F

flybye

Well Known Member
Has anyone considered using Anechoic Chamber technology to reduce the reflective qualities of their cockpit? The standard solution to reduce background noise levels is an ANR headset yet they are expensive, your microphone is still in a noisy environment and I've not seen much thought put into reducing sound levels before they reach your headset. Acoustically absorbent materials on the sides of the Fuselage, Firewall and baggage area would be effective though these materials are not designed for the sake of appearance. Some compromise between form and function would be inevitable but may be worth some consideration.
 
A number of people have experimented with dampening materials to reduce sound transmission with varying degrees of success. You'll find that for any appreciable reduction in sound you'll pay a stiff weight penalty. The ANR headset, or better yet, in-ear DIY passive, provides far better attenuation than any amount of absorber you can place on the plane. But, any reduction is a comfort factor, so experiment away and please report on your results -- use a dB meter to record before/after and also record RPM settings.

An aside: there is absolutely no benefit in making the cockpit an anechoic chamber. The purpose of an anechoic chamber is to make reflections in waves as close to zero as possible. Your sources of unwanted noises are outside the airplane, and thus you only need to make the transmission of sound into your cockpit near zero. HTH
 
Loboflyer said:
An aside: there is absolutely no benefit in making the cockpit an anechoic chamber. The purpose of an anechoic chamber is to make reflections in waves as close to zero as possible. Your sources of unwanted noises are outside the airplane, and thus you only need to make the transmission of sound into your cockpit near zero. HTH
Click to expand...

I had a momentary image of an RV with a cockpit all lined with that blue coated, carbon impregnated, "spiky" anechoic chamber foam stuff! :)

(Those chambers are weird to stand in the middle of...uber-quiet and oddly dark...)
 
Acoustic Adventures

Jeff's recommended strategy is essentially correct. Stopping the intrusion of the external noise sources into the cockpit is a job for "barrier" materials. The ultimate material would be lead :) and we know how well that works for airplanes. That's why acousticians opine that "there's no substitute for mass."

Besides absorption (the foam wedges, for example) and barriers, the 3rd strategy used is damping. This is a material, usually somewhat flexible, that's applied directly to the structure to minimize structure-borne vibrations. Think "oil-canning."

Back in the mid-1970's (this is why my handle here begins with "Oldie") I worked at Walker Mfg, an automotive exhaust system supplier. We had an anechoic chamber, and one day the PR crew wanted a photo of our Chief Engineer in the Chamber with a lab coat on, for use in the company's Annual Report. The bright young PR types asked lots of questions and duly noted our answers, including 1 response about "dead quiet" inside the Chamber feeling a little uncomfortable. The following year the pic appeared, and the caption read something like "Walker's Anechoic Chamber, where men find it difficult to work." :) I always tried to live up to the well-chosen words of the PR Department!

In my Student Pilot days, long before I worked at Walker, I used to practice my Turns About a Point around Walker's water tower in Ray Maule's rental Maule M4 Jetasen. I had no idea that people were on the ground trying to measure car exhaust noise while some annoying airplane was buzzing about. I never owned up to my former aerial trespassing while working there. It's a relief to finally get this off my chest. :)
 
noise sources

Way smarter people than me have done the noise reduction studies in aircraft.
Learn from them.
Look at why a Mooney has 1/2" thick windshield, or inflatable door seals.
you have to do what gives the most bang for the buck, and per pound.
I too would like to know exactly what that means for our RV's????
Am I wasting my time upholstering with leather, when a huge bubble canopy covers half the cabin, and transmits, and reflects every sound wave?
 
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