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Sunday, July 12, 2009

mending loudspeakers

Having been interested in music and audio equipment since the late 70's, I hate to see old speakers go to waste, especially when they classic British vintage designs like Wharfedale, Leak, ,Mission,Celestion etc.

I subscribe to freecycle and sometimes I see old speakers come up on there, usually because they are damaged in some way. I'm no expert on this, but have managed to cheaply get some pairs back to working and presentable state. It's actually not that hard. If certain collectable brands ever came up (i.e Tannoy, Lowther) I know enough not to attempt this kind of "get you home" repair and would consult the experts. The speakers described here are high quality models from the 70's/80's that were produced in large numbers, and while very good, they are not that valuable.

The Leaks

The first pair I got from freecycle were a pair of 70's vintage Leak 2020 sandwich speakers.
The term sandwich refers to the technology that Harold Leak used to make very light but stiff cone material. The speaker cone is a sandwich of expanded polystyrene (Styrofoam in American) between sheets of adhesive aluminium tape. This gave a strong , rigid yet light material. in the original advertising Harold was show standing on an inverted cone, to demonstrate how strong they were.

When I got these speakers they were in poor state. One of the drivers had a hole in the polystyrene, probably where a screwdriver had pierces it while someone was trying to remove it.
One of the ceramic tweeter soft domes had a tear, the cabinets had been used as plant stands and had substantial water stains and one of the grilles had a smiley face painted on it , still just about visible above.

I stripped the speakers back to basics, carefuly removing the grilles, drivers and rear speaker connector block. the signature Leak aluminium frame around the grille was removed. When removing drivers I always use a good quality philips screwdriver which I use my free hand to grip around the tip of he screw driver and the screw holding it in. This is to avoid the screw driver slipping and going through the speaker. I have done that before ! usually the bass/midrange unit is held on with 4 wood screws around the frame. I try to remember which screw went where. Internally most speakers use push connections to wire them to the crossover and rear connections. Always make a note of which coloured wire went where.

The cabinets of most speakers are made from veneered chipboard, though in older or more expensive speakers other dense forms of wood are used, such as marine ply wood. I decided that since these speakers were headed for my kids games console ("Guitar hero") , I needed a quick and easy fix to the badly scratched and stained cabinets. I had a tub of dark Jacobean briwax, a thick and gloopy wax used for restoring old furniture. You have to use it in a well ventilated place i.e outside, as the wax is held in toluene which is fairly nasty in an enclosed space.
Having wiped the cabinets down with a damp cloth, and left to dry, I applied a thick layer of briwax using a plastic pan scourer. Drastic measures, but these cabinets were in a bad way. I left the wax to dry a bit then polished them and they came up very well. The dark wax fills all the light scratches, so the cabinets look old rather than just tatty. 'Stressed' in other words.

Next I repaired the drivers. The bass driver with the hole just needed a little PVA glue (Evostick) to plug the hole. The schoolboy error I avoided was using polystyrene cement to repair a polystyrene speaker. This would have been a disaster as polystyrene cement is intended to glue the rigid form of the dense plastic form of the material, typically used for construction kits and yoghurt pots. It actually melts the expanded form, and achieves an effect somewhat like the yellow blood from the movie 'Alien' when it burns through the deck.

I also used a little PVA to repair the tear in the tweeter cloth cover. the tweeter itself was intact. Possibly I could have replaced the cloth completely, but these are not the highly prized Alnico tweeters found in some models, just the ceramic ones. I wanted this project to be zero cost.

All the fittings ( rear connector plate, connectors, screws ) were cleaned up, and after several attempts to get the aluminium grille frame clean with various chemicals (it was pretty dirty) ,eventually I found it came up like new after a session in the dishwasher.

This just left the grilles. the material was a plastic type, stretched over a hardboard frame. The hardboard would warp if too much wet was applied. I tried several good goes with 1001 carpet shampoo, and this mostly got rid of the face. The flash in the photo above still shows it but , it's hard to see in normal light.

Put them all back together and they sound great. The tweeter is the weak spot with these speakers and can sound a bit gritty, but the bass is very impressive. the styling is very 70's , which you either love of hate, but I'm rather fond of them and they served well as TV speakers in my kids den, also pumping out rock music for 'Guitar Hero'. This was until ...

The Missions

A pair of Mission 707 speakers came up on freecycle , described accurately as needing the foam replacing. I don't have a picture of how they looked, but indeed the rubber 'foam' that surrounds the cones had completely perished. Google revealed it's a common problem with this vintage of Mission drivers , and other speakers from that time. The Leaks , which were older had no indication of 'foam rot' , nor do an even older set of Goodmans Goodwoods, which also came from freecycle and required no work at all.

Otherwise the speakers were just rather dusty from having been in storage.

Same approach as with the Leaks, strip them down, carefully removing the drivers (bass and treble units) taking note of the wiring. the Missions were budget speakers from the early 80's as I recall, and had and have quite a following. The unusual features were the inverted arrangement of tweeter below bass, and the heavy plastic front baffle. This comes off, and I gave them a good wash in warm soapy water, taking note not to scrub off the Mission logo.

The cabinets had some scratches and were a bit grubby. Wipes down with a wet cloth and briwaxe as with the Leaks. I cleaned all the screws and rear connectors and plastic rear plate.

The Mission Grilles use a finer material stretched over a plastic frame. 1001 carpet shampoo didn't really bring these up as well as I hoped, so I ended up washing them in a sink of soapy water a couple of times. Fortunately the grille material retained it's tightness and the plastic frames didn't warp as the plywood ones would.

I put the speakers back together except for the damaged woofers.

A number of people on the internet/ebay sell re-foaming kits, and I had been iterested to try this for some time. Essentially the kit consists of a new set of rubber seals for the speakers , plus rubber glue. you remove all of the perished rubber seal, get them as clean as possible and re-glue the new seals. The complicated bit is getting the speakers centred.

If I pushed the free standing cones in, I could feel the voice-coil rubbing against the inside of the speaker. This was a bit troubling as I wasn't absolutely sure the speakers worked. If driven hard with broken foam surrounds the coil might have been pushed too far forward or burnt out.

I got a set of foam rings for he 707 from good_hifi in Holland, who sell on ebay. they cost around £17, but I figured these speakers were worth it. With broken drivers they had no value, with working frivers they probably go for around £30-40 on ebay.

The foam Rings took about a week to arrive. I was a bit nervous about this as I'd never done it before but the directions were straightforward on the site, especially this video. The centering approach using clothes-pegs worked a dream, and while the speakers seemed initially to rub in all directions, once I'd glued the surround to the cone and centred it on one axis, it worked well. I was then able to centre on the other axis as described in the video. The rubber glue dries quite slowly , so you can fine tune the position. Anyway the picture below is the finished results.

The missions are 10 years younger than the Leaks and it shows. They have replaced them for 'Guitar hero' by popular demand, but I intend keeping the Leaks as they are classics and the bass is very good. Who knows, with the arrival of Rock Band 'Beatles' on 09.09.09, the leaks might be better suited to the mid-sixties sound

DIY speakers

I have sometimes made speakers. I read some articles about an interesting full range driver from Japan called the Tangband W3-871S , which can be purchased reasonably cheaply. It works well in the Cyburg Needle design.

I was pondering making a pair of needles when I noticed some ethnic vases in a local shop called 'snip'. the vases were wooden spheres, and I wondered about making them into spherical speaker cabinets. After some fiddling around , they turned out quite well and work as good Computer monitor speakers.


strawmanaudio said...

Hi there - I came here having been searching for info on how to remove the grills from Leak speakers.

I thoroughly enjoyed your post, I am about to embark on a similar mission (pardon me!) with a couple of pairs of Leaks, if only I can get the damn things open...

Could I trouble you for the specifics of how managed this?

Many thanks in anticipation,

Mr Ives said...

Thanks Andy,

The Leaks are great speaker and worth spending some time on,

Are yours the same model as mine ? i.e with the aluminium frame around the grille ? If so that frame is actually screwed onto the speaker cabinet. The only part of the grille that removes is the grille itself. In my case the grille is made of hardboard with holes cut for the drivers and the plastic mesh stretched over it, all held in place by 4 small ball and socket type plastic push connectors. You simply need to get a ruler, credit card or better still a plastic spatula between the grille edge and the aluminium frame and VERY VERY gently prise out the grille. It should come out easily , I'm guessing its just a very tight fit on your examples. My grilles are rather warped and I can tease out the grille with just my finger tips. I have the same problem with a pair of LS3/5a speakers, but they have the advantage of a small ribbon loop protruding which enables you to have something to grip. Might be worth doing something similar in case you need to take the front off more than once ;) .If you are having to apply a lot of pressure, then ease off and rethink, it shouldn't be too hard, and there is always the possibility that someone has glued them in place, but I think it unlikely.

incidentally (and I should update the blog) there is a really good thread on the diyaudio forum about modern drop-in tweeter replacements for the Leaks that has come up in the just the last few weeks. See here :

strawmanaudio said...

Thanks for that - I've just got them open (had to be quite rough with them in the end). I've got two pairs, one a three way that looks like yours, and one a similarly sized two way that looks to be a newer version of your model (veneer, different grill, no aluminium).

The three ways have never worked properly since I picked them up.
I expected to find poorly drivers, and intended dropping in modern replacements all round; however they not only look fine, but appear to have been restored at some point.
Both sets having come from the same owner, they are displaying black surrounds, unlike any I've seen online, in perfect condition.

Thanks for the link - I shall head over there now - I'll have to do some research concerning possible upgrades/ rebuilds/ fixes - there's a part of me that really wants to convert the three ways to reference monitors for the studio (I'm a musician) though the prices for 12 inch woofers are steep enough to make it a foolish notion, unless I'm looking in the wrong place.

Thanks for your help,


Unknown said...

Hi there, just picked up a pair of 2020s and the sound is far better than I expected. On one of the woofers the surround is starting to lift up - do you know what sort of glue I should use to stick it down with? Thanks

Mr Ives said...

Hi, yes they do sound great. Well if you mean the surround i.e the rubber seal which surrounds the driver, then a rubber- glue would probably work, the kind you might use to rep[air a beach ball. maybe even puncture repair glue. PVA is safe for most things but dries stiff and you really need something that dries flexibly. THE glue to NEVER use on these speakers is polystyrene cement , the kind you use for model kit construction. It will dissolve the cone material.

The Bear said...

I was just given some old 707s that need the driver seal replacing... I purchased the rubber rings from the same eBay store as you but I cannot for the life of me get the driver out of the speaker to work on... All screws have been remotes but it will not budge. What am I doing wrong?! Help!

Mr Ives said...

Greetings the Bear, yes - that article is a bit old, but the speakers are still working fine.

Possibly the drivers have a gasket between them and the white baffle, its often double sided tape and it can be remarkably hard to budge. Perhaps it might be a good idea to remove the whole front baffle. from memory the 6 sockets that the front grille plugs onto are dual function and also are caps covering screw heads that attach the front baffle. if you try removing the baffle, you might see if any screws remain or you can apply some pressure from behind. I also used this as an opportunity to wash the plastic baffle in the sink as mine was moderately dirty.