Restoration of a true classic!

From about two minutes into the first listening test I immediately knew that the foam roll surrounds of the bassThe bass unit in it's original state. Note the rotted foam. Click to enlarge.units 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.

The driver covered by its muslin shroud. This is so that the packed wadding does not impede the cone. Click for a larger view.An 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 The bass unit in situ. Note the complexity of what is essentially a simple crossover. Click to enlarge.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 newly repaired bass units just prior to fitting. Click for a larger view

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).

The fibre glass wadding is repacked just before replacement of the chunky back panel. Click to enlarge viewOverall, 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