some cabinet questions

antichef

antichef

pornk rock
I have a fairly standard JCM900 1960B 4x12 cabinet. It was making some flubby buzzy noises at high volume, and I didn't like the bass response that much, so opened it to see what was going on. (it's got the stock Celestion 75 watt 12" speakers - I plan to change those to greenbacks at some point). I noticed that the wires connecting the speaker terminals to each other and the input of the cab were really thin. I also noticed a 2x2 wood plank running horizontally from the front panel in the center of the 4 speakers back to the back panel, where there's a screw that connects with it from the outside. Once the back panel is off, it's very loose and kind of hanging off the front panel. I removed the dinky wires and soldered in some fat copper 12 or 14 gauge speaker wire, but noticed that there were tiny little wires running from the speaker terminals to the internals of each speaker anyway.

On to the questions:

Electrical:

  1. with the tiny wires used internally in the speakers, was there any point to installing beefier speaker wire in the cabinet?
  3. I'm assuming that soldering can result in a better connection than the spade connectors the little connecting wires had been using. Does that really make any difference?

Structural:

The flubby buzzing I had heard appears to be the loose brace I mentioned. I don't want to remove the grill cloth if I can avoid it to tighten it to the front, so would it be a good idea to:
  1. glue and or diagonally screw it from the inside to the front panel,
  2. additionally brace it with a vertical piece of wood running from the center of the horizontal brace down to the bottom panel of the cabinet, or
  3. simply remove the horizontal brace altogether?
 
I don't know about the wires. Mine's a JCM 900 1960a stereo cab and it's got the pcb board thing and tiny wires running everywhere. I really don't suspect there's any benefit to running spark plug cables in there, but I don't really know. I left my spade terminals in place but glopped a tiny little blob of solder on each one to make sure nothing wiggles loose. No problems here.

That brace helps the structural integrity and the sound. One thing that a lot of people do with that 2x2 in Marshall cabs is put a thick piece of leather or felt on the side where the back panel goes and then screw it back together. Supposedly that tightens up the low end. I tried it myself and noticed nothing, but you never know. Mine fits together very tight anyway. If your brace is loose and wobbly, you should definitely tighten it up somehow. The last thing you want in a cab is a rattley piece of wood flopping around in there. If you can glue and screw it without removing the grill cloth, do it. Don't remove the brace.
 
I wouldn't hurt to use some better wire as the stock ones do seem a bit thin. Soldering is more reliable if you do it correctly. You don't want those spade connectors coming off with the amp cranking.
As for the brace you don't want to remove it because that's what ties the cabinet together so that it resonates properly. You could try the glue and screw thing first to see if it gets tight enough.
 
+1 with the leather or felt. The reason people say that it tightens up the low end is because a lot of people have a problem with the back buzzing on the brace. Once you put something soft on the brace, the buzzing stops...and the low end tightens up. I also sink a screw into the brace through the back.
 
I can only tell you that I have heard a recording of a mesa before the owner tightened everything up (screws etc...) and then after and was blown away how much better it sounded after he went over it.
 
here are some pics:


the brace is held against the front panel via a small piece of composite board - no need to remove the grill cloth
IMG_20130518_164246.jpg

the composite board was attached to the brace using only a staple. I drilled a hole and countersunk a deck screw to put them together, putting a thin layer of leather in between (leather not shown) - for the back side, I draped a thicker piece of leather over the end of the brace, then screwed the external screw through it.
IMG_20130518_164317.jpg

While inside the cab, I saw that some other screws, like the ones holding the front panel to the frame, were really loose - this pic is post tightening - previously it was sticking out like a half inch.
IMG_20130518_164644.jpg

also, the torque of the screws holding the speakers to the front panel was far from uniform - some were much looser than others, but all of them seemed a little loose. The speakers felt tight against the panel, at least. I tightened the looser speaker screws to about the same tension as the tighter screws to try and get them even, but at the end they were all short of hand-tight. I was afraid to push them too hard, since it seemed like I might bend the speaker metal.

Anyway, afterward the bass rattle / flub issues are gone! Thanks!!!

It still doesn't sound as good as this Orange 4x12 that I have with V30s in it. The Orange cab is a lot heavier, but I haven't opened it up. I gotta also believe that the V30s work better with the amp heads I'm using. I can't wait to get my hands on some greenbacks at some point. When I get a chance, I'll compare it to a JCM800 1960A that I have, with the same speakers - I bet they sound very similar
 
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