AVS Forum banner

DIY construction methods of hang-able acoustic panels & moveable Corner traps (not fixed frames)

232K views 192 replies 44 participants last post by  EpicFirth 
#1 · (Edited)
Background:
I've been thinking to make a separate thread on the DIY construction methods of hang-able acoustic panels, that can be located specifically only where needed.
Also moveable as your speaker type/location changes, your treatment needs may change.
Currently none exist that give a really good start-finish, I've searched AVS forum.

Just these for Fabric frames, which are integrated as part of the wall itself, not hanging and specific locatable.
(these are great threads btw for those whole wall coverage methods)
Fabric Frames - GPowers Thread , Another Fabric Frame Thread - Canvas Stretcher Bars

In my viewpoint, the Acoustical Treatments Master Thread is more for the theory, science, and practical application for acoustics of your particular room situation/issue, not the DIY construction methods, that will clutter it too much.

This thread purpose is NOT what your rooms acoustic needs are, rather once you study, plan, and develop your rooms acoustic needs, how to go about building it yourself.
[edit] since making this thread some specific acoustic issues have been discussed and addressed, however there are other more suitable threads for the theory, think of this as the application thread.

So, here it is, a dedicated thread for DIY construction methods of hang-able acoustic panels, to start I plan on sharing what I've done:
-DIY side wall absorption panels construction and hanging, http://www.avsforum.com/avs-vb/showthread.php?p=19947559#post19947559


-DIY ceiling absorption panels panels construction and hanging
http://www.avsforum.com/avs-vb/showthread.php?p=19987283#post19987283 and http://www.avsforum.com/avs-vb/showthread.php?p=20074007#post20074007



-Here is removable lower tri-corner superchunk bass trap made with 1/2-13 thd rod and OC705, from post #40 http://www.avsforum.com/avs-vb/showthread.php?p=19993984#post19993984
and Upper tri-corner bass traps (since I made these it's been proven via gas flow resistivity its best for deep traps like these to use pink fluffy)
http://www.avsforum.com/avs-vb/showthread.php?p=20085872#post20085872

Eric helped with his pink fluffy version of my movable corner bass traps
http://www.avsforum.com/forum/19-de...er-traps-not-fixed-frames-5.html#post22131618 .

Discussion related to corner bass traps; gas flow resistivity, why cover them to reflect mid-high's, etc


others in this thread:
-smokarz built his own side wall 2' x 4' panels, post #36 here http://www.avsforum.com/avs-vb/showthread.php?p=19993492#post19993492


-localhost127 built his own side wall 4" thick 2' x 4' panels with exposed sides for more absorption , post # 86 here http://www.avsforum.com/avs-vb/showthread.php?p=20271296#post20271296



There are already "fixed" bass trap threads, here are links to them.
AVS site:

Show us your custom made corner bass traps (pics)
(btw, as of 2/5/0-11 pepar updated his pict links, I need chinaclipper and pred02 to do same )
Other site:
Gearslutz.com, here is a link to their "How I built my bass (broadband) traps..." sticky, over 31 pages of info!
http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/87464-how-i-built-my-bass-traps.html

I added my own twist to building corner superchunk with "green" material, some might like a different approach.
http://www.avsforum.com/avs-vb/showthread.php?p=20588838#post20588838

I'd like others who make DIY hang-able acoustic panels, whether absorption, diffusion, reflection, etc. to also feel free to add your construction techniques/methods there.
>>We need to learn from you!

[edit Feb 2, 2011]
placeholder for those already done DIY hang-able acoustic panels-pm me your details and I'll post link here

Side note:
I have this general suggestion for those wanting to learn about acoustics:

A) read this Acoustics/Treatment Reference Guide , via gearslutz, its a easy read in layman terms, starts you off with basics and good foundation with practical discussion. Studio acoustics and Home Theater acoustics.
From that, simple/straight forward advice via Jens Eklund:
Quote:

1. Learn how to make measurements: REW - Room EQ Wizard Home Page
Don’t do anything without measurements.

2. Define your MLP (Master listening position). Confirm with measurements.

3. Identify and treat your modal and SBIR - Speaker Boundary Interference Response related issues and educate yourself about different bass-absorbing techniques.
Other info: SBIR by Bryan Pape

4. Treat areas that otherwise creates early reflections.

5. If the room is big enough, add diffusers

Always base your decisions regarding different treatment, on measurements. Avoid thin porous only absorbers (including wall to wall –carpet, drapes etc.) unless a measurement indicates the need for it.


B) Knowing that for “best” audio/sound in a listening room, these parameters are tackled in prioritized order:
1. Speaker location, 2. Listener position, 3. Acoustic treatments, 4. Electronic correction.
Understand the small room acoustic model you will follow.
Looking at this link, everyone can see visually the various small room models, it's 7 pages from the book "Acoustics and Psychoacoustics Applied"
http://eetimes.com/design/audio-desi...n?pageNumber=0

C) If you have desire for more knowledge:
-read one of many books out there, a great 1st book is "Master Handbook of Acoustics" by F. Alton Everest, a perfect follow-up book is "Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms" by Floyd Toole.
-shameless plug for Ethan Winers book also, "The Audio Expert".
.. ..

-study Ethan Winers site, http://www.ethanwiner.com/acoustics.html
-Become familiar with the different small room acoustic models for home listening spaces
-This is also a 101 read on Room Acoustics, http://www.crutchfield.com/learn/learningcenter/home/speakers_roomacoustics.html
-SAE Home Acoustics info site has many definitions and explanations http://www.sae.edu/reference_material/audio/pages/fullindex.htm
-There are many other sites on the web, like
........One of the first ones, StudioTips small room acoustics forum http://forum.studiotips.com/index.php,
........Acoustical measurements defined Rives audio http://www.positive-feedback.com/Issue12/rives2.htm,
........RPG Acoustics Library papers http://www.rpginc.com/news/library.htm, etc.
-Be careful of info overload all at once

D) Measurement info/threads:

-online downloadable file with the Sound System Engineering chapter 6 on measurements http://www.focalpress.com/uploadedFiles/Books/Book_Media/Audio/9780240808307.pdf
-Get the hardware side of REW down quickly, this thread by member omegaslast dummy's guide on setting up REW and his blog http://polaraudio.blogspot.com/2012/01/calibration.html easy 101 read with pictures to walk you thru the mechanical of set-up and taking measurements
-Highly recommend Nyal Mellor's site, http://www.acousticfrontiers.com/Aco...surements.html , and a very detailed/helpful white paper http://blog.acousticfrontiers.com/st...ist.%20Rms.pdf
-Room Measurement & Treatment by "fotto" (Floyd)

- Envelope Time Curve - ETC - Impulse gearslutz thread
-Using energy time curve for acoustic analysis: by "mtbdudex" (Mike R)
-Why just using 1" thick porous absorber treatment is "wrong" http://www.avsforum.com/t/1369498/early-reflection-panel-thickness
-http://www.avsforum.com/t/1421599/etc-isd-gap-question ETC - ISD gap by
-Basic acoustic measurement primer v2.1 (via gearslutz "DanDan")
-http://www.realtraps.com/art_measuring.htm

-http://www.avsforum.com/t/1316623/d...poster-acoustic-panels-cheap/60#post_20147783 DIY Custom-Printed Movie Poster Acoustic Panels
-first reflection software: http://www.avsforum.com/t/822273/fr...our-first-reflection-points/240#post_22619555
-a while back I downloaded this Measurement/calibration sequence from Dennis Erskine.
RoomMeasurementSet-up.zip 4.990234375k . file
 

Attachments

See less See more
14
#77 ·

Quote:
Originally Posted by scl23enn4m3 /forum/post/20086182


Wow, those traps greatly exceeded my expectations. You have skill bringing your ideas to reality. Clean lines and more shelf space! I like the halves more than a full trap now. The downside to a full trap is it makes the back of the room seem smaller, but this give the illusion it's still open.
Quote:
Originally Posted by PTAaron /forum/post/20087169


Those upper traps look great!

How does the room sound?

Thx guys! It feels good to have those done and turning out decently, I was worried with them hanging up high if they looked so-so what people would say...

And scl23enn4m3 I agree, having a shelf is functional and the 2 traps helps keep the room "openness feeling" decent along the rear wall.


PTAaron - I posted this in another thread;
Quote:
Did you treat your entire room at once, or did you treat just the first reflection points and then try it out?

I studied, planned, and implemented in stages.

Here is what I did in order and simple subjective opinion, scale 1-5, 5 being highest ranking;

-side wall treatments first - very noticable rank 5

-2nd row acoustic cloud - noticable rank 3.5 or 4, not as much as side wall treatments

-Rear wall lower bass traps - very noticable, rank 4.5 or 5

-1st row acoustic cloud - noticable, rank 3 or 3.5

-Rear wall upper bass traps - noticable, rank 4


Ethan W (and some others) recommend you tackle the bass traps 1st, then from there your side wall 1st reflections, then determine what needs treatment after that.

There is a diminishing return on $$ vs benefites gained, both subjective and objective.

Only each individual can judge when to stop and accept their acoustics "as is".


Funny thing, my ear definitley is now tuned better for acoustics, and I can hear a echo among the center channel and my rear wall back to my DW lamiante screen, it forms a echo chamber!

That's why people say go AT screen to elimiante that issue, now I will study on specific portion of rear wall diffusor and/or thin absorber to minimize that.....

That is my subjective ranking, this weekend I'll get REW hooked up and take objective measurements and post those as well, for fact based data/graphs correlation to the subjective rankings.
 
#78 ·
In response to a PM:

The upper bass traps are just sitting on (2) L brackets each, gotten from Lowes in the outside deck building area, painted them green.

By simple geometry they are trapped up there, not even attached screws to lower wood piece.

I did put 3/4" round felt on the top/ceiling piece to space it off the ceiling and ensure no vibrations.

Also on the wood edge to space it off the back/side walls, no issue with vibrations at all.



Other:

I did not take REW frequency readings this weekend for the bass improvements.

My AT picture samples for the side wall treatments from "spoonflower" are due later this week, therefore I will tackle that project (which supplier to work with on AT picture fabric) with the improved Bass readings at same time.

(it's a lot of cables/etc getting REW up and running......)
Quote:
Spoonflower Shipment Confirmation - Order #xxxxxxx

Thank you very much for your order from Spoonflower.com. Refer to this email for any information related to your order or visit your My Account page at: http://www.spoonflower.com/users/xxxxxx

Your Order has been shipped!

Shipping Method: We ship using the USPS, which typically takes less than a week. International orders may take quite a bit longer.

Order Detail:

Date ordered: Feb 24th, 2011 03:18 PM

Date shipped: Mar 4th, 2011 09:26 PM

Kit item ordered: Collection sampler of collection 'Test acoustic samples' by mtbdudex

Item Cost: $20.00

Shipping: $2.00

Order Total: $22.00

If you have any questions or concerns, please email help@abcxxxx.com or call +1 (000) 1234567

Thanks for your support of Spoonflower. Now get out there and make something!

Thanks for your purchase!
 
#79 ·
Got the samples in from Spoonflower last night, simply I was blown away by the picture quality!


Same test as before, I added the Spoonflower to the bottom, also a few from ats acoustics as comparison.


I did the breath test, comparing the Spoonflower material vs the ats acoustic sample pack I have http://www.atsacoustics.com/item--St...ack--1034.html


Subjective rating via breath test:

1) Spoonflower fabric passed more air than the ats acoustic sample I had for the microsuede

2) Spoonflower fabric passed same air - or slightly easier - as the ats acoustic sample cotton weave sample

3) The ats acoustic burlap definitely passed the breath test the most.


Picture quality comparison:

(these are all my original photos, so I can compare them)


This is w/o flash with HT lights on about 50%:



Pict with flash (white balance set according for each shot):



These close ups are all straight from my T1i camera, RAW format w/o any post processing added.

#1 ; the detail in the craters is fantastic, nearly same as original



#2 ; this racoon fine fur detail again quite good



#3 ; the star trails kept streaks and the star colors



#4 ; this B-17 shot in B&W was to see how it fared for B&W....really good



#5a ; tree @ night via spoonflower



#5b tree @ night (blocky weave from local supplier)



#6 reflection test - passed with flying colors!

The cotton weave has less sheen.



Ding - ding - ding: we have a clear winner! Spoonflower .

(Thx luma for pointing them out)


Very impressed with the picture quality, color matching seems spot on, much detail is there, only the star field with the 5 meteorites proved too much for their process to reproduce.


I will take objective freq comparisions later, however I see absolutely no reason not to recommend the spoonflower fabric and process for anyone looking to have Acoustic transparent artwork for their acoustic treatment panel covers.


[edit 3-9-2011: use their Quilting Weight Cotton, http://www.spoonflower.com/spoonflower_fabrics ]
Quote:
Quilting Weight Cotton: $18/yard ($16.20 with designer discount)


100% cotton fabric with a soft hand, easy to sew


* 42" wide printable area (107 cm)

* 3.2 oz per square yard

* 78x 76 threads per inch

* Appropriate for quilting, appliqué, shirting, blouses, dresses, children's clothing

* Estimated shrinkage 3%

* Wash on delicate setting, warm or cool using phosphate-free detergent
 
#81 ·
After doing the subjective "breath test" of various fabrics for the AT-ness (Acoustic Transparency ability), I did want to do some objective testing to get a feel for the AT-ness frequency wise of the various fabrics I've been considering for the art coverings on the wall treatments - and share with others.


This past Saturday I built a $20 test fixture out of 1 1/2" PVC pipe, used a closet flange to bolt it to leftover 3/4" OSB 19" x 19" board.

The "T" tee fitting is NOT glued to the 24" upright for easy rotation to simulate various angles of interaction like in real life off side walls / ceiling.


Quick and easy, and holds the test sample via tape.


The test zone is 16" x 16" so I can read the midrange and tweeter drivers separately by adjustment of the mic boom stand.

My Paradigm Monitor 9 midrange driver is 32.0" above base and tweeter driver is 37.25" above base.

I marked the baseboard every 15 degrees 0-15-30-45-60.

(but did not take measurements @ 15 or 30 deg)


The fixture is set to be 4.25 inches from the cone center, and the measurement mic is 0.75 behind the fabric being measured.


If I made the fixture closer to the speaker then I could only rotate it to 30 deg before it hit the speaker sides.

I realized not perfect "nearfield", but my goal here is to quantify the change in frequency amplitude being passed thru the various fabric's to compare the subjective breath test with objective AT data.

(and learn by doing)


As used in the HT, my RH/LH main speakers are 24" from side wall and 28" from back wall, toed inward slightly.

For this Sunday afternoon quick round of testing I did NOT put them more centered in the room.....

I had about 90 minutes to do all this in the basement while my 2 boys (7 and 5) were in the 2nd floor loft playing games, so had to work quickly.

(with HVAC/other off to lower the sound floor)


Here it is at 0 degrees measure (simulating direct reflection @ 0 deg)....Here it is at 45 degrees measure (simulating reflection @ 45 deg)



Here is the fabric from spoonflower being measured.

All measurement were done with REW5 driving thru the Ext-IN, bypassing any processing.

(cables and "stuff" everywhere)



Side view of set-up.........front 3/4 view of set-up



I took over 30 measurements via REW5, iMac 24", Behringer ECM8000, and will group them into logical parings for comparison purposes and review.

-Baseline of Midrange and tweeter w/o any fabric

-Midrange and tweeter thru spoonflower fabric @ 0,45,60 degrees

-Midrange and tweeter thru local supplier blocky fabric @ 0,45,60 degrees

-Midrange and tweeter thru kraft paper @ 0,45,60 degrees

-Midrange and tweeter thru 3/4" pink hard insulation board @ 0,45,60 degrees (for comparison to kraft paper for blocking mid-hi freq in bass traps)


Again, the fixture is set to be 4.25 inches from the cone centers, and the measurement mic is 0.75 behind the fabric being measured. Not perfect nearfield but close for this purpose.


I'll post those graphs later with my comments for discussion.
 
#83 ·
Quote:
Originally Posted by xzener
So I was thinking while installing my inwall speakers today, it would be nice to have an acoustically transparent movie poster to cover my rear surrounds.


Do you think it would be possible to print a movie poster on say movie screen material??
I understand your Q - if AT movie screen material is great for the projected light visual AND is AT, why not use that for printed coverings on rear surrounds (and possible fabric covers for acoustic treatments I'll add).


I'm simply not sure the printing process used by the online place spoonflower.com or the local place (used a HP 9000 series Designjet that is fed by material on a std size roll ) could do that.

Each uses equipment with its own set-up parameters.


Can you follow-up with an inquiry to the supplier who sell's AT movie screen material with your Q?

Can it be "printed on"? Has it been done before?

What size roll does their material come on? etc.


I'd be interested that result as well.
 
#84 ·
Set-up:

REW5, iMac 24", Behringer ECM8000, test date March 13, 2011

The fixture is set to be 4.25 inches from the cone centers, and the measurement mic is 0.75 behind the fabric being measured.

As used in the HT, my RH/LH main speakers are 24" from side wall and 28" from back wall, toed inward slightly.


I measured the midrange @ its center height position (32.0")and tweeter @ its center height position (37.25")

Did the 75db calibration @ midrange position and did not re-calibrate for tweeter position.

Applied 1/3 octave smoothing for all these, if subwoofer then I would have applied 1/12 octave smoothing.


paradigm monitor 9 Crossovers specs:

3rd-order electro-acoustic at 1.9 kHz

2nd-order electro-acoustic at 500 Hz



They graphed like this as baseline w/o any thing between them and the mic:

(Blue is midrange, purple is tweeter)
Chart 1 Baseline chart:



Note:

1) I always show the "baseline" midrange/tweeter curve for visual compaision on respective charts.

2) I always ran the measurement 80hz - 20khz, and plotted that way also.

3) When looking at the charts, the midrange you should look at the 500-1.9k freq zone, the tweeter the 1.9k and above freq zone

Spoonflower cotton cloth charts

Chart 2a Midrange with spoonflower cotton cloth, baseline and @ 0, 45, 60 degrees



Chart 2b Tweeter with spoonflower cotton cloth, baseline and @ 0, 45, 60 degrees


>>My conclusion from the midrange/tweeter charts: spoonflower cotton cloth is AT and good to go for acoustic absorber panels usage.

Charts showing mi-hi freq blockage:

Chart 3a Midrange with kraft paper, baseline and @ 0, 45, 60 degrees



Chart 3b Tweeter with kraft paper, baseline and @ 0, 45, 60 degrees


>>My conclusion from the midrange/tweeter charts: Clearly krafty paper does block significant hi freq, it appears not as good at mid-freq blockage


This show the "freq blockage" of kraft paper vs 3/4" pink foamboard:

Chart 4


>>My conclusion from the midrange: Clearly 3/4" pink foamboard does block significant mid and hi freq compared to the kraft paper

(I forgot to do same test for tweeter kraft vs 3/4" pink foamboard, maybe on Part III will do)


This shows a comparision of tweeter for baseline, spoonflower, and kraft @ 0 deg

Chart 5



This shows a comparision of midrange for baseline, spoonflower, and kraft @ 0 deg

Chart 6




I might re-do these as Part III with the speakers more mid room to more remove any wall interaction from these readings, but my quick experience gained is these fabrics seem more AT than I had guessed they would. But, this is my 1st time doing this so no real frame of reference.

I've not come across anyone else here @ AVS doing these, could be burried in the 200+ page Master Acoustics thread, that thread would be so much more useful if an index was at the beginning...There is great info burried in it, lost, and then re-talked about again. I truly feel for Dennis/Ethan/Terry/Ted/Others for answering q's multiple times.
 
#85 ·
Spoke with "Sal" @ acoustimac, http://www.acoustimac.com/index.php/...5/category/10/ .

I just ordered (3) more cases of their "ECOUSTIMAC Eco Friendly DIY Insulation (4 lbs/ft) 48"x24"x2" -Case of 6 ", guaranteed by Sal to be 24" x 48".

He gave me discount price on the 1st case due to prior situtation.

If I get these Friday 3/18 weekend project will be doing the Front Wall Broadband Bass Traps.

The front LH Corner will get a full floor-ceiling 24"x24"x34" superchunk, while on RH side due to IB sub I'll handle the top tri-corner only.

I've been trying to make all the acoustic treatments non-fixed, however for a whole floor-ceiling bass trap looks like a fixed one is best design.

The front RH top tri-corner will be similiar to the Rear upper bass traps I've made earlier.
 
#86 ·
just found this thread - nice work ,everyone.

just wanted to chime in --- those making frames that wrap around the oc703 (or equiv) need to take into account edge diffraction. an ETC graph will verify that you are properly absorbing all first reflections.


if you do NOT build a frame around the insulation, then you are effectively gaining 50% area coverage on a 4" thick trap (because the sides of the panel are exposed and able to absorb ingress/incident energy as well) -- just a FYI.


here's my contribution.

note, if you build a backing frame only, this leaves the sides of the panels open, eliminates edge diffraction off (what would be) a wooden frame wrapped around the insulations, and also provides an air gap (which is vital for porous absorption), spacing it off the wall. --- and also provides something to staple the rear and front fabric to.
















cheers,
 
#87 ·
mtbdudex,

very nice work on the corner chunks


i dont believe i saw any waterfall plots? if you really want to see how effective the corner chunks can be, take watefall plots (0-300hz, 0-500ms) and that will give you a good idea of the modal ringing that was cured and what still needs to be addressed. freq response is only one part of the story! time domain will tell you more.

cheers,
 
#88 ·
Your graphs aren't going to show any difference below about 850 Hz since that is roughly the frequency corresponding to 16" wavelength. Below that will just refract right around it. Someone did a test on Gearslutz like this (though with a different aim, like trying to figure out absorption for a material or something), and Ethan suggested the only accurate way to do this all the way down is to make a door of the material and mount it in a wall then run this type of test (after the guy got roundly and obtusely beaten down by SAC, heh). I can find the thread in my info stash if you'd like.


That said, great testing! I may want to use this stuff for some of my panels, so thank you for leading the way on testing it! This test method is awesome, and would be very useful for whatever sort of fabric was under consideration.


When I chose fabrics, I went to the fabric store with someone else, and not only chose one that I could breathe freely through, but also one that preserves the sound of my voice well when I speak through it. I figure that is a pretty decent fabric store test of AT.


Hopefully I didn't miss this from before: how are you removing reflections from the analysis? Tight (really tight) windows?


And did you use any sort of reflective facing on your chunk-style corner bass dampers?
 
#89 ·

Quote:
Originally Posted by aackthpt /forum/post/20384149

Your graphs aren't going to show any difference below about 850 Hz since that is roughly the frequency corresponding to 16" wavelength. Below that will just refract right around it.

this is entirely incorrect. you must have taken something out of context within that conversation.


yes, larger wavelengths diffract around - this is why we place bass traps in the corners
 
#90 ·

Quote:
Originally Posted by localhost127 /forum/post/20385473


this is entirely incorrect. you must have taken something out of context within that conversation.


yes, larger wavelengths diffract around - this is why we place bass traps in the corners

I wasn't referring to your stuff localhost127, I was referring to testing the AT transparency that mtbdudex was doing. YOU didn't post any graphs to which to refer! I doubt we are in disagreement on the acoustics. If I am incorrect that there will little difference between measured response with and without the 16 inch panel in place (regardless of material) below 850Hz, then please explain!


I'm sure that your panels as well as those mtbdudex has up, and his superchunk-style corners, are effective. With the caveat that, to have an actual meaningful conversation, we'd have to hash out the precise meaning of "effective" under a certain circumstance!



I apologize for not making it clear to whom and about what I was referring.
 
#91 ·

Quote:
Originally Posted by aackthpt /forum/post/20385779


I wasn't referring to your stuff localhost127, I was referring to testing the AT transparency that mtbdudex was doing

ahh, my mistake as well.


and i might note (regarding mtb's testing), when it comes to broadband absorption of specular energy (reflections), we shouldn't be measuring frequency response - but instead use the ETC to measure total specular energy at a reflection point before, and after the broadband absorption has been placed. since ETC is frequency independent, this will tell us how much the overall reflection has been attenuated. we don't care about absorption of specific frequencies. this is to attenuate early reflections, so all we care about is the total energy of the reflection and if the broadband absorber satisfied the requirements (e.g. attenuate signal -20dB of the original signal).


this is a must read regarding different types of fabric:
http://www.gearslutz.com/board/bass-...absorbers.html


specifically, this post:
http://www.gearslutz.com/board/6424136-post4.html
 
#92 ·
It just came to me a moment ago that SPL only doesn't account for all energy in an acoustical system as you say. Comparing ETC is one route to fix that. I believe another is to compare phase as well as SPL.


I know I don't have a complete grasp of control theory and this whole thing of phasors and such (need some study!) but I think I do recall needing both to completely characterize the behavior of a system.


I haven't completely reviewed the threads to which you linked, but I do think that SAC is suggesting to run the ETC in a scenario wherein the panels are placed on the wall in the room, which is a bit of a different setup than mtb's with the sound firing through the material under test. Such a test (of a specific reflection present / not present rather than mtb's looking for sound passed through or not) would definitely give you the actual needed information but has the disadvantage (I think) that it is not possible in practice to window the analysis (to see the frequencies reflected / absorbed) while maintaining enough frequency resolution to be useful.


But then the question "How much sound at a certain frequency goes through this material" is a different one from "What is the performance of an absorbent panel faced with X fabric vs Y fabric vs bare". The first actually has the advantage that one could use a material testing well as a grille cloth too. I think that's an intriguing idea, actually. Anyway, the answer always depends on the question asked!



I think if you just ran an ETC with mtb's setup, you might be able to compare the height of the initial response (if the software isn't normalizing) but since most energy is in low frequencies there could probably be a high-ish HF reflectivity and/or absorption and not see a large difference.


I think we run into the issue here of whether it is better to test a system as a whole or to reduce the system down into component parts and test them individually. Both have merit in a given situation, and ideally both would probably be done.
 
#93 ·

Quote:
Originally Posted by aackthpt /forum/post/20386256


I haven't completely reviewed the threads to which you linked, but I do think that SAC is suggesting to run the ETC in a scenario wherein the panels are placed on the wall in the room, which is a bit of a different setup than mtb's with the sound firing through the material under test. Such a test (of a specific reflection present / not present rather than mtb's looking for sound passed through or not) would definitely give you the actual needed information but has the disadvantage (I think) that it is not possible in practice to window the analysis (to see the frequencies reflected / absorbed) while maintaining enough frequency resolution to be useful.

i think the question that needs to be asked, is why are we measuring the frequency response of a broadband panel (meant to absorb/attenuate early specular reflections), to determine if a particular fabric bears any change??


broadband absorption should *only* be placed at areas of incident energy that will be reflected towards the listening position within the ISD. (ignoring bass traps/LF modal issues - an entirely different approach).


we do not care about removing/absorbing XdB energy at Y frequency from the room. we are discussing specular reflections, which should not be broken down by frequency.


absorption isn't to be placed blindly in a room unless there is a specific need to address specular energy at that particular location (measured within the time domain).


i dont believe testing the frequency response of different 'fabrics' on a broadband (specular) absorber panel is necessarily relevant. the ETC is the tool that will display whether *any* energy is not being attenuated to the design requirement (and making it to the listening position). and thus, thicker absorption can be placed, the panel can be mounted differently to change the angle of incidence, or the absorption could be spaced further from the wall --- and retested via ETC to verify the broadband absorber is performing to combat the problem it was procured for.



again, i recommend anyone interested to read this post:
http://www.gearslutz.com/board/6424136-post4.html

as well as the rest of that thread.

Quote:
But then the question "How much sound at a certain frequency goes through this material" is a different one from "What is the performance of an absorbent panel faced with X fabric vs Y fabric vs bare". The first actually has the advantage that one could use a material testing well as a grille cloth too. I think that's an intriguing idea, actually. Anyway, the answer always depends on the question asked!



I think if you just ran an ETC with mtb's setup, you might be able to compare the height of the initial response (if the software isn't normalizing) but since most energy is in low frequencies there could probably be a high-ish HF reflectivity and/or absorption and not see a large difference.

the initial response (direct signal from speaker --> ears) will not change.

we can place a fabric on the broadband absorber, measure pre- and post- via the ETC, and see if there is suddenly any energy being reflected from the absorber. we don't care if the fabric has a change in absorption at a particular frequency or even a freq range. we only care about the total energy (independent of frequency) that is reflected and thus will combine at the listening position with the original signal.


angle of incidence is very important! and mtb's test regarding the 'reflectivity' of one particular fabric will not necessarily translate to another user's room, as angle of incident will vary. we also must bear in mind the absorber itself (without fabric) will tend to reflect (e.g OC703).

Quote:
I think we run into the issue here of whether it is better to test a system as a whole or to reduce the system down into component parts and test them individually. Both have merit in a given situation, and ideally both would probably be done.

when it comes to specular energy (reflections), we measure with ETC one speaker at a time - so we can realize and then attack the specific reflection points that are impeding the ISD from each sound source (speaker).


if anyone has anything to add or correct, please chime in!

but i think spending so much time and energy on the frequency response for sonic energy that functions as rays is not entirely relevant during the treatment process. fixing the issues in the time-domain will generally solve the frequency response problems for us. absorbing first reflection points attenuates the reflection that would otherwise combine at the listening position with the original signal constructively and destructively, to impede on us the most conventional frequency response issues (e.g. comb-filtering). by addressing specular energy via the time-domain (and ETC) --- this will likely solve the bulk of the freq response issues.


one can then use the frequency response (waterfall) from 0-300hz, and begin to address modal and decay issues for the sonic energy that functions as waves.
 
#94 ·

Quote:
Originally Posted by localhost127 /forum/post/20387737


i think the question that needs to be asked, is why are we measuring the frequency response of a broadband panel (meant to absorb/attenuate early specular reflections), to determine if a particular fabric bears any change??

I agree that's a good question. I noted the possible use of the fabric as grille cloth to point out that the testing done isn't actually answering that question. But I think that the testing mtb is doing has value, because I could see people wanting grille cloth printed with pretty pictures to stretch over surrounds installed in columns or for false walls - anywhere that accurate direct sound through the fabric is desired.

Quote:
Originally Posted by localhost127 /forum/post/20387737


... mtb's test regarding the 'reflectivity' of one particular fabric will not necessarily translate to another user's room, as angle of incident will vary.

On the other hand I am sure the idea was that if he can prove a fabric acoustically transparent at a range of incidence angles (he tested normal/45/60), that the incidence angle then is not an important factor in performance of a device as its covering is concerned. This point of view could have its utility.


It's also worth noting that using ETC is beyond 99% of DIY type / amateur's capabilities or level of interest and time to spend on acoustics. They just want some simple guidelines on how to treat their rooms, and there's nothing wrong with that. It's perfectly workable and as long as they don't get exposed to too much broscience it produces a result that fits the purposes of their listening space. It's not as though anyone reading the DIY thread is working on acoustics at Skywalker Sound.
 
#95 ·

Quote:
Originally Posted by aackthpt /forum/post/20387992


It's also worth noting that using ETC is beyond 99% of DIY type / amateur's capabilities or level of interest and time to spend on acoustics. They just want some simple guidelines on how to treat their rooms, and there's nothing wrong with that. It's perfectly workable and as long as they don't get exposed to too much broscience it produces a result that fits the purposes of their listening space. It's not as though anyone reading the DIY thread is working on acoustics at Skywalker Sound.

i have to respectfully disagree. if a user is 'capable' of measuring the frequency response via sine sweep, then they can just as easily measure ETC.


can an automotive performance tuner give tuning advice over the phone without measurements of the engine? would we expect one to?


browsing through these forums, there doesn't seem to be any lack of measurements (or enthusiasm for measurements) regarding the freq response. there is no reason why we cannot except people to also perform ETC when they are looking to address issues outside of the LF/modal region. especially when those same people may be looking to cure specular freq response issues --- and may not even realize that the ETC tool (in the time-domain) can likely solve the bulk of their freq response problems!


tell me - if a user goes through the time, energy, money, trouble, etc, to build their own broadband panels, how do they know for certain they are placed properly? the mirror trick is a rough estimate. the only way to know for sure if the panels are placed correctly and are attenuating the reflection to the desired requirements (eg -20dB) for the entire listening position (which could be quite large) - is to verify via ETC, one speaker at a time.


users are expressing interest in room treatments, DIY, etc. we need to encourage that measurements are equally as important as the treatments themselves. measurements should be taken prior to procuring treatments, so one knows the specific issues they need to combat. measurements need to be taken again after treatment has been placed, to verify the original problem has been addressed!. measurements also help us test to verify we have placed the treatments in areas where they are most effective.


without measurements, we seem to have this sweeping generalizations regarding absorption. look how many users are treating entire walls with absorption. absorption needs to be surgically placed only at required areas. the object is not to create a dead room! and even worse, we have some who have installed insulation across their entire wall(s), but then also only do so with insufficient thickness in order to absorb the full range of specular reflections! a measurement would quickly show this. why would one want to suck all of the HF energy out of the room, and leave the mid/lower specular energy free to cause interference? this is a prime example when people install (for example) 1" OC703 covering their entire wall.


while one can assume all reflections points via a mirror and place broadband absorption at sidewall, ceiling, rear wall early reflection points, they may not even be aware that there are other areas of incident that are equally destructive (coffee table), until they can measure with an ETC.


if a user is also applying diffusion (which many seem to do), then the decay trail of the ETC becomes another visual aid to determine how the energy is decaying within the room.


yes, there are many who are not in a position to take measurements (nor they may simply not care) --- but that shouldn't stop us from exploring the proper effectiveness of troubleshooting and applying treatment to combat specific issues within a room - and communicating this throughout the community.
 
#96 ·
localhost....what software do you use to make measurements with (REW?). I would like to understand proper way to set up a sweep for an ETC (I use REW).
 
#97 ·

Quote:
Originally Posted by localhost127 /forum/post/20388413


i have to respectfully disagree. if a user is 'capable' of measuring the frequency response via sine sweep, then they can just as easily measure ETC.

Actually we don't disagree, I just have a softer spot for the ideal vs. the practical.



All tools have their uses; it is just a matter of applying the appropriate tool for the specific purpose.
 
#98 ·
aackthpt, localhost127, fotto....I missed your comments in this thread.


I'm willing to learn and improve my knowledge and capability based on your comments.


aackthpt (John) is coming to the HEMI meet @ my home we are having this Saturday 14th, we will discuss this then as info sharing for all members who will be there.
 
#99 ·

Quote:
Originally Posted by localhost127 /forum/post/20272742


mtbdudex,

very nice work on the corner chunks


i dont believe i saw any waterfall plots? if you really want to see how effective the corner chunks can be, take watefall plots (0-300hz, 0-500ms) and that will give you a good idea of the modal ringing that was cured and what still needs to be addressed. freq response is only one part of the story! time domain will tell you more.

cheers,

I saved the measurements, so I can generate the waterfall plots also, will do and post again.

Quote:
Originally Posted by aackthpt /forum/post/20384149


Your graphs aren't going to show any difference below about 850 Hz since that is roughly the frequency corresponding to 16" wavelength. Below that will just refract right around it. Someone did a test on Gearslutz like this (though with a different aim, like trying to figure out absorption for a material or something), and Ethan suggested the only accurate way to do this all the way down is to make a door of the material and mount it in a wall then run this type of test (after the guy got roundly and obtusely beaten down by SAC, heh). I can find the thread in my info stash if you'd like.


That said, great testing! I may want to use this stuff for some of my panels, so thank you for leading the way on testing it! This test method is awesome, and would be very useful for whatever sort of fabric was under consideration.


When I chose fabrics, I went to the fabric store with someone else, and not only chose one that I could breathe freely through, but also one that preserves the sound of my voice well when I speak through it. I figure that is a pretty decent fabric store test of AT.


Hopefully I didn't miss this from before: how are you removing reflections from the analysis? Tight (really tight) windows?


And did you use any sort of reflective facing on your chunk-style corner bass dampers?

I placed kraft paper on the front of my bass traps to block mid-hi freq:

Bottom corner traps:



Upper corner traps:
 
#101 ·

Quote:
Originally Posted by localhost127 /forum/post/20415676


looks great! did you go with 24" or 34" faced corner chunks?


As someone once said "Go big or go home!"


Fortuantely I had room for the 34" x 24" x 24" chunks in back of my 2nd row seats, can I say they are big!

And the lower's while "moveable" the OC705 is very heavy.

50lbs for the OC705 + 2 boards / 3 thd rods gotta put each one in the 65lb zone.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top