| R13?? [message #50799] |
Sun, 11 March 2007 13:34  |
Mark Andrews
Messages: 21
Registered: May 2009
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Chancellor |
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Guys can someone tell me what R13 is? I can get:
1) Poly fill
2) Fibre Glass
3) Compressed fibre glass (high density almost like sheets) Ta Mark
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| Sound absorbtion [message #50803 is a reply to message #50799] |
Sun, 11 March 2007 14:36  |
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Wayne Parham
Messages: 18791
Registered: January 2001
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Illuminati (33rd Degree) |
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R13 is simply fiberglass insulation that's 3.5" thick, uncompressed. It's used to absorb unwanted midrange frequencies inside the cabinet. Bass passes right through it because it isn't thick enough to absorb bass energy, and that's exactly what we want. We want the bass to react with the Helmholtz resonator formed by the bass-reflex cabinet. But midrange and higher frequencies would develop stading waves inside the cabinet, and we don't want that reflected back to the cone. So by using fiberous material inside, we absorb midrange and reduce standing waves.The same thing happens in rooms, but it happens at lower frequencies because of the size of the room. Standing waves setup inside rooms and cause peaks and dips at bass frequencies. So the best rooms are those that provide some damping. In North America, many homes are made using a framed drywall construction. This uses drywall panels mounted on studs with insulation in between. The panels flex fairly easily, and this allows some damping which actually does a lot towards reducing the strength of room modes.
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| Re: Sound absorbtion [message #50816 is a reply to message #50803] |
Mon, 12 March 2007 06:45 |
dB
Messages: 234
Registered: May 2009
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Master |
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Very nice info Wayne. 5 Stars.
(Wayne, for the first time I'm going to use a 3/4" Layer of Polyurethene Foam available from Spain i.e. COPOPREN by Recticel) There are a lot of technologicaly developed new materials (sound absorbing) available." A promising sort of material would be one that absorbed sound (rather than re-directing the air flow as leather does). Traditional sound absorbers are fabrics, such as batting, or knotted carpets. More recently, a number of high-tech sound absorbing fabrics have been devised which may work somewhat better, and are quite a lot thinner--very important in the restricted space of a concertina end.
Sound-absorbing acoustic fabric
produces a different sound quality The material I tried is a rough ribbed polyester fabric made by JM Lynne Co. and sold on the net by Netwell Noise Control under the name "silence wallcovering" for application to the walls of rooms; it is said to be "designed for light sound absorption where the human voice and other mid range sound sources are a culprit". It is thin: 0.175" (about 4.4mm). The mill width is 54 inches, so a single linear yard at that width will cut out into a dozen or more pairs of baffles, even large ones; it is light in weight, with a linear yard (54" wide x 36") weighing 24 ounces. The fabric is available in 24 colors ( I have used black and ivory.) A yard costs USD 22.50 (GBP 15.85, EUR 25.60). See below under Suppliers. This particular acoustical fabric is not at all air-tight--if you hold it to your lips you can blow through it just about as easily as through a single layer of ordinary t-shirt fabric. "
in www.concertina.com
(http://www.concertina.com/gaskins/baffles/)
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