Ohms ? - 8 ohms 16 ohms who gives a ....

jem7pbk · #1 04-19-2001, 11:21 PM

Can some one explain ohms to me I use 16 ohms cabs ( marshalls) but my heads say to use 8 ohms am I hurting my amps?

Vaibanez · #2 04-19-2001, 11:28 PM

I don't think so. If it were the opposite it would.

Think of Ohms as PSI and think of your amp as the air pump and your speakers as the air tank.

If your tank (speakers) can only hold 8psi(ohms) than your pump (output transformer) will back up and pop. If your tank (speakers) can hold 16psi (ohms) and your pump (output transformer) can only push 8psi (ohms)...get my drift?

I might have over simplified it...but I'm not an electrical engineer.

J>

jem7pbk · #3 04-19-2001, 11:53 PM

Thanks man, it makes since to me! good analogy

tomizm · #4 04-20-2001, 02:19 AM

With Solid State stuff *-- *You'll see a lot of bass rigs rated at 8 million watts at 4 ohms. *I dont know why they do this. *At 4 ohms the amp is working it's hardest and needs 8 million watts to push the speakers. *If you go with one 8 ohm cab, then your only pushing maybe 4 millions watts.
When you start getting into tube stuff then, you have to start watching what you're doing, although Mesa Boogie manuals state that Boogies cant really be harmed by messing up the load, although it might kill the tubes earlier then usual.

Beer

jem7pbk · #5 04-20-2001, 02:44 AM

Yah I only do the solid state thing any more. I use ampeg ss model amps and they are 150watts and its says 4 to 8 ohms

7 Dying Trees · #6 05-16-2001, 09:38 AM

Basically ohms are a measure of how well electricity flows through something. The lower the ohmage, the better electricity will pass though something. The ratings on your cabinet should be matched by the rating on your head. The reason for this is as follows:

look at the amp as a hairdryer, and upon the ohmage of your cabinet as how far away from the funnel of the hairdryer your hand is (the lower the ohmage the nearer your hand is). Say there is a distance that you can hold your hand that will keep it pleasantly warm. Now you turn the hairdryer on, and it has several settings. The higher ohm settings are meant for when your hand is far away, and the low ones when your hand is close by.

Now say you have your hand far away with the hairdryer on a low setting, in this case your hand will get cold (the analogy: your amp won't sound as loud/good, you lose tone).

Now say your hand is too near the hairdryer, your hand wil heat up quite considerably, but the main thing to worry about is that your hairdryer is getting warmer itsself, everything is heating up, and after a while the hairdryer dies. (try this at home with an old hairdryer, you'll smell something burning, or the hairdryer will switch itsself of, although I wouldn't recommend doing anything like this as it is a bit dodgy).
The analogy here: Telling your amp that the speaker is of a higher ohmage than it actually is will pump more power through the speaker, and more importantly will drive more power through the amp than it's designed for. Result? In the case of tubes, total amp death after a while. Like the hairdryer, it will function for a while and then die. (I have had this happen due to an incorrectly wired speaker cabinet, I had to have the transformers rewound by hand...(old amp)). In the case of solid state stuff there is no output transformer (the transistors do the job fine without one) and so it's not as important as valves, but will affect your tone etc.

The only other thing to remember is that if you connect two cabs/speakers up to a head, that you are connecting them in parrallel. What this means is that the amp sees the two cabs/speakers as one big cab/speaker with a lower ohm rating! So when you connect two 16 ohm cabs up to a head, you need to set the head to 8ohm output! *For any other ohmage combinations, here's how you work it out:

"big" speaker ohm rating =

1 / ( 1/speaker1 * + 1/speaker2)

So basically, make sure your amp is matched to your speakers...

I hope this helps...

Screamin · #7 05-21-2001, 11:49 PM

Somewhat related, but how about stereo/mono settings on Marshall cabinets.
Is there a difference? I'm running a 100w JCM800 into 1960A & B stacked cabinets. I've hooked them up about every possible way and they all sound basically the same.

Thanks,
Screamin'

7 Dying Trees · #8 05-22-2001, 06:32 AM

I think the stereo cabs have two settings:
a) One mono, 16ohms
b) two stereo 8 ohms each.(correct me if I am wrong, I haven't used one for ages).

If you hook up both cabs through the mono ports, you should use 8 ohms setting, if you use the 8 ohms sockets, (ie one cab, stereo) the you should use the 4 ohm setting if running of one channel (iif you are running of two channels, use 8 ohms/channel).

I do find that they end up sounding pretty much the same, but using an incorrect setting will either lower the power output that you percieve, or (in the long term) blow your amp (if it's tubes, I am not too sure about transisitor amps). Blowing your amp might take quite a while, I ran my mine with an incorrectly wired cabinet for about a year before it died on me. Having the transformers replaced/rewound(if it's an older amp).

Believe me, it's worth making sure

bammbamm · #9 05-22-2001, 07:29 PM

Trust me, with a tube amp, ANY tube amp, you can blow it up. I speak from experience. I wired up my 4x12 cab in complete parallel thinking all 4 speakers were 16 Ohms to obtain a 4 Ohm load right?
welp, it turned out that 2 were 8 ohms and 2 were 16 ohms. If we use this parallel resistance formula to determine the actual impedance :1/8 + 1/8 +1/16+ 1/16 = 0.375 now reciprocate that 1/0.375 = 2.666... Ohms not so good for the out put x-former. It didn't blow right away, but one day I noticed how crappy the sound was and then it finally died after about 3 mos of playing 2-4 times a week. THis was on my Boogie Studio .22 all tube amp. It blew the output trans. after 3 mos, no amp is impervious to load mismatches unless someone designed it to be. ( read not common except in solid state)
I replaced the trans. and all was well again, but I knew what and why it happened after it popped, others may not have the insight I do. Set your stuff up according to the impedance recommendations. I got off cheaply.
Bamm

Skaught · #10 05-23-2001, 03:41 AM

You have to be careful when it comes to speaker cabs and amps, if your cab says 8 is optimal, when then 8 is good. You can achieve that load with one 8 ohm cab or 2 16ohm cabs (like bammbamm just explained) Another thing to keep in mind is that if you're havign multiple cabs, you'll want all their ohmage to be the same. This is to keep the power from your amp constant as it flows into each cabinet. I've found that if you follow that kind of setup you'll never run into a load problem and your amp will live out to it's full potential!

judasbane · #11 05-23-2001, 04:14 AM

Ok, now i'm seriously lost within this conversation

Ok, my current rig so far is a Crate Blue Voodoo 120W head, which has a 8ohm/16ohm selection on the back. I have 2 Carvin Cabinets (top and bottom), both of which are rated at 8ohms, mono/stereo. The cabinets themselves have 2 inputs and 2 male XLR inputs. I have both cabinets setup in mono mode and is connected to each output the head has. One cabinet is connected through the main speaker output and the other cabinet is connected through the 2nd speaker output (via ordinary 1/4" speaker cables).
Question is, Am I damaging either the head and/or speakers at the same time by having the head setup to 16ohms?? I couldn't really hear much of a difference when I switch the head to 8 to 16ohms and vice versa (unless i'm tone deaf).
What should I do if I set the cabinets to run in stereo mode? Any differences in sound/load, etc?

Reg