TLAH Pro Repair

[slavedave]

Hi!
I built the above speaker as per plans a couple of years ago and have been a happy camper since then. However, yesterday the speaker was knocked over (thankfully no-one was near it when it came down off of its 1 foot high top hat stand - it is floor standing). The back panel has separated from the side panel due to de-lamination of the ply for about 60% of the long length. The obvious solution is to use PU glue to re-stick it but I can imagine that that is going to cause an almighty mess trying to get it between the two panels since I can only open them up a little bit due to the panels still being connected for the other 40%. It could make the cab unsightly since it occupies a prominent position when in use.

Does anyone have any suggestions?

Bill, I wonder if I can get away with brushing standard wood glue down between the panels before clamping them together? I assume that because the cabinet is not so much a horn as a transmission line that air tightness is not as critical (preparing to be shot down on this last statement though).

Also, as it fell face forward - is there any chance that a heavy impact could "unsettle" or affect the alignment the drivers in their baskets? The driver faces are somewhat protected by a half inch, proud, cloth-covered speaker grill. I guess the only way to check is to get it fired up and listen to each driver once it is repaired?

Thanks for your thoughts and advice everyone.

[Tom Smit]

Perhaps wedging a screwdriver in the crack, to spread it open enough to apply the adhesive, would work. I would still use PL.

Gently pushing in each driver cone might help in detecting a bad driver.

[CoronaOperator]

I would probably go to a hobby shop and pick up an ounce of thin and an ounce or two of medium cyanoacrylate adhesive, aka "ca adhesive" or "superglue". It comes in varying viscosities.

The thin stuff will penetrate deep into the crack all by itself without having to lift up the seam. You align the pieces perfect before applying any glue and once everything is aligned, generously apply the "thin CA" to the seam. It will penetrate into and bond the two panels. It does not fill any gaps so the seam will have to be pretty tight.

Once that has set (a few minutes or so) I would tilt the cabinet in such a way that the open end was higher with the damaged seam on the bottom and tilted as to make a shallow trench. Then I would squeeze a whole bottle of the "medium" on the inside of the cabinet so that it would flow along the seam towards the far end. Use enough to reach the far end of the cabinet. The "medium" CA should form a strong fillet on the inside and seal any air gaps.

You can buy a can of "accelerator" which can instantly cure the adhesive. It is useful for filling larger gaps. The accelerator will leave a white area where it cures if aesthetics are a concern.

This stuff will instantly bond your fingers/eyelids together, especially the thin stuff so be careful, wear gloves and or goggles.

I suppose gorilla glue could be used instead of the medium glue to make a strong fillet on the inside of the box as well.

[slavedave]

Thanks for those suggestions.

Tom - I did gently test each cone when it happened. Unfortunately, one of them seemed to be rubbing a little. Does this mean it could be damaged? Time will tell when I start it up after repair and give it the audio litmus test, I suppose.

Has anyone tried forcing some PU glue into a syringe with a large bore hyperdermic needle? I could probably get that down into the crack if the glue is not too viscous to syringe.

[Grant Bunter]

Thanks for those suggestions.

Tom - I did gently test each cone when it happened. Unfortunately, one of them seemed to be rubbing a little. Does this mean it could be damaged? Time will tell when I start it up after repair and give it the audio litmus test, I suppose.

Has anyone tried forcing some PU glue into a syringe with a large bore hyperdermic needle? I could probably get that down into the crack if the glue is not too viscous to syringe.

Re driver;
Sorry, but probably. If the fall was heavy enough to seperate part of the cab, it would be no surprise there would also be enough force to perhaps move a magnet on one driver (even a slight shift will be enough), being one possible cause for now apparent rub. Still, for sure, try it out.

Re syringe;
I've repaired more than enough drum shells and antique furniture in the past using that method with PVA glue.
Even with PVA glue, pressurising it like that makes it more difficult to do.
As to if you can do that with PL, it would be worth a trial run (nowhere near the cab).
Pull the plunger out of the syringe to fill it up with PL.
That's going to be a messy job lol.
If it works, I would have a number of 5ml syringes and 18G blunt needles available to do the cab repair...

[slavedave]

Thanks Grant. Now to tap my medic friends to see if they can source me a large bore needle!

[slavedave]

Corona - I will also run a bead of something down the inside edge to "belt and brace" any adhesive fix I make. Thanks for the suggestion.

[slavedave]

Update:
I managed to gently prize the two sections apart laterally enough to brush a thin bead of PL glue down nearly the whole length of the join. Lots of nice frothing going on prior to clamping them up. I hope it is going to be enough but....so far, so good. I had a quick look at the wiring and the drivers and there was nothing obviously amiss so will set it up on Sunday and give it a run through. I may have to re-commission our Bose L1 copy as a back up plan though, just in case.

Will keep this thread posted as to the results.

Thanks again.