Post by Denny StrauserPost by Phil Allison** Hi all,
the promised article on loudspeaker failures is finally up,
including 5 nice
pics taken by me.
http://sound.westhost.com/articles/speaker-failure.html
The article is rather tightly written, so you need to read it a bit at a
time and cogitate.
Also take a careful look at the links provided at the end of the article
too.
And before anyone asks, the 40mm voice coil and magnet gap are from a 10
inch woofer used in an AR2a.
Interesting & informative article.
One was obviously caused by a failing 'tinsel' wire. I have had these
braided wires occasionally break off, and some I've been able to
solder back on. But in this specific situation, not all the braids
broke off. But the few that were left intact heated up enough to catch
the cone on fire. It was a JBL 15" speaker. And between the chemical
fire extinguisher powder & the smell of burnt rubber, we had to clear
the theatre & open all the doors to let the fumes & powder dissipate
before we re-entered the room. Thank goodness it was during
soundcheck, and not the show.
The other interesting speaker failure was during set-up for a Static X
show. Their LD had a 3-phase PD, but we only had a single-phase AC
source. Without my knowledge he decided to use a Cam-Lock-Tee to get
three 120V feeds from me (the PD had no 240V outs). When I wired him
into our AC panel, I only wired his Red & Black tails, and left the
Blue tail coiled up in the bottom of the breaker box. I had metered
the tails to insure that the tails were hooked uo correctly. But I
didn't inspect how those tails were hooked up to his PD after I gave
him his tails. The LD's intent was to Tee one of the hot legs into two
inputs of the PD. But he had a brain fart & Tee'd one of those hot
legs to that Blue tail I left coiled up in the bottom of the breaker
box. When I flipped the main breaker switch on, I heard a BIG BOOM
come out of the sound system. I then powered everything down &
inspected all the wiring. I found the brain-fart-Tee. & fixed it. But,
because the Blue leg arced to ground/neutral ... some of my power amps
saw 240V input instead of the expected 120V for a few milliseconds. It
blew the voice coil completely through a 15" paper cone of the drum
monitor. I felt luck that it was the only driver destroyed. That could
have been a major disaster.
- Denny
Yeah, I've experimented with voice coil "cannons" on a few occasions
myself... :)
I remember blowing out a JBL 2220 once, and my recone guy (John
Meuller) used to work for Clair Brothers, and Clair left him have his
former Dimension 5 customers bring their recone work to him at Clair's
original Manheim facility (when they were still in the indoor tennis
court building).
When I entered the lobby in order to drop it off with John, Clair
engineer Ron Borthwick was walking by and noticed my blown woofer.
After looking at it, he laughed and said he never saw a driver blown
like that! I laughed, and thought to myself "Riiiiiiiiiiight...."
I knew better as I bought many a blown 15" JBL basket from Roy and
Gene that I hand picked off of a mini >mountain< of blown 15" baskets
in their warehouse.
Like you, I had a similar experience once where I had a rack of Clair
modified Phase ("Flame") Linear 700Bs that got damaged when the squint
on a job tied the PD into a wild leg. I wasn't so lucky however, and
took out all 4 of my 2441 drivers, a couple of woofers, and the rack
of Flame Linears (the output transistors did produce a few neat little
blue flame 'jets' out the back of the rack), and one Clair Brothers
SAE 2600.
--
MFB