Sound deadening materials

[Thor]

To my mind 'sewing machine' noise is high frequency noise. This is usually air-born noise, rather than due to structural vibrations, it is less likely to be stopped by dynamat and the like than by sound absorbing materials (as opposed to vibration dampening materials).

[GREG]

Being a Discovery channel addict , a few months ago I remember watching a programme about counter acting the noise in an aircraft cabin. I didn't fully understand it , but basically a computer controlled gizmo created a noise opposite to the noise in the cabin which led to the cabin noise being cancelled out !

The result was spectacular and better than any amount of sound proofing could do in a prop plain. I would like to think that this technology would eventually become economically viable to use in a car ! Or better still my living room :-)

For now , I will just turn the radio up a bit

[Thor]

Greg, Lotus have done loads of work on this area, but I think the car cabin has too many different sources of sound, and resonances mean that a sound which is intense in one area is less noticeable in another, so the only pratical location for the sound removal devices is close to the ears of the users.

They use a system like this, built into the headphones/ear defenders of air force pilots.

Lotus did achieve exhaust silencing without the use of conventional silencers and, of course, this work lead to the idea of making a cheap front wheel drive shopping car sound like a Dodge Charger Hemi for no extra cost.

[GREG]

Amazing ! thanks for the information - love all that sort of stuff !