Cure for saggy speaker cloth

[stevehertz]

If a speaker cloth is saggy, then an efficient and quick way to cure it - without taking it off and refitting it - is to apply steam to the saggy cloth. When it dries, the cloth will be pulled taught again.

A couple of provisos.. The speaker cloth will probably be affixed with glue around the edges, so be careful not to 'melt' the glue with overuse of steam. Also, although it may in some circumstances be possible to perform the procedure - carefully - with the speaker and everything else in place, it is probably best to remove the speaker and work on just the baffle board and speaker cloth. If the cloth is a close weave (through which steam is less likely to penetrate so easily), then a few seconds blast from a steaming kettle may be ok with everything in place, but again, you may damage the surrounding varnish. If in doubt, take the baffle out..

[G6Tanuki]

In times-past when I built 'indestructible' guitar-amps [using 805s/807s/813s] I was sometimes prevailed-upon to repair speaker cabs that had been dropped-down-a-flight-of-stairs/sat-on/had-beer-poured-over-them by students and room-temperature-IQ roadies.

The instructions with the speaker-fabric I used [I forget the name - something like 'Tygon'?] always said that after gluing it to the baffle you should shrink it to fit with a hair-dryer.

I'm thinking that this is probably going to be worth trying before going for steam: damp and speaker-cones/magnets are not natural friends.

[M0TGX Terry]

Tygon was/is a type of woven plastic, which is why it shrank and tightened when gently heated. If your speaker fabric contains cotton fibres, the dampening effect of steam could well cause enough shrinkage to tighten it, but I'd definitely recommend NOT letting steam anywhere near the speaker cone!

As Stevehertz pointed out originally in post #1, damp and speakers don't mix. I had a 'speaker which was left in a damp shed, and when I picked it up, the cone just fell out. The glue had lost its adhesive strength due to dampness.
Terry

[Gillian]

Remove any cones to avoid damage, as many drivers are hard to obtain and pulp cones can easily get fragile after many years they seem to sort of dry out.

Good tip on cloth though.
Gill

[Boom]

As a kid I used to watch Mums washing line for amusement/educational value. In the rain it would get wet and tighten and as it dried it would slacken off again. Wouldn't the same thing happen with speaker cloth?

[stevehertz]

Steam - obviously - is boiling hot. I'm not a physicist and able to explain exactly what's going on, but the process is not too different to washing clothes in water that is too hot - they can shrink when they dry out. So the effect of the boiling steam is to 'do something' to the strands of the material at a molecular level, causing shrinkage ie in this case, the speaker cloth to tighten against its anchorage points.

[stevehertz]

I may add, having just recently used this technique again, that it can take a few weeks for the 'tightening' to take full effect. A set that I did a couple of weeks ago and was only (seemingly) partly successful, has now tightened up quite nicely with no sign of remaining sag. So, patience is also key to this trick. Although I would imagine that if you live in a 'highly heated' house (I don't!), then that would speed up the process.

[Okto1984]

Originally Posted by stevehertz

Steam - obviously - is boiling hot. I'm not a physicist and able to explain exactly what's going on, but the process is not too different to washing clothes in water that is too hot - they can shrink when they dry out. So the effect of the boiling steam is to 'do something' to the strands of the material at a molecular level, causing shrinkage ie in this case, the speaker cloth to tighten against its anchorage points.

You're right. When thread is made, it's stretched and twisted. On the molecular level, billions of tiny hydrogen bonds exist between the stretched out fibres, holding them in their stretched position. Much like a spring, it's under tension. You don't really need to know what a hydrogen bond is, except that they're small and weak, but in large numbers can stabilise a structure. It's a bit like Velcro, no single little plastic hook is strong, but gather together many and pulling the Velcro apart is surprisingly hard. When exposed to hot water, the hydrogen bonds are disturbed and the stretching of the fibres is undone and the fibres contract back to their original length.

Knowing why is interesting, but not essential to understanding the procedure to shrink something. However, knowing why explains why the process has limitations and cannot be performed indefinitely. If it goes slack again in the future, it may not work again either. I also imagine it will work better with natural fibres than with plastic fibres.

Anyway, thank you for the tip. I'd never considered steaming to shrink fabric before.

[vu2nan-nandu]

I was into building speaker enclosures in the 1980s. On the very first piece the grill cloth, nailed taut, was sagging within a day. The quickfix was to nail wet grill cloth taut to get it tauter as it dried and retain it for keeps!

Regards,

Nandu.