[Boatanchors] Do Headphones Age-Away?

[hwhall at compuserve.com]

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
-----Original Message-----
From: Al Klase <ark at ar88.net>
To: boatanchors at mailman.qth.net
Sent: Sat, Aug 13, 2022 9:17 pm
Subject: Re: [Boatanchors] Do Headphones Age-Away?

Folks,

The permanent magnet is an important part of any transducer of this 
sort.  If the magnet were not there, the diaphragm would be drawn toward 
the pole pieces on both the positive and negative half-cycles. The sound 
output would be twice the frequency of the electrical input.  Think 
about it.

Al

ARK Sig Block Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/
On 8/13/2022 10:14 PM, hwhall at compuserve.com wrote:
> It is my understanding from reading old documents that its not correct that the permanent magnet is there to "hold the diaphragm in place" - or at least not the way that reads to me.  It puts a mechanical bias on the diaphragm, making it concave (pulled toward the magnet) so that the induced motions of creating sound never take the diaphragm through flat to convex.  The transition between concave to convex was said to induce buzzing.
> Wayne
> WB4OGM
>
> -----Original Message-----
> From: Brian Clarke<brianclarke01 at optusnet.com.au>
> To: 'Al Klase'<ark at ar88.net>;boatanchors at mailman.qth.net
> Sent: Sat, Aug 13, 2022 8:05 pm
> Subject: Re: [Boatanchors] Do Headphones Age-Away?
>
> I think you'll find that the permanent magnet is there only to hold the diaphragm in place. I cannot see how increasing the magnet strength would increase the audio loudness. The amount of variation in magnetic force to move the diaphragm is probably a thousandth of the permanent magnet's strength.
> 73 de Brian, VK2GCE.
>
> -----Original Message-----
> From:boatanchors-bounces at mailman.qth.net  [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of Al Klase
> Sent: Sunday, 14 August 2022 2:02 AM
> To:boatanchors at mailman.qth.net
> Subject: Re: [Boatanchors] Do Headphones Age-Away?
>
> Jeo Conner said:  Sometimes, it's simply the "aging" of our ears. LOL.
>
> That's not a joke.  I tested some headsets back in 1997.
> http://www.skywaves.ar88.net/xtalset102/headsets.htm
>
> I repeated the tests with some of the same 'phones last year.  I'm about
> 10 dB down.
>
> That said, it may be possible to spiff up the classic metal diaphragm
> 'phones by stroking the pole pieces with a strong (Chinese) rare-earth
> magnet.
>
> Al
>
> ARK Sig Block Al Klase - N3FRQ
> Jersey City, NJ
> http://www.skywaves.ar88.net/  
>
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