Connect a 2x12 and a 4x12 to my amp?
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Posted on Apr 18, 2007 10:25 pm
Shenanigans
Member Since: Apr 05, 2007
Is it possible? I have the Peavey 6505+(plus) 120w amp. I have the Peavey 5150 4x12 straight cab and im interested in getting a 2x12 also for long drives to shows so i wont have to use a truck or suv to get my 4x12 places (we have no trailor) I'm also just interested if it is possible for me to hook the 2x12 up to the amp with the 4x12 for like a 3/4 stack just for when im practicing. I dont know if its possible because thouogh i have 2 outputs for 2 dif speakers, they both dont have independent ohm control. Theirs the selector but its for both i can get 4,8 or 16 ohms
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Apr 19, 2007 12:46 am You probably can plug in another cabinet, but you need to match impedence carefully. If your amp has the two speaker outs wired in parallel, then you should get another cabinet with a matching impedence. You should then set the impedence switch on the amp to half the value of the cabinets.
Basically, two loads (a & b) wired in parallel present the following total impedence (t) to the amp:
t = (a x b) / (a + b)
If a = b then t = a^2 / 2a
Assuming a pair of 16-ohm cabinets, you get:
t = 16^2 / 16+16
t = 256 / 32
t = 8
So if you have 2 16-ohm cabs jacked into an amp with a two speaker jacks wired in parallel, then you need to set the amp impedence switch to 8 ohms.
Similarly, a pair of 8-ohm cabinets gives you:
t = 8^2 / 8+8
t = 64 / 16
t = 4
Except 2x12 8-ohm cabinets are rare, to say the least. 2x12 cabs tend to be either 16-ohm or 4-ohm due to how THEY behave when wired and the fact that they tend to use 8-ohm drivers. Basically, you'd need to find a 2x12 cabinet wired in parallel with a pair of 16-ohm drivers in it.
Apr 19, 2007 07:58 am Yeah my 4x12 is 16 ohms
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Apr 19, 2007 09:52 am Seems to me, if you have 1 16ohm cabinet now, and want to get another 2x12 cab, you're trying to put either :
1) 2x12 by itself
2) 2x12 & 4x12 at same time.
If you got a 16 ohm 2x12, then you can plug that in by itself, setting the amp setting to 16
If you plug both 2x12 & 4x12 (both 16ohm), then set the amp setting to 8, because (2) 16ohm cabs in parallel is 8.
Seems fine to me, just remember to change the setting when you switch.
Apr 19, 2007 05:54 pm Ok so I'd have to get a 16 ohm 2x12? I figured ohms were just a standard thing on speakers like 4ohms a speaker, 4 speakers in a 4x12 so 16 ohms.
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Apr 19, 2007 06:13 pm it can be, if you put the speakers in series.
This way, 4ohm, plus 4ohm would equal a 8ohm total load.
Whereas, in parallel, two 4 ohm speakers together would be 2 ohms total load.
So to get your 16ohm cabinet, the two speakers inside the box would be (2) 8 ohm speakers run in series (adding up to 16).
Don't worry about what the individual speakers are, just pay attention to the total load of each cabinet: (1) 2x12 16o cab + (1) 4x12 16o cab = 8 ohm total resistance, seeing as how the speaker jacks are in parallel.
Apr 20, 2007 10:34 am If you get a 2x12 with 8ohm speakers wired in series this gives 16ohms,plug in both cabs(16ohms each) set amp to 8ohms,this should be just right.OOPS, PJK just said it.Ok I second his statement.:)
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Apr 20, 2007 10:40 am Just looking at Laird's post again, his math is worth looking at:
you can put two different load speakers together to see different total loads.
Like a 4 ohm speaker paralleled with an 8 ohm speaker.
The total load would be 2.67 ohms, but the 4 ohm would be seeing twice the wattage that the 8 ohm would see.
Something to keep in mind if you ever start playing with mixing speakers.
Apr 20, 2007 10:44 am Quote:
but the 4 ohm would be seeing twice the wattage that the 8 ohm would see.
Which is exactly why it is generally accepted as wise to not wire speakers like that...if you are running speakers in parallel, make them have similar specs...
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Apr 20, 2007 03:17 pm That's why I put that out there, to act as a deterrent, in case someone wants to put two speakers in a box, and wire them up without thinking it through.
1. load will be way low.
2. wattage goes to one side a lot more.
3. you'll only hear one speaker, even though both are working.
Man, I love this firefox 2, it shows me how to spell things, with the little red line =).
Noize2uCzar of MidiAdministrator
Since: Apr 04, 2002
Apr 23, 2007 09:23 pm Firefox rocks!
But it doesn't correct my bad punctuation.
Yet.
Apr 24, 2007 02:37 pm Once you are done matching impedence, then you have to worry about power and efficiency.
Suppose you have two nice 12" speakers wired in parallel and the pair nicely impedence matched to your amp.
Now suppose one of the speakers has 103db sensitivity and the other has 97db sensitivity. (Neither of these values is unusual). This is a 6db difference in sensitivity - which will show in VOLUME. The more sensitive speaker will end up being about twice as loud as the other.
Using unmatched speakers - impedence, sensitivity, etc. can be tricky. You can do it, but there are a lot of not-very-intuitive factors involved. It can sound fantastic when done right - but you better be able to do the arithmetic.
Check our Dave Hunter's "The Guitar Amp Handbook: Understanding Tube Amplifiers". He has a whole chapter in there about speakers, sizes, cabinets, impedence, wiring, sensitivity...
Apr 24, 2007 10:38 pm Thanks guys! I'll probably just go the easy way out and just get 2 speakers that match and that together are 16 ohms.
