Concrete Baffled Speaker Renovation

[Ray P]

Back just before Covid came along I acquired a pair of speaker cabinets that have sat patiently in my garage awaiting some TLC ever since; well, this weekend they started to get some.

The cabinets are a TQWT design for Jordan JX92S drive units and a recent acquisition of another pair of the Jordan units gave me the impetus to get stuck in with a refurbishment. They're interesting because both the front baffle, and top/rear panels are made of 'concrete' - not concrete like buildings are made of, it's much less coarse, almost like plaster on the surface but much harder.The sides and internal structure are 18mm MDF. Needless to say they are very heavy. I believe the design is called Matteis, by Jon Espley.

Anyway, the veneer was in a poor state with a few splits and lots of places where it had lifted so I started by removing it. Most of it came away easily with a paint stripper blade and the rest was removed using the same tool supported with a hot-air stripper gun. This afternoon I've been using a Stanley blade scraper to get the glue residue off and have sanded the sides of one cabinet. More elbow grease still required!

The veneer seems to have been glued to the front and top using impact adhesive but I'm not sure that was very successful as I could peel most of it off without the scraper tool.

Some pictures of them from when they first arrived.

[Paul Barker]

Picture not showing. What thickness is the concrete? Oh after I wrote this the pictures appeared. Thinner than I expected.perhaps 10 or 12mm? Like gyprock plasterboard, but much better tensile strength?

Reminds me of my 6 x 3 12mm plaster board OB’s which sounded great. They’re propped up against the wall at the lockup resting.

There is a type of breese block you can saw with a handsaw. I recon they would make great OB’s.

[Ray P]

What thickness is the concrete? Oh after I wrote this the pictures appeared. Thinner than I expected.perhaps 10 or 12mm?

I haven't actually measured how thick the concrete is, Paul, but it's a lot more than 12mm, I guess around 25mm or so, possibly a bit more. I'll measure it next time I'm down in the garage. The second picture shows how the rear of the drive unit opening is flared and how the mounting nuts were cast into the concrete (the holes in the veneer are for the clip on round grills).

[Ray P]

The front baffle at the speaker location is around 32mm thick. I think that will be the same for the whole baffle.

I do know that they're heavy, I can only just lift them onto the workbench (given the weight and the lack of places to grip them).

[simon]

I imagine they have some kind of fibre reinforcement, cementitious materials don't have a lot of tensile strength.

They look like they're say 1m tall and 250mm wide Ray? If so at 32mm thick the baffle will weigh around 19kg perhaps. Or about 3 stones.

[Ray P]

They look like they're say 1m tall and 250mm wide Ray? If so at 32mm thick the baffle will weigh around 19kg perhaps. Or about 3 stones.

Not far off Simon, they're about 910mm tall. The back and top are of the same material.

[simon]

They're also cementitious? 6 stones then!

[Ray P]

Perhaps I'll take the bathroom scales down next time I work on them.

[simon]

Perhaps worth noting that bags of cement and sand are 25kg these days to minimise damage to backs and the like. Which is just under 4 stones.

[Ray P]

Yeah, I'm very conscious of that Simon, especially at my advanced years. I try to do the correct lifting technique but it is quite hard because of the shape/volume and being able to get a grip - I have to get them flt and then grip at the speaker opening and the base opening.

Next time they're on the bench I'll take some more pictures.

[simon]

I bet! A 4 stone bag of cement feels like a whole lot more if it's not carried close to the body - speakers aren't quite as easy to lug about. Those are heavy beasts you've got Ray.

[chris661]

Ray,

If there are any wooden external surfaces, there's no shame in adding a handle. The easiest would be a folding one, which screws to the surface of the wood. Even just one on the back would probably make life a lot easier.

Something like this: https://www.penn-elcom.com/black-sprung ... ish-h4054k
Would do nicely, and shouldn't rattle on account of being spring-loaded.

Chris

[Ant]

I could do with those on my stupid fanes

[Ray P]

Thanks Chris. I wouldn''t have any concerns about adding handles if the speakers needed to be moved regularly, like your PA units, but ultimately these will be essentially static in a domestic environment so it would be a shame to add handles.I can move them around on a padded sack trolley so the problem should be short term while I'm doing the refurbishment.

[Ray P]

I had some time today and finished scraping off the glue residue left after the veneer was removed from the MDF side panels. I also installed some 18mm dowels to brace the 'mouth' of the TQWT.

Next I have to try and remove some more of the impact adhesive from the concrete sections - a wire brush seems to do a reasonable job.