This is for all the Marshall 412 cabinet owners out there..........
I stumbled upon an interesting find on how to make your Marshall 412 cabinet sound better. I not too long ago picked up another 412, this time a 1960B Vintage Straight Bottom from my buds at the local Guitar Center who were having their yearly clearance sale. This cabinet was never used. I purchased it because I want to see if when I am onstage that by using straight bottom cabinets will I get a little more low end pushing through and also will it cut the feedback on the various house sound systems we play through. I heard that using slant cabinets have a lot to do with that so we will see if it tames the feedback.
So anyway I was watching this guy and he showed how to shore up a Marshall 412 to make it sound, fuller, tighter, punchier and just overall much better. The first thing he said which I never knew was that when you pull off the back panel from the cabinet that the screws securing the speakers to the baffle are 90 percent of the time extremely loose and need to be tightened as much as possible to the baffle because the looseness of the screws means the speakers are not seated on the baffle with the tightest seal and that air is escaping. Low and behold I checked and at least half the screws were 3/4 of the way ready to fall out completely. This was no matter because I was yanking the stock Vintage speakers out of that cabinet anyway and replaced them with a quad of new 25 watt Celestion Greenbacks.
Before I put the Greenbacks in, I washed the entire interior of the cabinet with a sponge, warm water and Murphys Oil Wood Soap. Wow was there a lot of saw dust and gunk in there. Once it was dry I took a couple cans of canned air and made sure I blew out all the cracks and crevices so that there was no more debris in the cabinet.
Next thing I did was go to my local Lowes Home Improvement Store and pick up a nice caulk gun for about $15.00 and a few tubes of clear silicone caulk/sealer and also a can of CNC Quick Dry Electronic Spray Cleaner and some Rosin Solder and headed home.
When I got home, I proceeded to take the clear silicone caulk and lay a nice thick bead completely around the baffle. There are some huge gaps in there where sound escapes and you lose tone. Anyway, I proceeded to lay out the bead, filling the cracks completely then ran my finger across the bead to not only press it into place but also create a smooth line. In addition I laid a bead line across all the top and bottom joints where the sides join the top and bottom. You can also seal around the handles but for right now I left that alone. Next, I installed the Greenbacks and tightened every screw to the baffle as tight as I possibly could. This created a more airtight seal.
Once the speakers were in, I cleaned the terminals and wire connectors and proceeded to solder the wire to the speaker terminals. Now this is purely optional, but for me, I like knowing that I always have the strongest electrical connection possible so for me I solder.
Next, remove the back input jack connection plate and clean it by spraying it liberally with CNC Cleaner and going into the terminals with a Q Tip to pull out all the black gunk in there then let it dry. Once dry, proceed to lay solder across all the lines on the green side of the connection board. Just trace over the lines you see and let the solder cool and harden. Once that is done, solder you wires to the plate, put the plate back on the backboard and throw a bead of clear caulk seal around it and then tighten all the backboard screws to the back of the cabinet as tight as possible.
The caulk will start to cure in about an hour but takes about 2 weeks to fully harden.
NOTE OF IMPORTANCE: When removing speaker wire from speaker terminals and input plate terminal posts make sure you tape numbers to both the wire and the terminal so that you don't confuse yourself as to what goes where upon reconnection. Just pair up the numbers as 1a to 1b, 2a to 2b and so on. You don't want to blow anything up now!!
The end result I must say was VERY noticeable. It was tighter, punchier, there was a TON more bottom end and the cabinet just sounded stronger overall. This is an easy, cheap way to shore up your Marshall Cabinet and get it to sound its absolute best!!
Give it a try and let me know what you think.