From jconli1@gl.umbc.edu Mon Aug 27 14:15:41 2001
Subject:KBR-M rotary driver failed, fixed

Hey all -

Just wanted to drop a line and say hello, and pass on an interesting
experience I had with my KBR-M this weekend.

I joined the list last weekend at the last minute, trying to get some
advice from you regarding an open diaphragm on the KBR-M... had to
find replacement at the last minute. I put a few calls in to Motion
Sound, but the guy I needed to talk to wasn't going to be in until
2:30 their time (4:30 mine), and my gig was at 6.

I wasn't able to get to "post" status in enough time here, so just
took a chance anyway and spent 2 hours searching for anything that
would work.

I wound up getting an Eminence titanium replacement for a bit less
than the Motion Sound OEM PD40. ($40, I think)

On my way home, I finally got through to John Fisher (?) at Motion
Sound and asked him if he thought my solution would work in a pinch.
He said "it might - but not for long" (no big surprise), "The
Eminence titanium drivers are designed for a 1200Hz crossover, and
the KBR-M's is at 800Hz. The lower crossover could kill the driver
pretty quickly."

As a precaution, he recommended applying 1.2mL of self-leveling
silicone around the edges of the driver to dampen the suspension
resonance a little bit. I couldn't find any self-leveling silicone,
so I just used regular gummy silicone, and I may have used a good bit
more than 1.2mL. It was a pretty high paying gig and I just didn't
want to risk anything.

Put everything back together, and headed off to my gig. Hooked it up,
and it sounded fine. With the silicone around there (I'm guessing
that's the culprit), the KBR-M has a noticeably less shiny high end,
which I really like. It sounds a bit more authentic and a bit
warmer... more like a Leslie.

While the KBR-M was open, I also tinkered with the acceleration pot
of the rotary horn... I sped it up to almost full accelleration. My
old 145 (admitted, it had the deflectors removed) was VERY quick to
hit full speed and I enjoyed being able to tweak particular notes
rather than wait for the ramp-up time. The KBR-M sounds good to me at
these settings, but I'm going to continue to tinker with rotary speed
and accelleration a bit more to find something I like. At full speed,
it sounds a bit more choppy than my 145 or 860 ever did.

I've got a Motion Sound PD40 now on standby when/IF this Eminence
actually does get beat up by the 800Hz crossover. Looking at the PD40
next to the Eminence titanium... I'm really skeptical about Motion
Sound's claims... the Eminence looks to have far better construction
and materials all around... but we'll see in time.

Gig went well, I got paid ('course, I'm out a hundred for both
drivers, but live and learn), and live rolls on.

Thanks-
Jeff Conlin
Beltsville, MD
XB-2/KBR-M C2/145 Wurlie140 Roland JX305