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How to make absorbents nice and square? Effects Pedals, Units & Accessories
Old 19th December 2010
  #1
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Bjorn Omholt's Avatar
 

How to make absorbents nice and square?

Can anyone tell how to make the absorbents nice and square in the front without using a frame in the front?

The corners in the front of mine become somewhat round as the fabric is stretched. I tried some corner hardener between the rockwool and fabric, which worked, but they were also clearly visible on the front and it really looked worse.
CRH4
I don't know if the idea was to use the corner hardened in between the rockwool material, but that didn't work when I tried it.

I don't want a reflective frame on the front.
Old 19th December 2010
  #2
Gear Addict
 

What density Rockwool?

705 Glasswool is pretty rigid. Perhaps use a thicker fabric that doesn't need to be pulled so taut.
Old 19th December 2010
  #3
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by Sebg View Post
What density Rockwool?

705 Glasswool is pretty rigid. Perhaps use a thicker fabric that doesn't need to be pulled so taut.
60 kg/m3 is what I've used. They now sell the same product in 70 kg/m3 which I haven't tried yet.

With acoustic fabric that stretches, like DMD from Acousticmac, it becomes more of a problem then using standard cotton. The nice thing about DMD though, is that it's more transparent then standard cotton from your local store. I've measured.
Old 20th December 2010
  #4
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Glenn Kuras's Avatar
As the other poster said I would stick with 705 if no frame to the front.
Old 21st December 2010
  #5
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amishsixstringe's Avatar
 

I use a regular iron for ironing clothes and make a crease where the fabric goes over the corner of the fiberglass. Works nice.

Neil
Old 21st December 2010
  #6
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I just made a bunch and made a wood frame for them. Super sharp edges, crisp look, easy to mount. Now queue everyone to yell at me for decreasing absorption from extreme side angles....
Old 21st December 2010
  #7
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my first traps still became a little rounded on the edges (OC703) when making sure the fabric was nice and tight.

i bought a few of these
CRH4

and it worked great..but id recommend trying your local hardware store for those/equivalent first...should be much cheaper.
Old 21st December 2010
  #8
SAC
Registered User
 

Quote:
Originally Posted by rcb4t2 View Post
I just made a bunch and made a wood frame for them. Super sharp edges, crisp look, easy to mount. Now queue everyone to yell at me for decreasing absorption from extreme side angles....

Congrats - by framing them you increased the edge losses due to diffraction ....heh



Unless you are making mega-thick porous absorbers where the edge surface area is large relative to the plane surface area (and if you are we can then wonder why...), its long past time for the frame-no frame debate to die.
For broadband absorbers 4" or less thick, use whichever you like and relax.

I can only imagine what going to a fancy restaurant must be like with quite a few, as they spend the meal debating what to tip over a penny.

Either that or we should bring back topics on how to EQ early reflections.
Old 21st December 2010
  #9
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by SAC View Post
Unless you are making mega-thick porous absorbers where the edge surface area is large relative to the plane surface area (and if you are we can then wonder why...), its long past time for the frame-no frame debate to die.
For broadband absorbers 4" or less thick, use whichever you like and relax.

I can only imagine what going to a fancy restaurant must be like with quite a few, as they spend the meal debating what to tip over a penny.

Either that or we should bring back topics on how to EQ early reflections.
I've used absorbents with frames for a while one sidewalls. Have been dealing with reflections arriving at 5 ms. Guess where they came from? The frames.

Some humility in life is good.

localhost127:
Can you post some pictures of yours (the front) with the corner hardeners? As mentioned in the first post, I've tried these but they simply became bulky on the outside.
Old 21st December 2010
  #10
SAC
Registered User
 

Then one might assume that they are either misplaced, or that they are not large enough to adequately cover the incident region.

You might want to use the ETC to better place them - especially as the incident region is not generally larger than a standard panel as the region that directs reflected energy to a particular spot is not large. (Not to mention the angles of the frame relative to incident energy and how that become reflected to the listening spot...as well as the amount of energy contained in frequencies that would reflect off a ~3/4 inch wide strip - (especially as any reflection will be a very narrowly focused beam!)- which should not be placed in the region of incidence anyway.

And moving the absorber does not resolve the issue of what would necessarily be a extremely highly focused reflection????? :S

In fact, the reflectivity of the assumed 'acoustically transparent'(sic) covering is a much greater issue !!!

Humility is nice, but applied knowledge solves problems.

In relatively thin panels, hard frames add losses due to edge diffraction in near equal proportions as exposed surface area.
Old 21st December 2010
  #11
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by SAC View Post
You might want to use the ETC to better place them - especially as the incident region is not generally larger than a standard panel as the region that directs reflected energy to a particular spot is not large.
Believe me, I have done that. Have moved them around a lot and measured. No more frames on close walls for me.
But let's stick to the topic.
Old 21st December 2010
  #12
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amishsixstringe's Avatar
 

Quote:
Originally Posted by bwo View Post
Believe me, I have done that. Have moved them around a lot and measured. No more frames on close walls for me.
But let's stick to the topic.
Your panel is reflective. There's no way your frame caused that reflection. If you moved the measurement mic or the panel even 1/2", the reflection should go away if was being caused by the frame. The cloth that covers your absorber is reflecting at some high frequencies.

I think the topic up to this point has pretty much been covered.

Neil
Old 21st December 2010
  #13
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by amishsixstringe View Post
Your panel is reflective. There's no way your frame caused that reflection. If you moved the measurement mic or the panel even 1/2", the reflection should go away if was being caused by the frame. The cloth that covers your absorber is reflecting at some high frequencies.

I think the topic up to this point has pretty much been covered.

Neil
You can't take a look at the two pictures of the sidewalls. I wasn't able to get rid of the reflection moving the panels. When I however tried panels without a frame in the front in place of these, it disappeared right away. The SPL meter in the pictures were not used for measurements by the way.
Attached Thumbnails
How to make absorbents nice and square?-room-003-large-.jpg   How to make absorbents nice and square?-room-004-large-.jpg  
Old 21st December 2010
  #14
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Quote:
Originally Posted by bwo View Post

localhost127:
Can you post some pictures of yours (the front) with the corner hardeners? As mentioned in the first post, I've tried these but they simply became bulky on the outside.

when not using corner hardeners:


using two 4" hardeners (8" total --- 6" OC703 + air gap backing frame)

sides



top


if you do that, it's also good to use some spray adheisive (same stuff used to bond 2 or more OC703 batts together) to bond the corner hardeners to the OC703 so it wont move around when you're wrapping the fabric.
Old 22nd December 2010
  #15
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amishsixstringe's Avatar
 

Did you take the same absorbers out of the frames for it to not reflect? I'm saying that you changed more than just the frame. If you used different fabric on the face of the new panels, you changed multiple things, therefore proving nothing.

Just a thought.

Neil
Old 22nd December 2010
  #16
Gear Maniac
 

the easiest way that I have found to keep the shape in the corners is to use something like pvc cement on the corners before I wrap them. Let it cure until it's hard, and then wrap your panel. Wear a mask.. That stuff has a strong odor
Old 22nd December 2010
  #17
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Old 22nd December 2010
  #18
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Bjorn Omholt's Avatar
 

Thanks localhost127 for the last picture. That explains it all......
Ordering more corner hardeners and will place them correctly.
Old 22nd December 2010
  #19
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amishsixstringe's Avatar
 

Won't the corner hardeners reflect high frequencies in the same manner that your frames did? Just because there is fabric covering them doesn't mean they aren't reflective. Granted, they are smaller...

Neil
Old 22nd December 2010
  #20


I used 1/2" Poplar boards to build frames for clouds. I'm sure it reflected some energy, but I wasn't going for full anechoic ceilings.

They sure were a lot prettier than 2 foot pyramids....




-tINY

Old 22nd December 2010
  #21
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Bjorn Omholt's Avatar
 

Quote:
Originally Posted by amishsixstringe View Post
Won't the corner hardeners reflect high frequencies in the same manner that your frames did? Just because there is fabric covering them doesn't mean they aren't reflective. Granted, they are smaller...

Neil
They don't cover the front like the frames, but yes, they will reflect some. I'll probably not use them for panels on sidewalls, but other places.
Old 23rd December 2010
  #22
SAC
Registered User
 

Let's see...

A 1/2" surface will be reflective at frequencies above 27,008 Hz.

While a 3/4" surface will be reflective for frequencies above 18,005 Hz.

The acoustical impedance of the fabric covering, especially with increasing incidence, is a much greater factor with which to be concerned.
Old 23rd December 2010
  #23
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Bjorn Omholt's Avatar
 

What's the best way to measure the fabric and what graph is most appropriate to look at?

I did measure two different kinds of fabric. Mic about 1 m from the midrange and treble of speaker and fabric in between. Taken in a environment with much dampening, but far from anechoic.

Blue: No fabric
Purple: Acoustic fabric
Green: Cotton fabric from IKEA
Attached Thumbnails
How to make absorbents nice and square?-1.jpg   How to make absorbents nice and square?-2.jpg   How to make absorbents nice and square?-etc-ingen-vs.-ak.st.jpg   How to make absorbents nice and square?-etc-ingen-vs.-ikea.jpg  
Old 29th July 2018
  #24
Here for the gear
I've been experimenting with the "No-Frame" edge coating from BuyInsulationProduct dot com. The promo pictures suggest covering the whole side and equiv. width on top, but that's overkill. I lightly paint on about 3/4" on front surface and over the side about the same. A bit extra on the corners. This gives a very rigid edge to pull the fabric over, maintaining the crisp shape without sacrificing too much absorption. Biggest difference in the last 10 years of building panels is the switch to speaker fabric. Near 100% acoustic transparency. Was using cotton/poly for a while and various performance fabrics (burlap type fabrics are just too ugly for my taste, Guifford is expensive, but haven't tried yet). The "No-Frame" is pricey too - around $32/QT with shipping - so looking for another product. Have started using a spray enamel, which dries in an hour, vs. 24 for the No-Frame. It's ok, but no where near as sturdy as the No-Frame. Trudging on. PS, I've built around 70 panels, and each round gets better. Practice is like that.
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