[Boatanchors] Do Headphones Age-Away?

[hwhall at compuserve.com]

>How can each cycle of AC cause a pull on the diaphragm? On one half of the AC cycle there is a pull from the coil, adding to the permanent magnetic strength<
 He was saying that half-cycle thing happens IF there WASN'T a permanent magnet. I think you missed that.
>Now consider a modern-day loudspeaker. It follows the same principles.<
It does not.  The speaker is a actually like a moving coil motor where as there is no moving coil in the classic phone-type receiver.  They both use a perm magnet but for different effects.
WayneWB4OGM

-----Original Message-----
From: Brian Clarke <brianclarke01 at optusnet.com.au>
To: hwhall at compuserve.com; boatanchors at mailman.qth.net
Sent: Sun, Aug 14, 2022 12:48 am
Subject: Re: [Boatanchors] Do Headphones Age-Away?

OK Wayne, you have copied accurately from Ralph Meyer's p22, but Meyer's knowledge of electro-magnetics is faulty. How can each cycle of AC cause a pull on the diaphragm? On one half of the AC cycle there is a pull from the coil, adding to the permanent magnetic strength, and on the other half of the AC cycle the magnetic force from the coil opposes the permanent magnet's force. Note that at no time does there appear any data - it's all assertion.
Now consider a modern-day loudspeaker. It follows the same principles. Does it produce sounds at double the actuating frequency?
73 de Brian, VK2GCE

-----Original Message-----
From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of hwhall at compuserve.com
Sent: Sunday, 14 August 2022 2:27 PM
To: boatanchors at mailman.qth.net
Subject: Re: [Boatanchors] Do Headphones Age-Away?

Al nailed it as to the necessity of the perm magnet. & that the magnet is not simply there to hold the diaphragm in place.  Here's an interesting source.
https://atcaonline.com/wp-content/uploads/2020/06/Ralph-O-Meyer-3rd-Ed.pdf
>From Chapter 3, Receivers:"The core of the coil must have a relatively large steady background magnetic field or bias. Without this steady magnetic field, the core would pull on the diaphragm equally during each half cycle of the electric current thus generating sound waves with twice the frequency of the electric current and would not reproduce intelligible speech (Fagen/AT&T 1975, 86-87; Burden/AE 1948, 56-57. Further, the magnitude of the deflections of the diaphragm would be only about half that with the magnetic bias thus making the receiver less sensitive."
WayneWB4OGM 

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