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Author Topic: Resonator Type  (Read 7354 times)

Greg Reierson

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Resonator Type
« on: January 27, 2009, 01:11:12 pm »

Hello all,

I'm trying to improve the LF response of my room. It's 18x15x11. The corners have built-in floor to ceiling traps that are 4' wide, using 2" 702, 2" gap, 2" 703, 2" gap - four layers deep to the corner. The rear wall has a 8'x 9" 'diffractal' type diffusors. The monitors are PMC MB1 with the woofers about 30" off the front wall. I sit WAY too close to the center of the room at 9.5' from the front wall, but that's just the way this room needs to work.

The problems are bumps at 60Hz (length mode) and 105Hz (height mode). I'd like to build some traps to deal with these LF bumps. There is a huge pressure build up right between the speakers from the floor to the ceiling at 105Hz, so I am considering placing a slat absorber there. There is also a huge pressure build up between the rear diffusor and the ceiling at 60Hz that could hold a large Helmholtz resonator.

The question comes down to type of device and size required to make a significant difference. I have a space about 5' wide by 1' deep by 8' high for the 105Hz device. I also have about 9' wide by 2.5' high by 1' deep for the 60Hz device. What makes the most sense, and, where can I find detailed instruction on how to build it?

A second consideration is the rear wall. I have an equipment closet behind that wall. Might it make sense to make that wall more porous to LF and turn the closet into a bass trap?

Any ideas welcome.

Thanks!

GR
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djwaudio

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Re: Resonator Type
« Reply #1 on: February 14, 2009, 05:51:39 pm »

Can anyone help Greg? He's really a good guy!
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Thomas Jouanjean

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Re: Resonator Type
« Reply #2 on: February 15, 2009, 03:55:17 am »

Pics would help...

Sounds to me resonators are not what you need. You need porous absorbers and membranes. Resonators placed just out there in the room would re-emit too much.
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Thomas Jouanjean
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Ethan Winer

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Re: Resonator Type
« Reply #3 on: February 15, 2009, 01:35:01 pm »

Greg Reierson wrote on Tue, 27 January 2009 13:11

The corners have built-in floor to ceiling traps that are 4' wide, using 2" 702, 2" gap, 2" 703, 2" gap - four layers deep to the corner.


Those traps are definitely large enough, but having layered gaps is not a good idea. Any chance you can redo the traps to be solid rigid fiberglass?

Quote:

The rear wall has a 8'x 9" 'diffractal' type diffusors.


The rear wall is very important for bass trapping. If you have any bare wall or corner space, you should also fill those areas with large thick rigid fiberglass traps. For a room that size, this will work better than tuned traps IMO.

--Ethan

Thomas Jouanjean

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Re: Resonator Type
« Reply #4 on: February 15, 2009, 02:48:32 pm »

Ethan Winer wrote on Sun, 15 February 2009 12:35

 traps are definitely large enough, but having layered gaps is not a good idea. Any chance you can redo the traps to be solid rigid fiberglass?


Air gaps are actually very good if you can afford the (albeit small extra) space - and if it's a calculated gap. Successive changes of impedance can be very beneficial - we use this technique often. Mixing different impedances is good too.

I would not recommend "solid rigid fiberglass" but semi-rigid Rockwool of about 60/70kg/m
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Thomas Jouanjean
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Bruno Gouveia

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Re: Resonator Type
« Reply #5 on: February 15, 2009, 05:18:01 pm »

Thomas Jouanjean wrote on Sun, 15 February 2009 19:48



I would not recommend "solid rigid fiberglass" but semi-rigid Rockwool of about 60/70kg/m

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Re: Resonator Type
« Reply #6 on: February 15, 2009, 07:30:41 pm »

But in his studios it isn't Rockwool but this product called Arkobel, an elastomer, that look like this: http://www.isolusa.pt/repre/arkobel/2.jpg

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Re: Resonator Type
« Reply #7 on: February 15, 2009, 08:35:42 pm »

Yes but Arkobel varies between 60 and 250 kg/m3 so.... lot to choose ! Smile

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Thomas Jouanjean

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Re: Resonator Type
« Reply #8 on: February 16, 2009, 02:29:39 am »

Bruno Gouveia wrote on Sun, 15 February 2009 16:18

That's how bass is trapped in Phil Newel's studios and it works!!!
Smile


Which one do you mean?

Arkobel seems to be compressed industrial foam in shreds, which is kept and compacted together by glue. I Don't like it very much...


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Thomas Jouanjean
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Bruno Gouveia

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Re: Resonator Type
« Reply #9 on: February 16, 2009, 03:39:29 am »

Thomas Jouanjean wrote on Mon, 16 February 2009 07:29



Arkobel seems to be compressed industrial foam in shreds, which is kept and compacted together by glue. I Don't like it very much...





Yes, Arkobel is something like that. I don't know the exact density he uses but it should depends on the dimensions of the conglomerate panels. Why don't you like it very much? Arkobel is also used in-between walls to decouple them and improve a lot sound isolation, and it also works very well!

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Re: Resonator Type
« Reply #10 on: February 16, 2009, 06:25:41 am »

Bruno Gouveia wrote on Mon, 16 February 2009 02:39


Yes, Arkobel is something like that. I don't know the exact density he uses but it should depends on the dimensions of the conglomerate panels. Why don't you like it very much? Arkobel is also used in-between walls to decouple them and improve a lot sound isolation, and it also works very well!




I never used the "Arkobel" brand, maybe it is different?

I tried "similar" stuff, and was never happy with it. To decouple I go straight to Sylomer or Merformer & Co these days - maybe spring systems now and then when only those can be used.

Before I found Homatherm, when looking for viable alternatives to Rockwool, I tried the industrial agglomerated foam thing which I got from CARDA near Brussels, seriously heavy stuff in general (like Andre said, it can come in very dense bats, couldn't lift it on my own!) which I did try in various densities, and after playing with it and getting some more info about it - I just dropped it and didn't look back so far. No use for it in decoupling schemes, nor in room acoustics correction.

BTW, so which did you mean in Newel's technique, the air gap?
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Thomas Jouanjean
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Thomas Jouanjean

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Re: Resonator Type
« Reply #11 on: February 16, 2009, 06:36:04 am »

Greg Reierson wrote on Tue, 27 January 2009 12:11

Hello all,

I'm trying to improve the LF response of my room. It's 18x15x11. The corners have built-in floor to ceiling traps that are 4' wide, using 2" 702, 2" gap, 2" 703, 2" gap - four layers deep to the corner. The rear wall has a 8'x 9" 'diffractal' type diffusors. The monitors are PMC MB1 with the woofers about 30" off the front wall. I sit WAY too close to the center of the room at 9.5' from the front wall, but that's just the way this room needs to work.

The problems are bumps at 60Hz (length mode) and 105Hz (height mode). I'd like to build some traps to deal with these LF bumps. There is a huge pressure build up right between the speakers from the floor to the ceiling at 105Hz, so I am considering placing a slat absorber there. There is also a huge pressure build up between the rear diffusor and the ceiling at 60Hz that could hold a large Helmholtz resonator.

The question comes down to type of device and size required to make a significant difference. I have a space about 5' wide by 1' deep by 8' high for the 105Hz device. I also have about 9' wide by 2.5' high by 1' deep for the 60Hz device. What makes the most sense, and, where can I find detailed instruction on how to build it?

A second consideration is the rear wall. I have an equipment closet behind that wall. Might it make sense to make that wall more porous to LF and turn the closet into a bass trap?

Any ideas welcome.

Thanks!

GR



I had a look at your website - can you describe what is between you diffusor's back and the studio shell? Any LF treatment in there?

Do you have somekind of plans of your room? It's really hard to figure out precisely what you need just from web pages and what you describe.

Sounds to me like you should find a designer to design an upgrade to clean up the LF problem properly.
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Thomas Jouanjean
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Bruno Gouveia

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Re: Resonator Type
« Reply #12 on: February 16, 2009, 10:22:01 am »

Thomas Jouanjean wrote on Mon, 16 February 2009 11:25

Bruno Gouveia wrote on Mon, 16 February 2009 02:39


Yes, Arkobel is something like that. I don't know the exact density he uses but it should depends on the dimensions of the conglomerate panels. Why don't you like it very much? Arkobel is also used in-between walls to decouple them and improve a lot sound isolation, and it also works very well!




BTW, so which did you mean in Newel's technique, the air gap?


He uses Arkobel or something similar attached with screws to conglomerate or MDF panels that are mounted in an array normally in the back wall of the control room. I've been at two studios designed by him here in Porto, but I think he has more. I think you can spot the array at the map at this site: http://boomstudios.pt

But of course everything you said makes perfect sense and Newel is also a man of science so he obviously uses the techniques you described!

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Re: Resonator Type
« Reply #13 on: February 16, 2009, 10:27:02 am »

Can you describe more about Sylomer or Merformer?

Steve Hudson

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Re: Resonator Type
« Reply #14 on: February 16, 2009, 10:39:03 am »

Ethan Winer wrote on Sun, 15 February 2009 12:35



The rear wall is very important for bass trapping. If you have any bare wall or corner space, you should also fill those areas with large thick rigid fiberglass traps. For a room that size, this will work better than tuned traps IMO.

--Ethan


My control room is 23.5' x 16' x 8.75'. We installed two large (6'x4') traps with 6" of 703 and a five inch air gap between the 703 and the rear wall. Would we get better l.f. trapping by eliminating the air gap and installing 4 more inches of 703? Or could we install some sort of membrane trap behind the 703 for the really low freqs?
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Re: Resonator Type
« Reply #15 on: February 16, 2009, 01:40:58 pm »

Steve Hudson wrote on Mon, 16 February 2009 10:39

We installed two large (6'x4') traps with 6" of 703 and a five inch air gap between the 703 and the rear wall. Would we get better l.f. trapping by eliminating the air gap and installing 4 more inches of 703?


A single gap as you describe is good, and the difference after filling the gap would be minimal. Yes, it will help a little! But only a little. Much better would be to apply the extra four inches of 703 on the outside of the panel. Then the absorption is 10 inches thick, and the air gap helps even more.

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Re: Resonator Type
« Reply #16 on: February 16, 2009, 02:24:32 pm »

Thanks, Ethan. We'd have to rebuild the frames if we were to add panels to the front of the existing ones.
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Thomas Jouanjean

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Re: Resonator Type
« Reply #17 on: February 16, 2009, 03:41:12 pm »

Bruno Gouveia wrote on Mon, 16 February 2009 09:27

Can you describe more about Sylomer or Merformer?


Good example of application using Sylomer:

http://recforums.prosoundweb.com/index.php/mv/msg/24611/0/0/ 19234/

Bench design system applied to decoupling the whole studio shell, from under 10Hz.
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Thomas Jouanjean
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Re: Resonator Type
« Reply #18 on: February 16, 2009, 03:47:45 pm »

Bruno Gouveia wrote on Mon, 16 February 2009 09:22


He uses Arkobel or something similar attached with screws to conglomerate or MDF panels that are mounted in an array normally in the back wall of the control room. I've been at two studios designed by him here in Porto, but I think he has more. I think you can spot the array at the map at this site: http://boomstudios.pt

But of course everything you said makes perfect sense and Newel is also a man of science so he obviously uses the techniques you described!


Thanks for the details! Interesting technique...

Nice studio! Variable acoustics in the LR Smile

Though visible ceiling in CR seems quite low for a room that size, do you happen to know which height... 2.60m, 2.70?

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Thomas Jouanjean
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Greg Reierson

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Re: Resonator Type
« Reply #19 on: February 16, 2009, 05:45:49 pm »

Thanks Dana! I almost forgot about the thread...

Thomas Jouanjean wrote on Mon, 16 February 2009 05:36

I had a look at your website - can you describe what is between you diffusor's back and the studio shell? Any LF treatment in there?


The empty wells on the back side of the diffusor are filled with fiberglass. The diffusor itself is directly in front of the rear wall which is two layers of 5/8" gyp board on metal studs about 24 IOC, 6" space with fiberglass, then another two layers of 5/8" gyp board.Looking back I wish I had build something into that wall. It's still an option. Just need to know what direction to take.

Quote:

Sounds to me like you should find a designer to design an upgrade to clean up the LF problem properly.


That will be my next step. I just want to understand the problem a bit better beforehand.

Thanks,


GR
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Re: Resonator Type
« Reply #20 on: February 17, 2009, 04:00:37 am »

Thomas Jouanjean wrote on Mon, 16 February 2009




Nice studio! Variable acoustics in the LR Smile

Though visible ceiling in CR seems quite low for a room that size, do you happen to know which height... 2.60m, 2.70?




Yes, maximum 2,80m to the cloth. There's office spaces above. Also there is a big hollow space for Newel's loudspeakers that aren't installed, and that space re-emits... Also the room is so dry that only at the sweet spot you can hear something really happening.  But the live room is great, 110m

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Re: Resonator Type
« Reply #21 on: February 17, 2009, 08:27:05 am »

Behind the 2.80 m there's over 1 m of rockwool I have been told
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Greg Reierson

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Re: Resonator Type
« Reply #22 on: February 19, 2009, 04:35:11 pm »

Thomas Jouanjean wrote on Sun, 15 February 2009 02:55

Pics would help...

Sounds to me resonators are not what you need. You need porous absorbers and membranes. Resonators placed just out there in the room would re-emit too much.


I'm a bit confused by that. When are resonators appropriate?


GR
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Re: Resonator Type
« Reply #23 on: February 19, 2009, 05:21:08 pm »

Greg Reierson wrote on Thu, 19 February 2009 15:35


I'm a bit confused by that. When are resonators appropriate?


GR


When there are no other options. They're usually buried deep in the room structure, behind the rest of the treatment.
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Thomas Jouanjean
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Re: Resonator Type
« Reply #24 on: March 23, 2009, 08:05:33 pm »

Progress report:

After taking everyone's comments into consideration I decided to tackle my back wall. I have the luxury of not needing to contain the LF in my room. Low end leakage doesn't bother anyone and there is no significant source of LF outside of the room to bother me. I removed the inner gyp board wall and added a huge amount of porous trapping above and to the sides of my rear diffusor. The combination of more LF leakage and trapping (the trap is now about 5' deep at its deepest point above the rear diff) has made a huge difference. The 60Hz bump is gone and the 105Hz bump is much better. No resonators needed!

The next step was to work on speaker placement optimization. With all of the LF changes, the apparent LF in the room was decreased. I assume the modal ringing of the room had been creating a false sense LF power, even though I knew it wasn't right. Now that the ring is gone, the LF is more even, but not as well reinforces as before.

Small speaker placement moves can make surprisingly large responses changes. After a few hours of moving the big PMCs a couple inches at a time, I found what seems to be the flattest LF response with the fewest peaks and dips. The RPlusD software (the update to ETF5) made the process of comparing many speaker locations a snap. If you need a measurement tool but don't need to make a career out of it, RPlusD seems to have everything you need.

I've been listening all day and I have to say I'm extremely happy with the results of a weekend's work. Thanks to everyone who encouraged me to do it the right way!


GR





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Thomas Jouanjean

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Re: Resonator Type
« Reply #25 on: March 24, 2009, 09:31:19 am »

Excellent!  Smile
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Thomas Jouanjean
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Re: Resonator Type
« Reply #26 on: March 25, 2009, 10:28:21 pm »

Awesome.. glad to hear it!
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