Cabin noise level

[tailwind]

Just returned from a 2 hour trip to dinner today. On the trip I took a sound level reading on the plane in cruise flight: 180 hp lyc with mt prop 2500 rpm 24.5 manifold pressure about 76 percent power and 10.5 gph about 115 knots true at 3000. I show 111 db at windshield level. If I position the meter at my firewall I exceed 120 db. Wonder if anyone else has sound readings.

[jaredyates]

I usually get around 90db in cruise in the cabin. In Mark's airplane I saw 108. This is on the ipad in my lap in both cases.

[Flygirl1]

Must be an app for that? I'd love to know the difference between 240BP and 241BP. I have lots of insulation all around and above me, whereas 240BP does not and he has a skylite.

[jaredyates]

Yes, there are several apps. Not sure how accurate they are, but it's better than nothing I suppose.

[Battson]

I have taken reading around the 110 mark, or a little less. Of course it depends on the measuring device a lot. The average mobile device seems pretty inaccurate / susceptible to user error.

[JimParker256]

From reading in "another forum", the microphones built into the smart phones and tablets are accurate only to about 94-95 decibels. Anything above that is wildly inaccurate. But that is 3rd-hand information from someone who claimed to be an expert. In any case, use hearing protection for all occupants. ANR headsets, passive headsets, earplugs, or whatever -- just use SOME form of hearing protection.

[tailwind]

We wear active headsets. The reading were taken with a sound meter. Loud sound is tiring and I did insulate to reduce the level. Wish while I had the meter that I had take readings at other power settings. Glad to hear that it seems that I improved it some.

[Bcone1381]

What did you insulate, what products did you use, and did you quantify the results afterwards with the sound meter?

[tailwind]

I insulated with 1/4 inch low density foam during the build. I think the foam was 12 lbs / cu ft if memory is accurate. I fabric covered the interior then glued the foam to the outside surface then covered the exterior. I do need to find some material to cover the back side of the floor though I have carpet on this surface. My biggest motivation for insulating was to try to reduce cold transmission during winter flying, sound was a secondary concern.

[Flygirl1]

I used foil backed bubble wrap stuff and a foil backed cotton cut up blue jean material from Home Depot. Also have carpet. These together really stop any "oil canning on the floor. I put the bubble wrap stuff between the aluminum floor and the frame. I also put a foil backed light weight cut up cotton blue jean type material under the carpet on top of the aluminum. This particular stuff is also on the side walls front to back and I have pink insulation on the entire top above the cabin behind and on top of the headliner. Now ya all can see why my plane is a bit heavier than some, most. ;-) (1247lbs) On a side note, whatever your using think about doing a burn test. I can't remember exactly what the criteria was, but all my materials passed. I think the fire had to go out in a rather quick time frame. I used this same blue jean material on the fire wall and sprayed it with Flex Seal to make it look better. After i had it installed I had an after thought about the burn test--it failed, miserably!! Switched to a high heat black spray paint.

[Chewie]

Just be aware, a cheap sound meter that feeds you one number (all the frequencies summed together) is really only good for relative comparisons. So if you're measuring with the same microphones, same pre-amps, same mic location, etc etc etc it can be useful. But that's about it!

[JimParker256]

My plan for the Patrol is to make it as light as I can make it (though I'm certain it won't be as light as Bob's!), so I don't plan to "line" the interior anywhere except the baggage compartment. I expect I'll use insulation only on the firewall - mostly to avoid heat transfer in our gloriously "warm" summer months (avg highs > 95F).

I already own two ANR headsets that are quite nice in the winter, but just too hot to be comfortable in the summer. I also own two sets of Halo in-ear passive noise reduction headsets that are amazingly light and comfortable, and provide very close to the same noise reduction as the ANR headsets. Hopefully, that will be enough to keep things comfortable, acoustically.

[Flygirl1]

Got a hold of a noise meter that was tested against big end commercial equipment and was told it performed really well. Results @ 24.5/2500 were both planes were about 99 dba and at 24/24 at 98 dba. This was with the meter held at chest level facing forward. My plane at full power with the meter in my lap, showed 104 dba and Dennis’ was 102 dba. Dennis also held it at the windshield and saw 104 dba. I was told there is a difference between the db’s used and we used dba’s ( apparently what the ear hears ).

[Bdflies]

So, Donna, I hate to point to the obvious... it seems that you've made an argument for not getting too involved with sound proofing. Or, is there a benefit (notable difference) that's not quantified by the meter?

Bill

[Flygirl1]

Yea, it would appear that way. In fact I'm not sure about the results. Just doesn't add up to me. You would think with a pretty good insulated ceiling and no skylite there would be a noticeable difference. I think we'll try it again with somebody in the back seat running the meter and taking notes. ;-)

[Bdflies]

Great idea! Nothing better than a good reason to have to fly!

I don't have a sound meter and I didn't do any sound deadening material. I do, however have a couple pairs of the wireless Zulu headsets. My Patrol is about the same noise level as my Husky was. I did notice a nice sound reduction when I installed weather stripping around the windows and doors.

Bill

[tailwind]

I don't think much noise comes from the top cabin area by comparison. The most noise comes from the firewall area and tunnel area which is what one would expect. I need to do something light in this area on mine.

[Bcone1381]

This pamphlet on soudproffing aircraft suggests Thick windows and layering "super soundproofing mat" with Aluminum Foil to 2 inch thickness at the firewall and boot cowl as an effective way to sound proof light aircraft. It also talks a bit about materials that are not effective. I have not tried this, but look forward to experimenting in the future.

LightAircraft.pdf

[Archer39J]

I recall a pretty lengthy discussion on another forum regarding insulation placed on the firewall and it acting as a "fire transfer material" to move fires from your engine compartment to inside your cabin. Seemed to make sense to me at least so I'm going to avoid putting any insulation cabin-side on the firewall. Folks are apparently taking to layering fiberfrax between stainless foil and bolting that to the engine-side firewall, I believe for heat deflection purposes. FAR 23.1191(g) states "Firewall materials and fittings must resist flame penetration for at least 15 minutes." if that's of any interest. For that reason I intend to use a stainless heat box as well.