteps directly behind you, not spaced out between two rear speakers that are far apart. THX recommends the latter placement, but, as with most things involving A/V gear, “one person’s trash is another person’s treasure” and what sounds great to me might sound anything but to you, so you should experiment with both types of placement and see what works best in your room with your gear.

Room Acoustics

The room plays a significant role in the performance of any speaker system. Every hard surface in the room reflects sound and what arrives at our ears is combination of direct and reflected sounds. Direct sound comes straight to our ears from the speaker diaphragms. Reflected sound is sound that bounces off walls, the ceiling, the floor and furniture, and arrives at our listening position after a slight delay. In general, direct sound is primarily responsible for the image and reflected sound contributes largely to the tonality.

The first thing to consider is the floor. The harder the floor is, the more it will reflect sound. The more sound gets reflected, the more it will suffer. Your speakers will sound bright or harsh. The sound that reflects off the ground will arrive at a slightly different time than the sound that reaches your ear directly from the speaker. This muddies the sound leading to intelligibility issues, especially for the centre channel. If you can, lay down a thick cozy carpet in your home theatre. If not, an area rug between the display and your listening position will also help. And if possible, don’t go putting a big coffee table on top of that rug. The table will also give off harsh reflections.

The next reflection points to consider are the side walls. Ask someone to hold a mirror along the side of the wall at the same height as the tweeters of your main left or right speaker while you sit at the listening position. The point at which you can see the reflection of the speaker in the mirror is the primary reflection point. This is the spot that should be treated with sound absorbing material. If the reflection point is a window, cover it with a heavy drape. Do this for both the left and right speaker primary reflection points.

The next reflection point to consider is the ceiling. This again will affect the performance of the centre channel. Putting some acoustic tiles up there should result in a much tighter dialogue.

The back of your room should have some absorption or dispersion characteristics as well. A book case works well, or some snazzy dispersion panels, “snazzy” being a relative term. Snazzy to you and me might translate into hideous to your significant other.

Subwoofer Placement

Subwoofers are sexy in the same way small block Chevy engines are sexy. They offer brute force and the bigger, the more you love showing it off to your friends. Engines are kept out of site under a hood. Subwoofers, unfortunately, are usually relegated to a corner where they will be as unobtrusive as possible.

Subwoofers are tricky to place. They interact with rooms differently and more awkwardly than full range speakers. They’re also big and cumbersome to move around. It takes a dedicated person to move the subwoofer, then go to couch to evaluate the sound, then move the subwoofer again and repeat this processes many times.

The easiest way to find a sweet spot for the subwoofer is to reverse the roles. Put the subwoofer in your listening position. Move the couch and put the sub in the area where you would normally sit. Then play some bass heavy music or a movie soundtrack. As it’s playing crawl around the room listening for the best bass response. Once you’ve found it, move the subwoofer to that spot and verify that the subwoofer sounds good in your listening area.

Further improvements to a subwoofer’s performance can be achieved with acoustic treatment. Start by placing a bass trap in the corner closest to the subwoofer. Then bring another bass trap home and experiment with its location in different corners of the room. Keep adding bass traps and acoustic treatments until someone stops you. If no one stops you, stop yourself if your room starts sounding a little dead. You don’t want to turn your home theatre into an anechoic chamber, which is what too much acoustic treatment will result in.

A/V Receiver Configuration

Every modern A/V receiver has a “Speaker Menu” that allows the user to specify which speakers are connected, the size of each speaker, the distance from the listening position to each speaker, individual speaker levels and a crossover frequency. Some receivers even allow you to set the impedance of the connected speakers. In order to set the speaker levels, you will need to use a Sound Pressure Level (SPL) meter which has to be purchased separately from the receiver. All of these settings are crucial and need to be set carefully in order for your home theatre system to properly reproduce movie soundtracks.

In addition to this “manual” speaker setup, all modern receivers also come with a built-in automatic speaker setup (or calibration) feature which goes under a number of different names. By plugging in the microphone supplied with the receiver and placing it in the listening position, the receiver takes numerous measurements as it plays a series of test tones. It then automatically sets the connected speaker sizes, distances, levels and the crossover frequency. Once these settings are configured, a good-quality automatic speaker setup will remove the distortion caused by room acoustics (walls, and materials that absorb and reflect sound) in the frequency and time domains.

Some receiver manufacturers have developed their own proprietary automatic speaker setups, while others rely on the well regarded Audyssey system (www.audyssey.com). A number of different automatic speaker setups are usually offered by each receiver manufacturer, each with a varying level of performance. Hypothetically speaking, the more expensive the receiver, the better its on-board automatic speaker setup can be expected. At their best, automatic speaker setups can produce very desirable results.

Many home theatre enthusiasts like to run the “manual” speaker setup first and then compare it to the automatic setup, so that they can determine if their system sounds better before or after the automatic setup.

Now that you’ve tried all these tips, how does your system sound? If you’re still not satisfied it may be time to upgrade your gear after all and go through the steps in this article all over again.

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