Xref: utzoo sci.physics:6542 sci.math:6182 sci.electronics:5685 Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!mcvax!ukc!strath-cs!glasgow!taylord From: taylord@cs.glasgow.ac.uk (Donald Taylor) Newsgroups: sci.physics,sci.math,sci.electronics Subject: Re: noise cancellation Summary: is it necessary to have a microphone and headphone combination? why not have a mechanical link.. i.e. no power required Message-ID: <2688@crete.cs.glasgow.ac.uk> Date: 27 Mar 89 20:46:06 GMT References: <723@wucs1.wustl.edu> <7260@fluke.COM> <453@corpane.UUCP> Organization: Computing Sci, Glasgow Univ, Scotland Lines: 35 In previous postings, the idea of a headphone/microphone combination to cancel out unwanted noise has been discussed. I started thinking, "why all the electrical stuff?" You have this (mechanical) wave, right, travelling along towards the ear.. by the time it gets there, it will have a flat wavefront (in the majority of cases)... a very small part of this flat wavefront will hit the ear and pummels the ear drum, while the rest of the mechanical energy bouces about uselessly.. you could use that waste energy to cancel the sound at the ear. a 'diagram'... ||||||| ||||||||||| | ||||||||||| | |_|| ||_| Large circular disk |( O O )| __ diaphragm |_@ @_| mounted on headphone structure. /| | ___ | | / | \ / | ear cup \_____/ Sound incident on the above diaphragm, will cause it to oscilate in a standing wave, with the centre moving in anti-phase to the sound... getting the proportions of surface area inside, and outside of the ring of the ear-cup correct will result in the diaphragm adjacent to the ear being entirely stationery i.e. NO SOUND Anyone got any further ideas along these lines?? The resulting headphones would be quite bulky.. could they be reduced by having more surface area in less volume? And what about directionality?? All these questions, and less, next week same bat time, same bat channel. Disclaimer: I don't know what a disclaimer is, but this one is going to be squiggly ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~.