[bdiament]

Hi oninthepipe,

What thickness is recommended?  Knaupf appears to make the insulation in diameters up to 24" ID and also in various  thicknesses up to 3".  If I can find some of this stuff locally, I might make a few of the bass traps.

I used the 1" thickness (in 3' lengths - using pairs of finished traps to make  6' columns).

Diameter depends on the room but unless the room is quite large, I've had good success using 16" (for 14" pipe) and 9" (for 7" pipe) insulation, to make 16" and 9" columns.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

[TRADERXFAN]

Thanks Barry.  I was curious since Glenn recommended stuffing them earlier in the thread.  When I built mine I was under the impression density was the goal, if there's improvement to be gained by leaving them empty, I'd be interested in knowing about it.  ASC are tuned tubes are they not?  I've always wondered how they tune them, is it in the size and the sealed empty chamber?

My current tubes are not sealed at all, open on top and bottom, when I redo them, I will be taking your cue and capping them with wood.

Are your current ones hollow in the middle?
-Tony

[arthurs]

I used 2" thickness last ones I made.  I'm going to use 15" total diameter in front and 17" total diameter in back corners for my current build (the 15" in front is due to space constraints but there is additional treatment planned for the front wall)  I found the 2" much sturdier to work with and would be really surprised if there's an audible difference with the extra 1" tube wall thickness.

[arthurs]

Thanks Barry.  I was curious since Glenn recommended stuffing them earlier in the thread.  When I built mine I was under the impression density was the goal, if there's improvement to be gained by leaving them empty, I'd be interested in knowing about it.  ASC are tuned tubes are they not?  I've always wondered how they tune them, is it in the size and the sealed empty chamber?

My current tubes are not sealed at all, open on top and bottom, when I redo them, I will be taking your cue and capping them with wood.

Are your current ones hollow in the middle?
-Tony

No sir Tony, they are stuffed and are not capped on either end.  I'm going to try both ways when I refinish them and build some new ones over the next few weeks.

[bdiament]

Hi arthurs,

...I found the 2" much sturdier to work with and would be really surprised if there's an audible difference with the extra 1" tube wall thickness.

Based on how they are designed to work (Tony provided some good links), I would be surprised if there isn't an audible difference.

Best regards,
Barry
www.soundkeeperrecordings.com
www.barrydiamentaudio.com

[arthurs]

I'm not finding where ASC specifies 1" wall thickness, can someone point me to it?  Thanks!

[bpape]

If they're designed to be tuned with a 'hump' in absorption, then filling them would damp that and the thickness would change the tuning as would the diameter.

If you're looking for something more broadband and smooth, then filling 1" vs filling 2" shouldn't really change much.

Bryan

[TRADERXFAN]

I'm not finding where ASC specifies 1" wall thickness, can someone point me to it?  Thanks!

There is a cutaway and reference to the 1"
http://www.audiophilia.com/hardware/tubetrap.htm

Having said that, I don't think there is anything magical about 1".  I am not math savvy, but there are equations provided here that tell you what the forces are.
http://www.tubetrap.com/articles/listening-room.pdf  specifically, page 4

However, I don't know how to actually apply this information appropriately for some other tube thickness. And not sure how a higher or lower density would be factored in, since it may not be exactly same insulation in both designs.

[TRADERXFAN]

If they're designed to be tuned with a 'hump' in absorption, then filling them would damp that and the thickness would change the tuning as would the diameter.

If you're looking for something more broadband and smooth, then filling 1" vs filling 2" shouldn't really change much.

Bryan

Bryan, (or anyone I guess...)
Could you explain or refute their comment that a solid lump of insulation in the high pressure, low flow zone in the corner is not going to be as effective?
 "Well, so far everything seems to be getting better. The traps are to be located in zones of maximum pressure fluctuations, the tri corners of the room. Unfortunately, few devices extract energy directly from pressure changes. The most common method for sound absorption is friction -- friction due to the air-motion part of the sound wave that is scrubbing through some micro-porous piece of material, usually fiberglass.
Now, air-motion is very small in zones of pressure fluctuation, by definition. For example, at 100 dB, 100 Hz, it?s on the order of 1/10 the diameter of 5 micron fiberglass fibers. Prospects for developing friction look poor unless we first transform energy. We?d like to convert the pressure fluctuations into substantial air motion, and then dissipate acoustic energy by friction against the air motion."

"The thickness of the wall tells us the distance over which that force is developed. Their combination tells us how much work is being done. We like as much force to occur over a large distance to get as much work out of each half cycle pressure fluctuation as possible.
If for example, the tube has a thin but highly resistive wall, the pressure drop would be very steep -- but the distance of the action would be too small for any real work to be done. Conversely, if the tube were simply full of loose fiberglass, the gradient would be too small, though the distance of the action would be large; again, the work would be minimal. The variables of wall material bulk flow resistance and the wall thickness, along with the air chamber volume can be manipulated to access any low frequency with optimal efficiency."

That seems to be the crucial difference from all I have read before. I had believed the thicker, the better for applying insulation for bass trapping. And that a panel trap worked on pressure and that was what occured at the room boundary. So it would seem to say that a block of insulation works best away from the boundary and a panel trap, (and perhaps one of these sealed chamber tube traps), would be better on the walls & corners for lower frequencies attenuation.

Is that incorrect?


a deeper explanation of the mechanics
http://www.tubetrap.com/articles/room-acoustics.pdf
lots more math there, for those better equipped... 

[arthurs]

author=TRADERXFAN
lots more math there, for those better equipped... 

I'm getting lost in the math as well.  I know this for sure, the 2" wall, uncapped and stuffed tubes I built previously did good things for the low end control of my room. 

[arthurs]

Next idea was to try some perforated poly film around the tube to further emulate the ASC trap, but man, that stuff is expensive!

[arthurs]

Need to find someone in Fort Worth who can die cut the circles for me and finish the edges, if I'm doing these, I'm going to do them so they fit the aesthetic of the room...those who know me are well aware of my limited skills at such endeavors, but high skill levels at outsourcing! 

[bpape]

While it's true that there is less movement as you approach a room boundary (with AT the boundary being zero), friction absorbers still work there.  A friction absorber will work opimally at 1/4 wavelength of the target frequency to be absorbed. 

A panel absorber (my definition anyway) is designed to work over approx 2-3 octaves and minimally elsewhere in the spectrum.    Thicker friction type absorbers work over a much wider area.  While potentially not as efficient at a specific frequency, they make up for it by being 'not quite as efficent' over a much wider area.  Bonding a membrane to the absorbant can minimize upper mid and high frequency reduction depending on the material chosen.

Corners have ALL frequencies building up in them.  They're a terribly efficient place to get at the entire spectrum.  I don't belive in 'wasting' those opportunites on something that only works over 2-3 octaves.

The ASC products from my experience work more like a damped membrane absorber than a sealed panel absorber. They're more broadband.  They also have secondary 'hump' and primary resonance due to the flexure of the tube itself rather than just the membrane applied to the face.

The drawback is sheer size.  To reach down into the last couple of octaves, the diameters of the tubes have to be very very large - much larger and taking up much more space than say a 6-10" flat absorber.  Think 16-20" diameter.

Bryan

[TRADERXFAN]

While it's true that there is less movement as you approach a room boundary (with AT the boundary being zero), friction absorbers still work there.  A friction absorber will work opimally at 1/4 wavelength of the target frequency to be absorbed. 

A panel absorber (my definition anyway) is designed to work over approx 2-3 octaves and minimally elsewhere in the spectrum.    Thicker friction type absorbers work over a much wider area.  While potentially not as efficient at a specific frequency, they make up for it by being 'not quite as efficent' over a much wider area.  Bonding a membrane to the absorbant can minimize upper mid and high frequency reduction depending on the material chosen.

Corners have ALL frequencies building up in them.  They're a terribly efficient place to get at the entire spectrum.  I don't belive in 'wasting' those opportunites on something that only works over 2-3 octaves.

The ASC products from my experience work more like a damped membrane absorber than a sealed panel absorber. They're more broadband.  They also have secondary 'hump' and primary resonance due to the flexure of the tube itself rather than just the membrane applied to the face.

The drawback is sheer size.  To reach down into the last couple of octaves, the diameters of the tubes have to be very very large - much larger and taking up much more space than say a 6-10" flat absorber.  Think 16-20" diameter.

Bryan

Thanks, very much, for providing more perspective.

[arthurs]

Thanks, very much, for providing more perspective.

Ditto Bryan, thanks much as always.

[Browntrout]

I'd just like to say thanks for the answer to my previous questions and all the really interesting posts and links in this thread. I think what bpape has said about these acting as a damped membrane absorber is spot on.
  If I could suggest to the original poster that he tries what I have currently arrived at in experimenataion which is 5 layers of soft mineral wool type panels totalling about 10 inches thickness straddling the corners behing my speakers. This gave improved clarity in the lower third of all music and improved markedly with each increase in thickness that I tried. Cost at present twenty pounds as unframed unclothed but very effective corner absorbers.
  Certainly I have found in most things that the best place to start when finding out what works is to start with the simplest approach and if the tubes have a concentrated absorbtion charactersistic then to utilise this correctly surely a detailed knowledge of the sound in your room is required, either that or there stands the posibility of making a noticable change to the accuracy of the music.
  I don't mean to come across as anti this design as I am learning myself (and shall be for some time to come) and look forward with interest to reading of some listening impressions.

[TRADERXFAN]

Next idea was to try some perforated poly film around the tube to further emulate the ASC trap, but man, that stuff is expensive!

Art,
Have a link to what this is?

[TRADERXFAN]

I'd just like to say thanks for the answer to my previous questions and all the really interesting posts and links in this thread. I think what bpape has said about these acting as a damped membrane absorber is spot on.
  If I could suggest to the original poster that he tries what I have currently arrived at in experimenataion which is 5 layers of soft mineral wool type panels totalling about 10 inches thickness straddling the corners behing my speakers. This gave improved clarity in the lower third of all music and improved markedly with each increase in thickness that I tried. Cost at present twenty pounds as unframed unclothed but very effective corner absorbers.
  Certainly I have found in most things that the best place to start when finding out what works is to start with the simplest approach and if the tubes have a concentrated absorbtion charactersistic then to utilise this correctly surely a detailed knowledge of the sound in your room is required, either that or there stands the posibility of making a noticable change to the accuracy of the music.
  I don't mean to come across as anti this design as I am learning myself (and shall be for some time to come) and look forward with interest to reading of some listening impressions.

Do you know what the density is of your stuff? I have the 8# panels (A LOT ~50 cubic feet. but only 6 panels in the room now @4'x2'x4"), and am wondering if the density is too high.

[arthurs]

Next idea was to try some perforated poly film around the tube to further emulate the ASC trap, but man, that stuff is expensive!

Art,
Have a link to what this is?

I don't Tony, sorry.  I did a google search at work using "perforated plastic film" and "perforated poly film"  either of those should pull up several options....

[bmckenney]

I'd just like to say thanks for the answer to my previous questions and all the really interesting posts and links in this thread. I think what bpape has said about these acting as a damped membrane absorber is spot on.
  If I could suggest to the original poster that he tries what I have currently arrived at in experimenataion which is 5 layers of soft mineral wool type panels totalling about 10 inches thickness straddling the corners behing my speakers. This gave improved clarity in the lower third of all music and improved markedly with each increase in thickness that I tried. Cost at present twenty pounds as unframed unclothed but very effective corner absorbers.
  Certainly I have found in most things that the best place to start when finding out what works is to start with the simplest approach and if the tubes have a concentrated absorbtion charactersistic then to utilise this correctly surely a detailed knowledge of the sound in your room is required, either that or there stands the posibility of making a noticable change to the accuracy of the music.
  I don't mean to come across as anti this design as I am learning myself (and shall be for some time to come) and look forward with interest to reading of some listening impressions.

Are those panels basically rock wool panels that I can buy anywhere and then return?  This isn't a DIY based experiment is it?

Bryan