Sound proofing. Anybody had any real success??

[nels]

1 hour ago, StinkBug said:

I'm hoping he just meant to pull the engine back to idle. Of course even pulling the mixture out the engine is gonna keep windmilling at around 1800rpm or so. I can speak from experience here after running a couple tanks dry on purpose and not anticipating the timing well enough. 

Oh I think Jerry realized that. Although it's really no big deal, as you say, the engine would just windmill. 

[Piloto]

Human bodies tend to absorb noise they do not reverberate. You may have notice that the noise level is less when you have four passengers on board, specially if they are overweight. When taking comparative noise measurements for measuring improvements it is important to always have the same number of passengers onboard.

José

Edited September 15, 2017 by Piloto

[Bob - S50]

Foam ear plugs, headsets, and a 4 place intercom.

Work great.  Reduces radio static.  I can't tell the difference between my ANR headset turned on or off.

[ArtVandelay]

Human bodies tend to absorb noise they do not reverberate. You may have notice that the noise level is less when you have four passengers on board, specially if they are overweight. When taking comparative noise measurements for measuring improvements it is important to always have the same number of passengers onboard.
José

Then Marauder must have the quietest ride.

[Andy95W]

2 hours ago, Piloto said:

Human bodies tend to absorb noise they do not reverberate.

Come talk to me after I've had chili with onions...

 

[jlunseth]

Be careful what you put in there.  When I first bought my aircraft the side panels were removed and the "cage" inspected.  There was a nice, warm, wool-type insulation in the walls that made the aircraft nice and quiet.  Well, the edges of that nice, warm, quiet insulation sit in contact with the frame bars, and the material traps and retains moisture, so over the multi-decade life of an aircraft it causes the "cage" to rust, which causes repairs to have to be made, which causes the skin of the aircraft to have to come off in the affected area, and causes sections of the cage bars to have to be cut out and removed, and replaced with new.  Don't ask me how I know.  You are probably better off with nothing in that space between the walls at all.

[nels]

On 9/16/2017 at 10:51 AM, jlunseth said:

Be careful what you put in there.  When I first bought my aircraft the side panels were removed and the "cage" inspected.  There was a nice, warm, wool-type insulation in the walls that made the aircraft nice and quiet.  Well, the edges of that nice, warm, quiet insulation sit in contact with the frame bars, and the material traps and retains moisture, so over the multi-decade life of an aircraft it causes the "cage" to rust, which causes repairs to have to be made, which causes the skin of the aircraft to have to come off in the affected area, and causes sections of the cage bars to have to be cut out and removed, and replaced with new.  Don't ask me how I know.  You are probably better off with nothing in that space between the walls at all.

I know what you mean and I want to be careful for sure. I think I would like to re epoxy coat all those frame tubes and possibly install a closed cell foam product possibly glued lightly to the skin? I really hate to do anything until I know where the bulk of the noise comes from.

[Baxsie]

Fair warning: I am not a pilot or owner (yet), but I have tackled noise on my boat and a car project--with some success.

What about using a Mass Loaded Vinyl Barrier dampening system like DynaPad?  

http://www.dynamat.com/automotive-and-transportation/car-audio/dynapad/

This appears to be a automotive version of the Marine acoustic barriers like these:
http://soundown.com/AI.htm

Except much thinner (~1\2"), and plastic faced rather than foil. 

These are heavy (by design), but maybe a judicious application of DynaPad on the firewall (cabin side) could reduce the transmitted noise from the engine.

Perhaps small (6" square?) sections (at ~1/4 lb each) could be mounted to skin panels that resonate.

[carusoam]

Interesting...

The first challenge you fall upon after 'does it work in an airplane?' will be 'does the FAA allow it to work in your airplane...?'

A certain level of approval is going to be needed...

How much material did you need for your car?

Did you focus on the interior of the car only?

I see they have extensive material to cover the hood and trunk areas... if these are needed to work in the plane properly, how much does all that weigh?

It Sounds like $1000 of material and about $9000 of proper installation/documentation/testiing/etal...

Best regard,

-a-

[bradp]

You want closed cell foam that won't absorb water.  You want foam that slots in but doesn't sit against the steel tubular structure.  Adding a vapor barrier in has its unintended consequence of trapping moisture between the foam and most likely the aluminum skin.  Moisture anywhere is bad.  Make sure the windows are water tight and this will do more to limit corrosion than any concerns about relative humidity. 

[Baxsie]

carusoam said: How much material did you need for your car?
Certainly less than $1000, it is an automotive product, so it is low cost:
https://smile.amazon.com/s/ref=?url=search-alias%3Daps&field-keywords=dynapad+by+dynamat

carusoam said: Did you focus on the interior of the car only?

Since we did not have weight, flammability or regulatory issues, we covered the interior floor, some parts of the doors, and the sunroof. 

We used a 1" foil-faced marine product on the engine side of the firewall. Since there was room and we had material, we also used the 1" marine material in the side panels beside the rear seat.

bradp said: You want closed cell foam that won't absorb water. 
I think so. For the car, we covered every bit of a surface we could. For an airplane, I think you would want to do small patches in the center of panels that have vibration or resonance. I would only apply this kind of material to a finished panel -- for the car that is epoxy primer+panit. Not sure what the aviation equivalent would be. I guess if you did a couple panels with a self-adhesive product, you could remove it at the next annual to check for corrosion?

Here are some photos of the car installation:
 

 

 

Here are some of the relevant posts from the build thread:
Doors: http://www.thesamba.com/vw/forum/viewtopic.php?p=7384405#7384405
Floor: http://www.thesamba.com/vw/forum/viewtopic.php?p=7605329#7605329
Sunroof: http://www.thesamba.com/vw/forum/viewtopic.php?p=7659656#7659656

With the weight penalty and regulatory requirements of certified aircraft, I am not sure that this approach would be useful for airplanes. Just a thought from a similar sound reduction project.

[nels]

Interesting. I'm sure the "aircraft" stipulation would negate lots of what you have done but maybe not all of it. Do you have any before and after sound measurements?

[N201MKTurbo]

On 9/13/2017 at 9:41 AM, Jerry 5TJ said:

This isn't going to read well in the NTSB report. 

Sounds like my ATP check ride. That airplane had the most unreliable engines ever!

[carusoam]

Baxsie, thanks for sharing your addiction!

Best regards,

-a-

[nels]

Took my Mooney from I69, Cincinnati area, up to Dunkirk, NY yesterday. I flew up at 7500 and back at 6500 ft. 2400 squared and took some noise samples with my new meter. The center of the cabin at ear level was about 97 decibels. This reading changed very little through the cruise altitude range. I had tightened up the cowl doors before I left as one was open about an inch when closed. In doing so I noticed at cruise the interior noise seemed to actually have gone up with the doors closed. Before adjusting them I seem to have noticed a reduction in noise when closed but don't have any measurement to tell me this was the case. However, I think when closed tight against the cowling they probably vibrate against the cowling increasing the noise. The increase was hard to measure but was there so I'd say it was about a half decibel. The passenger floor area was a solid 99 decibels with an occasional 100 reading. The pilot floor was about a 98 decibels. I assume this is due to the exhaust being on the passenger side near the floor.

Maybe cushioning the engine cowling from the airframe and gear and flap doors from the cowling could lesson the mechanical vibrations and noise translated through the tube structure to the cockpit? I will probably play with this idea over the next few weeks.

[JohnB]

On 9/17/2017 at 9:41 PM, Baxsie said:

Fair warning: I am not a pilot or owner (yet), but I have tackled noise on my boat and a car project--with some success.

What about using a Mass Loaded Vinyl Barrier dampening system like DynaPad?  

 

This appears to be a automotive version of the Marine acoustic barriers like these:
http://soundown.com/AI.htm

Except much thinner (~1\2"), and plastic faced rather than foil. 

These are heavy (by design), but maybe a judicious application of DynaPad on the firewall (cabin side) could reduce the transmitted noise from the engine.

Perhaps small (6" square?) sections (at ~1/4 lb each) could be mounted to skin panels that resonate.

Well I had my entire airplane "soundproofed" with removing my interior, placing soundproofing material then reinstall, and I can say honestly that it made absolutely no difference in engine noise, that i could tell. But it does sound quieter inside when the doors are shut and the engine is off, as it seems effective in blocking noise outside of your airplane. So it helps for a moment when you shut your door, blocking the noise from surrounding airplanes before you start up, but once you take off, there's essentially no noise other than your engine and wind coming through any openings (see comment on door seals).   So in my opinion, that's probably not a helpful spending of money. Bose headset and door seals absolutely yes. I might think about adding baggage door inflatable seal one day. Another thing that helped mine was at annual, I had my mechanic check to make sure all of my engine mounts and anything else that can rattle fixed.

JB

[Baxsie]

(Apologies for waking the dead thread.)
From this PDF:

https://mooneyspace.com/applications/core/interface/file/attachment.php?id=52878

Mooney Encore ARTICLE- AOPA.pdf (@LANCECASPER)

There was this quote relating to this thread:
"A new acoustic firewall pad drastically reduces engine noise in the cabin."

I wonder what that firewall pad on an Encore is made of? 

[LANCECASPER]

6 hours ago, Baxsie said:

I wonder what that firewall pad on an Encore is made of? 

Not sure what it is made of, but if you look in the background of this picture you can see the firewall pad. (This was a picture taken during the pre-buy of an Encore I bought in 2014. I had the baffle seals replaced after this picture was taken during the pre-buy/annual.)

[Cyril Gibb]

I'd really like to hear what the noise levels are (Db and Dba) with that firewall pad.  On the other hand, retrofitting that would only be possible with an engine removal, and even then a pile of work.

[nels]

I had mine up again the other day and again at 24x24 and 7k. I checked the noise between the glare shield and the windshield......pretty loud at 103 decibels.

[211º]

Just for comparison. In the center of the cabin of the E at 3,000 ft

25x2500 - 99 dB

21x2350 - 93 dB 

[BKlott]

A couple of years ago I spoke with the owner of an interior shop that had done a lot of work and testing on different soundproofing systems. His conclusion and recommendation to me was not to bother. The added weight and expense wasn't worth it. His advice was to buy a good noise cancelling headset. That was the best soundproofing system he ever found.

[Jerry 5TJ]

1 hour ago, 211º said:

Just for comparison. In the center of the cabin of the E at 3,000 ft

25x2500 - 99 dB

21x2350 - 93 dB 

Thanks for the data points.   

By comparison, inside a very loud car (Audi R8 with a V10 just behind the seat) reads about 75 dBa at 85 mph.  Ref: http://www.auto-decibel-db.com/

The Mooney cabin is 20+ dB or over 100 times louder than the R8.  

Sound levels consistently above 85 dBa are generally taken to be harmful.  Ref https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5308171/

Wearing a good headset in the Mooney you can get the noise at your ears down to around 75 to 80 dBa.  

[Jerry 5TJ]

18 minutes ago, BKlott said:

A couple of years ago I spoke with the owner of an interior shop that had done a lot of work and testing on different soundproofing systems. His conclusion and recommendation to me was not to bother. The added weight and expense wasn't worth it. His advice was to buy a good noise cancelling headset. That was the best soundproofing system he ever found.

My Mirage had extensive insulation added to the cabin.  The result -- it is not much quieter but is much easier to keep warm when OAT is -35.  

[nels]

9 hours ago, BKlott said:

A couple of years ago I spoke with the owner of an interior shop that had done a lot of work and testing on different soundproofing systems. His conclusion and recommendation to me was not to bother. The added weight and expense wasn't worth it. His advice was to buy a good noise cancelling headset. That was the best soundproofing system he ever found.

You are kidding yourself if you think noise canceling headsets are the answer. I thought the same thing but noticed rapid hearing loss over the period of two years while using them. They ONLY protect low frequency range leaving the high frequency range of hearing vulnerable!  Simple foam ear plugs combined with noise canceling headsets will take care of the high range and low range frequencies. Try it, you will hear the tower better when communicating also.  Once your high range is gone conversation in a room full of talking people is very difficult, hard to isolate the voice you are trying to hear. You won't notice hearing loss until it's too late. It doesn't fix itself or grow back! The FAA agrees with me on this and has published a good three page article on the matter. To quote: 

• Combinations of protection devices. The combination of earplugs with earmuffs or communication headsets is recommended when ambient noise levels are above 115dB. Earplugs, combined with active noise reduction headsets, provide the maximum level of individual hearing protection that can be achieved with current technolog.

•