one cabinet..8 or 16 ohms????

[tfinn1313]

i have two combo amps. one with 1-12" 8 ohm speaker and an external jack for a 4-ohm input.
the other is a 2-12", each 8 ohms and currently wired in series for 16 ohms. ( plugs into amp w/1/4" plug)
my question is this..can i connect another set of wires to the 2-12"s, but instead of in series hook them up in paralell so that the total will be 4 ohms? (with a 1/4" plug)..then i can use my 2-12 cabinet as an external cabinet to my 1-12 combo and have all impedance correct. i would not, of course, have my 2-12 amp on nor would i have the series 1/4" plug plugged in. i'm guessing i can do this but don't want to ruin some classic speakers or damage anything else. my 1-12 amp is an old peavey aritist, with 120 watts rms so i'd like to get some more "punch" outta the old girl.

 

[Major Tom]

No, you cannot have 2 speakers wired for parallel and series at the same time. Unfortunately I can't draw it and post here, but try drawing it out...The only thing you could do here would be to rig up some "quick disconnect" arrangement to rewire the speakers for each application.

 

[tfinn1313]

thanks for the input. do you mean something in the way of an "a/b" box or switch. something that when in "a"...."b" is disabled. or some sort of quick disconnect to the speaker connections. suppose i could get some slip on connectors instead of soldering.
anyway, you've helped as i wanted to know before i drag the monster out to the shop and do anything.
thanks again

 

[Major Tom]

Actually, I guess you could buy a couple of project boxes from Radio Shack, and build 2 "configurator" boxes. Each box would have 2) 1/4" speaker out jacks, and 1) 1/4" input jack. One box would house the series wiring, the other would house the parallel wiring- wire 1/4" plugs on to the ends of the wires from each of the 2 speakers, plug both into the speaker out jacks of the appropriate "configurator" box, then connect your amp's speaker out to the input of the magic box and wail. You would actually have 3 impedances available from your rig; 16 ohm series, 4 ohm parallel, and 8 ohm if you only hook 1 of the speakers to the parallel box. You could also use Molex or Amphenol style plastic multi-conductor connectors and make 2 "harnesses" instead of the boxes. Buy all the stuff, drive on over and I will wire it up for you....

 

[tfinn1313]

thanks again for continuing to assist me on this. let me ask you this....i talked to a local amp guru (?) yesterday and he said that no harm would come to either the speakers or the amp if i use the speakers set up in series, as the ohm rating is higher than required. he said that harm only comes when you use speakers at lower ohm ratings. is he the guru he claims to be or should i seek another sage? i did plug the 2-12's into the amp and it sounded alright, but would i gain any appreciable difference if i wired them to the 4-ohms in parrell? the speakers are celestion g12-80's and sound great in the rockand roll 50 that they're intalled in. i would not want to damage them just for the sake of playing around to get more uhmmmmph outta my other amp.
thanks for the offer on wiring up the magical box but the distance is more than i want to drive and besides, the sun always shiines in florida.
thanks again

 

[Major Tom]

If it is a solid state, you're ok to go with a higher impedance (16 vs 4) it won't be as loud, but that might balance better with your single 12 combo anyway. If it sounds good, use it that way. Solid state amps may be damaged when there is too little impedance on the output, but should be fine with higher impedance. If it is a tube amp, it is not recommended to use a higher impedance, everything I have read about tube amps state emphatically not to deviate from the rated output impedance, either higher or lower, for the attached speakers or else damage may occur to the amp. As far as damage to the speakers, they generally get blown from solid state amps that are driven into clipping, but I don't think you will have that problem with a modern guitar amp, either tube or solid state. You might want to check the manual for your amp, the 4 ohm output might mean TOTAL, including the onboard speaker if it is connected, which would mean that it wants an 8 ohm outboard speaker. I forget the formula, but 1) 8 ohm + 1) 16 ohm will yield something like 6 ohms total, not real far from the 4. Impedance is kind of a slippery rating anyway, it depends on the frequency content of the signal, ratings like 4, 8 or 16 ohm are "nominal" ratings, based on average use. The lower the frequency is (or the more low end content of a guitar signal), the less impedance the amp will see from the speaker load.