Trapping Traps

[boggy]

Originally Posted by G. E.

This result came from a corner mounted trap, call it an enhanced porous absorber.

Is there any steel membrane or not?

because you wrote:

Originally Posted by G. E.

.....and some new exiting results from a VPR-inspired configuration (single big trap with EDIT: 2m^2 [~21 square feet] front) that reduced the T60 time of the first three modes (calculated by REW) as follows:

(Bolded by me)

[G. E.]

Originally Posted by boggy

Is there any steel membrane or not? ...

Yes, it's a porous absorber combined with a steel plate without rigid backing. From what I've found out since then thickness both of the absorbents and the plate is critical. Still I'm not sure why it works much better than typical wall mounted configurations.

[boggy]

EDIT: I have wrong assymption that your "vpr-inspired" is mounted as is described in patent... sorry.

Originally Posted by G. E.

Yes, it's a porous absorber combined with a steel plate without rigid backing. From what I've found out since then thickness both of the absorbents and the plate is critical. Still I'm not sure why it works much better than typical wall mounted configurations.

Ummm... I'm not sure too, but.. now, I have an idea from this post in other thread...

Can you try this "enhanced 'porous' absorber" (which isn't porous anymore, this is a resonant membrane absorber) freely hanged vertically in air from ceiling and, how it works rigidly backed to wall (you can use some screwed chipboard to wall to simulate rigid backing without much mess with glueing directly to wall)... where stell plate didnt touch anything other than glue on IsoBond.

Also, this "vpr-inspired" absorber may be tested hanged in four point on ceiling, not rigidly backed (this may form a "parasite" poly-diffuser with Euler-Bernoulli shape, but who cares! )

EDIT: Publishing graphical ARTA tone burst testing results before and after, like you already did in your old post, is absolutely ok (or prefered?) for me...

[T1M0N]

Originally Posted by G. E.

Yes and we need absorption of the moving air that those resonances create. I think I get your idea and the ceiling would be a great place if it works. On the other hand absorbent in front of the steel never enhanced the bass absorption in my experience.

No, it won't do anything for bass absorption, it's only for the steel plate to rest on and will of course have the effect that the high frequencies will be absorbed. Kind of like the BKA principle with the front absorbent being the hi freq absorber and spring at the same time.

Originally Posted by G. E.

We'll find out...

Yes we will :-). Thanks for listening.

[G. E.]

Originally Posted by T1M0N

No, it won't do anything for bass absorption, ...

Now I lost you -- why would you suggest it then? It's about bass traps here.

EDIT: we can do it anyway, I'm open for surprises.

[andrebrito]

Hi

It would be interesting to test a low perforated MDF board with absorbent on the back and air cavity...

maybe 16 or 22 mm MDF with a 1 or 2 % perforated area and foam glued behind the MDF plus air cavity. MDF board should not be clamped to the wall

if you need more info PM me

[G. E.]

Originally Posted by andrebrito

... interesting to test a low perforated MDF board with absorbent on the back and air cavity...

maybe 16 or 22 mm MDF with a 1 or 2 % perforated area and foam glued behind the MDF plus air cavity. MDF board should not be clamped to the wall

...

There's a Helmholtz absorber included in the Sketchup file. It's (airtight) constructed like this (see image). Detailed suggestions are up to you -- I've always failed with my Helmholtz-devices.

[G. E.]

Originally Posted by G. E.

... it's a porous absorber combined with a steel plate without rigid backing. From what I've found out since then thickness both of the absorbents and the plate is critical. ...

I've posted the absorber scheme in another thread.

[T1M0N]

Originally Posted by G. E.

I've posted the absorber scheme in another thread.

Thanks, great information. So how about finding out (measuring) the difference between this setup mounted diagonally across the corner and mounted at the walls of the corner. Grey is the walls, white is the Iso Bond and black is the steel plate.

[G. E.]

Originally Posted by T1M0N

... So how about finding out (measuring) the difference between this setup mounted diagonally across the corner and mounted at the walls of the corner. Grey is the walls, white is the Iso Bond and black is the steel plate. ...

In this case I prefer to compare absorbers of the same size (here: the same absorber) only varying the position:

[T1M0N]

Originally Posted by G. E.

In this case I prefer to compare absorbers of the same size (here: the same absorber) only varying the position:

Yes you are right, in terms of material expense this is even more interesting. However terms of space expense ("how can I get the most effect out of treating one corner") this isn't as significant.

[boggy]

Originally Posted by G. E.

In this case I prefer to compare absorbers of the same size (here: the same absorber) only varying the position:

I agree, this is ok for comparison...

[G. E.]

Originally Posted by T1M0N

... However terms of space expense ("how can I get the most effect out of treating one corner") this isn't as significant.

... sure, that's a different question. Doubling the trap would look like this (floor usage: 0,44m^2 [~4,74 square feet] versus 0,45m^2 [~4.84 square feet] for the corner mount variant):

[boggy]

1. I hope that I don't ask too much but, can you recreate measurements of influence of your Enhanced Porous Absorber with Stell Plate (EPAwSP) between two CIB panels, with different stell plate thickness? At least it is most interesting to have measurement reasults for 2.5mm and 1mm steel plates, but if it's not to difficult to measure more different steel plates with different thickness, this other measurements may be also great.
This question come from here.

2. Also, it can be possibly interesting how this "enhanced" perform when is stacked, two or more, in same position, where already one work excellent, in corner, with same stell plates or with different stell plates...

3. Hanging of this absorber (freely) may be done with piece of rope, two holes in steel plate, and piece of double side adhesive tape (or more rope). Measurement results of this will be also interesting. I mostly ask this because we have ceiling corners which can't be treated using "lying enhanced absorber" method of mounting... we have to hang it from the ceiling.


If you find my suggestions are too difficult to realize, please reject it, as you already announce in your rules:

Originally Posted by G. E.

........

1. No PM in regard to suggestions.
2. Testing can be attended (5 seats).
   
3. Suggestions may be rejected.
4. Test results of approved suggestions will be published.
5. No publishing of test results for commercially available 3rd party bass traps.

(bolded by me)

[G. E.]

Originally Posted by boggy

1. I hope that I don't ask too much but, can you recreate measurements ... with different stell plate thickness? At least it is most interesting to have measurement reasults for 2.5mm and 1mm steel plates, but if it's not to difficult to measure more different steel plates with different thickness, this other measurements may be also great. ...

The various setup and mounting options multiply quickly... I stand by my offer to publish test results for 1mm and 2,5mm steel.

Originally Posted by boggy

... it can be possibly interesting how this "enhanced" perform when is stacked, two or more, in same position, where already one work excellent, in corner, with same stell plates or with different stell plates...

I like the stacking idea...

Originally Posted by boggy

... Hanging of this absorber (freely) may be done with piece of rope, two holes in steel plate, and piece of double side adhesive tape (or more rope). Measurement results of this will be also interesting. I mostly ask this because we have ceiling corners which can't be treated using "lying enhanced absorber" method of mounting... we have to hang it from the ceiling.
...

Ok, but I don't expect substantially different results comparing vertically "standing" with vertically "hanging" absorbers.

[amishsixstringe]

For comparing options in corners, would it not help magnify differences by placing similar setups in multiple locations? This could help combat missing something due to standard deviation and such.

Neil

[G. E.]

Originally Posted by amishsixstringe

For comparing options in corners, would it not help magnify differences by placing similar setups in multiple locations? ...

For those traps showing promising results doubling to check their "scalability" is valid idea! Furthermore I'll include a check with two simple porous absorber to show if the test setup is able to measure this scalability.

EDIT: you've probably meant to test the same trap in different corners, don't you? From my experience this kind of test (reduction of the T60 times of the lowest modes) shows quite small deviations for different corners. I'll include a check in the beginning of the test series.

[amishsixstringe]

G.E. I think you had it the first time. I meant using an identical (as close to as possible) trap in multiple corners simultaneously in different configurations (i.e. the same area configured differently). Since just altering positioning is likely to prove very little difference in performance, you could multiply that subtle difference by using more than one instance of the same configuration.


Neil

[boggy]

Originally Posted by G. E.

The various setup and mounting options multiply quickly... I stand by my offer to publish test results for 1mm and 2,5mm steel.

I missed that offer somewhere , so, as I already said, this is absolutely acceptable for me.

Originally Posted by G. E.

I like the stacking idea...

I'd expect that stacking with or without the gap, makes difference too

Originally Posted by G. E.

Ok, but I don't expect substantially different results comparing vertically "standing" with vertically "hanging" absorbers.

Hm.. in first case (laying on the floor) steel plate isn't tense, but if we hang it, plate will become streched and I expect that resonant frequency may go up... this is only my guess, and that is a reason why i suggest this type of measurements. Second reason is that you will get another movement, (very) low resonant frequency, like standard pendulum, when you hang absorber from the ceiling... I don't try to tell that this movement is exceptionally usable, but this is a difference between hanged and non hanged steel plate in enhanced porous absorber, when they try to reach sympatethic resonance (a necessary step for this type of absorption). Third reason is that your type of mount (laying on the floor) may generate noise when high LF SPL is applied in room, and (some) people don't like it.

If you don't like holes in your ceiling, ... you can knock off some stands using wooden batons... btw, i never attach panels from the ceiling directly, i always use some additional construction. I don't like to make holes in my customers walls.

Also, hanging this panels to the ceiling (parallel or "parallel" to it) will help understand how this will works for ceiling-floor resonances, when we don't have anything other than ceiling where we can mount absorbers...and this frequencies can go pretty low too.

As you can see, I'm interested only for your "Enhanced Porous Absorbers" (EPA?) and different ways of designing/using it.

[G. E.]

Originally Posted by boggy

I missed that offer somewhere ...

The list of available items is in the Sketchup file.

[G. E.]

Originally Posted by boggy

... Hm.. in first case (laying on the floor) steel plate isn't tense, but if we hang it, plate will become streched and I expect that resonant frequency may go up... this is only my guess, and that is a reason why i suggest this type of measurements. ...

The hanging plate would "stretch" in the range of ~0,005mm [0,0002"] under its own weight and the plate's modes are dense either way. I am expecting very comparable results for "hanging" vs. "standing" in this test.

Originally Posted by boggy

... Second reason is that you will get another movement, (very) low resonant frequency, like standard pendulum, when you hang absorber from the ceiling... I don't try to tell that this movement is exceptionally usable, but this is a difference between hanged and non hanged steel plate in enhanced porous absorber, when they try to reach sympatethic resonance (a necessary step for this type of absorption). ...

Note that corner mounting doesn't allow for a pendulum motion (absorber side corners touching the wall). Again, since the pendulum motion (< 1Hz) would be joined by the absorbent as well no enhanced bass absorption expected... we'll see.

Originally Posted by boggy

... Third reason is that your type of mount (laying on the floor) may generate noise when high LF SPL is applied in room, and (some) people don't like it. ...

Could you please explain what you mean with "laying" and where the noise comes from?

[G. E.]

Originally Posted by G. E.

... I kindly take your suggestions until the end of the year 2011 to compare different configurations directly for further public reference.

How to "apply" if you are interested:

1. Check if a similar idea to yours has already been suggested.
2. Use the attached Google Sketchup 8 file to "build" your setup with what's available focusing on the corner opposite the microphone (see example).
3. Disable unused layers.
4. Save your file with a unique filename (with date and your Gearslutz user name in it).
5. Upload your suggestion as a Google Sketchup file to this thread together with at least one image for visual reference.

...

2011 is gone and we've mostly seen ideas making use of the metal plates in this thread, no qualified suggestions (see above) yet though.

Happy 2012 bass trapping!

[boggy]

Originally Posted by G. E.

The hanging plate would "stretch" in the range of ~0,005mm [0,0002"] under its own weight and the plate's modes are dense either way. I am expecting very comparable results for "hanging" vs. "standing" in this test.

I know this but I think that it is better to check this (even it is redundant as you expect), because hanging is better way to mounting this traps (hanging on walls corners, ceiling-walls corners etc..)

Originally Posted by G. E.

Note that corner mounting doesn't allow for a pendulum motion (absorber side corners touching the wall). Again, since the pendulum motion (< 1Hz) would be joined by the absorbent as well no enhanced bass absorption expected... we'll see.

Yes.
Theory:
1. It is good to keep in mind that music is the mix of discontinued signals (with beginning and end), so it is better to include step response (response to Heaviside function) in overall absorption analysis because we have significant increase of energy in every beginning of bass note (not only energy of duration of this note), which may be called apperiodic... so I do not see any harmful effect in (extra) VLF component of absorption if we talk about music, not continous noise (printing house, industry, etc)
2. Also, even very powerfull subwoofer can't move hanged traps more than couple of parts of millimeter, rarely couple of millimeters.... this is only vibrations... and this "part of millimeter" vibrations are responsible for killing room modes in your room... so it is unreasonable to expect that pendulum motion of hanged absorber may be something like "jumping" or "shaking"... its not a case.

Originally Posted by G. E.

Could you please explain what you mean with "laying" and where the noise comes from?

Steel plate isn't fastened anywhere, it lying on the floor, if you have ten or twenty of this "enhanced porous".... at least one of it MUST generate buzz noise with every (particular) bass note, because stell plate touching the floor...
Plates must be firmly screwed to the floor, or mounted on the stands, or hanged from the ceiling (or stands, no matter) and they must not touch ANYTHING (stiff)* ....... if we like NOT to have a possibility to have a buzz noise in control room sometimes when one or two (particular) bass note appears (sometimes I spent weeks to find out WHAT generate noise, which is easily audible, but "generator" is buried in other acoustic treatment )

Great discussion...

*EDIT

[G. E.]

Originally Posted by boggy

... Steel plate isn't fastened anywhere, it lying on the floor, if you have ten or twenty of this "enhanced porous".... at least one of it MUST generate buzz noise with every (particular) bass note, because stell plate touching the floor...

This is what I mean with "laying" on the floor -- there's absorbent underneath (otherwise there's no absorption):

[boggy]

Originally Posted by G. E.

This is what I mean with "laying" on the floor -- there's absorbent underneath (otherwise there's no absorption):

ok... I mean if you lean steel plate against the wall, bottom edge laying on the floor (your picture is attached)... and there may be a problem (from my experience)




Also there are no use in studio of absorber which laying on the floor as you show on picture in your post above, except for measurement purposes... For ceiling/walls we must glue it to ceiling, screw it someway or hang it from with rope/chain... this is some real situations. In all this cases we change tension of steel plate, and I'm afraid that this may have influence to characteristics of absorption, so if you will to measure, it is good to measure some of this real aplications, this is my point. If you find this is too complicated, I will understand you.

[G. E.]

Originally Posted by boggy

... I mean if you lean steel plate against the wall, bottom edge laying on the floor (your picture is attached)... and there may be a problem (from my experience) ...

The image doesn't reveal how the plate touched the bottom. Anyway, glueing the plate to the absorbent without floor contact didn't enhance absorption in this configuration.

Originally Posted by boggy

... For ceiling/walls we must glue it to ceiling, screw it someway or hang it from with rope/chain... this is some real situations. In all this cases we change tension of steel plate, and I'm afraid that this may have influence to characteristics of absorption, so if you will to measure, it is good to measure some of this real aplications, this is my point. ...

I prefer sandwich constructions (absorbent-plate-asborbent) because of the more broadband absorption characteristic so there are mounting options without glueing. No "stretching at all, the plate is bedded on absorbent in either case, ceiling or floor.

[boggy]

Originally Posted by G. E.

.... No "stretching at all, the plate is bedded on absorbent in either case, ceiling or floor.

Ok, but how you fix/mount whole enhanced porous absorber construction on the ceiling? (if not glue, screws or rope/chain)

[G. E.]

Originally Posted by boggy

... how you fix/mount whole enhanced porous absorber construction on the ceiling? ...

... some (hanging or self-standing) support from underneath:

[boggy]

Originally Posted by G. E.

... some (hanging or self-standing) support from underneath:

Oh... I missed this... it is ok.

[RhOdEz]

I'm sorry if i missed it but has anyone mentioned possibility of
mineral wool - metal plate - mineral wool sandwich construction (glued or not) ?

thanks