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We pick up where we left off last week with our insight on the effectiveness of carpet in a Hifi environment. Some general guidelines were provided, but we can focus on specifics about why the best carpets really do give you the best sound.

This week ASC President and TubeTrap Inventor, Art Noxon, PE shares his extensive knowledge on the subject.

Let’s Talk Persian Rug Acoustics

The timeless image of Hifi is a high-flying Persian carpet sporting a listening chair and a pair of loudspeakers. Yes, it’s true. A good sound system set up on a Persian carpet can transport any audiophile into a wonderful adventure in some other place and time.

But, what about this Persian carpet? Does it have to be a real Persian carpet, or just look like one? How about a cheap Chinese Persian carpet? What kind of Persian carpet? The old original short-knap type or the more modern thick and plush type? And what does a Persian carpet have to do with the sound anyway – does it just help with one’s imagination or is there something real about the Persian carpet?

Carpet Facts

Let’s look at some of the rules-of-thumb that fly about the air regarding Persian carpets.

• Thick carpets do not need a carpet pad but thin carpets can use a carpet pad.
• Thick carpets are so stiff and massive, they do not need anti-slip pads.
• Thin carpets are light and floppy and do need anti-slip pads.
• Old style short knap tight pack carpets reflect sound, pad or not.
• Newer long knap tight pack carpets absorb sound even without pad.
• Thick carpets can be 1” deep and weigh over 1#/sq ft.
• Thick carpets provide tippy support, audio spikes should be used.

Sound Absorption

Sound is absorbed on the surface of objects. Fibers have a huge surface area to weight ratio, which is why fiber-made objects make good sound absorbers. The density of glass is 2.5 times that of water. The density of wool is 1.3 times that of water. Wool fiber weighs ½ the weight of glass fiber, all other dimensions being equal.

We have seen that both fiberglass fibers and soft wool fibers are made in about the same diameter, 8 microns. (1 micron equals one millionth of a meter.) The surface weight of a plush 1” thick Persian carpet is 1.1 #/sq ft. The bulk fiber density of a Persian carpet is about 13#/cubic foot. But the fibers of the Persian carpet have half the weight as equivalent fiberglass fibers. A fiberglass sound panel with the same number and size of fibers as a Persian carpet would weight twice as much as a Persian carpet.

To compare to a 1” carpet, the sound panel would have a surface weight of 2.2 #/sq ft.

A typical sound panel is made out of bulk fiberglass whose density is between 4 and 5 #/cu ft. The standard 2” sound panel has the surface weight of about 0.75 #/sq ft. To have a surface weight of 2.2 #/sq ft, a sound panel would have to be 6” thick. A 1” thick plush Persian carpet has the same amount of acoustical fiber as a 6” thick sound panel. Now that’s an impressive comparison.

Continue reading the entire article and be sure to check out all the amazing acoustic treatment solutions ASC has to offer your Hifi Room or Recording/Mixing Studio.