Salem Oregon conference center studio

I am still unclear about how to apply the calculator in the corner application

For a Helmholtz design, just realize that the distance in the equation is the distance from the slot to the wall. Like John said, because it is in a corner, each slot will have a different distance to the wall (with the max distance being the slot in the middle of the device). This is awesome because it makes the device cover a larger range of frequencies. Greg

Here is what I drew up from what I could ascertain from John's bass trap design that he graciously offered. I am using dimension lumber, starting with 2x4" on the outsides, switching to 2x8 and finally two pieces of 2x12 in the middle. These are the dimensions his drawing looks like (although he only specifically mentioned 2x6). This is going to be REALLY heavy, but that's no problem. I intend on facing the exposed areas with birch skins (I have experience with this and it's not hard at all), which should look great! I will trim the outside with solid birch for appearance. I did some calculating and it looks like this will be close to 1/3 the price of the hanger design! It should be easier to build too and in the end look better. :o Here is another view from above with the framing removed for clarity: So to weigh the difference: ... let's see.... cheaper, easier to build, better trap, looks better! Gee, which way to go?! :roll: :D I want to put the dimensions through the calculator for each gap and see what it yields. I'm quite sure the differences in the lumber width is the right thing to do, believing that it was drawn that way for a reason. My intuition is that it widens the frequency range of the trap. Please correct me if I'm mistaken. How about the insulation in the back? Should I line the wall with a layer of 3" Roxul Safe-n-sound? It's readily available and cheaper than shipping in OC703. I'm pretty jazzed about this design!! 8) -Ron

That looks amazing. We're going to have to rely on John here to advise on the insulation and to confirm that your design matches his vision for the device. Great work and yeah, I'm very impressed with how awesome it looks. I hope you'll share an .skp file of that device when you're done so that others like myself could implement it in one of my personal rooms! Greg

Hi Ron that looks great. You must line the back of the timbers with black cloth so you don't see through the spaces. Leave the center slots till last and toss all your insulation offcuts into the cavity ;) cheers john

I used the handy Hemholtz calculator to calculate each of the 19 slots individually to see what it would show for absorption frequency. Not sure if this is the correct approach, but it's interesting and here is a graph of it (from left to right slots): Any comments on this? -Ron

It looks awesome! I'm just confused about John's recommendation to fill the cavity with insulation. Everything I've ever read about Helmholtz devices is that filling the cavity really widens the Q of the device but it drastically reduces the absorption. Maybe I'm misunderstanding his design. Anyone care to chime in on this? Greg

Take a coke bottle and blow over the neck and it will produce a note. Now add some insulation to the bottle and blow over the neck and the note is gone. It's been absorbed. That's how helmholtz resonators work to reduce the note in your studio. cheers john

Gregwor wrote:

I'm just confused about John's recommendation to fill the cavity with insulation. Everything I've ever read about Helmholtz devices is that filling the cavity really widens the Q of the device but it drastically reduces the absorption. Maybe I'm misunderstanding his design. Anyone care to chime in on this?

I would also like a little more information about this if you get a minute John. So in your Recording Manual (I know it's quite old now!) you show that you have a thin layer of insulation behind the mouth of the slots, and the rest of the cavity is empty (but sealed). Are you saying that a fully filled cavity is simpler to achieve (as there isn't any need to glue/attach the insulation to the slats) but still has the same effectiveness? I ask because I've also read that over damping the cavity can negatively affect the absorption. I suppose chucking only low density off-cuts into the cavity and not compressing them would leave a lot of gaps between them and potentially prevent over-damping. Obviously, you use these all the time! So they must work, but can you expand on how heavily/compactly you fill the cavity? Thanks, Dan

I suggested to add offcuts to the cavity in this corner trap as it's cheap, easy and simple. When I add angled slots, like on side walls we just line the cavity walls with insulation. When I add slots to an inside out wall we just add insulation as usual set to the back of the cavity. cheers john

A couple of months ago we rang the control room for the first time. It took a while to figure out the whole setup and I hope we did it right. In the meantime, I got busy on the rear bass trap design and didn't get around to finding a cloud to post the first data. So for what it's worth, here is the first ring data. It would be nice if someone with experience could take a look at it and tell me if it looks right. Stuart was a big help when we started. We haven't figured out all the tools, and graphs nor their meanings yet. A lot of fumbling, but I think we rang it right. Here's the link - first ring with an empty control room, except for front soffit framing. https://drive.google.com/file/d/1YupEGv ... sp=sharing Please let me know if this looks right for my first worst-case ring.

When I try to open your file, REW tells me that it is not a .mdat file...I use the latest version of REW. Can you re-safe your file? Also, it is it possible to ge the .skp file? It would be more easy to valuate if you can measure the distances to the mic, etc.

The mdat opened fine on my REW. It looks crazy and scary just the way it should! Greg

When I try to open your file, REW tells me that it is not a .mdat file...I use the latest version of REW. Can you re-safe your file? Also, it is it possible to get the .skp file? It would be more easy to valuate if you can measure the distances to the mic, etc.

TomessAI, the mic was precisely 77" away from the speakers, 47 3/8" high, pointing straight forward at 60 degrees. Looks like Gregwor got it loaded OK. Thanks for your efforts! :)

The mdat opened fine on my REW. It looks crazy and scary just the way it should!

Ha Ha! Thanks Greg. I am spending all the time I can on building the rear bass trap until I go back to work on 1/2/2020. Bought the lumber and began cutting the pieces today. Got birch skins on the way. Man! This is going to be VERY HEAVY! :wink:

Guit-picker wrote:

When I try to open your file, REW tells me that it is not a .mdat file...I use the latest version of REW. Can you re-safe your file? Also, it is it possible to get the .skp file? It would be more easy to valuate if you can measure the distances to the mic, etc.

TomessAI, the mic was precisely 77" away from the speakers, 47 3/8" high, pointing straight forward at 60 degrees. Looks like Gregwor got it loaded OK. Thanks for your efforts! :)

The mdat opened fine on my REW. It looks crazy and scary just the way it should!

Ha Ha! Thanks Greg. I am spending all the time I can on building the rear bass trap until I go back to work on 1/2/2020. Bought the lumber and began cutting the pieces today. Got birch skins on the way. Man! This is going to be VERY HEAVY! :wink:

Mhh, that's really strange...I tried to re-download, but same result. To be precise, I'm using REW 5.19, not the newsest beta version. Maybe you can post some pictures of the measurement? I'm curious... Another question: I'm in the process of copying your speaker mounting system :lol: , and I was asking myself if you really need those two sorbothane hemispheres on the side of the speaker. The reason I'm asking is because I'm located in Germany, and it is really expensive to get those sorbothane hemispheres delivered from the states. And I'm planning for surround, so I have three more speakers and a subwoofer to isolate from the framing...

To soffit mount you don't aim to isolate the speaker from the framing. The framing becomes and extension of the speaker box which is held tight in a box within the framing. cheers john

Tomess, Stuart's recommended way of isolating the speaker from the framing does require sorbathane on all four sides, but as John said, he doesn't isolate the speakers from the framing at all. Just make the framing really solid and keep the speakers held tightly in the frame. Someone posted an interview with some well known studio designers (I can't remember now who it was though) and they both agreed that isolating/"floating" speakers is completely unnecessary. Dan

Thank you both, John and Wakka, for your input. I'll re-draw my sketchup...again. :mrgreen: I think I'll start my own post here in the forum. I've already have a thread in Stuarts new forum, but he seems to be a busy guy and has not time to go into some details I'm still struggeling with (Stuart, if you read this, no hard feelings, you've helped me a lot! :wink: )

Tomess, Stuart's recommended way of isolating the speaker from the framing does require sorbathane on all four sides, but as John said, he doesn't isolate the speakers from the framing at all. Just make the framing really solid and keep the speakers held tightly in the frame. Someone posted an interview with some well known studio designers (I can't remember now who it was though) and they both agreed that isolating/"floating" speakers is completely unnecessary.

Wow! I wish I would have seen this discussion a couple of years ago. I guess I missed that one! :o

I am busy making good progress on building the rear bass trap (all 700 pounds of it), but I have one question: I am planning on lining the inside walls, as well as ceiling and floor, with Roxul Safe-n-Sound (3"). Is it necessary to fill the ENTIRE cavity with Roxul (kind of like super-chunk style)? I hope not.

I am busy making good progress on building the rear bass trap (all 700 pounds of it), but I have one question: I am planning on lining the inside walls, as well as ceiling and floor, with Roxul Safe-n-Sound (3"). Is it necessary to fill the ENTIRE cavity with Roxul (kind of like super-chunk style)? I hope not.

This is a hot topic for debate. My understanding of Helmholz devices is to line the walls with say 2" of insulation, then use a very light pretty thin layer of insulation along the backsides of the slots. If you check out the pdf I've attached, it states that over filling the cavity will hinder the performance. Hopefully some people chime in here and shed some light on the topic. Greg

Thanks Greg, What do you mean by "light pretty thin layer of insulation"? Can you give an example?

What do you mean by "light pretty thin layer of insulation"? Can you give an example?

For example, take a batt of pink fluffy and rip off a 1 cm layer of it. Greg

Thanks Greg, I can easily do that. I will post some pictures soon on the bass trap progress. I've been busy every night after work cutting, painting, veneering (birch) and now applying finish to a whole bunch of lumber. :lol:

Guit-picker wrote:

I am busy making good progress on building the rear bass trap (all 700 pounds of it), but I have one question: I am planning on lining the inside walls, as well as ceiling and floor, with Roxul Safe-n-Sound (3"). Is it necessary to fill the ENTIRE cavity with Roxul (kind of like super-chunk style)? I hope not.

Erics Super Chunk was designed and tested using owens corning 703, a ridgid insulation. Your results would be completely different. But to your point, fill the cavity but do not "cram" the insulation in and it will be more effective at the lf you are aiming at.

Brien, to confirm, you're saying that for a Helmholz device he should completely fill the cavity? Greg