Just put a new 12" Green Beret in my Blackstar closed back cabinet. This was to replace the existing 10" speaker. I don't have the new grill cloth or t-nuts yet, so I decided to just build up a temporasry baffle, to try out the new speaker. First, I love it. It's exactly as advertised. Shines with some dirt, and at loud volumes. OK clean, low volume. Not spectacular.
Here's the thing. At moderate volume, I'm getting a trailing metalic sounding feedback sort of noise. Almost as iff it's coming from the speaker cage. It's not coming from the head. And nothing is lose.
The temp speaker baffle is 3/4"plywood. Perfect hole cut out. Front mounted, with supplied pads put under the speaker frame radius. It is screwed with drywall screws to the plywood. Everything is snug.
Wondering why the metallic feedback after the note/chord trails off? Cab to small? Need ported? Open back?
Help! I otherwise love the speaker and tone.
Yours is tough to know for sure because of the seriously non-conventional mounting.
I'm sure the 12 is not happy firing through the 10" hole ... not sure if that has anything to do with it or not ... never tried that myself!
Can you put it in a legit cab made for a 12? That would be worth a try before sending it back.
Did you properly match the speaker impedance to your output transformer? Simply, if you replaced an 8ohm speaker, is the new one 8 ohms? Improperly matched load impedances can create magnetic resonance in the output transformer and can affect the NFB loop in a heavy NFB amp. Also, any time I hear a 'ringing' sound coming through the speaker, I first check the preamp tubes in the amplifier for microphonics. Not sure of the specifics of the Blackstar head you are using, but if the preamp tubes are all the same, i.e. 12ax7, try switching the preamp tubes into different sockets. A microphonic tube in the front end of your preamp will be amplified 1000's of times by the time the signal reaches the output. A microphonic tube later downstream i.e. phase-inverter tube will usually not be audible.
I have mounted larger speakers onto smaller baffles with mixed results. In a closed cabinet it's NOT a good idea. In an open or semi closed cab, some speakers like a load in front of the cone, and some speaker/amplifier combos will sound better this way. Some speakers will get 'bound up' with a load in front of the cone. I have mounted 12 inch speakers onto 10 inch baffles in open cabs in order to tighten up the low-end response, or when the baffle is glued or dovetail mounted in place and cannot be accessed for enlarging the hole. But like I said, I DO NOT recommend this in a closed cab.