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PMH

Rock Wool for noise

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Has anyone had any experience, positive or negative using rock wool for noise attenuation? Where is it available? Better or worse than lead foam?

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It's all about the mass of the damping layer. And then isolating it with something soft - so the heavy layer can absorb the sound without transmitting it further into the structure. So 2 layers of foam with lead/vinyl in the middle works very well.

 

Rock wool is not as good as lead/foam - unless you do something like a thin layer of plywood between 2 thick layers of rockwool.

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Try a dynamat like product. Dense foam rubber used for noise damping in car audio applications. I am sure i've seen something similar to it with a foil layer for heat in engine compartments.

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The beauty of the rock wool of course is that it is wonderful fire protection. The vendors give tables of noise attenuation but it has been too many years since I was in a physics class and I don't really understand the tables.

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Well, yes, that's what Rockwool is for - structural fire protection. But it's not ideal for sound attenuation if that's your main goal.

 

Point me to the manufacturer's tables and I may be able to interpret for you.

 

And to be clear most of the sound insulation does a good job at say 2 kHz and above but poorly at low frequencies. A diesel might be emitting sound at around 100-125 Hz. Best way to attenuate diesel noiseis:

 

- air intake filters

- good mufflers (pick "residential grade" or better if you're doing dry exhaust)

- sound traps in engine room/ventilation fans

- very soft engine mounts

- torsionally soft couplings

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That's all good information, I've heard that something like 1/3 of the noise comes out of the engine intake. When I was a commercial fisherman we were very partial to cowl mufflers for our dry stacks so I think I have room to put one of these very close to the exhaust manifold. Won't be able to do anything about the engine mounts in the short term or couplings (maybe down the road). The noise attenuation table can be found at cyber-bridge-marine.com. Scroll down a bit and it's on the right hand side of the page. Really do appreciate the help. Cheers

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Actually, Rockwool is primarily a thermal insulation product. That is also really good fire and sound insulation is naturally a plus. Rockwool does make a special version of its material (which is melted, spun rock) for sound studios and it is a leading material for this (obviously in the traditional cone shaped form). Low frequencies are obviously always tough to dampen but Rockwool could be worth a try - maybe a rockwool/lead/rockwool if you want to get fancy

Well, yes, that's what Rockwool is for - structural fire protection. But it's not ideal for sound attenuation if that's your main goal.

 

Point me to the manufacturer's tables and I may be able to interpret for you.

 

And to be clear most of the sound insulation does a good job at say 2 kHz and above but poorly at low frequencies. A diesel might be emitting sound at around 100-125 Hz. Best way to attenuate diesel noiseis:

 

- air intake filters

- good mufflers (pick "residential grade" or better if you're doing dry exhaust)

- sound traps in engine room/ventilation fans

- very soft engine mounts

- torsionally soft couplings

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