Researching acoustic materials for passive accoustic attenuation

[salukikev]

Hi there- I couldn't find a specific forum for acoustics so here goes: I've recently taken on a project in which the goal is essentially to create a low profile, comfortable headset solution for passive sound attenuation.

Our goal, of course is to achieve the highest NRR while compromising comfort as little as possible. We are specifically targeting a low frequency range of sound for this, but I wonder what realistic benefit I can expect from these "tuned" materials. In practice what I expect is going to effect results more than anything else is fit to/around the ear (pressure applied and complete conforming to the geometry of the ear or ear area).

Having said that, I am still tasked with indexing all available materials for sound blocking that I can manage. Flexible closed & open cell foams, silicone gels, wax, & various polymers are all valid contenders for assessment.

My initial research suggests an NRR of up to 36 is achievable using a combination of foam ear plugs and a headset. Also, an additional reduction of 20 NRR can be achieved using active sound canceling. Is that accurate information?

Anyway, for the moment, I'm focusing on compiling some solid leads to further research materials. I would also greatly appreciate any leads to specific manufacturers or applications engineers I might speak with.
Thanks for any help!
-k

 

[MikeHalloran]

These guys sell, among other things, 'loaded sheet' goods that are very effective at source isolation:

http://www.soundown.com

I don't know to what extent they can help with receiver isolation, but they have some pretty sharp application engineers who would know.



Mike Halloran
Pembroke Pines, FL, USA

 

[salukikev]

Hi Mike! It does look like their focus is on much larger scale applications, but I will give them a ring tomorrow morning. Thanks!
-k

 

[IRstuff]

Have you consulted makers of acoustic anechoical chambers?

http://www.eckel.ca/products/test-chambers/anechoic-chambers/anechoic-chamber-wedges.html

http://www.meyersound.com/products/technology/chamber.htm

http://www.acousticsfirst.com/acoustical-foam-anechoic-chamber-wedges.htm

TTFN

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[salukikev]

IRstuff:
I hadn't considered anechoical chamber manufacturers, but as their scale is also much larger than we are targeting, they would not be my first choice. I assume the materials that the wedges are manufactured from are relevant to sound blocking, but I would also suppose that the dynamic of sound wave blocking on a smaller scale suggests that a much more specialized manufacturer would be a better resource to target. However, I'd be glad to follow up with some if you or others think otherwise.

If our final solution can't fit into a shoebox, it's not going to be acceptable to our client.
Thanks!

 

[cloa]

Here is the mechanical acoustics forum.

http://www.eng-tips.com/threadminder.cfm?pid=384

 

[patprimmer]

Completely off topic, but my ex breeds Salukis and has acquired some fame in doing so and even some infame in promoting brindles.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[salukikev]

Cloa:
I saw that one, but after much consideration posted here as I think my question has more to do with materials (ie. foam, MLV, silicone, polymers). If that forum was simply "acoustics", I'd have gone for it. If mods think otherwise, feel free to move it. (please let me know before deleting though, so I can copy it).

Patprimmer:
Although I'm a huge dog person, my handle was a carryover college mascot. Also, because its unique enough to be always available.
(and now back to topic!)

 

[mcgyvr]

Oh the memories of Carbondale. Go Southern Illinois

 

[IRstuff]

While scales are larger, the materials decisions are the same, and in some cases, even more severe, given that most anechoic chambers are attempting to reduce ambient noise levels down to audio calibration equipment levels.

I can tell you, as a user, that urethane foam cushions around the ear, with polystrene insulation around the outside seems to work very well in helicopter flight helmets. This does require a VERY tight seal around the ears. I couldn't hear someone talking to me from 2 ft away with the helmet on.

However, given that there are literally dozens of sound mufflers, etc., on the open market, aren't you reinventing the wheel, as it were? Seems to me that getting your hands on a few decent examples will get you farther than your compilation of materials. Because, after you get the list, you still have to figure out the best mechanical construction for the muffler, which will still require you to physically examine a few.

TTFN

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[salukikev]

IRstuff:
Yes, we're definitely re-inventing the wheel, but I've come to expect that of lots of the projects we come across at this job, and so I'm just patronizing the statement of work while still finding the best materials I can document. I'm sure lots of engineers can relate!

Between our starry-eyed client's "nanomaterial" citations and our marketing department's dialogue, they have it in their head that the material is going to make or break this product. Per my OP, I have explained otherwise, and definitely share the opinion that pressure and sealing is going to be WAY more critical to the task and estimated the materials would make a 10-20% contribution toward effectiveness. Still, that's significant, and that's the phase I'm in, so I'm trying to be as through as possible. Also, yes- certainly I want to get some physical samples, and we have discussed even creating a test-box rig to evaluate materials & assemblies. Not sure how phase 2 is going to pan out.

thanks for the info!
-k

 

[IRstuff]

I feel for you, bro. Good luck...

TTFN

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[salukikev]

Thanks! Also, I just realized you were the guy from the eddy current thread who suggested the HD magnets! I'm not sure whether to be thankful or not for that, because we'd have given up (aka. "escaped from") the magnet concept if we hadn't gotten such a positive result! haha... but seriously- thank you, that was a great suggestion!