Perforated Panel with Porous Absorber trap

[boggy]

Originally Posted by PaulRain

actuallt about my failure I didn't say all.....
the 70Hz dip I have....I'm pretty sure it's coming from the back wall, exactly where I'm not able to put the treatment I will like to......so, yes, the cause of the failure could be the position of the traps....
during summer vacations I will focus on this.
So, again, most important thing is locate the problem

Try to find better position for loudspeakers too. Dip at 70Hz, sometimes can be sensitive to loudspeaker position.

Cheers.
Bogic

[PaulRain]

+1
Speakers position and listening position
It's incredible how much difference few cm can make....but often is like having a short blanket.....if you pull it to cover your shoulder the feet stay out :(

[boggy]

Originally Posted by PaulRain

+1
Speakers position and listening position

Yes!

Originally Posted by PaulRain

It's incredible how much difference few cm can make....but often is like having a short blanket.....if you pull it to cover your shoulder the feet stay out :(

I know :( , but there wasn't many remaining ways to solve problems.

[G. E.]

Originally Posted by DanDan

... There is another which shows actual success building reasonable sized panel traps, by G.E. Anyone have that link handy? ...

... these posts come to my mind as starters:

• "Comparative measurements setup"
• "How I accidentially built a 26Hz? basstrap"
• "Tuned measurement"

Personal résumé: good (narrowband) success with well tuned membrane absorbers, little to no success at all with perforated tuned absorbers, 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:

• ~42Hz (1.0.0): 4,643s > 294ms (-94%)
• ~55Hz (0.1.0): 1,602s > 590ms (-63%)
• ~70Hz (1.1.0): 2,873s > 531ms (-82%)

[boggy]

Originally Posted by G. E.

........some new exiting results from a VPR-inspired configuration (single big trap with 1m^2 [~21 square feet] front) that reduced the T60 time of the first three modes (calculated by REW) as follows:

• ~42Hz (1.0.0): 4,643s > 294ms (-94%)
• ~55Hz (0.1.0): 1,602s > 590ms (-63%)
• ~70Hz (1.1.0): 2,873s > 531ms (-82%)

It's really exciting result.

BTW is it 1m^2 or 21 square feet (2m^2) (just curious)

Best regards

Bogic

[G. E.]

Originally Posted by boggy

... is it 1m^2 or 21 square feet (2m^2) ...

I've corrected the typo in the original post, actually it's 2m^2.

[boggy]

Originally Posted by G. E.

I've corrected the typo in the original post, actually it's 2m^2.

Thanks

[boggy]

Here is a burst decay sonogram response of Pressed Lizard studio, designed following MyRoom acoustic design principle. Room has near square horizontal cross section (double room mode at ~50Hz). Description of this design you can find in my signature (please, look above in my other posts... if this post doesn't have any signature below).

I hope this may be usefull for some reference.

EDIT: Dimensions of Pressed Lizard room (before any treatment) are: width=3.56m, length=3.67m and height = 2.55m (w-11.7', l-12', h-8.4')

[G. E.]

Originally Posted by boggy

Here is a burst decay spectrogram response of Pressed Lizard studio, designed following MyRoom acoustic design principle. ...

You're showing an outstanding burst decay result -- very even and controlled response over the whole frequency range (FYI: my own measurment above was done with a subwoofer with driver, trap, mic all placed in corners).

[boggy]

Originally Posted by G. E.

You're showing an outstanding burst decay result -- very even and controlled response over the whole frequency range (FYI: my own measurment above was done with a subwoofer with driver, trap, mic all placed in corners).

Thanks.
I measured finished studio, left channel, at listening position, full range three-way loudspeakers are already in best possible position, ... and someone call that type of designs "100% diffuse"... figuratively, of course.


BTW, the "woofer" in Pressed Lizard monitors, was 12" long stroke driver , then, some "usable" frequency response is actually from about 4Hz to 25kHz ...

Cheers

Bogic

[Jens Eklund]

Burst decays of a halfway treated room using only pressure based absorbers (except at early reflection points of course), panel absorbers (with diffusers as front end) targeting the 60 Hz mode:

[G. E.]

Originally Posted by Jens Eklund

... Burst decays of a halfway treated room using only pressure based absorbers (except at early reflection points of course), panel absorbers (with diffusers as front end) targeting the 60 Hz mode: ...

Given that a constant decay rate (over different frequncies) results in greater numbers for the periods necessary for the level to drop by let's say 60dB as in the screenshots absorption at 100Hz and above works really well in your example.

Do you have before/after numbers for your modes from REW's calculations (T60 in REW's modal analysis, EQ section)?

BTW: we're propably "comparing" different rooms and different measurement setups!

This is what my measurements look like recreating your viewing options:

[boggy]

Originally Posted by boggy

Here is a burst decay spectrogram response of Pressed Lizard studio, designed following MyRoom acoustic design principle. Room has near square horizontal cross section (double room mode at ~50Hz). Description of this design you can find in my signature (please, look above in my other posts... if in this post isn't any signature below).

I hope this may be usefull for some reference.

EDIT: Dimensions of Pressed Lizard room (before any treatment) are: width=3.56m, length=3.67m and height = 2.55m (w-11.7', l-12', h-8.4')

Same as above, but right channel.

[Jens Eklund]

Originally Posted by G. E.

Do have before/after numbers for your modes from REW's calculations (T60 in REW's modal analysis, EQ section)?

30-150 Hz
Analysis Length: 500 ms
Noise Threashold: 45 dB
Min T60: 300 ms
Max T60: 3000 ms
Min SPL: 75 dB (impluse about 90 dB).


Untreated:

31,7 100,4 363,5
40,8 88,6 757,3
55,4 80,6 426,2
59,8 104,5 832,8
74,0 85,1 798,1
80,2 98,5 701,5
86,1 97,9 890,8
94,3 80,4 746,0
98,9 88,8 986,7
105,2 83,3 573,9
109,1 90,2 1677,5
114,0 100,3 539,8
116,2 102,5 784,4
119,2 107,2 689,6
121,8 100,0 533,4
129,5 84,2 805,8
135,0 86,8 396,8
146,7 96,0 653,4


Halfway treated:

30,1 80,9 305,3
37,2 81,9 649,8
43,4 79,9 442,6
57,8 92,4 364,9

[DanDan]

Well done Gernot. Really convincing results from quite a small VPR.
Would you share the construction details? I suggest that this really deserves a new thread.

All of the results presented seem very interesting, with good eyesight and patience :-)

Waterfalls? Or post the exported IR as WAV?



DD

[G. E.]

Originally Posted by DanDan

... Would you share the construction details? I suggest that this really deserves a new thread. ...

I'm in the process of fine tuning my experiments...

Originally Posted by DanDan

... Waterfalls? Or post the exported IR as WAV? ...

Here we go:

[DanDan]

Thanks G. You have made my day. I have been suggesting for some time that VPR may be a holy grail. I hoped to try them myself. I got some costs on steel and Basotect. LOL, Ireland is certainly not Greece.
I will put it this way. Bob Dylan played here last week. Tickets €95.
He also played San Francisco recently, Tickets $40.
I am really looking forward to seeing how you made these.

DD

[laagman]

Originally Posted by DanDan

I am really looking forward to seeing how you made these.

DD

This looks to good to be true, only one (big) trap? I really hope G.E. will share details with us when he has finished this experiment.

[G. E.]

Originally Posted by laagman

... only one (big) trap? ...

Right, one trap -- the most effective sub bass trap (<80Hz) that I've built so far (amongst ~50 different trap configurations such as porous absorbers, tuned perforated devices, tuned membrane absorbers, VPRs).

Right now I'm trying to figure out how it translates to different rooms in studios in (and around) Vienna and to build an enclosure for easier transportation.

[DanDan]

If you wish to reveal details I am sure many of us would try it.
I would of course totally understand if you chose not to.
This is beginning to look like a very sellable trap system!
I am curious. I thought the VPR had to be totally mounted on a pretty solid boundary. From the picture yours looks like a large damped sheet straddling a corner. Again, kudos G, I wish you every encouragement possible and am quite willing to throw in any support possible, up to and including building and testing here.
DD

[laagman]

If G.E. wished to reveal details, it should definitely be in new thread.

If not, as least let us know how much ($$$) it's gonna be ;-)

[hsal]

impressive work G.E

[jayfrigo]

I've had good luck with perforated panel absorbers. I've used them in several rooms in conjunction with other traps and absorbers and they have proven to be effective and fairly straighforward. Mankovsky did excellent work on the subject, and enough of it is outlined in Everest's "Master Handbook of Acoustics" to get you started.

I really don't think they're that difficult to build, and if you half-fill the cavity with porous absorption, the Q widens sufficiently to give you a margin of error for the center frequency. Of course the extra absorption at frequencies to either side of the design frequency comes at the cost of a bit of a reduction of peak absorption at that design frequency, but for several practical reasons you're most likely better off with some porous absorption inside.

[Jens Eklund]

Originally Posted by jayfrigo

I really don't think they're that difficult to build, and if you half-fill the cavity with porous absorption, the Q widens sufficiently to give you a margin of error for the center frequency.

+1

If low enough flow resistively, you can usually fill the cavity completely.

[PaulRain]

I don't want to give up the perforated panels path....my first attempt was a failure but I didn't expect to get it right at the first shot
I found out that different calculators give different results and the Absorber Model used to calculate the Absorbtion coefficient will plot very different results.
So it's a little bit complicate for me to decide the way to proceed

[DanDan]

I hear Kate Bush singing to Peter Gabriel.....
I will certainly encourage any attempts to do LF properly. It seems obvious to me that any tuned trap will have to have tunability in the design.
Way back, G.E.'s most successful trap, after many many attempts, was a panel one.
His high performing new VPR one might also be loosely called a panel design.
Similarly the BBC settled on a Panel design, again after much research.
Some of the pro designers around here have also recommended panels over perf. In the real world, I see lots of broadly tuned slatted designs.
DD

[G. E.]

Originally Posted by DanDan

If you wish to reveal details I am sure many of us would try it. ...

I've put up the basic construction scheme and a thread for comparing different bass traps for a deeper discussion of the object.