Crystal Microphone

This document covers Crystal Microphone

1. Crystal Microphone

By Prof. Hitesh Dholakiya

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2. Outlines
“ Basics of Crystal Microphone
¢ Structure of Crystal Microphone
« Elements of Crystal Microphone
< Working of Crystal Microphone
“* Directivity of Crystal Microphone
“ Characteristics of Crystal Microphone
“ Features of Crystal Microphone
« Applications of Crystal Microphone

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3. Basics

“+ based on the principle of ‘Piezo Electric Effect’

* ‘Difference of potential between the opposite faces of some crystals is
produced when these are subjected to mechanical pressure.’

+ crystals : Quartz, Tourmaline, Rochelle salt and ceramic.

* Rochelle Salt : high piezo electric effect but is susceptible to moisture —
cannot withstand with high temperature of 50° C

“ Quartz and Tourmaline : low piezo electric effect

% Ceramic : most suitable for crystal microphones as it is not susceptible to

moisture and can withstand high temp up to 100° C
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4. Structure of Crystal Microphone

housing twin piezoelectric crystal

SOUND WAVES
E

DIAPHRAGM CRYSTAL

OUTPUT
VOLTAGE

ELECTRODES

5. Elements

Crystal is cut along certain planes to form a slice.

“ Metallic foil electrodes are attached to two surfaces to carry the potential
difference to the output terminals.

« Two thin crystal slices suitably cut are placed in an insulating holder with
an air space between them. Large number of such elements are combined
to increase emf.

< Diaphragm : made of Aluminum, is attached to the crystal surface through
a push road.

« The whole unit is enclosed in a protective case.

6. Working

+ sound wave compression — compresses crystal

% rarefaction — converse takes place — crystal is extended and is
under tension

“ due to this compression and extension — varying potential
difference is generated which is proportional to the mechanical
pressure applied to the crystal by the sound waves — Pressure

Microphone

7. Characteristics

< Sensitivity
“ SNR

“ Freq Resp
+ Distortion
+ Directivity

“ Out Imp

: good — about 50 mV for 0.1 Pa
: high - about 40 dB

: 100-8000 Hz

:low — about 1%

: Omni-directional

: high - about 1 MQ

8. © an be spolen ined dee rung
$ high imp = requires relstively short | the input eut of the
amplillcrio prevent lues of higher orpick of hum.

$ niser chealt will lead i: and

be uned in nui :
$ dues not need a bles
$ should not be esposo to direct sun ph for long timo
dl)

9. Applications
+ Home recording systems
“ Amateur Communication

<% Mobile Communication

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