# 4 OHMS + 8 OHMS= ???

Discussion in 'Amps and Cabs [BG]' started by Dean_CustomJazz, Mar 21, 2002.

1. ### Dean_CustomJazzGuest

Jan 23, 2002
woburn
The head i plan on getting is r1000, which is 1000 watts. It is very versatile with ipeidances (2,4,8 ohms) i want to get the most power, so i want to run 2 4 ohm cabs for a total of 2 ohms. I have a 4 ohm swr goliath jr, but i want a 1x15 cab to go with it, but i can find to many cabs that are 4 ohms! Tons of 8 ohms, but no 4's. What were to happen if i use a 4 ohm and an 8 ohm and is it a good idea? please, i need suggestions

(p.s. i'd like to keep the 1x15 \$600 or under)

2. ### Oysterman

Mar 30, 2000
Sweden
4 + 8 ohm in serial would add up to 2 (2/3) ohms. If you can run the amp with 2 4 ohm cabs, you can run it with a 4 + 8 config. No problems.

Using the decimal system, 4 ohms + 8 ohms config would roughly be 2.67 ohms . Just thought I would help translate the above fraction from Oysterman to clarify things.... That said, 2.67 ohms is real close to 2.0 ohms and your amp will do fine and almost be at it's full porential. Don;t sweat the extra .67 ohms....

4. ### MM

Umm..wait a sec. 4 ohms and 8 ohms in series would be 12 ohms.

4 ohms and 8 ohms in parallel would be 2.667 ohms.

Parallel: (A*B)/(A+B)=total impedence
Series: A+B=total impedence

5. ### JMXVorsprung durch Technik

Sep 4, 2000
Cologne, Germany
Not quite right!

4 and 8 Ohm in serial add up to 12 Ohm

Rt=R1+R2

4 and 8 Ohm in <b>parallel</b> will give you 2.667 Ohm

1/Rt=1/R1+1/R2

1/4+1/8=1/Rt

Rt=8/3 Ohm = 2 2/3 Ohm

6. ### Dean_CustomJazzGuest

Jan 23, 2002
woburn
in terms of wattage, how many watts would the 4 ohm Goliath jr recieve and how much would the 8 ohm 1x15 recieve?

7. ### Oysterman

Mar 30, 2000
Sweden
Oops. I always do that wrong. I hate physics.

At least I knew the math.

8. ### cubeenzGuest

True, but... Most cabs are not designed to be wired in series. In fact, I've never personally seen a cab that you could wire in series. So the series/parrallel thing isn't really an issue. For common use, you won't be able to wire in series. That requires some fancy internal wiring.

Another thing to keep in mind. Amp and cab impedence ratings are approximate ratings, so a 4 ohm cab might be something like 4.1 ohms. Plus, impedence varies slightly with wattage, so you can never perfectly measure a constant impedence. I believe this is right; correct me if I'm wrong.

9. ### JMXVorsprung durch Technik

Sep 4, 2000
Cologne, Germany
You're right.

10. ### Jon R

Oct 16, 2001
Frostbite Falls, USA
11. ### Dean_CustomJazzGuest

Jan 23, 2002
woburn
the way i originally planned was:
------------------
jack 1 (to)
4 ohm 2x10
-----------------
jack 2 (to)
8 ohm 1x15
if there is another way, just tell me, or copy my fancy shmancy art and alter it.Thewhole series/parellel thing i dont understand. please explain.
what im tryin to get at is should i do this and will it dramatically decrease my power?

12. ### Jon R

Oct 16, 2001
Frostbite Falls, USA
Sorry... I wasn't trying to confuse things. You'll be in great shape... no problem with loads and near max output.

That third option was mainly informational... most people assume that if you have multiple speakers in a cab the effective Ohm rating of that cab will either be lower than the individual speakers (4 x 8 Ohm speaker = 2 Ohm parallel load) or higher than the original speakers (4 x 8 Ohm speaker = 32 Ohm series load). There is however a third option that would not change the overall Ohm rating... (4 x 8 Ohm speaker = 8 Ohm series/parallel load).

Good luck

13. ### Richard Lindsey

Mar 25, 2000
SF Bay Area
Hang on, just thought of something. When you said R1000, did you mean the Carvin R1000? If so, then things change a bit, because that head has two separate amps, which can be used separately or bridged mono.

If you run one cab off one side of the amp and the other off the other, the 4 ohm cab will get about 350 W and the 8 ohm cab about 250. Note: you CANNOT run both cabs daisychained off the *bridged* output (which is rated for 1000 W at 4 ohms bridged--this is the same as putting a 2 ohm load on each side of the amp), because your total resistance is 2.67 ohms, which is too low (equivalent to a 1.33 ohm load on each side). If you daisychain both cabs off one side of the amp, you'll get maybe 450 W. Each side can take loads down to 2 ohms, but the bridged output cannot.

If you're thinking of a different amp, never mind.

14. ### Geoff St. GermaineCommercial User

The only amps I know of that have a series output are the Nemesis Combo amps. When you add an extension speaker you will increase the load and lose power. Maybe there are others, but for a separate head it seem like a bad idea.

Geoff

15. ### Richard Lindsey

Mar 25, 2000
SF Bay Area
You're right, and in fact this is how just about every 8 ohm 4-10 is wired and virtually any Marshall 4-12 cab as well (four 16 ohm Celestions wired in series-parallel for a total of 16 ohms).

16. ### JoelEoM

Mar 11, 2002
Lancaster, PA
im doing the same thing with my rig right now-
hartke HA2000
hartke 2.5XL(8ohm)
Ampeg V-4B 2x15(4ohm)

the head is 200 watts at 4 ohms, it has 2 8ohm outputs. im still kinda confused from reading above..
i know im running the amp at 2.67ohms(correct?) but i want to know how a load like this could potentially damage it. i dont know a whole lot about resistances...or am i ok with running my rig like this?

17. ### JayPeaTea

Jul 24, 2001
Finland
About the HA 2000 @ 2.66 ohms...

I did the same thing for two years with 8 Ohm 4x10 and a 4 Ohm 1x15 (which I ASSUMED to be 8 Ohms - 2115 combo)

I had no problems with it... tough it did start to smell a bit after long a session... bit like 'old cigaret smoke' smell(?).

...The answer; is it Ok to run HA2000 @ 2.66 ohms
- Well, no. You will probably BURN the poweramps outputstage sooner or later! (= expensive to repair)

- my HA 2000 hasn't failed me yet... 6 years old and all!! Some "friends" did blow the 15" speaker last month tough, so now it's an 8 ohm 1x15...

18. ### JoelEoM

Mar 11, 2002
Lancaster, PA
thanks jaypeatea...ive had my 2000 for about 4 or 5 years now, and its served me well. im not too worried about blowing it up, if i do it will give me an excuse to go ahead and buy the rig im planning out...hehe, preamp, dual poweramps, 2 eminence omega 15s, new 210

19. ### geshel

Oct 2, 2001
Seattle
Most of this has been said before, but to sum up:

R1000 + 8ohm 1x15 + 4ohm 4x10

1. R1000 Bridged, speakers in parallel: 2.66 ohms, below the amp's min, don't do it

2. Each channel to separate speaker: 250W into the 1x15, 350w into the 4x10 (numbers from Carvin I'm guessing?). That's not much difference, and you'll have separate gains for the two channels. Recommended way to go.

3. One channel into both speakers in parallel: Not quite 500w into 2.66 ohms. Amp should be fine. Not as much total power as option #2. Also, the 4x10 will *always* get twice the power that the 1x15 gets.

Seems like option #2 is the way to go.

If you do find a 4ohm 1x15 you like, then I'd still go with option #2.

20. ### MM

I wasn't commenting on whether or not you find cabs that are wired in series. It was a clarification on the statement by Oysterman. Also, it isn't uncommon for people to replace speakers in which case series/parallel is an issue.

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