Shielding a speaker?

[mumford]

I've been working on an old Gibson Scout lately. The other day I put in a speaker, a 12" Pyle Driver. Everything says the Scout had a 10", but the baffle is cut for a 12", shrug.

With the speaker in, the reverb is humming like crazy. I've moved the tank around, the only place I lose the noise is a couple of feet from the speaker. Is it possible to create a shielded bag or something, or am I going to need to get a different speaker with a smaller magnet? Ideas?

[Cygnus X1]

Are you sure you didn't flip the tank?
As in...rotate it on the long axis?

[Phil_S]

I own a Scout. I'll confirm it is a 10" so yours has been modified. I'd agree on checking tank orientation before doing anything else. Open side is down. I don't recall which side the connectors are on but I think the cable length is not adequate to allow end to end rotation. Mine is in a closet that is hard to get to or I'd take a look. Sorry, about to leave for vacation, so I wouldn't be able to actually do that for another week.

I'll also ask the obvious. There is a bag for the tank and the bag is screwed to the cab floor. Is yours in a bag?

Beyond that, I think I might think about a piece of aluminum flashing, which is relatively easy to cut and bend. You can probably make a modified doghouse above the tank and screw it in place without too much trouble. As I recall (could be wrong), the cable is fairly standard fare coax, so there is already an outer shield on that.

Thinking about this...your view may differ...it may be simpler (although a bit more work) to cut a new 10" baffle and put in the correct size speaker. If you can be patient, I'll get mine out when I return and give you a good measure on the placement of the hole.

[Firestorm]

I don't see how the speaker would cause that. It's a fixed field, the magnetic equivalent of DC. Maybe recheck the cables, especially their grounds.

[mumford]

Thanks for the replies. I've moved the tank all around the box to try to find a quieter spot, no dice, although some are louder. With the speaker moved away from the box the noise goes away.

There is no bag in mine, I plan on making one once I figure out the shielding issue.

I may have to go to a 10", but I'd like to try a doghouse or something first.

[Phil_S]

Get or make a bag. IMO, it's essential.

You can buy vinyl upholstery tolex-like fabric at the likes of JoAnn Fabric. You don't need much. In case you don't know, to make a neat bag, you sew it inside out. For this you could just as easily do it any way you like. It isn't a fashion item!

Aside: besides me, I wonder how may guys here actually know how to use a sewing machine. I can't really sew anything that needs much more than a straight line. My mother was a dress maker. She showed me how the machine worked when I was about 20 years old so I could hem my own blue jeans. I'm short and the standard length is nearly always too long. It was a useful lesson. 40 years later, I still do them on my own. This isn't high fashion...that goes to a real tailor.

[mumford]

I can make a bag, and I can see the advantage for isolation, but that wouldn't affect the hum, would it?

[xtian]

You sure it's not the relationship of the reverb take to the transformers?

[JazzGuitarGimp]

I wonder if the speaker's magnet could be interfering with or possibly amplifying the flux coming off the transformers? Just pondering out loud here. It might be interesting to build a set of extension cables for the reverb tank so that the amp chassis could be removed from the cab, keeping the same relationship between the speaker and the reverb tank.

[vibratoking]

You sure it's not the relationship of the reverb take to the transformers?

I have experienced this and/or relationship to the tubes.

[mumford]

I did a little test this morning, removing the speaker. You guys are right. It's not the speaker. I'll start checking other stuff. Thanks.

[M Fowler]

Reverb pan in bag screwed to bottom of cab. Keep far away from the PT as possible.

Mark

[JazzGuitarGimp]

Reverb pan in bag screwed to bottom of cab. Keep far away from the PT as possible.

Mark

And keep the output end of the tank (the return back to the amp) on the opposite side from the PT.