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I'm planning to build some bass traps to place in the corners of my listening room to tame my room modes. I'd like to know whether a round, i.e. cylindreical trap would work better or worse than one with a square cross section.I'm thinking the the square might be easier to make and can fit snuggly int the corner or flush against a wall. The cylindrical trap would leave a gap in the corner.
Follow Ups:
The round shape of the more common tube trap type bass traps is due to the fact that a round/cylindrical shape is stronger than a square column or rectangular column shape.Think in terms of the original Hsu subwoofers, which used sonotube like cylindrical tubes for a subwoofer enclosure, the cylinder responds well to internal bass pressures, as the stresses are distributed equally, except for the end caps, which aren't that big and can be made very rigid. A square or rectangular shape column would have the middles of the walls moving a lot more for an equal thickness and stiffness.
Same thing for bass traps, you COULD make a square one, but the strength of the sides would be a lot less than that of a cylindrical shape, you would need LOTS of internal and external bracing to keep the fiberglass compressed uniformly over the entire surface of the trap, and even then, it would not be as evenly distributed as it would be for a cylindircal trap frame and shell.
RE rock wool, it will work OK too, just so it's final density is close to that of the compressed fiberglass, and the amount of compression applied ends up in the same ballpark.
See:
The original DIY Acoustic Treatment Note:
http://www.geocities.com/jonrisch/a1.htmWhere I talk about the amount of compression used. Regular building grade fiberglass in the US runs around 0.5 lbs per cubic foot.
My recommendation is to compress that down to from 1.7 to 1.5 lbs. per cubiic foot density.
It sems to make a difference if the material is already at the higher density, it does not work as well, I suspect that it is due to the sheer amount of resin bonding material used to hold the higher density materials together.See also:
Common Problems In DIY Bass Trap Construction:
http://www.AudioAsylum.com/audio/tweaks/messages/29191.htmlthe original post where I reveal the latest Super Quick & Dirty easy bass traps recipe:
http://www.audioasylum.com/audio/tweaks/messages/15737.html
and petew's post where he goes into detail on what he did.
http://www.AudioAsylum.com/audio/general/messages/70817.htmlhttp://www.AudioAsylum.com/audio/tweaks/messages/17498.html
PeteW's directions of building classic bass traps w/wire.
Andrew Chasin's description of his build-up:
http://www.AudioAsylum.com/audio/tweaks/messages/110285.htmlYou might want to consider a Super Quick & Dirty type trap, these can be made to be "square", by taking the basic round rolls of fiberglass, or the batts that are sometimes bundled, and placing them inside of a square framed outer shell. Since there is no significant pressure on the outer shell frame, the sides do not need to be braced or reinforced as they would with a pressure type bass trap, you are just using sheer amounts of fiberglass to do the job.
My original DIY bass trap, which is of the same type as the ASC tube trap, uses a resistively controlled pressure differential that is created with the internal cavity full of air, which interacts with the outer air pressure through the compressed fiberglass, which is what creates the pressure differential between the inside and the outside due ot it's resistance to the air pressure flow. With the Super Quick & Dirty, you are just crudely throwing sheer quantities of fiberglass (or rockwool, or polyester batting, etc.) at the problem of absorbing bass in the corners.
Jon Risch
I'd also like opinions on how well the tube trap works compared to a device such as the RPG Modex Corner (http://www.rpginc.com/products/modexcorner/modexcorner.pdf)Is anyone familiar with this device and have experience of how well it works and know any other similar device?
-wcvb
> I'd also like opinions on how well the tube trap works compared to a device such as the RPG Modex Corner <Those are completely different types of traps. Tube traps are mostly broadband and Modex traps are tuned. Either design can work well, but broadband traps are generally preferred. Especially in smaller rooms.
--Ethan
I built some of the round traps as per the Jon Risch method. I also find them to be more effective as I pulled them away from the wall a bit.As far as fabric the burlap is acoustically transparent so that the traps will work across the whole frequency range. Cotton and other such materials are only good at letting the bass through, but can tend to reflect other frequencies. Also for a better looking fabric you can use the guilford 701 which is a designer fabric that is also acoustically transparent. Silentsource.com has good prices on the guilford 701. Also see my post above for a link to pics and info on my bass traps.
WC,> I'd like to know whether a round, i.e. cylindreical trap would work better or worse than one with a square cross section. <
What matters more than anything is the total size and volume of the absorbing material. Round, square, flat panel - they all can work well if they're big enough and made from the right materials.
--Ethan
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 system
enjoy the music!
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
Thanks Ethan.What are the "...right materials"?
I'm thinking of using mineral wool (basalt rock fibers). It's more available over here (Trinidad) and fibreglass is an uncomforatble material to work with. Please advise of the issues here and recommend alternatives.
I'm thinking of using a cotton fabric to cover the traps so that I can produce something aesthetically pleasing. What would be the issues of using this vs the burlap that I've seen recommended, both in terms of impact on the bass frequencies and impact on the mids and highs?
wcvb
> I'm thinking of using mineral wool <Sure, that's fine. But that's just as irritating to work with as fiberglass!
It doesn't matter. The important issue is to block and absorb the reflection from the corner. Make sure you tune the height of the trap to suit your listening needs.Alan
Thanks for the response. To questions:1. Please explain what you mean by "...tune the height of the trap to suite your listening needs." What considerations dictate the height and the depth and thickness of absorbing material?
2. Will the work better fitted into the corner of flush with the wall or will an air gap between the trap and the wall or corner be more effective?
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