Sport Aviation article on sound control.

[65eTurbo]

About 20 years ago there was a great article in sport aviation where a bunch of sound deadening experiments were conducted.  It had a ton of great data on what actually works.  Anyone familiar with that article or know how to find it?

[MB65E]

13 minutes ago, 65eTurbo said:

About 20 years ago there was a great article in sport aviation where a bunch of sound deadening experiments were conducted.  It had a ton of great data on what actually works.  Anyone familiar with that article or know how to find it?

I think Dave Morss wrote the article. I have a full set of EAA mags I have access to. I will try to find it! Or feel free to call Dave directly. He’s a really neat guy. His website is http://www.davemorss.com/

But 20 years ago? Already? Dang!! I remember the article. Ouch! 

-Matt

 

 

[65eTurbo]

Thanks!  I'm guessing 20 years.  I know, I have had to adjust my time estimates, that's why I guessed 20 years.  Is there an online sport aviation guide somewhere?  I probably have the issue buried somewhere, but doubt I could find it. I'm doing my interior and I remember some interesting details came from that testing, like surface finish mattering and such.

[Andy95W]

I don't remember the article, but I can give some information about the subject.

My current 1964 Mooney has/had 1" thick closed cell foam installed everywhere, including the firewall.  It made absolutely no difference in sound proofing.  I've been removing it as necessary when I do work on the airplane.  In some places I replace it with 1/2", just so it matches.  Again, no difference.

[65eTurbo]

1 minute ago, Andy95W said:

I don't remember the article, but I can give some information about the subject.

My current 1964 Mooney has/had 1" thick closed cell foam installed everywhere, including the firewall.  It made absolutely no difference in sound proofing.  I've been removing it as necessary when I do work on the airplane.  In some places I replace it with 1/2", just so it matches.  Again, no difference.

Thanks for the pirep.  Yeah, I think the article found that, but interior surface finish is mattered.

[DXB]

Very curious to see this article. Good to know more sound deadening foam is worthless.

I will say installing a 201 windshield made no perceptible difference in speed for me but created a dramatic reduction in noise!

[bob865]

I work in the automotive industry and am currently working on a on a sound deadening automation poject. I will tell you a little about what I know about sound deadening without getting into trade specifics that I can't share.  In cars the sound deadening is done with an asphault type material.  It's some complex stuff that a chemist would have to tell you about, but as I understand it, it works by cnverting the vibration of the metal to heat.  Pretty cool I thought when I learned that.  Anywho, this stuff is typically applied in one of two ways.  The first is a die cut pad that conforms to the body and glues itself to the metal when the car body is baked.  The second is a liquid type material that is sprayed in the car and then baked.  Either way, when we try to determine how much of this suff to add or if enough has been added, we measure how much weight is added.  The amount of sound deadening you get is a function of how much weight is added and how much surface area is covered. 

[65eTurbo]

3 hours ago, bob865 said:

I work in the automotive industry and am currently working on a on a sound deadening automation poject. I will tell you a little about what I know about sound deadening without getting into trade specifics that I can't share.  In cars the sound deadening is done with an asphault type material.  It's some complex stuff that a chemist would have to tell you about, but as I understand it, it works by cnverting the vibration of the metal to heat.  Pretty cool I thought when I learned that.  Anywho, this stuff is typically applied in one of two ways.  The first is a die cut pad that conforms to the body and glues itself to the metal when the car body is baked.  The second is a liquid type material that is sprayed in the car and then baked.  Either way, when we try to determine how much of this suff to add or if enough has been added, we measure how much weight is added.  The amount of sound deadening you get is a function of how much weight is added and how much surface area is covered. 

 I used to work in the automotive industry about 20 years ago. Back then IMO that tar based sound insulation stuff was placed in patches were would most chains the resonant frequency of a piano to move it outside Will be audible or physically offensive frequency ranges. We also used shredded recycled fabric based flocking in some areas To absorb sound or prevent squeaks.The article I'm talking about had interesting data out a bunch of different techniques.   To think I recall some techniques being effective without being particularly heavy.

[65eTurbo]

Deb sent me the following, which was exactly the article I remembered.  I wish more Sport Aviation articles were this technical and data rich:

“About 20 years ago there was a great article in sport aviation where a bunch of sound deadening experiments were conducted.  It had a ton of great data on what actually works.  Anyone familiar with that article or know how to find it?”

Taming the noise, EAA April, 2005? http://acversailles.free.fr/documentation/08~Documentation_Generale_M_Suire/Bruit/Taming_the_noise.pdf

 

[65eTurbo]

As a general gist, I wonder if covering all the interior panels with porous fabric would reduce reflected acoustics, and if cloth seats reduce noise relative to leather.  Also, it makes me think heavy wool carpeting might help noise from floorboards and firewall relative to the lighter weight stuff.

Anyone have any data on that?

In air cooled engine cooling, sealing every tiny hole leads to much better performance.  I wonder if interior sound is the same way, heavy carpeting and cloth covered interior surfaces providing a noticeable benefit.

[Hector]

I don't remember the article, but I can give some information about the subject.
My current 1964 Mooney has/had 1" thick closed cell foam installed everywhere, including the firewall.  It made absolutely no difference in sound proofing.  I've been removing it as necessary when I do work on the airplane.  In some places I replace it with 1/2", just so it matches.  Again, no difference.

I would have to agree here. Just recently did my interior and had all the panels out. Installed acoustic foam from Spruce everywhere and I can’t tell the difference. I have a DB meter and for the life of me did not think of taking before and after readings (major fail) but I believe if it had made a significant or even some difference I would have noticed. My Bose A20s do far more to control the noise.


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[carusoam]

Great input PMc!

My air handling guidance used air speeds less than 90fpm to minimize air noise coming out of HVAC ducts... just over 1 mph... roughly...

And it does get noisier the faster the air goes... so don’t skimp on the duct size when doing the design work... adding a little more CFM to the room to control temp, can get noisy before the temp gets controlled... 

 

Prop tips at 2700rpm are incredibly noisy...especially if they are aluminum... inside the cabin, with my halo headset on... I don’t hear it as much as the people outside the cabin do...  

Other not so practical recommendations... the Ovation moved the prop a couple more feet away from the windshield... that seems to make things a bit less noisy... might be the angle of the windshield helping... or the insulation that is used...

Does the noise drop significantly if flying at 20k’ as the air is less dense?

Best regards,

-a-

[65eTurbo]

What makes the biggest difference for me is engaging the Turbo charger. Because I have a manual Wastegate rajay, I can tell the difference when the wastegate closes, and it is slightly quieter if I can close it all the way.  So, I like to run 2400 rpm wastegate closed and LOP and 27 inches or under for cruise, somewhere just under 10 gph.  The 201 windshield seemed to help a bit too.  I think I'll go for the ultralight weight carpet if the wool won't help.