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PostPosted: Fri Mar 13, 2020 6:24 am 
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Is this a helmholtz or a bass trap? It has been called both.

Anyway, whatever is part of the bass trap, yes.

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PostPosted: Fri Mar 13, 2020 4:50 pm 
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Is this a helmholtz or a bass trap? It has been called both.

Anyway, whatever is part of the bass trap, yes.

From what I understand, it's a Helmholtz in the corner of a room. So that's why I'm trying to clarify the design.

Greg

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PostPosted: Sat Mar 14, 2020 7:49 pm 
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Hi John,

I wonder if you could confirm that the depth of the timber uprights vary in your design? You only mentioned 2x6 but the drawing has differing depths. Are the different depths crucial?

Also, what do you mean by "leaving the centre slots til last?"

Many thanks,
Paul

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PostPosted: Wed Mar 18, 2020 5:08 am 
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This might be a stupid question, but should I seal the perimeter around the bass trap where it meets the wall to close any air gaps, or is that unnecessary?

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PostPosted: Wed Mar 18, 2020 6:06 am 
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This might be a stupid question, but should I seal the perimeter around the bass trap where it meets the wall to close any air gaps, or is that unnecessary?

If it is indeed a Helmholtz design, then yes, seal it.

Greg

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PostPosted: Thu Mar 19, 2020 4:03 am 
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If it is indeed a Helmholtz design, then yes, seal it.

That's what my understanding is from what I'm told on this forum. With all of the different inputs, I am getting a bit confused as to the right way to go with this and I am standing by for some confirmation as which way to go, primarily about the internal insulation, before I install the three heavy sections. I hope John can clear things up soon.
I will go ahead and seal around the trap. Couldn't hurt it anyway! :)
Thanks, as always for your help.

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PostPosted: Thu Mar 19, 2020 8:26 am 
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If I can ask, where is the "design" you based this on?

It is true a helmholtz is sealed. It is also true that the throat and spacing are specific to the frequencies you are targeting.

And...low frequency trapping is almost always broad band. A helmholtz is designed for specific frequency range that is not broadband as most bass trapping is.

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PostPosted: Thu Mar 19, 2020 9:18 am 
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xSpace wrote:
And...low frequency trapping is almost always broad band. A helmholtz is designed for specific frequency range that is not broadband as most bass trapping is.


John provided guit-picker a design of a large corner helmholtz design.
It is a true helmholtz, using a slot design in the same way John's inside out walls work.
The timber is standard construction timber and can range from 4 x 2 to 10 x 2. It is arranged to provide some non numeric scattering from the front face.

John didn't set a specific amount insulation to put in, but said to place some offcuts in the cavity before fitting the middle timbers.

John said he usually places it over a corner in an inside out wall, so his standard design would have insulation in the walls themselves exposed to the inside of the helmholtz. He lines the back face of the timbers in the helmholtz with fabric.

This fabric combined with the wall insulation is what dampens the resonance.

Although research suggests having the insulation right in or near to the slots would be more efficient, John has found the design very effective with his method, and it's very easy for them to construct.

John's suggestion to leave the middle open and just place insulation in the cavity is just for ease of construction and can be tuned by measuring and removing the middle timbers again to add/remove insulation.

The walls themselves are completely sealed, then when the timbers are placed over the corner, they are the slots. You just need to seal where it meets the wall/floor/ceiling.

Also, by being placed over the corner of a room you will get low/low-mid frequencies targeted.
There's no accurate way of estimating these frequencies, but a nice reduction with quite a wide Q should be achieved.

John says it works great and uses it in all his designs 8)

I've installed similar designs in my studio but haven't been able to measure yet due to doing crazy over time (remotely) as we have a software release due in a week or so at work, that is running behind.
I hope to have measurements with you all... soon :horse:

Dan

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PostPosted: Thu Mar 19, 2020 10:14 am 
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Quote:
If I can ask, where is the "design" you based this on?

Here is a post John has made about the design:

viewtopic.php?f=2&t=12365&p=135094#p135094

--------------------------------------------------------

Also, it seems to tie in with John and Thomas Barefoot's design mentioned here:

http://johnlsayers.com/phpBB2/viewtopic ... 3&start=15

--------------------------------------------------------

And I can't link to the direct post for some reason, but it's the 6th post down on this thread (you can see the Helmholtz device in the corner on the picture that John posted):

http://johnlsayers.com/phpBB2/viewtopic ... 23&start=0

--------------------------------------------------------

And Thomas comments on it here:

https://johnlsayers.com/phpBB2/viewtopic.php?f=3&t=1775

Greg

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PostPosted: Thu Mar 19, 2020 10:39 am 
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This is post on this thread that John showed the design:

viewtopic.php?f=2&t=19690&start=105#p151926

Dan

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PostPosted: Thu Mar 19, 2020 11:37 am 
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John Sayers designs have been an effective use of combating acoustic contamination over many decades.

That said...it has to be like the picture he drew. If you think yours is like what those links suggest, good job.

I will watch as it unfolds.

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PostPosted: Sat Mar 21, 2020 4:02 pm 
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We are about to start building our hangers for the front soffit area.... at last! On Stuart's good advice, I have designed the whole array for 1/2" Homasote centers and 2" OC-703 on either side like this:
Attachment:
SoffitHangers.jpg

My partner on this project located a supply of Knauf ECOSE 1" 3lb panels rather than OC-703. These panels we are able to get for FREE! It was a cancelled order and my partner managed to get it. He made a sample section for me by putting together two 1-inch layers on either side like this:
Attachment:
20200320_221111.jpg

I looked up the Sound Absorption Coefficients for both:
Attachment:
20200319_223249.jpg

I see that they are both in the same ballpark, but as one would expect, the biggest difference is in the lower frequency (125Hz with ECOSE = 0.08 vs OC-703 = 0.11). My intention is to take advantage of this free material and proceed with building the hangers in the front soffit with them unless someone vehemently convinces me not to.
Do you guys agree?


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PostPosted: Sun Mar 22, 2020 3:18 am 
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Acoustic hangers don't absorb low frequencies simply by absorption, so you can't really base it off of the absorption coefficients.

Owens corning is only really recommended because they tend to have acoustic data on it and people have used it and it works.

There's nothing magical about it though. Rockwool should be fine. The main thing is about having a similar gas flow resistivity. But that's not usually available in the data sheets, so it has to be estimated based on kg/m3.

The Rockwool you found should be fine (great job getting it for free though!)

I don't think most studio designers recommend only owens corning. Unless they're really particular.

They can't estimate the effects accurately, so it needs measuring after it's installed anyway.

Dan

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PostPosted: Sun Mar 22, 2020 4:30 am 
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Guit-picker wrote:
We are about to start building our hangers for the front soffit area.... at last! On Stuart's good advice, I have designed the whole array for 1/2" Homasote centers and 2" OC-703 on either side like this:
Attachment:
SoffitHangers.jpg

My partner on this project located a supply of Knauf ECOSE 1" 3lb panels rather than OC-703. These panels we are able to get for FREE! It was a cancelled order and my partner managed to get it. He made a sample section for me by putting together two 1-inch layers on either side like this:
Attachment:
20200320_221111.jpg

I looked up the Sound Absorption Coefficients for both:
Attachment:
20200319_223249.jpg

I see that they are both in the same ballpark, but as one would expect, the biggest difference is in the lower frequency (125Hz with ECOSE = 0.08 vs OC-703 = 0.11). My intention is to take advantage of this free material and proceed with building the hangers in the front soffit with them unless someone vehemently convinces me not to.
Do you guys agree?


If you have enough of that insulation then you could always use 2 layers per side. My hangers are built from even lower density, lower GFR insulation but has a thickness of 150mm per side. Lower GFR and density but at a greater thickness than higher density/GFR will usually perform better in the low end of the spectrum.

Paul

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PostPosted: Sun Mar 22, 2020 6:56 am 
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Thanks Paul and Dan, I'm forging ahead! :yahoo:

Quote:
If you have enough of that insulation then you could always use 2 layers per side.

Yes, that's exactly the plan (see photo above). Thanks for looking out for me! :)

-Ron

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