Home Mix Room Overhaul - DIY Panel Build - w/ REW Charts/3D Sketchup

#151

Here are the photos. Didn't have room in the last post.

Also, I think the dip around 700hz in phases 2 and 3 of the above charts might be due to the new desk and different spacing from front wall. I am further back now and with a smaller desk. The speakers are a bit further apart than originally and also angled inward less than before. Maybe it's a desk/floor bounce? Not sure how to read that but it wasn't there in my original setup with the older bigger desk that was closer to the front wall.

Trevor

#152

Also, I plan to move the couch out in the near future! Trying to get the room as symmetrical as possible. Gotta figure out what I’ll be doing with it though lol.

And my two custom racks are in the works. I’m really stoked for these. A buddy of mine has access to a CNC machine so we are doing some custom cuts that will work really nicely with that $80 Amazon desk! :lol:

#153

Soundman2020 wrote:Source of the post Right. But rather than lose more space for thick absorption back there, I'm thinking that a single large poly or wedge back there might be a better option. It would look nicer too, and not suck out even more highs like porous absorption would. Might be an idea. If it is decently large (wide and high) it should do the job well. Make it from flexible plywood, with "ribs" inside to give it the shape. Fill it with insulation, and you'll get some bass trapping too. And if you make it in the form of what I call a slot wedge, you could get some tuned Helmholtz action as well! Or you could do something I call a "slatted poly", which is the best of many worlds all at once: A series of vertical slats of varying sizes and/or with varying spacing between them, arranged along the same curve shape as a poly would have. Something like this:

Hi Stuart, I'd love to dive into this idea for the back wall a bit more! But I'm still unclear on the details. Not sure how exact things need to be. I don't want to go to a bunch of trouble and end up making matters worse! If you or anyone else has any quick guides on building "polys" let me know. I'm all ears. The internet seems to be filled with a million different opinions on these and I'm not sure how to apply it to my room in its current state.

Cheers
Trevor

#154

So I've been doing some more research on polys. I've learned a few things, I think...

1. Polys (as well as QRDs) work better when not placed side by side IF the same exact panel/pattern is being repeated. i.e. one poly is better than 3 of the exact same poly side by side (same with QRDs) BUT if the size (width of chord) of the poly is varied by 10% or more, then it can be ok to place them side by side(?). I found this hard to believe but it was based on a measured test (I hope) by Glenn Kraus (post #18) here: https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/266361-sonotube-diffusor.html

2. Poly's can work to varying degrees of reflection and absorption depending on the material density/depth used for the curved surface. I have seen these built from dense cardboard Sonotubes (used for forming cement cylinders), plywood of varying thickness, Masonite (a type of plywood??), and even this cardboard-like plastic called Coroplast (https://www.coroplast.com/)...BUT WHAT I DON'T KNOW is how to calculate what frequencies will be reflected vs what will pass through into the insulation for absorption.

3. Placing the insulation against the back of the curved surface changes the low end absorption of the poly. John Brandt discusses that a bit here on his design:

Poly Panels.pdf: (171.42 KiB) Downloaded 1161 times

Poly Panels.pdf: (171.42 KiB) Downloaded 1161 times

. He says that when the insulation does not touch the curved surface, the poly can help with LF decay below 100Hz but if a more broadband LF absorption is desired, then go ahead and let it touch. (He also mentions keeping the upper and lower ends of the poly open and not sealed. Some others mentioned if you seal it that it's like a tuned hemholtz that attenuates a single frequency...yea?)

4. Polys --> better for spatial scattering, poor temporal diffusion

QRDs --> worst spatial scattering, nice temporal diffusion

BUT I have no real idea what that means for a room like mine. :lol:

EDIT: Stuarts post that I linked to below explains this very well. Spatial scattering has to do with sending sound waves in different directions whereas temporal diffusion changes the time between returning sound waves (the varying depths of a QRD for instance...if I am understanding correctly)...here is that quote from Stuart:

The incoming wave travels down all of the wells, and bounces off the bottom of each one, then exits again. But the part that hit a deep well takes a longer time to come back, thus it has been "temporally shifted": some parts of the wave came back sooner, others later. This is one form of diffusion. But since the waves coming back out of adjacent wells are shifted in time, they are also shifted in phase relative to each other, which means that they can partially cancel each other out, or reinforce each other, in varying patterns, depending on frequency, well depth, angle of incidence, etc. So phase shift is another form of diffusion. And finally, the interaction of the phase differences also causes some parts of the reflected wave to be steered in different directions form other waves. That's a third form of diffusion, called spatial diffusion. So the wave coming out is very complex, with different parts doing different things, and going in different directions at different times and with different phases. Thus, if you have your ear up close, within a few feet, you will hear different things in different places. Ditto for the mics! These differences do eventually even out, as the wave-front moves away form the diffuser, and at greater distances the wave-front is just plain "diffuse", and sounds roughly the same wherever you listen to it..... or wherever you place the mic in it.

(here is some type of study that proves the benefits of polys over other types:

Measuring Diffusivity Using Traditional Methods.pdf: (1.55 MiB) Downloaded 1340 times

Measuring Diffusivity Using Traditional Methods.pdf: (1.55 MiB) Downloaded 1340 times

)

Uhhhhh yea and probably some other things I've picked up to think about but I think my biggest question is the Sonotube vs plywood vs Coroplast subject. I'd like to know what to expect in terms of frequencies reflected vs. absorbed. That would help me make a decision (I think??)...

Here are some other threads I've skimmed (sorry Stuart for the gearslutz links! :oops:

...I have been searching this forum as well but haven't seen as much on detailed poly builds EDIT: I apologize Stuart, this is a FANTASTIC explanation you made of various forms of diffusion here on post #6: https://www.digistar.cl/Forum/viewtopic.php?p=2816#p2816 that helped a lot...I am still searching/reading more)...Andre, Glenn, Ethan, and John Brandt seem to have some pretty productive cross talk on these.

https://www.gearslutz.com/board/studio-building-acoustics/559833-polycylindrical-diffuser-design-2.html
https://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/469065-d-i-y-polys.html

Cheers
Trevor

#155

If these estimates are correct, it looks like the density of sonotube cardboard is similar to that of plywood??? Could that be even close to true? And if so, does that mean the sonotube cardboard would perform similarly to the plywood of made into a poly?

Reference: https://www.cloudynights.com/topic/137631-weight-of-12-thick-sono-tube-that-is-72-long/

#156

Ok, so I've been doing more research on the tube trap thing and have decided to try a version without the sonotube for now. Basically it's just one of those fiberglass tubes (meant to be used for pipe insulation). I plan to stuff it with pink fluffy and wrap with fabric. I ordered a single 3 foot 10x1 (10.75" inner diameter plus 1" for insulation on both sides of circle so 12.75" total diameter) from here:https://www.buyinsulationproductstore.com/Fiberglass-Pipe-Insulation-SSL-ASJ/

I confirmed the density of the insulation is 3.9pcf which is a little high compared to the 2.5pcf Rockwool AFB I used in the panels. I've been trying to figure out how much low end absorption this combo of 1" rigid 3.9pcf fiberglass filled with 10" of low density pink fluffy will offer. I've used that one calculator that was recommended and it seems like this should have decent results.

The reason I'm doing this is to hopefully add some additional help to the lows and mids without the need for building more panels. These would be much easier to construct but still portable and I could sell them down the road. I could also leave the wrap on half of it for some flexibility on high end reflections.

Am I way out of line for thinking 10-20 of these could offer some further improvements? I am thinking of placing them along the front wall between the speakers and then stacking 2 high on each side of the speakers. Then placing about 4 or 5 on the mantle and a few more in front of those on the panels I already have in front of the fireplace. Might look kind of crazy or it might look cool! I'm not sure lol.

I also still want to figure out the Sonotube question because I think those could work really well to break up the flutter on the upper side walls and maybe even at the top corner of the back wall? Plus offer some additional low end absorption without sucking out more highs?

Cheers!
Trevor

#157

Yooooo I've been playing with the multi-layer absorber calculator trying to figure out the potential results of these tube traps mentioned in my previous post...

I'm using the following numbers for the calculations...accurate to the best of my knowledge based on researching the forums but please chime in as I'm sure they might be off!

1" of 3.9pcf fiberglass insulation tube (~20000 Pa.s/m2 GFR ?)
filled with
10.75" of R13 "pink fluffy" fiberglass insulation (~8000 Pa.s/m2 GFR ?)

NOTE: On the calculator I used 3 layers since the sound would hit the 1" then the 10.75" of pink fluffy and the the other side of 1" again (right?)

(Granted, I don't believe this accounts for the tube being well, a tube (and not a flat panel) but not sure how that changes things...)

I then calculated what would happen if I wrapped this all in 4mil painters plastic which I used this density: 0.14083 Kg/m2 (as a limp membrane...?)

The 4 lines on the graph represent:

• 10.75" fluffy x 1" OC Tube
• 10.75" fluffy no tube
• 10.75" fluffy x 1" OC Tube (4mil plastic wrap)
• 10.75" fluffy no tube (4mil plastic wrap)

Reason:
I was trying to see how the 1" fiberglass outer layers were affecting the absorption compared to fluffy by itself and then also what a plastic wrap would do.

Results:
For the tubes without plastic, the fluffy with 1" of OC tube seems to do a bit better below 80Hz but not as well from 80Hz-5000Hz as just the fluffy with no 1" OC tube.

For the tubes with plastic, the fluffy with with 1" OC tube also seems to do a bit better below 80Hz but not as well from 80-600Hz (and above that they are roughly the same and start reflecting more and more due to the plastic).

Here is the graph (and link:

Conclusions/questions:
So if this is at all close it seems like I can expect decent results taming the lows and low mids a bit more. And though the fluffy by itself would technically do a bit better through the low mids, that was more of a hypothetical scenario since the OC tube is what makes these easier to build. I just wanted to make sure the tube wasn't hindering low end or low mid performance too much which it seems it helps the super lows and only somewhat diminishes performance in the low mids.

But since I don't need much absorption past 700hz maybe I should go ahead and wrap these in plastic?

Though I've read putting reflective cylindrical surfaces side by side can cause issues since it creates areas of "focused" reflections (concave-ish shapes?) and interrupts the good parts of the "diffusive/scattering" characteristics...thoughts?

Maybe thats where I can just leave the vinyl film on half of the OC tube and not worry about wrapping the whole thing in plastic that way it can be turned depending on if I want the absorptive or reflective side facing the room...thoughts?

OK done for now... :ugeek:

Hope everyone is finding time to start winding down for the year! I can't seem to stop my obsession with acoustics for the time being... :shock:

Cheers
Trevor

#158

Hi Trevor,

It got very quiet here. All OK?

Regards, Frans

Soundman2020 - Studio Design Forum