Anyone got any cool projects or designs they wanna test?

[deadbolt24]

Hey guys,
I've been a bit of a lurker here @ gearslutz for awhile. Long story short is I'm a senior studying mechanical engineering @USC and this fall we have our senior design projects. I've always been a bit of an acoustics nut so i figured this is a perfect opportunity to finally marry ME and acoustics.

Anyways I was looking for some feedback or ideas from you guys. I know a lot of the home studios I've checked out here in LA seem to have a lot of reflection problems in the low end of the frequency spectrum (including mine), so that's something I'm strongly leaning towards, especially because i work most closely with the EDM scene and have enough problems as is trying to keep track of all that bass.

I know theres a ton of treatments out there (heres to you glenn et al) but i would really like to either do more testing on them, or come up with my own.

my first idea is somewhat of a novelty. I've been fascinated with diaphragm absorption, most particularly with the idea of a resonant panel over an airtight cavity. Here's where the novelty part comes in, I was thinking about testing the panel with different gases providing the damping, but I'm really worried about the gas permeability of the plywood, as having to provide constant positive pressure to the assembly would not be fun, easy to do, could become dangerous, and makes it entirely useless in the real world. Although it would be really interesting to see how much of an effect the gas density has on damping, and if it could be comparable to using fiberglass in the cavity.

my second idea for the experiment as to just test as many different wall offset distances possible for a common 703 or 705 panel, (if i'm lucky with varying thickness as well). I was hoping to focus in on the below 250 Hz range, especially <100 Hz if possible, although I know there isnt really any standardized testing procedure for that large of a wave length since its really a different beast at that point. (from my understanding)

For both of these experiments i would have access to an untreated empty concrete room, although I'm still waiting to see what so i can get the dimensions and start mapping modes. I was hoping to stick as close as possible to ASTM c 423 standards, but I know i'll only be able to really replicate them by the most liberal of definitions. I will also have access to the equipment (mics, DAQ, monitors, and hopefully software) needed to carry this out.

Huge brownie points if anyone actually finished reading this post, and please gimme and feedback you've got, or any other project designs. I've got the entire semester to carry out this experiment, so i'm really looking for some advice to make it something interesting.

Thanks,
Dave

[gullfo]

hmmmm. sounds interesting. maybe something challenging like VPR or pistonic panel absorbers? i'd skip the gas idea though as leaks happen.

[deadbolt24]

Thanks for the reply! I really like those VPR designs, it got the nerd in me going.
I have couple of questions though
1) every time i try to open the pistonic helmholtz rez google sketch crashes. I'm not sure if its the file or me, but is there any way you could upload a new file?

2) Even better by any chance do you have/use solid edge or solidworks? I know google sketchup is the preferred modeling software for this forum, but your project idea seems like a CNC sort of affair. I'm just hoping that i'd be able to have someone to show plans on this forum for advice and not have to keep redrawing things in google sketchup.

3) When i was looking at the modex diffusors from RPG it seems they took the pistonic route for the damping. Every time i hear that phrase i think springs, but am i correct in assuming that the resilient absorption material in the diagram is more of a membrane? or are you leaving it open ended since that could be another interesting thing to test.

4) i've seen hunts in this forum for the patent relating to the RPG modex, anyone out there had any success?

5) since this is a steel plate covering, wouldn't there be a fair bit of HF reflection? or does the absorption "spring" effectively act as a broadband absorber combating this issue? The main application I'm shooting for is a small, <3000 cu ft (82.95 m^3), studio. from what i understand the vpr was designed as a broadband, but i gotta brush up on my german i guess.

6) any ideas for what material was used as the resilient material in the modex? I'm just looking for somewhere to start if i'm going to be testing materials

Thanks again, and i really gotta work on writing less

[deadbolt24]

as a self answer to 6) it seems that melamine foam was used. Anyone have any comparisons to fiberglass such as OC 703/705? or is this something else interesting to test

and was the first design you posted along these lines? except with a membrane absorber instead of spring.
Room mode bass absorption through combined diaphragmatic and helmholtz resonance techniques - Patent # 7440580 - PatentGenius

[gullfo]

i'll post a new SU file later today as i simplified the construction and i'll save it as SU 7 compatible in case that's the issue. i could export it as DXF if that helps or some other 3D format. the front panel is suspended on the rubber edge and is damped by foam plugs (instead of springs) which also support it. the MLV membrane is free to vibrate and is damped with insulation in the back.

the steel plate is highly reflective. so there were a few options for diffusive faces like the perforations etc. basotect or other melamine foam can be used but agglomerated foam could also be the answer.

[gullfo]

maybe this works better?

[deadbolt24]

thanks again, that helped a lot. when i was researching the rpg modex series they talk of a damping material bonded to the membrane in some of the literature, which is different than the airgap that seems to always be recommended here on the forums. Any thoughts on that?