Salem Oregon conference center studio

Is this a helmholtz or a bass trap? It has been called both. Anyway, whatever is part of the bass trap, yes.

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

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

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?

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

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.

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.

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

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

This is post on this thread that John showed the design: viewtopic.php?f=2&t=19690&start=105#p151926 Dan

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.

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: 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: I looked up the Sound Absorption Coefficients for both: 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?

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

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:

Not preserved: 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:

Not preserved: 20200320_221111.jpg

I looked up the Sound Absorption Coefficients for both:

Not preserved: 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

Thanks Paul and Dan, I'm forging ahead! :yahoo:

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

My project partner will be building up the hanger panels. He has the idea to mount each section of hangers by "stringing" them across horizontal bars like this: I have been figuring something more like this, using zip ties (which are very strong and adjustable), which would allow them to freely swing like this: My concern is that the first method may hinder the panel's function, being to "stiffly" mounted. What do you think? Am I right? -Ron

I have mounted the first of three sections of the rear hemholtz resonator / bass trap in the rear: This is the ugly side up, when I couldn't flip it over (~250 lbs) without the help of four 20-year-old volunteers: We hauled it into the control room and got it installed. I'm pretty jazzed: I am almost done with section two. I am still in a quandary over what exactly should go behind it for insulation before I can install the 3rd section. There seems to be no consensus in our discussions. Can I get some help deciding the right thing? :horse: :wink: Also, some input on my last post is needed about hanging methods before my project partner starts up building them. I don't want him to go off in the wrong direction. :shock: I'm getting into some really interesting phases now and things are stepping up in speed. I have more time lately to work on the studio since my job hours are reduced, due to the virus issue. Stay safe and healthy out there! -Ron

I would use zip ties to hang the hangers, this method was recommended to me by John and it’s how I did it, ended up working well. Paul

Ron, Three things: 1. I love your signature. 2. You should be jazzed about the resonator. It looks unbloody real! 3. Zip ties would be better than the other method. Greg

Yo, thanks you guys! :-) I feel assured now! :) So thankful for this forum! :-) What about insulating inside the bass trap? I have heard three ways: 1. Fill it up with Roxul 2. Line the back with Roxul and put a thin layer of fiberglass along the rear of the timber 3. Just throw the out cuts of Roxul in there (Not sure if that meant fill it up or what). -Ron

Guit-picker wrote:

Yo, thanks you guys! :-) I feel assured now! :) So thankful for this forum! :-) What about insulating inside the bass trap? I have heard three ways: 1. Fill it up with Roxul 2. Line the back with Roxul and put a thin layer of fiberglass along the rear of the timber 3. Just throw the out cuts of Roxul in there (Not sure if that meant fill it up or what). -Ron

If it was me, I’d cover the walls, floor and ceiling behind and then loosely fill the cavity with low density fibreglass. Paul

Thanks Paul! 8) Well, as of last night, section two of three has been installed..... after re-assembling about 3 times to get it right. :roll: It will be a while until the 3rd section goes in. I have to insulate and then start from raw materials on the lumber. I had to wait to see what the remaining heights and widths would be (because of tolerances adding and slanted top, etc) before I could start cutting out the lumber and veneer and such: -Ron

If it was me, I’d cover the walls, floor and ceiling behind and then loosely fill the cavity with low density fibreglass.

I wonder how hangers back there would do :?

It will be a while until the 3rd section goes in. I have to insulate and then start from raw materials on the lumber. I had to wait to see what the remaining heights and widths would be (because of tolerances adding and slanted top, etc) before I could start cutting out the lumber and veneer and such:

Ron, it looks so good. Are you able to take a nice close up picture for us to see the finish? Also, did you joint any of the lumber to get a nice straight look? Greg

Thanks Greg!

Are you able to take a nice close up picture for us to see the finish? Also, did you joint any of the lumber to get a nice straight look?

I have been away from the project for about 3 days - between work and just had a team of guys replace ALL my windows and patio door to the tune of $35,000 (the good stuff). I did not joint any of the lumber. I had a tough time finding decent lumber and bought the straightest and driest I could find. I had to pick through it, looking for straightness and a good edge to support veneer. Ironically, the kiln-dried that I COULD find was worse than the rest! That being said, I had to deal with some warping effects. I used spacers to help line them up and a lot of screws and clamps in the process. I will take a close up of the birch surface next time out there - possibly tomorrow. As I build the last section in the next week or two, I will try to snap more pics and share kind-of a step-by-step of the method used. This isolation thing with the Covid-19 has allowed me more time in some areas and in others it's been a hindrance, being isolated and working alone. Be careful - stay healthy! -Ron

As promised, here is a closeup of the wood veneer finish on the rear Helmholtz / bass trap. I made the resolution as high as I dare go, according to forum rules: I cut the lumber to size for the last third of the trap. I am now prepping for the addition of the veneer. I had to order an additional 4/8 sheet of birch veneer to finish. When it came, it looks quite different. It has much more figure and a bit darker :shock: . That means that four of the pieces will look different than the others. I hope it doesn't stick out like a sore thumb. I wish the first veneer looked like the new! :roll: -Ron