What does 4 Ohms or 8 Ohms mean?

pilsener · Posted: Mon Jul 28, 2003 3:03 pm Post subject: What does 4 Ohms or 8 Ohms mean?

What does it mean when an amp description says it can handle 75watts at 8 Ohms or 100 watts at 4 Ohms? Does this depend on the type of speaker the amp has or is it something you can switch back and forth?

Rufio · Posted: Mon Jul 28, 2003 3:34 pm Post subject:

Ohm's is not like a switch that you can change. Different amps have different Ohms. With some you can choose to buy a 4 or 8 ohm. Your cab and head need to have the same amount of ohms or else it will blow the cab out.

BassMan02 · Tiger Joined: 15 May 2003 Posts: 848

If your amp is an 8 ohm amp you ususally can run it and 8ohms meaning only having one cab connected to it or at 4 ohms meaning you have 2 cabs hooked up. 8ohm amps run stronger if they have 2 cabinates hooked up to it.
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pilsener · Posted: Tue Jul 29, 2003 8:41 pm Post subject:

Thanks for the help. I was very confused regarding the subject and couldn't find any information about it. So just to make thing clear if I have an 8 Ohms amp, I could connect it to two 4 Ohms cabinets, right.

pilsener · Posted: Tue Jul 29, 2003 8:49 pm Post subject:

Thanks for the help. I was very confused regarding the subject and couldn't find any information about it. So if my amp runs at 8 ohms, would it be better to connect one 8 ohms cabinet to it or two 4ohms cabinets?

bassman80189 · Posted: Tue Aug 12, 2003 2:01 pm Post subject:

One 8 ohm. It's just a matter of resistence of elctrical current. A 4 ohm amp can run two 8 ohm cabs or one 4 ohm. What amp do you own?

Christov · Posted: Sat Sep 13, 2003 9:00 am Post subject:

The "ohms" thing is the impedance of the speaker cabinets, and what the amp. is "looking" for. Tube amps are very critical with the impedance selection. Impedance is basically the resistance of the alternating current signal that is being produced by the amplifier. If an amplifier is rated at 8 ohms or 4 ohms minimum load that is the lowest impedance the amplifier will safely work. Zero ohms is a dead short, which will fry most amps. The lower the impedance of the speaker cabinets the closer to a dead short, as seen from your amplifier.
The wiring of the speakers is critical. You have basically 3 ways to wire speakers: series, parallel, and series-parallel. In series the speakers impedance will "add", in parallel the impedance will "half" and in series parallel, it will vary with the configuration. Usually by adding two cabinets this will put the speakers in parallel as seen by the amp. It is harder to wire speaker cabinets in series, but it can be done with 3 cables. On the first cable from the amp only have the tip (+) connectors soldered into place, in between the two cabinets a standard speaker cable is to be used with both the positive and negative wires connected, and on the third cable only the negative (-) wire soldered in as a return to your amplifier. This will usually reduce the power of your amp however, and if you blow a speaker, all speakers will stop working, much like some Christmas lights. Best of luck.
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