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Kit Aircraft Acoustic Educational Info

• Aircraft Acoustics 101
  • There are many products out there, which one should I use?
  • Why the emphasis on vibration?
  • How do I eliminate vibration?
  • What about damping?
  • Is that it for passive vibration control? What's next?
  • So what about absorbers?
  • Is that all there is?

• At a Glance, Making an Aircraft Quieter

• Glossary

• Making Templates

• Oshkosh Presentation: Practical Noise Solutions for Aircraft Interiors

• 
• Composites

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Aircraft Acoustics 101, A Quick Overview

There are many products out there, which one should use?

All of the acoustic treatment products out there will have some effect, the question becomes which one will work best and fits your needs. Generally, a systematic approach is best so some understanding of the technical aspects may be needed.

There may be many materials to treat noise, but there are really only four types of "passive" treatment. Two are noise treatment and two are for vibration. They are:

1. Vibration isolation
2. Vibration damping
3. Acoustic barriers
4. Acoustic absorbers

Balancing moving parts is extremely important but since this would normally require a specialized engine and propeller shop, I will only mention it in passing. However, you will get a sense of how important vibration is by the time you finish this article so it is something to keep in mind.

Not related to acoustic treatments, there is a side benefit to precision balancing of the prop and engine in that wear on the engine is reduced so it merits serious thought. Nor am I discussing Helmholtz resonators and bass traps or active treatments such as Active Noise Reduction (ANR) and its close relative, Active Vibration Canceling, (a mass is moved opposite a structural vibration instead of a speaker broadcasting sound waves opposite noise).

The order these were written is not random. It is the order in which the most efficient treatment should be done and starts from the biggest noise generator (the engine) to the last treatment, absorption.

Stated another way,

	1.	Get between the vibrating part and the airplane, (engine mounts). Keep vibration away from the airframe by separating the vibrating object from the structure.
	2.	Reduce the vibration that does get through. This is done with "Dampers".
	3.	When the remaining vibration is turned into noise, place a barrier between it and you.
	4.	Once inside the cabin, noise can only be treated by absorption. This means the noise that does get past the barrier should be absorbed as should any noise generated INSIDE the aircraft like speech or perhaps some moving equipment.