Absorption and Reverberation

For most readers, the opportunity to influence the distribution of sound output from the speakers is very limited. But it is important to understand the factors which affect it. In a living room the sound waves travel only a very short distance freely before it strikes some object. They are reflected and some of the energy contained in it is dissipated by absorption before it gets progressively less and less. The time taken for the sound energy to fall to one millionth of its original value is known as reverberation time. It depends on the size of the room, but about half a second is considered satisfactory for listening to reproduced music; the theory applies to middle frequencies.

Not only does the materials on the floor, walls and ceilings absorb energy, but so also do the normal furnishings of the room and the listeners themselves. Modern furnishings tend to utilize the materials which do not absorb sound readily particularly glass which is one of the worst materials acoustically. Large windows are nevertheless, very desirable.

Only limited improvements can be done to room conditions. Thick carpets are good on solid floors. The shape of your room and how it's furnished will affect the sound you hear. For instance, too many bare surfaces can cause reflections that may add harshness to the sound. Adding carpeting and drapes can help.

If you have a choice of rooms, avoid ones that are perfectly square or have one dimension exactly twice another.These rooms can aggravate resonance that color the sound.

If possible, center your seating area between the surround speakers. The closer you place a speaker to intersecting room surfaces (corners, wall and ceiling, wall and floor), the stronger the bass output. This can help bass-shy speakers, but it can also add too much bass. Again, just moving a speaker a few inches can often make a big difference in sound.

Speaker Placement Tips

Speakers form one of the most important part of the home theatre and will decide the final sound quality. Where you place them around in the room will be a key determinant to the theatre experience.

The front L/R should go on either side of the TV with at least 5-6 ft. between them for stereo separation and imaging.
Since the speakers will also be used for stereo music listening, place them such that it will sound good for movies and music. For music the general criteria is to keep a little away from room boundaries.

Centre channel should be either below or above the TV so that the dialogues are locked on to the screen. If it is not at the ear level, point it towards ear level of the sofa. But ensure that the speaker edge is in line with the TV edge to avoid diffraction.

Surrounds are to be ideally to the sides of the listener and at a height of 6 ft. from the floor for optimum spread.

Of course, it's not always possible to place your speakers exactly as shown in the speaker placement diagrams. The diagrams give a range of placement angles, so you have some flexibility. Sometimes you'll have no choice but to mount the surrounds behind you, but if you follow the guidelines as closely as you can, you'll have good sound.

Ideally, your front speakers, high-frequency drivers, or tweeters should be positioned at ear level (when you're seated). Our recommended height for the surrounds is above ear level, as soundtracks are likely to be optimized for that location.

Beyond keeping it on the floor, there's no specific rule for placing the subwoofer, as bass sound is non-directional. However, the amount of bass may vary depending on room location. You might want to try a few different places to determine what's best for you (sometimes moving the speaker even a few inches can change the sound).

Speaker Shopping Tips

Most speaker manufacturers offer complete home theater systems, usually based on a satellite/subwoofer configuration. You're assured of speakers that match sonically (and cosmetically). Generally, the satellite speakers in these systems are shielded, so they can be placed close to your TV set. If your stereo speakers are not shielded, don't place them too close to the TV. (They're too close if the picture starts to distort.)

If you're expanding a stereo system and want to keep the speakers you have, try to stick with the manufacturer of your current speakers when you choose your center channel, surrounds and subwoofer. Most speaker manufacturers can offer advice on complementary models. For example, Jamo has full theatre systems which will have the sub, surround and centre speakers matching their tower models on the same digit the speakers are numbered.

Room resonances and size/type based Tips

Where any dimension is one half of the wavelength of the sound, resonant vibration will be excited in the air. At a frequency of 40 Hz, the wavelength of sound is 8.5 meters, so the length of the room that will resonate is the one with half the length. Which is 4.25m or 14 ft. Then there are harmonics to this which is 80 Hz, 120Hz etc. So resonances will occur at many points in the room due to height and diagonal dimensions as well. So in such a complex scenario with many frequencies in the room, standing waves are likely to form up which creates sound pressure regions in some of the pockets. So we cannot have the builders to alter the rooms always in such situations, but by placing dampers such as furniture or dividers or free standing book shelves etc correction can be applied.

Size of the room also decides mostly your speaker and power amplifier selections.
Some of you who are very keen to preserve the convinience of your rooms and can't afford to have so many speakers blocking your freedom of movement, we have some exciting models which are architects choice that can get into the wall without loosing any of the quality of sound. Check them out in our speaker categories in the products section specified as in wall spekers. Similarly if you have small rooms and square rooms please avoid having overly powered speakers. We have high fidelity systems for varying power requirements. This will save lot of money without compromising any way on quality. The bigger ones will just not add any value if the room is too small but no harm buying them if you have plans to move them out and in. So ensure that you take the right speakers for the room acoustics too. Please check our building theatre at home for more on making the room dead to ensure that your speaker and the rooms cooperate to make the live concerts real rather than reverbs adding incorrect tones to the records. We also have in-wall speakers which do not compromise on the quality nor on acoustics matching our regular speakers which will be to your architects delight to design a neat room for you..!

Building your theatre at home

Do not think that your room acoustics is poor for the theatre you plan to buy. Just like the way Laurie Baker builds low cost homes, there are low cost materials that can be used to pad up your room right from curtains and glass wool, egg crates etc to make it a dead room for perfect theatre experience. Many a time if you have the right furniture you might not even need any padding up to mange sound in your room. As you know, sound is very personal and something you like might be unique and hence no studio designer can blindly design one for you. We have our studio consultants and carpenters who can design / fix your absorbants, reflectants and the like in the right sequence to match your room size. You might have to cover up at lot of places and remove echo sources out of your listening room.

Speaker placement diagram

5.1 Setup

This system has six channels: five full-range channels, and a low-frequency effects channel (the .1 of 5.1) usually expressed through a subwoofer. Many DVDs and digital broadcasts feature a Dolby® Digital (5.1) soundtrack, so this will give you optimum sound for most programming. It also most closely approximates the sound in most cinemas.

6.1 or 7.1 Setups

The most advanced home theater systems feature six (with Center Back) or seven (with Left Back/Right Back) full-range channels that allow viewers to take full advantage of Dolby Digital EX soundtracks and Dolby Pro Logic® IIx matrix-surround decoding technology. Both of these processes add surround information for greater realism and more dramatic effects.