m II wrote:
Anyone have any insights into speaker life? What is a reasonable life
span for a small paper cone speaker? It's a bad question, I know. It's a
variation on the 'How high is up?' theme, so it's pretty much unanswerable.

The reason for asking is the Sangean 909 is slowly losing it's voice.
It's been a slow deterioration, with the sound getting more garbled as
time goes on.

I'm hoping it's the speaker and not the audio section, but I haven't
opened it up to look yet. The earplugs have all gone into hiding, so
that's no help.





A paper cone speaker, if not abused, can last indefinitely. I"ve
got wire recorders from the 40's with paper cone speakers that still
work as new. Same for transistor radios dating back to Bill
Shockley's second ego.

Now, that's not to say that speakers don't fail. But if they're
cared for, failure is not common.

Points of weakness for a paper cone are, first and foremost, the
surround, and second, the adhesives that hold the coil form to the
back of the cone. The coils themselves can fail due to corrosion,
or, again, abuse.

High humidity can cause the cone, itself, to distort. This can
cause rubbing of the voice coil on the magnet structure in the gap.
Failure of the adhesives can cause the voice coil form to detach
from the back of the cone, entirely, or in part, which can also lead
to rubbing of the coil on the magnetic structure.

If the wire coil has incomplete coating on spots of the wire, or
if the coil wire coating was nicked at assembly, corrosion of the
copper at a single point could, but rarely, lead to rubbing due to
expansion of the wire at a point due to the growth of oxide at the
point of exposure. This, also due to high humidity. It would also
have a second effect of increasing coil resistance, which would
reduce audio output.

Surround failure--the surround is the corrugated paper, or rubber
ring that surrounds the cone and attaches it to the frame--would
result in audible distortions by both paper rubbing against paper,
as well as de-aligning the voice coil in the gap allowing the coil,
again, to rub in the magnet structure.

Excessive volume can cause the voice coil to heat, and distort
the form. It can also cause a speaker to bottom out in the magnet
structture, putting a lip on the bottom of the coil form which will
strike parts of the magnet structure.

Now, all these are results of abuse. And you'd have to abuse the
radio hard and for a very long period of time to make any of these
failure occur. So, if you're the type to work your radio in a body
shop, or at a construction site, then, yes, the speaker can be at
fault.

Absent abuse, not likely your problem is a failure of the speaker.

Reduced output can be caused by a transistor failure in the audio
stages. Also not common, but it does happen.

Reduced output can be caused by a capacitor that hss lost form.
HIGHLY likely this is could contribute to your problem. VERY highly
likey. Electrolytics lose form with age, and lack of use. Many
technicians replace them at this age, as a matter of course.

Garbling...that can be a number of things. Misaligned IF's can
put the passband on the skirts of the filters. This makes for both
garbled and reduced audio output. Also a high probability. A
transistor failure early in the audio path can cause several types
of distortion which can result in garbled audio. A resistor in the
audio path, or in a bias circuit that's drifted can do the same
thing. Also, given the receiver's age, a likely issue.

You should be able to plug a Walkman style headphone or a pair of
iPod earbuds into the earphone jack for a quick test. Only one
driver will work, but it will be enough to tell you if the speaker
has failed, or if the audio/if stages need attention.