I am buying an Ashdown MAG C210 300W head, and two cabs. One is 2x10, while the other is 1x15. I want to plug my both cabs into the head at the same time, while also use them individually at small venues/jam etc. Can someone plz explain the DOs & DON'Ts of using & maintaining a head-cab, and what are the things to watch out for?

What about the 4 Ohms/8 Ohms, etc. And isnt impedance measured in Per Ohms? (Ohm reciprocal) Plz explain these as well, I never concentrated in Physics classes. Feel free to go technical, im a bit geekish myself.
Well its an entirely different topic than that thread, and it needs detail that is worthy of a new thread. That thread's title & flow of conversation is in another directon so this question wont gather as much or as fast opinions/answers.
^ That's only true when the speakers are in parallel rather than series to one another. If they're in series, then you do add the ohms regularly.

I would say refer to your manual. For example, when I'm running 2 8-ohm cabs with my Mark IV, I have to use the 4 ohm speaker jacks, since the amp recognizes them as parallel. On the other hand, some amps don't make the distinction and require that you match the ohm rating on the speaker jack to the ohm rating on the speaker box. Generally, you want to MATCH the ohms, or have the speaker box have a HIGHER ohm rating than the amp. NEVER use a speaker box rated for less ohms than the speaker jack is rated for.
Hi, I'm Peter
Last edited by Dirk Gently at Feb 23, 2007,
Quote by Bassface_505
I am buying an Ashdown MAG C210 300W head,

There is no such thing in the Ashdown product catalog.

C210 means "combo with 2 x 10" speakers".

You probably mean a "MAG 300h head"

... and two cabs. One is 2x10, while the other is 1x15.

The MAG 300 has two speaker outputs wired in parallel on the same output power stage with a 4 ohms minimum load for that stage.

The MAG 210 and MAG 115 cabs are both 8 ohms each.

When one cab, either cab, is connected to the amp, you have a 8 ohms load on the amp's output stage.

When both cabs are connected to the amp, each cab connected with it's own speaker cable to one of the amp's outputs, you have a 4 ohms load on the amp's output stage.

Clear enough ?
Quote by voodoochilli499
I'm pretty sure that when you add ohms they dont ad normally. I think it's 4+4=2, 8+8=4 and so on. you need to figure out how much the amp can handle before you buy the stuff.

The overall impedence Z of 2 loads R1 and R2 wired in parallel is in physics geek-lingo:

the inverse of the sum of the inverse of each load

in calculator lingo: Z = 1 / ( (1 / R1 ) + ( 1 / R2 ) )

derived from the ohms law for parallel circuits that says: 1 / Z = ( 1 / R1 ) + ( 1 / R2 )
Well guyz first off, dont snap at me. I didnt ask an ultimate stupid question.

Yes my mistake. I was set on C210 combo, and then decided on the head-cab, but forgot that the names are a little different. Sorry.

Dirk dude, can u plz explain how ohms etc. work? so tht I wont have to post everytime I have any tiny tweeny confusion. I'll seriously appreciate that.

ColdGin, man sorry but not clear enough. Maybe I am stupid, but plz tell me whether its ok to use that 4 ohm setup as u mentioned. And in general, is a 4 ohm setup prefered, or an 8 ohm setup?

I have read that cab modification thread, and the post in it abt ohms and series/parallel circuits. But still need more fodder. More elaborated, but not too hard to chew. Thanks if u can do that.
K When you have two cabinets of the same ohmage (which is a measurement of electrical impedance)(thank GRADE 9 SCIENCE!) you half the ohmage they are. Ex) 8 ohms + 8 ohms = 4 ohms because cabs are almost %100 wired in parallel. NOW heads don't have ohms that are related to sound at all for they don't take any electricity from that particular circuit. SO if your cabs are running at 4 ohms and your head says 300 watts @ 4 ohms (the musicians friend page didn't say what ohmage but I'm assuming 300 @ 4) you will get 150 watts to each cab. SO in short yes this set up will work fine.

Generally 4 omhs is proffered.

Ohms are basically a measurement of how many Coulombs of electrons are taken out of the circuit for each resistor.
Last edited by jazz_rock_feel at Feb 24, 2007,
^ It's hard to understand without some sort of graphical representation, but essentially it works this way:

If each speaker is wired independently to the amplifier - that is, both have their own positive and negative wires and are not wired to each other - you get the total ohms the amplifier will see by getting an average of the number of ohms then dividing it by the number of speakers. So if you have 2 speakers that are 4 ohms wired in parallel, they have an average of 4 ohms (obviously). Since there are 2 speakers, the amp will actually see 2 ohms. Likewise, if there are 4 4-ohm speakers wired in parallel, the amp will see only 1 ohm (the average of 4 speakers at 4 ohms is 4 ohms, divided by 4 speakers = 1)

On the other hand, if speakers are wired in series - that is, positive from the amp to one speaker, and then the speakers are connected in a chain, negative -> positive, until it goes back to the amp - then you just add the number of ohms for each speaker. So if 4 4-ohm speakers are wired in series, the amp will see 16 ohms.

That also works for cabinets. If an amp is hooked to 2 8 ohm cabs in parallel, it will actually see 4 ohms. On the other hand, if they're wired in series (amp --> cab 1 --> cab 2) the amp will see 16 ohms. But, as I've said, when in doubt the best place to look is the owner's manual.
Hi, I'm Peter
Off-topic - I like your sig, although Lions of Al-Rassan, IMO, is Kay's best work. BTW, did you know he has a new book out now?
Hi, I'm Peter
Yeah he's touring Canada right now I think. I just got into him a couple of weeks ago when I got the Sarantine Mosaic series for Christmas and I was just floored by the depth of his writing it absolutely amazed me. He's actually replaced J.R.R Tolkien and Margeret Weiss + Terry Hickman duo as my favourite writer. I'll have to remember Lions of Al-Rassan though. He's also from Winnipeg which I found interesting.
The Sarantine Mosaic is good work. Compared to Kay's other stuff, I'd say it's middle of the road - but of course, if another author wrote that, it'd be considered their masterpiece. If you want modern Tolkien, then The Fionavar Tapestry is great. Kay actually assisted Christopher Tolkien in the completion of The Silmarillion. My favorite individual works by him are A Song for Arbonne (I cried at the end - ok, ok, I'm a big bitch), Lions as previously stated, and Tigana.

Also, if you love GGK's work, check out George R. R. Martin's "A Song of Ice and Fire" series starting with A Game of Thrones.
Hi, I'm Peter
I almost cried in the Mosaic when they were tearing down his work. You just become so attached to the characters it's insane. But I was in public so I didn't think that would be appropriate, but the feeling was there.
Quote by Bassface_505

ColdGin, man sorry but not clear enough. Maybe I am stupid, but plz tell me whether its ok to use that 4 ohm setup as u mentioned.

Here is a pic of the rear panel of the MAG 300.

The "4 ohms minimum load" in the pic above is for the total load connected.
So, what do you think ?

And in general, is a 4 ohm setup prefered, or an 8 ohm setup?

None, it's like asking what voltage between 110v and 240v is better.
Quote by jazz_rock_feel
because cabs are almost %100 wired in parallel.

This is incorrect.

Determining the resistive load of a 1 speaker cab is easy, it's generally the load of the speaker itself.

I wrote above generally because some cabinets have tweeters with-built-in crossovers and the tweeters load need to be accounted for in the total load.

For cabinets with 2 speakers:

- usually, cabs have 8 ohms speakers wired in parallel, for a total cab load of 4 ohms

- occasionally, cabs have 4 ohms speakers wired in series, for a total cab load of 8 ohms

- rarely, cabs have 16 ohms speakers wired in parallel, for a total cab load of 8 ohms

For cabinets with 4 speakers, generally

- usually, cabs have 4 ohms speakers, pairs wired in series, each pair wired in parallel, for a total cab load of 4 ohms. When one speaker blows up, all 3 others keep working.

- occasionally, cabs have 8 ohms speakers, pairs wired in parallel, each pair wired in series, for a total cab load of 8 ohms. When one speaker blows up, only the 2 speakers of the other pair keep working.

I have yet to see a cabinet with 4 speakers all wired in parallel.

And then there are cabinets with 8 speakers. I'll skip that part, assuming owners of 8 speaker cabs know their gear.

What is almost 99% true is the following:

mono amps almost always have a unique electronic power stage output, but may offer several outputs of different impedence. The rule of thumb is that ALL outputs are connected to the amp's electronic output stage in parallel.

This way, if you make sure that you don't daisy chain cabinets, or in other words connect each cabinet to the amp with it's own speaker cable, you are certain that both cabinets are connected to the amp in parallel, and subsequently use the calculator formula Z = 1 / ( (1 / R1 ) + ( 1 / R2 ) ) , to figure the total load when both cabinets are connected to the amp, before strictly following the instructions in the amp's manual.

Finally, to calculate the total load, always use the specific impedence given for each cabinet.
Last edited by ColdGin at May 27, 2008,
Hmm... Great posts ppl. THat helped a lot. Thanks very much ColdGin, Dirk, Jazz_rock_feel, all u guyz. Keep rockin.