R

rv72004

Well Known Member
Have any of you sound proofed the firewall after flying with it un-soundproofed?
What were the results? Basically is it worth the trouble to soundproof?
 
No but I have some soundproofing info

I bought the sound proofing material from FLYGBI. It is a black foam material with an aluminum face on one side. It has to be piece fitted in (you design the pieces of course because each firewall is different - penetrations, etc.) and it is glued inplace with 3M Super 77 adhesive. I put aluminum tape over all of the seams. I do not have the before and after sound comparison because I did the work as I built the plane. It does seem quiet by GA airplane standards (similar to my old Archer with the "Executive soundproofing package" from Piper) but you still need the hearing protection of a good headset. The negatives involve covering everything up (forget about adding platenuts later), the aluminum will tear if the sound proofing is compressed with something like a rudder pedal and the tape is not adhering perfectly over the seams. I am currently doing the annual and will address the cosmetic issues but it does involve some nuisance maintenance.

Bob Axsom
 
Last edited:
peeling off and then replacing

I have some first-hand experience with noise level comparison with and without firewall foam. Well, sorta.

I have 1/2" Super Soundproofing foam on my firewall. Or I should say had. About a third of the panels of foam peeled off over time, and until this last condition inspection a few weeks ago, I had gotten tired of replacing them only to have them fall off again (Super 77 wasn't doing the trick).

Anyway, at the condition inspection I diligently cleaned the firewall, that is I cleaned the residual dried adhesive off with lacquer thinner. I also wiped the back side of the peeled-off foam itself with lacquer thinner. I reinstalled all the missing pieces with Super 77 (yeah, I know they'll peel off eventually, oh well).

Now, before I say anything else I need to mention that I also installed carpet on the baggage area floor. Previously it was just bare back there.

The noise level is noticeably reduced. Now...whether it's the carpet or the reinstalled foam, that I don't know. So understandably this "account" is half-ass at best. But I can definitely say that with the foam replaced and carpet in back, it's quieter than it was before, when I was flying around with 1/3 of the foam panels off the firewall and no carpet in back.

I didn't measure the noise level...shoulda.
 
Sound levels

The EAA magazine had an excelent article about soundproofing last year--------had lots of db info, also lots of tech info as to "what and why".

Sorry I dont know the exact issue, but should be easy to find, in fact I wouldnt be surprised to see someone to post it here.

Mike
 
Actually, I think it's more to "heatproof" rather than soundproof. I'm sure it helps to keep the noise down too, but the heat transmitted through the stainless was the reason for my installation of Van's insulation blanket. I used high temp RTV to hold them in place and then aluminum tape along the edges.
 
Soundproofing is relatively easy until we need to compromise something. The basics would be:

Mass: More heavier construction will reduce more. It's up to you how much you are willing to put weight on the firewall but as without anything it is very light/thin and therefore even smaller amount of material will reduce noise. For low frequency noise the mass is kind of a only way to reduce it in this case. The real sound proofing materials are relatively easy to use but expensive. However thumbrule would be: the most heavier by volume is the best for proofing and it may not be the most expensive and most advertised...

Distance/space: The further you get, the less you'll hear. In this case, your engine will be on the other side of the firewall and you on the other -- I hope. Therefore this can be considered as constant here.

Damping: Some things can get "resonating" and damping these down will reduce noise. Usually mass helps to reduce effect of this.

Use any search engine and you'll find a lot of information about the basics of soundproofing and different solutions to do it. But the basics were here already -- if we also consider that we ain't have space to make air gaps between the protective walls.

However since reducing noise remarkable by adding mass is relatively difficult in case of the airplane I would suggest another lighter option: active noise reduction (ANR) headsets or any other good headsets. ANR technique will reduce noise much more you can "ever" reduce by adding mass to the firewall and together these will get you to the new level of soundproofing.

Personally I would (I've) select ANR headsets, which has also passive attenuation due if electronics of ANR headsets will fail, I'll have my hearing after the flight. If you haven't ever tested ANR headsets do it now. They are more expensive than normal headsets, but will be defenitely worth of every penny. Headsets will last long and therefore calculated per flight hour the cost should be reasonable. Test before you judge them due high price!

I also found some articles about bigger plane sound proofing. I didn't read all through but there might be some tricks:
http://www.earaircraft.com/lit.php3

About the basics of ANR techniques I would suggest to read this:
http://www.anrheadsets.com/tutorial101-1.asp

Hopefully these helped even a bit.
 
Right on.

Pirkka, I think you hit the noise right on the head. I have been thinking about this lately. I really didn't want to deal with the mess of having to re-glue junk on the firewall after a year or two. You know as soon as you cover it up the firewall, you will need access to something right after the glue is dry.
Very good post....Money well spent on good ANR headsets..
 
You must log in or register to reply here.