Watts, ohm loads, heads, cabinets... I'm lost!!!!

[funnygames]

I've been reading about ohm loads, parallel hookups, series hookups, total impedance calculations, and soforth for the last hour and I'm no closer to figuring out what I need to figure out.

I got a screaming deal ($50) on a Randall Century 170 head last week. It's solid state, 150 watts, 4 ohms. Right now I have it going to an Orange 412 which is rated at 240 watts, 16 ohms. The rig is loud and gorgeous and, go figure, I would like to add another cab. I want the head to run at it's fullest (read: LOUDEST) capacity. But, of course, I don't want to blow anything up. And the cabinets will need to run in series because the head only has one speaker output.

What should I be looking for? What wattage and ohm-load would be optimal? Do I need to rewire the head to run at a different ohm load? Will the ratings change if I hook up the series of cabinets in a different order?



Thanks!

 

[ocnor]

Shavano Music Online - Speaker Wiring; Impedance Calculator

 

[Lt. Bob]

I've been reading about ohm loads, parallel hookups, series hookups, total impedance calculations, and soforth for the last hour and I'm no closer to figuring out what I need to figure out.

I got a screaming deal ($50) on a Randall Century 170 head last week. It's solid state, 150 watts, 4 ohms. Right now I have it going to an Orange 412 which is rated at 240 watts, 16 ohms. The rig is loud and gorgeous and, go figure, I would like to add another cab. I want the head to run at it's fullest (read: LOUDEST) capacity. But, of course, I don't want to blow anything up. And the cabinets will need to run in series because the head only has one speaker output.

What should I be looking for? What wattage and ohm-load would be optimal? Do I need to rewire the head to run at a different ohm load? Will the ratings change if I hook up the series of cabinets in a different order?



Thanks!

there's really nothing confusing about it. In an ideal world your amp will put out the most volume into 4 ohms. If it's 150 watts into 4 ohms and you're running it into 16ohms you're probably getting around half that.
And no, an extra cab doesn't have to be in series because there's only one jack on the amp. Why would you think that?
If you wire a second cab in series you'd have a load of 32ohms!
You'll just daisy chain a second cab and you'd do it in parallel. Most cabs have 2 jacks on the back and they're parallel. If yours doesn't ..... add one. And lastly ...... go slap yourself in the face for suggesting you might "rewire" the amp .
Rewiring an amp to accept a different load is something that even those here who do know something about amps don't consider.
Add a second cab and you'll be at 8 ohms.

You could rewire the cab though. If it's 16ohms right now it's almost surely series/parallel.
So you could go in there and simply wire all 4 speakers in parallel and you'd have a 4ohm cab. That's IF the speakers are 16ohms each which they probably are.

 

[stevieb]

One simple thing to remember, when considering amps, speakers, and ohm ratings:

GOING TOO LOW MAKES THINGS BURN OUT.

A message on your amp that says something like "MINIMUM IMPEDENCE 4 OHMS" means, in part, that if you hook up multiple speakers to that amp and the amp "sees" a load of UNDER 4 ohms, chances are it will overheat and burn out before the night is over.

The good news is that 4 ohms is pretty low, already, so unless you get carried away, you will probably not cross that line. If you got another Orange cab like that one (which I would recommend- you obviously like that cab, and you needn't worry about impedence mis-match,) you would probably "show" your amp an 8-ohm load- it will be plenty happy with that, and will show it's happiness by giving you lots of volume. Oh, sure, if you were to get the total ohm load closer or at 4 ohms, you might get more volume, but 150 watts pushing 8 12's should be enough for ANYBODY.

As for the speaker cabs having to be wired in series because your amp has only one speaker out, most cabs that have two connections have those connections wired in PARALLE (and "Parallel" is usually printed on the jack plate)L- run a speaker cable (NOT instrument cable) from your amp's speaker out to speaker cab #1, and another speaker cable to cab #2. Done. Play music.

As for "rewiring the head to run at a different ohm load," it's not worth the trouble. Easier ways to skin that cat.

(For everyone else, yes, I know my suggestion here may be overly simple- but the OP is saying he is getting overwhelmed by the technical arcania, so I thought a simple answer would be best.)

Hope this helps. Much of it is paraphrase of what Lt. Bob says, so you now have two ways of getting the same basic message. Maybe my words work better for you, maybe Bob's do. Whatever, at least you get the message.

 

[Farview]

The reason the amp is rated at 4 ohms is because if they rated it at 8 ohms, it would only be a 75 watt amp. Which doesn't sound impressive, even though it is a lot of power for a guitar amp.

As everyone said, adding another cabinet will be done in parallel. You want to use another 16 ohm cabinet, otherwise the cabinet with the lower impedance will be louder. And that is just stupid.

The reality is, a doubling in power only gives you 3db more volume. A doubling of speakers, all things being equal, will give you the same amount. So adding another 16 ohm 4x12 will double the power output of the head and double the coverage to give you 6db more volume...which is about twice as loud.

If you want the rig to be as loud as possible, you will need four 16 ohm cabs in parallel to get you down to 4 ohms and 16 speakers. Unless you are playing outdoor sheds or arenas without PA systems, there is no point to it.

 

[funnygames]

Much clearer now. I feel like a hazy cloud of ohm confusion is letting up, every so slightly, as everything that I've owned in the past (guitar amps, bass amps, studio monitors, PA) have been either combos and/or powered speakers.

Thanks for the information, much appreciated!