cutting cockpit noise?

[wildirishtime]

After upgrading from a Model 3 Rotax 582 to a Model 5 912ULS, the only complaint I've got - is engine noise in the cockpit. When that 912 cranks over about 4900 or 5000 it gets loud enough my Zulu's even have trouble drowning it out. Any suggestions on effective noise dampening? I have no noise padding anywhere.... a thin sheet seperating the firewall
padding and my feet, but none on the belly under my feet or anything - figured it wasn't doing much so i pulled it last annual

[jrthomas]

I've worn ear plugs along with the headset. It doesn't seem to bother my intercom or radio reception but it sure helps with the engine noise. It's an easy fix that works real well. James Thomas

[Monocock]

What prop are you spinning wildirishtime?

The reason I ask is because when I had a GSC prop the noise was deafening. I then tried out (ie borrowed) a Warp Drive (to solve some vibration issues that the GSC was causing) and it was a little bit quiter. I ended up buying a Kiev on advice from this forum and it is even quiter still, as well as being by far and away the best performer.

I don't think it's all directly the engine noise. Prop and exhaust noise are probably the main contributors. I don't have any soundproofing either, other than the metal fire wall.

I find 4650 (100mph) the most comfy power setting. If I need to get somewhere and I want to see 120mph I go for 5200, but it's certainly a fair bit noisier!!

[HighWing]

While building my first model IV, I went to an EAA meeting in the SF Bay Area and a sound engineer made the presentation. A couple of things stuck in my mind. Mass is what you need to attenuate noise. To eliminate the transmission of noise - through a thin firewall - you need to bulk up the weight bacause the thin sheet metal just vibrates and the sound passes right through. In aviation, this is not practical, so he gave some alternatives. Much of what we hear is reflected sound that just bounces around our enclosure. Upholstery and carpeting will help there. Then he mantioned a fairly effectve sound absorber which consisted of a rubbery type foam - like the temper foams - which is enhanced by a hard coating on one side like an aluminum skin. I found that ACS had such a thing and used that on the firewall. I also used a half inch foam sheet between the floorboard and bottom fabric to help with exhaust sounds.
Lowell

[wildirishtime]

...highwing you're hitting my question dead on. During my KF5 restoration I took all that crap out of the floorboard cause it was soaked with brake fluid (broken master cyl) and threw it away. Figured I didn't want the mass so I left it out. There is SOME dampening on the firewall side and that's not very efficient at this time to swap.

Do you, or anyone, have any 'before and after' experience to tell me "yes, put that metal back foam in the floorboards will make a measuarable decrease in engine/exhaust noise"?

Thanks guys!
~Wild

[wildirishtime]

Anyone have specific material recommendations they found to provide the best noise reduction? (comparisons preferably?)

[akarmy]

sorry, no comparisons, but this is the stuff I used on my RV9 a few years ago. Just cut it to fit the floor and firewall. Think it would dampen the firewall on the Kitfox, but myself I've not really had that much of an issue with it. I use active headsets which tame the Rotax for the most part.

http://www.aircraftspruce.com/catalo...oofinstall.php

[wildirishtime]

I've been eyeballing that stuff and the other stuff from ACS. My noise is enough that my Zulu2's mics pic up a lot of ambient noise when making radio calls, and hearing the COM clearly is not easy at RPM's over 5000.... hoping to get that addressed. Thanks !

[rogerh12]

I "strongly" suggest any noise dampening material you use does not burn or absorb fuel (safety first guys !!!) Does anyone know if that Super Soundproofing Foam Mat for noise control (as linked below) supports combution or not?

[wildirishtime]

I second that question. Also, does anyone know of any online videos, or good online documentation on soundproofing? I am confident there is a lot of science behind it, but I don't find much good info on the EAA website about it strangely enough. Maybe I missed the details - if someone has links please let me know.