[Don Pearce]

On Mon, 14 Jan 2008 07:16:19 -0800 (PST), EADGBE
wrote:


I recently found a very clean pair of JBL L19
speakers. These speakers look new.

Before buying them, I examined the speaker
surrounds thoroughly. All of them appear to
be in perfect condition.

I took them home and hooked them up.

They sound very good, but I am hearing
a slight rattle coming from one of the woofers.
The rattle is not very loud at all, and in fact
is almost inaudible most of the time. But you
can definitely hear it if you are listening to
certain things like a bass-heavy radio
announcer's voice or a soft piano solo.

The woofers on the JBL L19's have a
bowl-shaped piece of paper glued to the
center of the cone. I have verified that the
glue is solid all the way around; I have even
run a very fine bead of glue left over from a
speaker surround kit all the way around the
bowl, but the rattle persists.

I can make the rattle go away if I gently put
my finger on certain places in the center of
the woofer cone. I can make the rattle worse
if I put my finger on the surround, near the
top of the speaker.

One more thing: I can hear a slight rubbing
noise if I gently push the woofer's cone back
and forth on the top half of the speaker. I do
NOT hear this rubbing noise if I push the cone
anywhere on the bottom half, and I do NOT
hear the rubbing noise if I push both the top
and bottom halves at the same time (in other
words, if I push the cone in a "balanced" way).

I have verified that NOTHING is touching the
back of the speaker; no wires, no insulation
or anything else.

I am suspecting that maybe the spider is
out of round or off-center, or maybe the voice
coil is off-center.

What can I do to further diagnose, and then fix,
this annoying problem?

When the rubbing is very slight you can usually cure it by unbolting
the speaker, rotating it 180 degrees and bolting it back in.
Everything sags slightly the other way and bits that were touching
stop doing so.

d

--
Pearce Consulting
http://www.pearce.uk.com