Restoration of a true classic!
From about two minutes into the first listening test I immediately
knew that the foam roll surrounds of the bassunits
were rotted and a fair amount of phase cancellation was taking place. I had
experienced similar problems with my old Tannoy Cheviot's. For those of you
that don't know, the shelf life of the foam outer suspension for a vintage loudspeaker
is around fifteen years. The foam is degraded over time by the effects of light
and any humidity it is exposed to. The biggest problem is a fungus which breaks
it down and causes it to disintegrate.
hour later we were struggling to get the back panels off which were sealed and
had not moved in thirty years, they eventually relented and we were soon pulling
fibre glass damping material out and away from the backs of the bass units.
Inside the bass unit is covered with a cotton shroud which is stapled in place
to stop the damping material from touching the cone. The shrouds were removed
and eight bolts later the first bass unit was out.
The first thing that I noticed was the date stamped on the back
of the bass
unit (Sept 1975) I was only four when these beasts were built. The other thing
was that this bass unit had a special basket casting which is not used on the
first versions of the series. the profile of the front surface of the casting
is actually convex which integrates exactly with the concave back of the curved
front baffle. Earlier versions of the DM70 (standard and continental) had conventional
flat faced baskets which were bolted to contoured wooden (gasket like) sections
made to fit the curved front baffle.
As expected both bass units being totally original and removed
from the cabinets for the first time in thirty years had lost their foam roll
surrounds. The foam was more like dust than actual foam and disintegrated as
soon as it was touched. Every other part of the bass units seemed remarkably
intact. They were packed and sent off to Wembley loudspeaker repairs (site)
in London to get new surrounds. Wembly repair a lot of P/A gear but have been
in the business for a long time and have extensive experience with vintage drivers.
It is of course fortunate that all my bass units required was for the cones/baskets
to be cleaned up and new foam surround to be stuck on (a bread and butter job
for any loudspeaker reconer). Paul MacCallum (the boss) took on the job personally
and soon they were ready.
The return of the bass units!
The bass units were delivered from Wembley and were fitted. I bolted
them in pretty tight and hooked them up. They tested ok so I proceeded to staple
up the cotton shroud, I wasn't as neat as when we removed it but a load of staples
and a few tie wraps later I had the shrouds in place. About ten minutes later
and I had packed in the fibreglass damping material and was screwing the back
panels into position. I set the DM70's up for the second listening session,
hopefully it was to be worth the effort (click).
I was very pleased with the way things had gone. I had bought a pair of very
complex vintage loudspeakers which could have been a potential restoration minefield.
This pair were thirty years old and were in far better condition than anyone
could reasonably expect, the ESL panels were very good, the overall condition
of the cabinets were excellent, in fact the only problem (the bass units) was
expected and was a very easy repair. I am more used to restoring Spendor BC1's
which suprisingly give me a lot more trouble than these units had presented.
So the job was done and they sound fantastic. I have
a great pair of speakers which eclipse the performance of many of the classic
loudspeaker systems in existence. They have survived 30 years and should be
good for at least the next fifteen. Am I pleased that I took a risk with em?
Damn right I am!
Matt O'D 2006