Salem Oregon conference center studio

[Guit-picker]

I’m back after travelling to Scandinavia and then “paying for it” with undone obligations etc upon return, BUT I HAVE been getting SOME work done in the meantime.

After contacting Sorbothane and getting advice from their engineer, I went back to work and altered the shelf and absorber apparatus.

Here was the method:
My speaker is 33 lbs, 2 oz (33.125 lbs). Sorbothane recommended the largest hemisphere with a Duro of 30 for the top and sides. Their hemisphere (p/n 0510150-30-10) is 2.5” dia; 1.25” height Duro = 30 and is rated from 25-35 lbs at 30% compression. Therefore, adding the weight of the speaker with the 35 lbs from the top hemisphere is 68.125 lbs. of load on the bottom .

I selected five hemispheres (p/n 0510140-30-10) which are 2” dia; 1” height; Duro = 30 and is rated 11 – 16 lbs each. 68.125 lbs divided among the five bottom hemispheres will be 13.625 lbs each, right in the middle of the bottom hemi’s range.

The side hemispheres are the same as the top. The top and sides are positioned to be right in the middle of the interior hollow cavity of the speaker (there is an internal “back” that separates the speaker cavity from the electronics cavity in the rear). The sides feature T-nuts embedded into the wood for the bolts. Here are drawings with and without the speaker to illustrate:

Spkr_shelf_absorbers_B.jpg

Shelf_absorbers_B.jpg

I added my plan to line the back & sides with Rocksul insulation. Next I will begin drawing the bass trap hangers above and below the speaker.

Soffit_Insulation.jpg

This view shows my current plan for the front baffle. I have two sheets of cement backboard (one ½” and the other ¼”) with ¾” birch plywood over the top of it all.

Soffit_Baffle_B.jpg

That should be OK, but to make sure, see if your speaker will over-balance of you set it at the edge of a piece of wood with an inch and a half sticking out beyond the edge. It should be fine.

I checked on the 1 ½” overhang and we’re OK – no problem with overhang causing balance problems.

Also, for the sides of your soffit next to the window in the middle, don't make them too solid: you are going to need insulation there, to deal with the artifacts caused by that sharp corner, and the "cavity" between the soffits.

I am planning only one ¾” thick layer of OSB on the sides by the window. Is that what you had in mind?

It feels good to be back in the action again!
-Ron

[Guit-picker]

I'm wondering if the 3" Roxul in the back of the soffit should be thinner or, perhaps, 1.5" 703 to allow deeper hangers for the bass traps? Any input on this?

[Gregwor]

The sides feature T-nuts embedded into the wood for the bolts. Here are drawings with and without the speaker to illustrate:

I'm concerned about the noise created by the sliding top piece vibrating on it's "rails". Once your speaker is mounted with the right torque, could you fasten the joints/caulk them?

How will you make a clear air path up the back side of the speaker?

I am planning only one ¾” thick layer of OSB on the sides by the window. Is that what you had in mind?

The soffit wall will now act like the front of your speaker cabinet and have edge diffraction artifacts. A way to tame this effect would be to have the side of your soffit (in the window area) hold insulation. You do have insulation in between the 2x4 soffit studs, but you covered it up with the thick OSB. Depending on how your finishing the outside, you basically need to allow that insulation to be exposed. You also need to close off the speaker area to the window area.

Maybe you could move your OSB to the other side of the studs which would seal off the speaker area. Leave the insulation in the between the studs. Build a little fabric frame to cover that up (where you OSB is right now).

I'm wondering if the 3" Roxul in the back of the soffit should be thinner or, perhaps, 1.5" 703 to allow deeper hangers for the bass traps? Any input on this?

I recently asked this same question and the answer I got was that either or is good. Basically go with whatever is cheaper in the end and what makes sense material-wise. See how much waste you'll have from going the thicker Homasote route. Then check your waste going the thicker insulation route. Also, if your Homasote is expensive where you live like it is where I live, experiment using thicker (2" instead of 1") insulation on your hangers themselves.

Greg

[Guit-picker]

Hey, thanks Greg! All great input!

I'm concerned about the noise created by the sliding top piece vibrating on it's "rails". Once your speaker is mounted with the right torque, could you fasten the joints/caulk them

Excellent point! I will definitely do that!

Maybe you could move your OSB to the other side of the studs which would seal off the speaker area. Leave the insulation in the between the studs. Build a little fabric frame to cover that up (where you OSB is right now).

Oh!, I get it now! I really like that idea, but I'm running into clearance problems on the inside. I had to rotate one of the studs on the window side (unorthodox) to allow clearance for the adjustment bolt on the speaker dampener assembly.

Clearance_bolt.jpg

I will do some re-thinking and see if I can angle the side wall more to allow room for it all. I will post an updated drawing on that when I can. Alternately, it might be better to nudge out the speakers a tad wider to make it all fit? Maybe it's as simple as shortening the adjustment bolt if possible. On the window side, I barely had room for the OSB without running into the window trim. There's a solution there somewhere!

How will you make a clear air path up the back side of the speaker?

There is a chunk of open space behind the speaker. The current plan is for the air path to come from the grill below the speaker shelf, through the hangers up the back and out the top grill. Here's a shot of the area behind the speaker:

Air_path.jpg

...experiment using thicker (2" instead of 1") insulation on your hangers themselves.

Is wrapping with "fluffy" fiberglass bats OK, or is that not dense enough? I found a local outfit that does live sound willing to sell me 703 4x8x1.5" sheets for $65. That's all they have. Otherwise, getting large sheets of 703 shipped is a pain, not to mention expensive. If I used roxul around the homosote, how is it attached? Wires, perhaps? What density on either fiberglass or Roxul, I guess, is my basic question. I need to search more on the forum too!

[Guit-picker]

... and as always, THANKS for your inputs! What a great resource this forum is!

[Soundman2020]

I'm wondering about your framing: I don't see enough strength and rigidity in there for a good soffit. You might want to consider beefing it up a bit.

- Stuart -

[Guit-picker]

I'm wondering about your framing: I don't see enough strength and rigidity in there for a good soffit. You might want to consider beefing it up a bit.

Do you mean the front frame around the speaker or do you mean the rear frame holding up the speaker shelf (not shown in these latest pictures in order to show the clearance problem. I'm a bit uncertain how you mean to beef it up. I will post another picture showing ALL the framing of the soffit when I get home from work. Speaking of work, I better get back!

[Gregwor]

I will do some re-thinking and see if I can angle the side wall more to allow room for it all. I will post an updated drawing on that when I can. Alternately, it might be better to nudge out the speakers a tad wider to make it all fit? Maybe it's as simple as shortening the adjustment bolt if possible. On the window side, I barely had room for the OSB without running into the window trim. There's a solution there somewhere!

Mount some cleats in your studs and inset some MDF or OSB. The cool thing about this is that you could make the sheathing removable (with screws) so that if you ever needed to adjust the settings of your speaker, you could reach in from this side panel. The brad nailed fabric covered frame could be removed without too much hassle, or you could even mount it using some decorative hex key screws for ensured easy removal.

There is a chunk of open space behind the speaker. The current plan is for the air path to come from the grill below the speaker shelf, through the hangers up the back and out the top grill. Here's a shot of the area behind the speaker:

I'm still skeptical. The insulation inevitably will sag and move around. You need to dampen that entire speaker area as much as possible. Typically people use chicken wire. I haven't seen any in your design, so I'll ask, are you putting divider type shelves in your soffit? They will increase the strength of your soffits drastically. A bottom divider will be a consistent anchor point for your lower hangers. A top divider will be a definitive point between your upper hangers (or super chunk) and your speaker area insulation. Cutting a hole in both dividers and covering it with either chicken wire or a breathable fabric will ensure air flow and eliminate the chance of any insulation getting from one section to another below. Connecting the top and bottom divider pathway via chicken wire with a clear path to the back of your speaker is where thing get confusing in my head. Ideally you want to entirely stuff behind the chicken wire even. This is just me being picky of course. I mean, maybe you could just stuff a bunch of insulation on the sides of your speaker and leave the back open relying on your wall insulation.

Is wrapping with "fluffy" fiberglass bats OK, or is that not dense enough?

I would say it's not rigid enough. I've seen a lot of people successfully mount safe'n'sound and of course 70x series insulation.

I found a local outfit that does live sound willing to sell me 703 4x8x1.5" sheets for $65.

Per sheet?

Otherwise, getting large sheets of 703 shipped is a pain, not to mention expensive.

I too am limited to the thickness where I'm at even though the main distributor for the Western half of my country is in my city! I CAN get any size I want as long as I order a truck load (not happening). The same goes for Homasote. 1/2" 4'x8' is all I can get.

If I used roxul around the homosote, how is it attached? Wires, perhaps?

A very clean and effective method is to use proper length screws and larger diameter fender washers to hold the insulation on the Homasote.

What density on either fiberglass or Roxul, I guess, is my basic question.

The relationship between the density and gas flow resistivity is believed to be related close enough that most people suggest using a range of densities per frequency band.

Fibreglass in kg/m^3
High Freq = around 40 (others say 60-80)
Mid Freq = around 35
Low Freq = 20-25

Mineral Wool in kg/m^3
High Freq = around 65 (others say 90-120)
Mid Freq = around 55
Low Freq = around 30 (others say 40-45)

As an example
OC705 is 90 and OC703 is 45
OC EcoTouch R24 is between 20 and 23 (this is the heaviest pink fluffy they make)

In general
Lighter is better for bass (light fluffy fiberglass insulation)
Heavier is better for higher frequencies (heavy mineral wool)

Greg

[Guit-picker]

Wow! Thanks Greg and Stuart for your wealth of input! I went to work this weekend and redrew the right soffit again. I pivoted the left side (window side) - out on the front and in on the rear, so that it made room for the side absorber assembly, which meant redrawing just about everything. It also made room for me to add the OSB to the INSIDE of the soffit (Top to bottom) rather than the outside, like you (Greg) said. Now the insulation will be facing the window with the cloth grill covering it.

Soffit_4_Framing_new.jpg

I'm wondering about your framing: I don't see enough strength and rigidity in there for a good soffit. You might want to consider beefing it up a bit.

Stuart, do you mean more cross pieces... or more double studs? The picture above shows all the framing I have so far, including the inner frame, supporting the speaker.

I'm still skeptical. The insulation inevitably will sag and move around. You need to dampen that entire speaker area as much as possible. Typically people use chicken wire. I haven't seen any in your design, so I'll ask, are you putting divider type shelves in your soffit? They will increase the strength of your soffits drastically.

Soffit_4_Insulation.jpg

Yes, I have been planning on lining the entire soffit walls with Roxul (pictured) and using chicken wire to hold it in place on the walls and the ceiling part, and especially not to block the ventilation path. The section directly behind the speaker will be open back to the Roxul "liner" on the wall behind. I just don't know how to draw chicken wire. I haven't started drawing the bass trap hangers yet. I was planning to put up some "shelves" below the speaker and below the ceiling to hang the bass trap hangers from. These "shelves" are currently planned to connect to the inner frame that holds the speakers, not unlike the speaker shelf itself.
Are you suggesting I put shelves in there to flank between the inner framing and the outer framing? I have been having the impression that we do not want direct flanking from these two frames. Do I have this wrong?

Per sheet?

Yes! $65 per sheet! I don't know if it is still available at that price, but I expect I will use them as a source for my future OC703 needs, even if I have to order it through them.

I would say it's not rigid enough. I've seen a lot of people successfully mount safe'n'sound and of course 70x series insulation.

I'm wondering about using chicken wire around the hangars to hold up either save'n'sound or fluffy fiberglass? I'm not sure, but I thought I may have seen someone on this forum do that?

Hey thanks, Greg, for laying out those density guidelines on different types of insulation. That really helps me to have a bit more intuition.

-Ron

[Soundman2020]

Stuart, do you mean more cross pieces... or more double studs? The picture above shows all the framing I have so far, including the inner frame, supporting the speaker.

More cross pieces. Right now, there is nothing at all supporting your front baffle, except the edges. Thus, the entire baffle is free to vibrate, and "pump" from the large air pressure changes inside the baffle at low frequencies. Check out Frank's thread, to get an idea of how much framing you need.

Also, you do not need two separate frames! If you float your speaker properly on Sorbothane, then there's no need for ALSO isolating the framing that holds it in place. It complicates things greatly, and takes up too much space. It also prevents you from using a "shelf" to place your speaker on, that also divides the interior into the actual speaker section, and the bass-trapping section below the "shelf".

Yes, I have been planning on lining the entire soffit walls with Roxul (pictured) and using chicken wire to hold it in place on the walls and the ceiling part,

You seem to be missing the point: the ENTIRE CAVITY is filled with insulation! Not just the walls. The chicken wire is not there to hold the insulation against the walls: it is there to create a very small "chimney" up past the rear of the speaker, just for the cooling ventilation air flow. Take a look at Frank's thread, to see how he did it...

The section directly behind the speaker will be open back to the Roxul "liner" on the wall behind.

Again, you are missing the point: you only need a small "chimney" back there.

I was planning to put up some "shelves" below the speaker and below the ceiling to hang the bass trap hangers from. These "shelves" are currently planned to connect to the inner frame that holds the speakers, not unlike the speaker shelf itself.

Once again, you are missing the point: the speaker shelf IS the shelf form which you hang the hangers! You do not need multiple shelves. Just one (thick! massive!) shelf, with the speaker sitting on top, and the hangers hanging below, and a slot at the rear for the ventilation path.

Are you suggesting I put shelves in there to flank between the inner framing and the outer framing? I have been having the impression that we do not want direct flanking from these two frames. Do I have this wrong?

You do not need the "inner frame" at all! You are not following the Barefeoot design here, since you are floating your speaker on Sorbothane, and therefore you do not need an independent "inner" frame for just the speaker. Here too you can see how Frank did it, in his thread.

I'm wondering about using chicken wire around the hangars to hold up either save'n'sound or fluffy fiberglass?

And once again, just use Frank's method: it works great.

Frank's thread:

http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368

- Stuart -

[Guit-picker]

Got home from work eager to see a reply and was not disappointed! Thanks for "tearing up" my plans again, Stuart! I have some homework and redrawing to do. I bookmarked Frank's topic and will dig in. Thanks again!

[Gregwor]

Got home from work eager to see a reply and was not disappointed! Thanks for "tearing up" my plans again, Stuart! I have some homework and redrawing to do. I bookmarked Frank's topic and will dig in. Thanks again!

Check out how I've designed mine.

http://www.johnlsayers.com/phpBB2/viewt ... 6&start=60

Greg

[Guit-picker]

Thanks, Greg. I'm studying yours too! Working on soffit version #5 now.

[Soundman2020]

Working on soffit version #5 now

Only #5? Pffff! (Just kidding....)


- Stuart -

[Guit-picker]