Sound proofing. Anybody had any real success??

[nels]

I'm sure this topic has been beat to death but has anyone had any real noticeable sound reduction success with their Mooney. If so, what did you do. I checked my Mooney at 3k feet and about 145 knots and the decibel reading was about 7 to 10 decibels higher than a newer 172 at 3k ft but didn't get the airspeed. I took the readings within an hour of each other. I would love to trim 10 decibels out of the cockpit of my Mooney but I want it to make sense and don't want to reinvent the wheel. I don't mind adding a few pounds if i can really take a chunk out of the noise.

[Seth]

Thicker windscreen glass is said to help but I have not seen scientific proof.

Same with lower RPM.

ANR headsets too.

 

-Seth

[Andy95W]

A previous owner installed 1" black closed cell foam on my M20C, plus installed a thicker 201-style windshield.  He put the stuff everywhere, ceiling, walls baggage wall. He even put 1" foam on the firewall.

End result: about 92 decibels, which is about the same as everyone else around here.  Not worth the effort.  A good headset (I suggest the Quiet Technologies Halo) is a MUCH better investment.

[Oscar Avalle]

I also agree with Andy. No worth the effort. Mooneys are loud. Get a good pair of headsets. I use a Bose and it is ok.

Oscar

[N201MKTurbo]

When I had my old F Mooney I got a little rust on the steel tubes from wet fiberglass. I fixed the corrosion and replaced all fiberglass with some high tech soundproofing stuff. I put in a thicker windshield at the same time. It got noticeable quieter but you still couldn't carry on a conversation without yelling.

One side benefit is the plane stays warmer in the winter. To that point, the biggest thing you can do to quiet the plane is to fix all the air leaks. A new door seal will do more than an insulation job. 

I wouldn't mess with the insulation unless you had the interior out for some other reason.

[JohnB]

I have done lots of this with my airplane, and the biggest noise reduction per dollar spent was

1. BOSE ANR headsets
2. Inflatable door seals

Soundproof paneling, although cuts noise down a tad,  it's expensive, and it's probably not worth the extra money per decibel reduction, but it does improve noise a tiny bit.

JB

[peevee]

Bose also. I keep meaning to wear ear plugs too but I always forget to put some in my flight bag. Oh well.

The real question is why are mooneys so loud?

[Jerry 5TJ]

49 minutes ago, peevee said:

The real question is why are mooneys so loud?

Could it be from the engine roaring away just above our feet?  

Noticeably quieter GA planes seem to:

• Move the propeller further out front or behind the cabin
• Have  more prop blades
• gear the engine so the prop rpm is lower
• pressurize the cabin
• switch to an engine that goes "whoosh" instead of "bang bang bang"
• add active noise cancellation to mitigate structural audio resonances

 

 

 

 

[peevee]

I wonder what it would take to certify an add on active noise cancellation system. Maybe not too much. It would be an interesting problem for someone with the knowledge to work out.

[nels]

Are the new Mooneys loud inside? They had to quite them down I would think?

[Oscar Avalle]

I have done lots of this with my airplane, and the biggest noise reduction per dollar spent was

1. BOSE ANR headsets
2. Inflatable door seals

Soundproof paneling, although cuts noise down a tad,  it's expensive, and it's probably not worth the extra money per decibel reduction, but it does improve noise a tiny bit.
JB

I forgot to mention the inflatable door seal! If you ask me that is what REALLY made a difference


Sent from my iPhone using Tapatalk

[carusoam]

The R is incredibly quieter than my old C.  Unfair comparison... they were built 30 years apart... 

+1 for Jerry's list...

Shorter blades, really far forward helps.  Blade tips turning 2700 rpm are just loud. Short props get some pretty funky wide chord airfoil designs...

Good insulation, keeps the cabin nicely warmed. Helpful in winter. Easier to put up with all the noise when you are comfortable...

One thing you can change...RPM.  Get out your sound measuring app, alter the prop speed and see if it makes a difference.

Doing the same test at varying altitudes (MPs) will account for some change in power/engine sound.  

Higher altitude has less dense air and transmits sound less/poorer...

PP thoughts only... we have a sound guy around here...

Best regards,

-a-

 

[Bartman]

Reduce the number of molecules that transmit vibration to your ears....

Just fly higher and it gets much cooler, more efficient, better visibility, and quieter too 

[Guest]

Of all the the airframe types I've worked on, the older Mooneys from 252 down are up there in the noise department both of my E models would out perform most noise cancelling headsets on takeoff.

Clarence

[Piloto]

A lot of the noise comes from the glareshield reverberation and door air leaks. For the glareshield I cover the edges around with the Velcro soft strips. This keeps the airframe from making direct contact with the glareshield thus vibrating like a loudspeaker cone. For the doors I used foam weather strip. It conforms nicely on uneven door frames.

To keep the side panels from reverberating I glued carpet like material on the back surface and taped the tubing with aluminum tape where the carpet makes contact to prevent corrosion.

José 

[Skates97]

4 minutes ago, Piloto said:

A lot of the noise comes from the glareshield reverberation and door air leaks. For the glareshield I cover the edges around with the Velcro soft strips. This keeps the airframe from making direct contact with the glareshield thus vibrating like a loudspeaker cone. For the doors I used foam weather strip. It conforms nicely on uneven door frames.

To keep the side panels from reverberating I glued carpet like material on the back surface and taped the tubing with aluminum tape where the carpet makes contact to prevent corrosion.

José 

Can you explain the soft side velcro around the glareshield a little more? Maybe a picture? 

[Piloto]

18 minutes ago, Skates97 said:

Can you explain the soft side velcro around the glareshield a little more? Maybe a picture? 

The M20C does not has a plastic glareshield like the M20J and later models. 

I took Velcro 2" x 4" soft side strips folded and stick it around (top and bottom) the front perimeter to keep the glareshield from making contact with the aluminum and the windshield. I have no pictures of it.

José

[StinkBug]

I thought my C model was noisy, until I started flying a stripped down C206 skydive plane with the door open all day :-p

[bradp]

I did a thick windshield and new thick foam for insulation.  Almost not a bit of notable difference.  Cabin is 87 Db and down by the firewall it's like 90 Db.  Thenfirewall seems to be the loudest part of the airframe.  

[RLCarter]

I installed 1/2" closed cell foam on the sides and ceiling, foam backed carpet and even put carpet in front of the rudder pedals, it's still pretty loud, would be a pain to do the firewall but I think that's where most of the noise comes from

Edited September 13, 2017 by RLCarter

[bradp]

23 hours ago, RLCarter said:

I installed 1/2" closed cell foam on the sides and ceiling, foam backed carpet and even put carpet in front of the rudder pedals, it's still pretty loud, would be a pain to do the firewall put I think that's where most of the noise comes from

Real pain.  It's like a pleather skirt that has everything important passing through it in the most inopportune or locations.  I thought it wasn't worth it.  

[nels]

On 9/11/2017 at 5:41 PM, bradp said:

I did a thick windshield and new thick foam for insulation.  Almost not a bit of notable difference.  Cabin is 87 Db and down by the firewall it's like 90 Db.  Thenfirewall seems to be the loudest part of the airframe.  

The last db check I did was at 3k ft and about a 160 cruise. It was 105 db's. This is with an ap on my cell phone. What measuring device are you using? I certainly don't trust mine but if I start making changes and want to verify results, I will need to use the same device for all measurement and would like it to be a good unit.

Also, are there any directional units that might give us some insight as to where the loudest nose comes from?

[nels]

Anybody ever take a sound measurement at cruise and then cut the engine and take another? This would give a good indicator of sound contamination from exhaust or power strokes from the engine.

[Jerry 5TJ]

Just now, nels said:

Anybody ever take a sound measurement at cruise and then cut the engine and take another? This would give a good indicator of sound contamination from exhaust or power strokes from the engine.

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

[StinkBug]

9 hours ago, Jerry 5TJ said:

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

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.