Good article on home theater acoustics by Acoustic Sciences Corp

There are many occasions that we were being asked about the importance of room acoustic by customers. Many failed to address the problem while some think that by buying a better system, the problem can be minimized, which is wrong.

A good system in a bad acoustic room will sounds just as bad. That is why room acoustics is very important and should be dealt with in order to truly enjoy your HT or hi-fi system.

This article is very informative and we find it to be useful for other HT enthusiasts as well as audiophiles. As the article is very long, we only extract a portion of it. For the remaining, you may click at the attached link.

Happy reading.

Home Theater Acoustics

One of the first things the novice acoustician does upon entering a room is to deliver a sharp clap of the hands. This is followed by a grave shake of the head and comments about how bad the room sounds. Next comes a proposition to fix the room and the fee. The unsuspecting client then administers a sharp hand clap, nods the head in agreement, and gives the guru a retainer. The only problem here is that these people are busy buying and selling modifications to the sound of their own hand clap. We don't listen to a speaker while holding it in our hands, yet we can be tempted to consider acoustics based on the sound of our own hand clap.

Home theater audio systems have an ambiance channel. It usually delivers a bandwidth-limited (no bass), mono signal to a pair of speakers that have been mounted high on the wall and to the side of the listener. If you stand on a chair and clap your hands in the location of the ambiance speaker, you will hear a very funny and undesirable sound effect. Is this really something we can hear? If so, do we want to listen to this sound effect or provide it to our clients? If not, there might be something we can do about flutter echo colorations.

THE ACOUSTIC CLAP TEST

On a practical basis, the only time that a self-administered and self-audited hand clap is directly relevant to anything in audio is when the recording engineer is setting up mikes in a studio. Only in this special circumstance does the desired audio signal leave from and return to the same place. Listening to one's own hand clap duplicates this round trip, acoustic process and thereby is a relevant test. If someone ever wants to know how a loudspeaker sounds to the listener, a different technique must be followed, one that mimics the actual speaker/listener acoustical path.

A hand clap contains only high frequencies. For a loudspeaker, the high frequencies are directional, forward of the speaker box. To properly administer a hand clap that mimics the high-frequency beaming pattern of a loudspeaker, the hands must meet at waist height while the clapper is facing the same direction that the speaker does. The body of the clapper blocks the expansion of the clap sound backwards. The listener is no longer in the clapper position, the listener is now seated in the listening position. This time, the hand clap is cast forward from the speaker position and is heard by the real listener. It is how the listener hears the speaker that counts and not so much how the speaker sounds to itself, at least in hi-fi playback settings.

In order to properly evaluate the consequence on the listener of the strange sound we heard when standing on the chair and clapping our hands overhead and near the mounting position of the ambience speaker, we must repeat the test while a listener is seated in the listener's chair. True enough, in this case, the zing we hear when we clap is also heard by the listener. And so, is the sound we hear, good, bad, or inconsequential? Certainly this sound effect is distracting and that alone is enough to warrant its eradication. On the other hand, we want to retain an overhead liveliness so as to promote the ambience signal. We can't sacrifice the lively quality of the overhead space in the room, yet we must try to get rid of its distracting effect known as flutter echo.

For more info :

FLUTTER ECHO/FLUTTER TONES

Multiple subwoofers system

In current market, many of the av receivers have multiple subwoofer pre-out. Previously, most system is only a 5.1 system. Now, we have 11.3, 9.2, and the getting common by the day 7.2 system.

However, getting multiple subs to work perfectly is not easy. There will be cancellation if it is not being set up correctly. Many will recommend to use the same model in order to make it blend well. Normally, the subs will be located in front with equal distance from walls.

Many people will ask what if the subs are not the same model. In this scenario, one has to play with position, phase and delay. It is not easy though and needs a lot of time and patience to get it correct.

All is not lost. Audyssey has came out with MultEQ XT32. It also has Sub EQ HT which is a powerful software that properly integrate two subwoofers in a home theater systems. Sub EQ HT makes the integration seamless by first compensating for any level and delay differences between the two subwoofers and then applying Audyssey’s room correction MultEQ technology to both subwoofers together. The result is great sound with fantastic bass minus the headache. For those av receivers without XT32, you can buy Antimode 8033 or AS-EQ1 which is very effective.

It may not 100% eliminate the integration problem due room acoustic and different subs. Here we explore different positions of dual subwoofers system and the respective result.

1. Both subs in front

There is a serious dip after 31Hz until 63Hz. The graph is not flat. Many details are lost in this region making the sub less punchy and dynamic.


2. One sub in front and another at the back

In this graph, we see a big improvement with lesser and smaller dip. The graph is also flatter from 54Hz and below. The tactile bass becomes more apparent. It also improves on the bass texture as well as details.

In both occasion, Denon AVR-4311 is being used since it has MultEQ XT32. Many people believe that the subwoofer is non-directional and it does not need specific placement. It is a MYTH as past experience has proved otherwise.

You need to do find the best placement in order to bring out the best from a sub. Some will resort to proven and tested Sub Crawl Method while some will be busy with REW, XTZ or other similar gears to plot the FR graph of different positions to check any abnormalities in order to improve or troubleshoot it.

It is never been easy for multiple subs system but once you are able to find the best positions for both and also the correct setting, the end result is very rewarding.

Are you ready to Ruummmbllleee?