4x12 G12M-70 Cabinet.

Hi guys, I'm having a problem with a second-hand 4x12 (280w) Cab I have just purchased. I just can't get enough volume out of it. The speakers are G12M-70 Celestions which all seem to be putting out sound, except that the max. output I get is only bedroom volume. The cabinet is a Marshall type, but has no badging or tolex & there are 2 input jacks. One has 2 wires connected & the other has 4. Only the 2 wire jack works.

I'm using the external output jack of a Marshall JCM 900 50W 1x12 combo. The internal speaker is disconnected when I do this. I've run this amp flat out & it only produces a weak output from the 4x12. This amp is more than loud enough to drive another Marshall 2x12 100 watt cabinet that I have. I've played around with the impedance selections on the amp (4/8/16 ohm) & I still can't get any geater output from the cab.

I've also used an old 70's Fender Bassman 100 head & have exactly the same problem with the cab.

I'm no expert on the wiring & soldering, but the connections & wire look to be intact on the cab & jacks.

The next step looks to be to get a tech to look at the cab wiring & setup.

Should a 50w Marshall combo, or the 100w Bassman be enough to produce sufficient output to drive a 280 w cab to be able to gig with it?

Any advice would be greatly appreciated.

Steve N.

One Watt would be enough to get plenty of volume. If your amps drive the combo speakers you are disconnecting fine then there is a problem with your 4 x 12 cab. Impedance wouldn't make a difference at low outputs on the amp in terms of volume or trouble over driving the amp this is not the dilemma. If the wiring in the cab is fine them maybe you have blown speakers. Don't drive the cab possibly causing more damage until you get the cab checked out. I'm sure someone will have a link with proper wiring in this thread soon.

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Have you tried running it out of the internal speaker jack? Or out of the extension speaker jack with the internal speaker connected normally?

Got a meter? Check the resistance of the speaker cab and get back to us.

Take a flashlight and a 9v battery... while looking in the grille cloth at the speaker cones, touch the 9v battery to the speaker cord. You should see all four speakers jump the same way (either out or in). My guess is that some are jumping out, and some in (out of phase).

Good simple test BUT any single D, C, AA or AAA one and a half volt is way more than enough. (9V is the equivalent of a huge amount of watts)

OK, genius... you tell me how many watts a 9v battery will put into a 4x12 16ohm cab... better take into account the internal resistance (source impedance) of the battery, you'll need something besides infinity for your I when you do P = EI and P = (I^2)(R).

There are two reasons I spec'ed a 9v... 1) it's very easy to touch a 9v to a 1/4' plug... try that with any other battery (6V lantern OK too) and 2) 9v is the easiest battery for a musician to come by... everyone's got

Hello, Watt is not just a matter of voltage. Power needs juice(the current). 9V is most commonly used for easy access to terminals. Cable guys use it all the time for an example.

Damn Steve, relax. I used to use a 9V myself for years. But a 1.5 Volt gives enough excursion to tell also. Now yes the 9V is easier but...maybe I should have said if you don't have a 9V around any 1.5 Volt will do BUT you will need leads to get to either end of the battery. When I said good simple test, that was a compliment. It is the best easiest first thing that can be done. The other suggestion of trying the other output on the cab was a good one too.

The back of my amp has one 8 ohm out and two 4 ohm outs but the back of th OP sounds like he has one that says internal and one that says external so maybe by not having the internal plugged in and just the external that could be it, maybe.

So I would proceed with testing the speakers with a battery and then testing each of the outputs.

As for the wattage and the impedance and the resistance, since I'm not a genius I don't have the figures.

Do NOT use that cab until you find the problem! Have you done a simple resistance check of the cab? Something ain't right. When you did try it, did you verify sound coming from all speakers (if not, don't try it again).

You could open it up, check wiring, and check resistance of each driver.

A 9V is not the equivalent to a huge amount of watts, not to mention that there isn't enough current available to do any damage.

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Listening is not always good... the drivers interact, hard to hear if one's dead, since it will act as a passive radiator for the others.

By far the best alternative... after watching for speaker jump with DC