Friday I set up a small Loudspeaker Test Station at our Equipment Rental Depot (CenterStaging, LLC Burbank, CA) to start going thru all of the failed guitar and bass cabinets first, to see what I could cobble together from the pile, before moving on to the preventative maintenance end of checking thru the rest of the rental cabinets inventory.
I added the spare Bruel & Kjaer 1027 Sine-Random Generator to the 1022 Beat Frequency Oscillator I just restored. Added an old Yamaha P2100 power amp that I also just repaired, it having one channel not working. I got one of our 4ft banquet tables from inventory, set that up at the end of one of the tall shelving units in the warehouse, parked the two oscillators at one end of the table, with the Power Amp standing on one end underneath the bench. I had to add some bungie cords to strap the tall 1022 BFO to the tall shelving frame so it doesn't get knocked down by accident, or shaken loose by any earthquake that sometimes occurs.
I added my laptop for logging in my service notes, along with a Fluke 8060A DMM, my small Rion NA-61 Precision Impulse SLM and a collection of tools.
The most common failure mode I found was radial crease cracks on the lightweight cones of the 410 cabinets from everyone....Ampeg SVT 410HLF, SWR Goliath 410, Eden 410 XLT, TC Electronic RS-410-8, Aguilar GS410 so far......all of these have accordian-style surrounds where the cones terminate. Long Throw Cones...essentially. What seems to happen when pushed hard in the first octave with bass, is the cones can develop their own flexure joints out near the surround, which now can jump out of of the magnetic gap, eventually ripping the cones over time at these radial fractures. On the front of the cabinet, you can barely see the crack marks unless you look close. On the back side of the cones, they have developed cracks, on the way to eventually tearing open.
Using the B & K 1027, which conveniently tunes down as low as 2Hz, AND the Yamaha P2100 will pass that nicely to the cabinet, tuning the oscillator down into the 5Hz range, you can easily see the cones now flexing at the cracks, though you don't see this behavior at 40Hz and above. You do begin to see it a bit at 32Hz (around a Low Open B string on a 5-string bass). I was able to cobble a couple cabinets back together with woofers that hadn't yet failed in this area, swapping out the same Eminence 10" woofers of a particular cabinet. I'll get some additional photos what clearly show this. You can somewhat see the radial cracks just out near the edge of the cones before terminating into the surrounds, under 5Hz LF drive, with the cones extended out forward.
A lot of the cabinet repairs were just a matter of missing or loose speaker mounting screws, loose cabinet panels, missing spacers & screws from the metal grilles. Two of the center domes were crushed....in particular the upper left speaker above in that SWR Goliath 410 cabinet. Using Gaffer's tape to try and get it to adhere to the dome, and give a quick upwards pull only pulls paper pulp off the dome. I've had resort to using Dental Picks...poking thru the dome with the right-angle picks, and carefully pulling up from the insides. It didn't do a perfect job, but, considering it was fully crushed from slamming into the back side of the metal grille, it's a whole lot better than before.
And, of course, I've encounted a few kazoo's from burnt voice coils, as well as open voice coils.