RATTLES
Rattles in the room are structural resonances (as opposed to standing waves, which are airborne resonances) which the system may stimulate due to its broad frequency response and wide dynamic range. They are particularly prominent for sounds in the lower frequencies, and can sound like distortion. Sources of rattles include: furniture, loose window frames, walls, lighting, fixtures, ventilation systems, and even
As the sweep makes its way up the frequency range, you will probably find a surprising number of rattles in your room. All of these rattles will occur at one time or another during music or movies, but are usually perceived as background noise or distortion in the system.
Once identified, eliminating the rattles is usually straightforward. As an example, small pieces of felt can be affixed to the back of a painting (in the bottom corners) to prevent audible rattles against the wall. Likewise, strips of felt can be wedged into a loose win- dow rattling in its frame. Recessed lighting fixtures can be tightened up. A piece of cloth can be placed under offending
Every Home THX Audio System should be subjected to the rattle test at least once— the difference in low level resolution and in freedom from
BACKGROUND NOISE
The effects of background noise on system performance is dramatic, yet often over- looked. Most people might think of it merely as a minor inconvenience, yet it has a pro- found effect on the way we perceive sound.
The presence of
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