Speakers & Ohms

[charvel750]

Hi, all. I have a red knob Fender Twin from 1992. It has two 12 inch speakers, each is rated 8 ohms. When I connect the speaker cable to the amp's output, do I choose the 4 ohms setting?

Also, how are the Twin's speakers wired, series or parallel, and what is the difference? Is there an advantage to series vs. parallel? I appreciate the help...

[DonP]

What's the difference? In parallel, you two 8 ohm speakers are a 4 ohm load. In Series, they are a 16 ohm load.

Parallel: A wire is connecting positive to positive on the speakers, and negative to negative. In series, you have one wire to the positive, a jumper from the negative of one speaker to the positive of the other, and a wire on the negatiive.

This is a pain in the ass to describe, someone post some pictures. I give up.

[RacerX]

What DonP is trying to explain:

http://caraudio.biggz.com/parallelseries.html

Here's an online ohm calculator:

http://www.the12volt.com/caraudio/boxcalcs.asp

[gpig]

Radio Shack has some good/cheap multi meters, run down and get one. You'll get a ton of use out of it.

[Spivonious]

Now the ultimate question:

Assuming that the amp supports 4, 8, and 16 ohm output, is there any reason to choose one over the other?

[GodWentPUNK]

Here's an online ohm calculator:
http://www.the12volt.com/caraudio/boxcalcs.asp

cool.

joe...

[DonP]

Now the ultimate question:

Assuming that the amp supports 4, 8, and 16 ohm output, is there any reason to choose one over the other?

Yeah, you will fry your amp if you don't match them up.

With a tube amp, if you set the load to 4, and plug in a 16 ohm load, that's BAD.

Transistor amps just the opposite - if the amp wants 16, and you give it 4, you'll blow the output stage by pulling too much current.


If you mean a 4 ohm speaker with a 4 ohm amp vs. a 16 ohm speaker with a 16 ohm amp, I think there is a slight difference (more or less bass?) and it might be safer running one way vs. another, but I can't remember.

[TheSteveMan]

Transistor amps just the opposite - if the amp wants 16, and you give it 4, you'll blow the output stage by pulling too much current.

This is one point about impedance matching... putting a load on that's too small draws too much current.
The other thing to note is that the power that gets through to the load is maximized when the load impedance is exactly equal to the source impedance. Anything else and you're drawing power with your source that isn't getting fully utilized.

[Spivonious]

If you mean a 4 ohm speaker with a 4 ohm amp vs. a 16 ohm speaker with a 16 ohm amp, I think there is a slight difference (more or less bass?) and it might be safer running one way vs. another, but I can't remember.

That is what I meant. I would guess that in 4-ohm mode there is more current going through the speaker, so you could get louder? V = IR, so if R goes down, I must go up, unless the voltage changes...

[DonP]

That is what I meant. I would guess that in 4-ohm mode there is more current going through the speaker, so you could get louder? V = IR, so if R goes down, I must go up, unless the voltage changes...

4 Ohms will work only if the amp can deal with it (i.e. big power transistors and good cooling). But when you start mis-matching impeadance, the tone could change and other issues might come up.

[charvel750]

Thanks, guys, I appreciate that.

[danastas]

I just bought a brand new unloaded cab. I don't have speakers yet, so I have the option of wiring it anyway I want.

There's only one input jack.

What are the pros and cons of going...

Series: two 8 ohm speakers for 16 ohm cab
Parallel: two 16 ohm speakers for 8 ohm cab?

Which would you choose (my amp can do both)?

With one input, I can't daisy chain them, so I'm thinking that serial would be the easy wire job.

Does 16 ohms vs. 8 ohms make any difference?

[danastas]

I got my answer

Andy Fuchs of Fuchs amps answered this question in someone else's thread elsewhere:

FUCHS WROTE: The general consensus is that higher impedances offer the potential to sound better. Reasoning is that it takes less windings to match the high impedance (4 to 6-K) of the power tubes to a 16 ohm speaker. A 4 or 8 ohm match takes more wire. No transformer is perfect. More wire means more resistance. It's a coil, which means more inductance. It has layers, which means inter-winding capacitance, and so forth. You can improve on all these factors, but never eliminate the effects, only minimize them. Less windings means less phase shift and wire between you and your tone. Depending on the transformer type and quality, it can be subtle or sometimes clearly heard.

I sometimes wonder when people say "the 16-ohm 1265 sounds better than the 8 ohm versions" if it's because of the transformer issue more than the speakers themselves....."


Well, since my transformer can be 4, 8, 16 ohms, I'm not going to worry about this. I'm after a new cab/speaker not a new amp. So I'm going with what I think is the most popular amp ohm out there, 8.