Crystal Radio
stay tuned crystal radio and tube radio website
crystal set


Sound Powered Phones for Crystal Sets
Introduction Part II



What makes a "Sound Powered" element more sensitive than

a old style "Balanced Armature" element or a set of "Magnetic Headphones"?
Good question. There are several things that make it more efficient. Lets start with some basics.



Magnetic Headphones Basics

See figure #1
Magnetic headphones, new or vintage, work the same. Wire (a coil) wrapped around a pole (iron) which attracts a disk of metal when a current is applied to the coil (see "A" in figure #1).

Magnetic forces travel through Iron easier than through air. The "Reluctance" of the magnetic field to travel through air makes a headset less efficient than if it travels through iron. Therefore "A" is less efficient than "B" in figure #1.

"B" is called "bi polar"



Figure #1

A single pole ("A" in figure #1) design is less efficient than  a double pole design ("B" in figure #1) because it has less "reluctance".

The most "sensitive" spot on the disk being pulled by the magnetic poles is in the center. This is without a dough the most sensitive spot. Sensitivity drops off rapidly as you go to the sides of the disk.

"A" pulls from the very center and "B" pulls from the sides just a little, but the bi-polar design is still much more efficient than the gains you get from pulling from the exact center.
 
 

What we learn here is that the we need a design that pulls from the center  to be more efficient and more "sensitive".


Balanced Armature Headphones

Enter Balanced Armature headphones such as Nathaniel Baldwin's vintage headphones.

See Figure #2

Notice the reluctance for the lines of force for the magnetic field is very low. The magnet field has an iron path most of the way.

Also the "lever action" works on the center of the disk or diaphragm which also increases its efficiency.
 
 


Figure #2

What more could you want???

OK

 
 

Sound Powered Elements






Enter sound powered designs. See figure #3

This is basically a improved "Balance Armature" element with design improvements such as:

Duraluminum diaphragms (a more flexible disk, mechanically attached so it did not have to be magnetic).

The mass of the moving parts was reduced (less mass, more efficiency).

Coil windings were improved.

On some elements (RCA's) the magnetic fields are brought into play using laminated bars instead of solid iron.
 
 

These and other improvements were possible partly because of better machining of parts at the time.
 
 



Figure #3





Crystal Radio




Return to "Stay Tuned " Home Page


© 1999-2010  Darryl Boyd,  All rights reserved
Copyright Notice:
My website is copyrighted. This includes all images, text, drawings.
If you are thinking of downloading my copyrighted items and selling them on ebay (or anywhere) keep this in mind,
I monitor ebay for such violations.  I will pursue the issue with ebay and in the courts if necessary.
I do not furnish them for  your gain from my hard work.



Send Email To:








b o
y
d
@
b
o
y
d
h

o
u
s
e
.
c
o
m
Because of antispam techniques, you can not "cut and paste" the above text

We have made every effort to ensure that the information provided on this website is accurate and up to date.
All information on this website is informational only and no
guarantees to the accuracy of any of the projects
or circuits on this site or calculators. If you find something you feel is inaccurate, please inform us by e-mail. Be sure to provide a thorough argument to support your case. Confirmed changes will be made as quickly as possible.

The images on this website  are protected by copyright.  They are the property of the owner of this website and may not be used without the owners permission. Please don't use the images made by us on this website without