[bdiament]

Hi arthurs,

Now, stuffing or no stuffing?

Try both (on a few traps) and compare for yourself.

As to end caps, the idea of reducing area is in my view less critical than whether the particular design (not simply a shape) works or it doesn't work.  If the design depends on the walls of the cylinder being the only way sound can enter (or exit) the trap, leaving the ends open removes a fundamental aspect of the design.

From my perspective, this would be like saying I can get more air in my tires is I leave them open.  ;-}

If you try it, you'll be the best judge of what works for you and what doesn't.

Have fun!

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

[sl_1800]

Whether to seal or not seal the ends of tube traps with wood.  I am only assuming here, but I would think sound waves, like electricity and like people, will take the path of least resistance.  If the ends of the tube trap are open, then very little will pass thru the fiberglass, which is the desired path is it not?

[bdiament]

Hi Steve,

Whether to seal or not seal the ends of tube traps with wood.  I am only assuming here, but I would think sound waves, like electricity and like people, will take the path of least resistance.  If the ends of the tube trap are open, then very little will pass thru the fiberglass, which is the desired path is it not?

Exactly.
Actually, the lowest frequencies will pass through the walls as well but the trap itself will have been defeated, its entire purpose having been bypassed.

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

[Browntrout]

Does sound take the path of least resistance?  Whilst I sort of get a tuned trap and don't see how a tube of highly permeable insulation can be a tuned trap as even with the end caps on it is not an airtight structure. Or am I not understanding what a tuned bass trap is?

[TRADERXFAN]

Actually, the lowest frequencies will pass through the walls as well but the trap itself will have been defeated, its entire purpose having been bypassed.

Not trying to be argumentative, but truly don't understand... just on what acoustic principle is this capped tube of insulation  supposed to operate? 

-Tony

*edit* found info here
http://www.acousticsciences.com/articles/db1191.htm

[bpape]

This has been argued many different places for a long time.  The idea behind capping the tubes is that it forces all sound to go completely through the tube.  The caps create a SMALL increased pressure area inside the tube which can help cause additional resistance.  When not capped, the waves that enter the tube cannot cause additional pressure inside since the air can escape through the top and bottom into free air - and will do so trying to maintain a pressure equilibrium - basic physics. 

The only way to really know for yourself is to test/listen both ways. 

As for stuffing it, personally, I've always found that to be beneficial.  No different than a solid chunk of insulation on a wall vs layers with gaps between them.

Bryan

[bdiament]

Hi Browntrout,

Does sound take the path of least resistance?  Whilst I sort of get a tuned trap and don't see how a tube of highly permeable insulation can be a tuned trap as even with the end caps on it is not an airtight structure. Or am I not understanding what a tuned bass trap is?

There is no need for the structure to be airtight in order for it to be tuned (or to have a fundamental resonant frequency). 

For example, any good drummer will tune their drums, none of which are airtight structures.  Another example would be our listening rooms, all of which have fundamental resonances and none of which (I hope) are airtight.

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

[bdiament]

Hi Tony,

Actually, the lowest frequencies will pass through the walls as well but the trap itself will have been defeated, its entire purpose having been bypassed.

Not trying to be argumentative, but truly don't understand... just on what acoustic principle is this capped tube of insulation  supposed to operate? 

-Tony

*edit* found info here
http://www.acousticsciences.com/articles/db1191.htm

There is also a short summation here:
http://www.tubetrap.com/technical.htm

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

[TRADERXFAN]

Interesting. There is a bit more specifics given here
http://www.audiophilia.com/hardware/tubetrap.htm

and the argument against just using friction in the corners (filling it) here:
http://www.tubetrap.com/articles/listening-room-aes-1985-4.htm

Too bad they didn't specify test results like most other big vendors.
-Kind of a big endeavor to construct one's own comparative experiment!

Did you build the inner chambers on yours? or helmholtz resonator inside?

-Tony

[bdiament]

Hi Tony,

Interesting. There is a bit more specifics given here
http://www.audiophilia.com/hardware/tubetrap.htm

and the argument against just using friction in the corners (filling it) here:
http://www.tubetrap.com/articles/listening-room-aes-1985-4.htm

Too bad they didn't specify test results like most other big vendors.
-Kind of a big endeavor to construct one's own comparative experiment!

Did you build the inner chambers on yours? or helmholtz resonator inside?

-Tony

I built relatively simple cylinders; no inner chambers or resonator inside.
So far, I've put them in a few rooms beside my own studio and the results have been exactly the same each time - big smiles.

Where bass would change by moving a foot to the left or to the right from the main listening position, it became consistent (and more dynamic) anywhere one chooses to listen from.

Some of the traps can be seen in the photo on the BDA home page at www.barrydiamentaudio.com
Better views can be seen on the site for one of the client studios I designed at
http://www.swordinthestonerecords.com/totw/photos.html
(click on photo for a larger view)

By the way, after building them and loading a bunch into my car for the drive, the system in the car never sounded so good (before or since).  ;-}

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

[TRADERXFAN]

Ok, I don't know if I should open a new thread for my experiments or not... OP, or admin let me know?

I ordered a "bunch" (relative term, may not be much to some) of pipe insulation today.
~$250 bucks.
All of this is 1" knauf
2 pieces of 3'  of 20" diameter
2 pieces of 3'  of 16" diameter
4 pieces of 3' of 9" diameter

So I will cut some mdf tops and bottoms and partially wrap them with something reflective.  I will try them empty, and compare them to some 8# 4'x2' mineral wool panels that I have been using, to what I would deem to be very small effect.

Will these things stand up on their own, or do I need to put in a lengthwise support?

-Tony

[Browntrout]

Cool look forward to your findings.

When I said airtight I did not mean a sealed volume rather a ported one which is airtight apart from it's mouth, just like a drum. The pipe insulation with caps is not a tuned trap is it?

[TRADERXFAN]

An airtight, "ported" enclosure is more like a helmholtz resonator.  The old "blowing across the bottle" analogy.
http://en.wikipedia.org/wiki/Helmholtz_resonance

This is very different because the insulation is not airtight. More specifically the argument here is that the air enclosed by the capped cylinder of insulation  is going to act on the sound in a way more effective than a solid block/column of insulation.

I am reading up on it. I guess worst case is insulation will do SOMETHING in the room. and the reflective part should add a little diffusion/deflection.

-Tony

[TRADERXFAN]

Barry, what do you use to cover for the reflective part?

I was surprised to learn it was perforated plastic on the asc
"This hybrid acoustic is made possible by the suspension of a thin, precisely weighted, and perforated sheet of limp plastic that covers the front half of the cylinder surface. The properties of the diffusor sheet are such as to make it an acoustical crossover, passing low frequencies into the interior but back scattering high frequencies.

Hi Tony,

Interesting. There is a bit more specifics given here
http://www.audiophilia.com/hardware/tubetrap.htm

and the argument against just using friction in the corners (filling it) here:
http://www.tubetrap.com/articles/listening-room-aes-1985-4.htm

Too bad they didn't specify test results like most other big vendors.
-Kind of a big endeavor to construct one's own comparative experiment!

Did you build the inner chambers on yours? or helmholtz resonator inside?

-Tony

I built relatively simple cylinders; no inner chambers or resonator inside.
So far, I've put them in a few rooms beside my own studio and the results have been exactly the same each time - big smiles.

Where bass would change by moving a foot to the left or to the right from the main listening position, it became consistent (and more dynamic) anywhere one chooses to listen from.

Some of the traps can be seen in the photo on the BDA home page at www.barrydiamentaudio.com
Better views can be seen on the site for one of the client studios I designed at
http://www.swordinthestonerecords.com/totw/photos.html
(click on photo for a larger view)

By the way, after building them and loading a bunch into my car for the drive, the system in the car never sounded so good (before or since).  ;-}

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

[arthurs]

Pipe wrap (some anyway) comes with an aluminum backed scrim paper on it, you can just cut part away and leave the rest to reflect higher frequencies...

[TRADERXFAN]

Thanks. I guess I will see what they look like next week.

Sounds like it would be a bit too thin though...

[bdiament]

Hi Tony,

Barry, what do you use to cover for the reflective part?

Arthurs already beat me to it.  The Knaupf insulation comes with a paper/foil wrap already on the insulation.  All you need to do is use a razor knife to cut it away from half the cylinder (in the long dimension).

When covering the cylinders with fabric (if you do), I found it a good idea to ensure the seam ends up in the middle of the foil/paper side.  That makes it easy to orient the traps.  Of course, you can also tell by tapping your fingers on the outside of the trap.  The foil side will sound different than the "soft" side.  But the seam provides a visual cue I find easier.

Here's an interesting article on the subject:
http://www.asc-hifi.com/articles/iar89.htm
I don't agree with everything in it but there is still plenty of useful information.

Have fun!

Looking forward to hearing about your experiences.

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

[sl_1800]

traderxfan,  where did you order the insulation from?

[oneinthepipe]

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.

[TRADERXFAN]

I have a local supplier here (Aurora, IL) Amerisafe.  They didn't stock the larger sizes so they ordered them.

Since the literature on the asc stuff specified as 1" thick that is what I ordered. Here is what they say about the balance on thickness...

"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."


-Tony