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In Reply to: Re: Corner bass traps - Round or Square? posted by Ethan Winer on November 15, 2005 at 12:46:44:
Hi Ethan,
First I'd like to thank you so much for helping me prove that my wife is still in love with me after 13+ years. Our basement is slowly getting filled with large panels and bass traps spread all around. She just smiles and winks ;) *maybe she just feels sorry for the poor crazy guy she married :p)Really though. Thanks so much for your participation in these audio forums and for your FAQ pages. Jon Risch too...thanks.
Ok...back to the question. What's the facination with burlap fabric being recommended to cover panels and traps?I know that you want something that isn't going to reflect any high frequencies...but why the burlap recommedations?
Near as I could find out...Many times todays Burlap fabric is a desnse, yet open weave of 100% cotton. If you would blow thru it you may encounter a fabric that does allow for air to pass. Yet, similar to a screened window...the rest of the material is quite course and dense. A screen window is actually over 70% closed...the "weave" is what allows for the passage of air.
Now...if you could actually get some real burlap (created from jute, hemp or flax fibers) you actually have a very course strong fiber. I really don't see how real burlap would be a good choice either???
I'm not trying to start any flames...I really do wonder if there is reasoning or a science behind the burlap recommendation...and which "burlap" this recommendation is made for??? Real or cotton?
Then you have recommedations for some slighlty more expensive acousticaly transparant fabric. Is this simply material similar to speaker grill cloth? (for a side note...I certainly can't imagine any speaker grills being covered in burlap)
But if this is fabric similar to grill cloth...aren't you then talking about a 100% polyester fabric with a very loose interlocking weave? If so...you can get these in varying thickness and weave...you can also get the polyester fabric in anything from an extreme dull "sheen" to a high gloss type silk sheen. But wouldn't an extremely light thread and loose 100% polyester interlocking dull weave perform well?
Then you have a comaprable light thread with a loose interlocking weave in 100% cotton. Which is much lighter and looser than many of the fabrics out there today that are being badged as "burlap".
Even still...if real burlap is recommended...why?
*ok...I'll duck now ;)*thanks,
dan
CLick the picture below to see my systemenjoy the music!
Follow Ups:
The orignal jute based burlap, which is still readily available from most of the larger Wal-Marts with a fabric department, and most decent sized fabric stores, is NOT acoustically transparent, it would NOT make a good speaker grille.What it does do, is to avoid reflecting mid and high frequencies, due to the fact that the large yet loosely yarned fibers actually seem to absorb sound compared to most other materials used to make cloth, such as polyester. This may have something to do with the natural fiber being so convoluted on it's surface,(similar to real long hair wool for T-lines, it has a highly convoluted surface compared to synthetic fibers).
The burlap is still a fairly inexpensive material compared to most other fabrics.Many polyester and poly-cotton fabrics tend to reflect HF's, and some of the thicker ones can even reflect some of the upper midrange too. Thick and heavy velours, which seem like the fuzziness would be a good absorbing surface, tend to reflect a significant amount of upper midrange and lower HF's.
Straight cotton is usualy too densely woven to avoid reflecting some of the mids, upper mids and lower HF's.The only reason any of this matters, is that for sound absorbing wall panels, (or for bass traps that you want to be tunable by placing a reflecting strip down one side, the other side has to be fully absorbing), you want maximum sound absorption across the whole frequency range.
For a fabric on a bass trap to be used ONLY for bass absorption, most any cloth can be used, but I have found that many folks are surprised at how much reflection they get from fabrics that seem like they would be "OK", and they are also surprised at how much sound ends up reflecting (albeit diffused) from the corners with such fabrics.
Jon Risch
Dan,I don't think it really matters a whole lot what the heck you use. The main thing is to avoid shiny, reflective fabrics like silk and synthetic equivalents. And even then, that's only for panels that are meant to absorb higher frequencies. Bass goes right through all fabrics. And with mid/high frequency absorbers, there's no need for "acoustically transparent" fabric either. If the fabric absorbs a little more on its own, no harm is done. This is very different from fabric that will go in front of a tweeter.
That said, burlap is often recommended because it's open weave, it doesn't cost much, and is available in lots of colors.
--Ethan
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