Mylbopay wrote:Source of the post
Also, use more dense material for the bass trap, 8 lb for example
Adding more to what I said here before: Bass traps need lower density materials, not higher density. Lower density has better absorption at low frequencies, all other factors being equal. And 8lb is way too high.
Also, the correct density for any given application varies according to the insulation family: fiberglass, mineral wool, recycled denim, cellulose, polyester, other synthetic, etc. There's an optimum density for each product and each application. For example, typically for wall insulation, if you were using mineral wool, the density would be something around 50 kg/m3 (about 3 pcf), but if you were using fiberglass insulation then it would need to be around 30 kg/m3 (roughly 2 pcf). Your suggest for 8 pcf works out to 130 kg/m3, which is way too heavy for most acoustic applications, regardless of the family.
In any event, it isn't the density that matters, but rather a property called "gas flow resistivity" ("GFR"). That's the measure of acoustic impedance, and that's the important factor for understanding the acoustic properties of any porous absorber. For each family of insulation there is a very approximate relationship between density and GFR, but it is different for each family. It is far better to check the GFR number for any insulation product you plan to use in a studio, to see if it is suitable for the job.
Here's a graph that shows the rough relationship between the density of some insulation products, and the associated GFR:
It's in German: Sorry. But I'm sure you can figure it out!
- Stuart -