# Wacky Impedance Question...

Discussion in 'Amps and Cabs [BG]' started by Mike, Dec 10, 2002.

1. ### Mike

Sep 7, 2000
Cali
4 ohms and 8 ohms create about a 3 ohm load, I think. I'm still and forever will be a techno idiot. If I had a 4 ohm cab and a 16 ohm cab what would my impedance be? (This sounds like a dumbass riddle.)

What would be the drawbacks of running a system like this? I have a 4 ohm cab in transit. I'm hoping one cab will do it for me. (I think it will). But, if ever I wanted to try two cabs, could the above be a possibility? The (HUGE) problem would be finding a 16 0hm cab...

Just curious.

Thanks.

2. ### PacmanLayin' Down TimeStaff MemberGold Supporting Member

Apr 1, 2000
Endorsing Artist: Roscoe Guitars, DR Strings, Aguilar Amplification
moved to amps

Sep 7, 2000
Cali
Oh, sorry.

4. ### throbbinnut

4 ohms // 8 ohms = 2.67 ohms, here's why -

Impedance in parallel:

1/Rtotal = 1/R1 + 1/R2 + .... + 1/Rn

So 1/Rtotal = 1/4 + 1/8 = 3/8, then flip it, so 8/3 = 2.67.

Same thing with 4//16 gives 1/16 + 1/4 = 5/16, or 16/5 = 3.2 ohms

Most amps are only 4 ohm rated. You'll need an amp rated at 2 ohms to be able to handle any cab in parallel with your 4 ohm cab.

The drawbacks are that the 4 ohm cabinet will get twice as much power as an 8 ohm cabinet in parallel, and 4 times as much power as a 16 ohm cab in parallel. No way around this.

It's best to just use (1) 4 ohm cab or (2) 8 ohm cabs.

Chris

5. ### Mike

Sep 7, 2000
Cali
I guess I lose...

6. ### BruceWane

Oct 31, 2002
Houston, TX
If a cabinet has multiple speakers, i.e. 4x10, 2x12, etc., you could rewire them internally to a different impedence. For example, a 4 ohm 2x10 has 2 8 ohm speakers wired in parallel, so you could rewire them in series and get a 16 ohm load. Your options depend on the impedence of the individual drivers. This is really only practical with 4 ohm multi-driver cabs; 8 ohm cabs are gonna end up at either 2 ohms or 32 ohms depending on the drivers and wiring scheme, and neither load is very useful. Example; 4x10 8 ohm cab has 4 8 ohm drivers in a series/parallel configuration. If you put them all in series, you get 32 ohms, if you put them all in parallel, you get 2 ohms.

7. ### Mike

Sep 7, 2000
Cali
All right. I have a 4 ohm EBS 2x12 on the way. No idea wht the speaks are. Either 4 or 8 I suppose. I'm hoping this will be it. However, as you mentioned, I could rewire these for 8 ohms, add another 8 ohm cab and be set with a 4 ohm load? I'm hoping I won't need to do this but, if so, it could be done in this manner?

Thx.

8. ### BruceWane

Oct 31, 2002
Houston, TX
Uhh, no....if the cab is 4 ohm, then it has 2 8 ohm speakers wired in parallel (technically, it could have 2 2ohm speakers wired in series, but I've never seen a 2 ohm speaker). You could wire them in series and get a 16 ohm load. There is no way to wire 2 8 ohm speakers to get an 8 ohm load.

You can safely run a 16 ohm cab and an 8 ohm cab; the total load will be 5.33 ohms. BUT, the 16 ohm cab will not be recieving as much power as the 8 ohm cab.

Sep 7, 2000
Cali
GOt ya.

10. ### AndyGL

Nov 20, 2000
Wellsville, NY
What would 3 eight ohm cabs work out to be cabled one to the other?

11. ### geshel

Oct 2, 2001
Seattle
Figure it out. . .

1/8 + 1/8 + 1/8 = 3/8

flip over, 8/3.

Same as one 8 and one 4, which makes sense: put two of the 8s in parallel -> 4 ohms. Put that in parallel with the remaining 8 -> 8/3 or 2.67 ohms.

12. ### AndyGL

Nov 20, 2000
Wellsville, NY
thanks