The Electro Voice EVM12L is a legendary vintage guitar speaker, favoured not only by Mark Knopfler who uses this speaker in various 4 x 12 speaker cabinets. I have these in a 4 x 12 cab as well, and I like the sound of these very much.
The last time I played with this cab there was an unpleasant surprise: one of the speakers produced a strange noise as soon as I turned up the amp to a medium volume. It sounded like a scratchy voice coil, something that unfortunately happens on vintage speakers and often requires a re-cone job.
I opened the cab to examine the speaker. When carefully moving the cone a bit with my hand however everything seems fine, no hint of any scratchiness that is associated with a defective coil. I need a while until I discovered the cause of the problem. I will describe how I managed to repair the speaker, hoping this blog post can help others who might have a similar problem.
The problem was that the dust cap that is glued to the speaker cone and covers the center of the speaker became loose, the glue seam had broken over a distance of about 1.5″. This was almost invisible. In fact a speaker produces surprisingly loud noises as soon as something is not 100% firm but vibrates or rattles, like the two paper edges here.
I used some drops of bottled hide glue to fix it again, pushing the glue with a toothpick into the gap. Hide glue is great for a lot of materials besides wood, it is durable, and requires only a thin film. I let it dry over night and tried the speaker again the next day: problem solved, no noise, even at high volume.