# Ohm Math

Discussion in 'Amps and Cabs [BG]' started by Bassman 100, Oct 22, 2010.

1. ### Bassman 100

Apr 4, 2008
Ireland
Total=?

I can add = numbers no problem, I know 8+8=4 ohms & so on, but I'm confused with this one unequal numbers

2. ### Alex1984

Jan 16, 2010
Vancouver
48/14 = around 3.5?

For a tube amp, I'd use the 4 ohm setting.

3. ### mongo2

Feb 17, 2008
Da Shaw
Series: 14

Parallel: 3.4

4. ### john mSupporting Member

Jan 15, 2006
6 ohms in series with 8 ohms = 6 + 8 = 14

6 ohms in parallel with 8 ohms = (6 x 8)/(6 + 8)= 48/14 = 3.4

5. ### Bassman 100

Apr 4, 2008
Ireland
Fantastic thanks guys & know I know how to add.
Follow on Question. I have a MarkBass MiniMark. 150 Watts. If I add an 8 Ohm Cab I get 250 Watts. I have a Phil Jones 6B Cab which is 300 Watts, but 6 Ohms, am I out of luck here? (mismatch 0.6 is this significant?) if I have my math correct

6. ### FunkMetalBass

Aug 5, 2005
Phoenix, Arizona 85029
Endorsing Artist: J.C. Basses
Unless the amp is 2-ohm stable, yes, you're out of luck.

Does the 0.6-ohm difference matter? Probably? I'm no expert on amp design, but I imagine there is a fairly small tolerance associated with an amplifier's stability at running with impedance outside of the scope of the amp's specs.

7. ### Alex1984

Jan 16, 2010
Vancouver
With solid-state, the main concern is current draw (ie. heat). If you're not pushing it really hard, and you don't have any other alternatives, I think it'd survive, but not something I'd want to do repeatedly. On a side note, 6 ohms, really?

8. ### Dubista

Jan 5, 2009
Melbourne, Australia
Resistors in Series = R1+R2+Rn

1/Resistors in Parallel = (1/R1) + (1/R2) + (1/Rn)

9. ### lindseyp

I think a 4 Ohm amp should handle a 3.4 Ohm load since that's the average Ohm level (I'm NOT paying for your amp if it melts!). Just don't crank the amp to max, or at least periodically check the amp for too much heat if you use this load. A 2 Ohm amp will handle this just fine, one of the reasons I like my Yamaha BBT500H.

10. ### mrkreuzschlitz

Jun 30, 2008
Dacula, GA
I've seen people run 4 ohm amps at 2 ohms all night. Now, I'm not recommending this... at all, but its possible.

11. ### lowendfriend

By george, he's got it.

Serial or parallel matter a whole lot as you can see.

12. ### BassmanPaul

Aug 25, 2007
Folks, when the company who make the amp says don't use it below 4&#937; it's a warning that you should listen to. I've repaired way too many amps that have blown outputs because of doing precisely this. It's simply not worth the risk. It's called abuse and a persons warranty will be void in these cases.

13. ### greenboy

Dec 18, 2000
remote mountain cabin Montana
greenboy designs: fEARful, bassic, dually, crazy88 etc
Yeah, and some people are assuming that an 8-ohm cab or a 4-ohm cab doesn't actually dip lower yet, than its stated nominal loads. But that's not the case. Since these loads are all over the map, amplifier designers are already addressing some lower impedances than the stated nominals. No sense to throwing gas on the fire. Do it right.

14. ### Ekim

Aug 20, 2002
Indianapolis, IN, USA
Another OHM MATH question.

If two cabs have equal resistance (say, two 8-ohm cabs) but different wattage handling and you run them off the same channel in parallel (making the 4-ohms together, right?), how do figure out how much wattage they can handle?

If one is 300watts max and the other is 800watt max, what's the max wattage you should pump into them to avoid damage?

15. ### jmleeCatgut? Not funny.Supporting Member

Jun 16, 2005
Halifax, Nova Scotia
If both have the same impedance and they're in parallel, the current produced by the amp will be equally split between the two speakers and the power "absorbed" by each will be the same. So...600 watts out of the head should translate into 300 watts to each. You want to protect the "weaker" of the two elements in the circuit.

16. ### Ekim

Aug 20, 2002
Indianapolis, IN, USA
Thanks for the quick reply. Of course, I won't NEED that info til I get another cab, but I really, really want one so I want to be ready when I do!

17. ### B-string

Exactly, double your weakest link and that is the "THERMAL" limit of the combined cabs (mechanical limit may be less).

18. ### runmikeyrun

Jan 10, 2001
northeast Ohio
the formula to figure out resistance in parallel is:

R1xR2

divided by

R1+R2

So- to figure out two 4 ohm loads in parallel-

4x4=16
4+4=8

16/8=2

Got it?

Series resistance- just add the numbers together- 4 ohm + 4 ohm = 8ohm.

I agree with Paul- never EVER go below your amp's rating. While some MAY tolerate it most will not. Blowing your amp is not worth it.

19. ### Ekim

Aug 20, 2002
Indianapolis, IN, USA
I have no intention of blowing any amp. Gear is spendy!

20. ### Stick_PlayerBanned

Nov 13, 2009
Somewhere on the Alaska Panhandle (Juneau)
Endorser: Plants vs. Zombies Pea Shooters
Too much work!

Use this: Impedance Calculator