[TRADERXFAN]

A discussion from another thread led to the question how well do sealed hollow tubes of compressed insulation work (like ASC tube traps) in comparison to just a full tube of insulation, of the same size, in the same place.

I ordered 1" thick, 3' high pipe insulation
2x 20"
2x16"
and 4x 9"

So, to make this more scientific, (I know its going to be far from controlled testing) I am thinking of setting the speaker system up in a smaller, empty room. This way the surface area is smaller and so these devices occupy a higher proportion of the room and should see greater effect. Would that be correct?

I have an extra bedroom that is about 11x10. There is one big window in it though, which I think leaks bass, correct? So not sure if that would be a confounding variable.

I think I would just use my behring mic which is not calibrated, and use REW to do some sweeps and real time analysis shots.

This sound like all my ducks in a row, for a proper, fair, comparison?

-Tony

[Ethan Winer]

This sound like all my ducks in a row, for a proper, fair, comparison?

Yes, mostly, but it is critical that nothing move from one test to the next. If the measuring microphone moves even one inch it will skew the results. Same for the traps. So set the microphone in one place and leave it, and when you stack the small tubes inside the larger ones be careful not to move that either. And make sure all doors and windows to the room are shut tight.

One limitation is you have only two traps, and even in a small room that might put the differences down in the noise so to speak. A better test would be to use four corners and the four larger tubes, then stuff them semi-tight with fluffy fiberglass. Or do it your way and with four traps too.

I look forward to your results. Be sure to post waterfalls, not just raw response.

--Ethan

[ecramer]

To insure placement of the tubes i would make 1/4 inch bases with a pin in the center and use double sided tape to tape them to the floor and build the traps with a keyed board on the bottom that way i could quickly change tubes and be assures that they were always in the same place

ED

[Ethan Winer]

Also Tony, if it's not too much trouble, please do a second test with the tops of the tube traps capped using a piece of wood or drywall when they are not filled solid. This is another myth that needs busting - that tube traps work better when they are "sealed." So that's three tests total: empty tubes, empty tubes with the tops capped, and tubes filled with additional insulation.

--Ethan

[TRADERXFAN]

Well the original comparison was going to be between the capped empty tubes, and uncapped tubes filled with insulation. I could put a top on the filled tubes as well...

quick question. The behringer mic is omnidirectional.  Should I point it straight up at the ceiling (the way I see in some pictures) or does it not matter? I have been pointing it at the speakers.


-Tony

[terry j]

absolutely excellent!!

One of my biggest problems in audio..as conducted on the net...way too many JAIBs who simply sit in their own fog of ignorance and never have the kahoonies to TEST their religious beliefs.

So to see someone TEST something/anything in audio, particularly net truisms, gets a huge thumbs up from me!

Looking forward to your results, and the main thing is that you enjoy it and it does not become a chore. Learning, as always, should be FUN!

Here is what I believe to be another internet myth (after all, I have tested it and found it to be so to my satisfaction) is that when measuring bass frequencies the statement 'moving the mic as little as one inch will skew the results', well at least this time the language seems to have tempered slightly and the word skew was used, which IS admittedly much more reasonable than say 'ruin' or 'destroy' or similar.

If you can, then yeah why not, don't move the mic at all (saves that little bit of work as well, so why not place it and leave it?) but in the bass frequencies, a slight movement like that will still give usable results.

(tho my room is 'huge', maybe a small room like yours could be the confounding factor and such a slight movement WILL lead to unusable results??  Hmm, when you have finished all your testing w/out moving the mic maybe move the mic gradually and see how much movement is needed before we can call the results tainted?? Haha, just how MUCH do you like experimenting)  All I am saying is don't fret that particular issue, pretty close will give pretty close results.

FWIW I find the idea of a performance increase by sealing properly a tube trap to be perfectly reasonable and plausible. (whether it is better than stuffing it or not we won't know till you 'publish' your results)...after all it IS how an altimeter works for example.

And we trust them I hope??

[TRM]

a mic isn't like a flashlight but an omni-directional mic is more directional at the high frequencies so yes, I would "point" it straight ahead

[TRADERXFAN]

absolutely excellent!!

One of my biggest problems in audio..as conducted on the net...way too many JAIBs who simply sit in their own fog of ignorance and never have the kahoonies to TEST their religious beliefs.

So to see someone TEST something/anything in audio, particularly net truisms, gets a huge thumbs up from me!

Looking forward to your results, and the main thing is that you enjoy it and it does not become a chore. Learning, as always, should be FUN!

Here is what I believe to be another internet myth (after all, I have tested it and found it to be so to my satisfaction) is that when measuring bass frequencies the statement 'moving the mic as little as one inch will skew the results', well at least this time the language seems to have tempered slightly and the word skew was used, which IS admittedly much more reasonable than say 'ruin' or 'destroy' or similar.

If you can, then yeah why not, don't move the mic at all (saves that little bit of work as well, so why not place it and leave it?) but in the bass frequencies, a slight movement like that will still give usable results.

(tho my room is 'huge', maybe a small room like yours could be the confounding factor and such a slight movement WILL lead to unusable results??  Hmm, when you have finished all your testing w/out moving the mic maybe move the mic gradually and see how much movement is needed before we can call the results tainted?? Haha, just how MUCH do you like experimenting)  All I am saying is don't fret that particular issue, pretty close will give pretty close results.

FWIW I find the idea of a performance increase by sealing properly a tube trap to be perfectly reasonable and plausible. (whether it is better than stuffing it or not we won't know till you 'publish' your results)...after all it IS how an altimeter works for example.

And we trust them I hope??

Thanks for the encouragement!

My purpose isn't to debunk anything though. Just interested to see what they do.

Well the static mic placement can give a false sense of bass performance. If you move it an inch or 2 and it changes, does it really mean that the original was correct? However it is the only way to make an fair, but simple, comparison.

When setting up multiple subwoofers, Geddes recommends sweeping the mic in an arc while looking at the RTA response, with averaging to really gauge what is happening on bass. That way you avoid the 1" "sweet spot"

-Tony

[TRADERXFAN]

a mic isn't like a flashlight but an omni-directional mic is more directional at the high frequencies so yes, I would "point" it straight ahead

Ok, will do. I do have a tripod so maintaining exact placement should not be a problem.


Tony

[terry j]

yeah, Earle is all about averaging the response when he set's up the multiple subs bit, and he does it as you say with RTA as opposed to sweeps.

Re the bass, in my room and with my systems at least I have long since found that I easily have a foot each side of the LP where the results are repeatable (as opposed to the higher frequencies where it WILL change dramatically) that I simply don't bother too much anymore.

There will always be exceptions I guess, if you happen to have your LP right where a null is, then yeah it could very well be that you move the mic an inch or so will give dramatically different results.

Got it re 'debunk', tho let's not kid ourselves!! This is audio, as conducted on the net.

Therefore anything that is tested scientifically for honest answers WILL be debunking some JAIBs belief system somewhere!!! You know the drill by now

'science cannot measure everything you know'...(so they never bother to look, which was the whole thrust of how welcome it is to see someone TEST something!!)

So, no matter how laudable and without agenda your investigations are, you will be debunking someones prejudice!

It's just the nature of the beast.

[Ethan Winer]

the original comparison was going to be between the capped empty tubes, and uncapped tubes filled with insulation.

The problem with that is two variables are being changed. So if a meaningful difference is measured, you won't know if it was due to filled versus hollow, or capped versus uncapped. Ideally you'll measure all four combinations.

The behringer mic is omnidirectional.  Should I point it straight up at the ceiling (the way I see in some pictures) or does it not matter? I have been pointing it at the speakers.

It depends what you're measuring. If both speakers are sounding - or you're comparing left versus right, or balancing speakers in a surround setup - the microphone should point straight up. If only one speaker is playing then you can point it toward that speaker. At the low frequencies considered here, 300 Hz and below, I doubt it matters.

--Ethan

[Ethan Winer]

the statement 'moving the mic as little as one inch will skew the results'

This is true! At least at high frequencies. But at low frequencies, even four inches can make a very large difference. Look at what happens across four inches at 71 Hz in this graph (halfway between the 56 and 92 Hz markers):



As you can see, at one place it looks like a peak and four inches away it looks like a null. The difference is 13 dB! This is large enough to totally swamp the change in response after adding only a few traps.

--Ethan

[bdiament]

Hi Tony,

A discussion from another thread led to the question how well do sealed hollow tubes of compressed insulation work (like ASC tube traps) in comparison to just a full tube of insulation, of the same size, in the same place.

I ordered 1" thick, 3' high pipe insulation
2x 20"
2x16"
and 4x 9"

So, to make this more scientific, (I know its going to be far from controlled testing) I am thinking of setting the speaker system up in a smaller, empty room. This way the surface area is smaller and so these devices occupy a higher proportion of the room and should see greater effect. Would that be correct?

I have an extra bedroom that is about 11x10. There is one big window in it though, which I think leaks bass, correct? So not sure if that would be a confounding variable.

I think I would just use my behring mic which is not calibrated, and use REW to do some sweeps and real time analysis shots.

This sound like all my ducks in a row, for a proper, fair, comparison?

-Tony

Two reasons why I think the test might be better run in the room in which you normally do your listening:

1. Most importantly, that is the room you are familiar with from having done your listening there.  As such, that is the room where you will best hear changes to the sound with which you are familiar.

2. An 11 x 10 room, with dimensions so close to each other is a problem room for music.  If such a room were to be treated in order to make the best of what can be done in such a space, it would need a LOT of treatment.

Two or four traps is not really enough to get the full picture in the room you normally use (which I am guessing has more rectangular dimension?).  In a near square room, I'm not sure eight traps would do the trick, let alone only two or four.

Further, if you really want to take some measurements, I would suggest time based measurements and not static frequency response measurements.  While the latter will show you a little bit, room issues tend to be time-based (some sounds last beyond the time they've ended in the signal), with frequency aberrations only being symptomatic side effects.

ASC makes what they call a MATT (music articulation test tone) that you can find on Stereophile test CD #2.  This is an excellent signal for checking the effects of room issues (and treatments).  Listening to the MATT via headphones, then via your speakers (with and without treatments or with treatment A, then treatment B) will be an education in itself.  The headphones of course, will give you the tone without room effects.  After hearing this, you'll find it a lot easier to hear what the room/treatments do in between the pulses of the tone.

Just my perspective.

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

[TRADERXFAN]

Hi Barry,
Well, I was trying to make it less subjective.  I could try and find that test tone. I do understand the time aspect. I think that is why Ethan was asking for waterfall information. Perhaps that isn't enough? I am open to all input on how to make the setup and measurements.

The idea to use a smaller room came from the ASC site itself where it discussed the amount of treatment for a given listening space. I don't doubt the room would be severely compromised listening space. But I am guessing that it should allow the traps to make a more distinguishable effect, (hopefully no one is expecting a miracle).

My current listening room is open to the rest of the house and I am not sure so little of the product could make a big impact. Although I would try them while I have them!

-Tony

[Ethan Winer]

I think that is why Ethan was asking for waterfall information. Perhaps that isn't enough?

Yes, exactly, a waterfall plot is all you really need. That shows the response and the ringing, which is what bass traps affect.

The idea to use a smaller room came from the ASC site itself where it discussed the amount of treatment for a given listening space.

Again I agree. What matters most is hard data, and the "delta" between trap types in a small room is greater than in a large open room.

Also, it's important to clarify why measuring always trumps listening with room acoustics and treatment. Rooms have peaks and nulls and resonances at only certain frequencies. The music you'd play when listening has only certain frequencies. If those frequencies are present in both the room and the music, then you can hear a difference after adding or changing bass traps. But (as a simplistic example) if the room resonances are in the key of G and the audition music is in the key of A, the bass traps have much less effect. Modern room measuring software uses a sine wave sweep across all frequencies.

Another reason measuring software is better than listening is when assessing small changes. In this case you have only two (or hopefully four) bass traps, which will not make a huge change. Worse, you're comparing filled versus not filled, and capped versus not capped. The difference there is even smaller. With only a few traps, the differences may be only one or two dB if that. Such a small change is easily seen on a graph, and impossible to hear reliably.

--Ethan

[Browntrout]

Or..... knock them together, chuck them in the corners and listen to something with strong bass in it then let us know what you think.

[bdiament]

It would be a mistake to think the music -or any other sound in the room- has to contain frequencies that match the room's modes in order to excite them.

If the music contains frequencies *near* a room's resonant modes, the modes will be excited.  This can be heard -or measured- in the decay (what Art Noxon refers to as an "anti-resonance").  Those with a good sense of pitch can hear this as some notes going "sour" as they decay, where the note is at one frequency and the room responds with a nearby frequency.

(Aside from this, the larger effects of rooms and room treatment can be heard without any music at all.  Normal conversation will sound very different.  Even the "silence" of the room will sound different.)

As always, my suggestion is to try this and listen for yourself. 
Especially if you know the frequencies at which your room rings, if you have a good sense of pitch, find program material in a key that will provide frequencies near (but not the same as) the room's.  Play an appropriate section and use the Pause button on your player or Mute the preamp, so the music stops instantly.  Listen to what the room does.  Draw your own conclusions.

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

[Ethan Winer]

If the music contains frequencies *near* a room's resonant modes, the modes will be excited.

Excellent point Barry. Of course, it depends on the Q of the room mode and how far away (in frequency) the musical note is from a given mode's center frequency.

Normal conversation will sound very different.  Even the "silence" of the room will sound different.)

Yes, though in this case we're talking about only a few bass traps. And further, the difference between filling and capping etc which is even smaller.

--Ethan

[bdiament]

Hi Ethan,

...And further, the difference between filling and capping etc which is even smaller...

My experience with a number of fully outfitted rooms is that the differences between what essentially become two very different devices are not small at all.

I do agree that with any treatment like this, numbers become very important.  Two or four will not reveal the inherent differences as much as a fully outfitted room.  Not that differences won't be audible (and measurable); just that in my experience, their magnitude increases with the degree of treatment.

Just my perspective.

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

[Ethan Winer]

Two or four will not reveal the inherent differences as much as a fully outfitted room.

Exactly. When I did my Density Report test, we had 12 panels all straddling corners in a small (17 by 11 by 8 feet) room. That was just about enough traps to see the differences between the various densities.

I'm wait with anticipation to see Tony's results.

--Ethan