What would the ohms be?

Discussion in 'Amps and Cabs [BG]' started by xring, Jul 4, 2005.

1. xring

Sep 16, 2003
Ohio
...if I ran 3 - 8 ohm cabs?
Is the formula 8x8x8/24 or 8+8x8/24? Probably neither.
Thanks, Randy

2. xb100

Mar 24, 2004
NH, In
well 2 8ohm cabs will equal 4 ohms. Then if you add another 8ohm cab it will be somewhere around 2.62 ohms, or something.

heres how it goes

2 32ohm speakers will =one 16ohm load
2 16ohm speakers will =one 8ohm load
2 8ohm speakers will =one 4ohm load
and 2 4ohm speakers will =one 2ohm load.

3. xring

Sep 16, 2003
Ohio
Quick math! Thanks! That's great as I have a 2 ohm capable head. Randy

4. paintandsk8Pushin' my soul through the wire...

May 12, 2003
West Lafayette, IN
all three in parallel = 2.67
all three in series = 24
two in parallel plus 1 in series = 12
two in series plus 1 in parallel = 5.33

5. LowtonejoeSupporting Member

Jul 3, 2004
Pasco, WA
I believe it is Rt=1/((1/R1)+(1/R2)+(1/R3)). You can throw as many 'cabs' (1/Rx) in there as you like

So that means for three 8ohm cabs Resistance total = 1/((1/8)+(1/8)+(1/8))

or Rt = 1/(.125+.125+.125)

or Rt = 1/.375

or Rt = 2.666666666

or Rt = 2.67 ohms

Joe.

6. xring

Sep 16, 2003
Ohio
Alright now, You two are just being wise guys.
Now come down to my level and talk sloooowly.
If I daisy chain the 3 cabs, it is 2.67 right?

7. LowtonejoeSupporting Member

Jul 3, 2004
Pasco, WA
Sorry to have contributed to your confusion!

(But the formula is real.)

Yes, you are correct.

2.67ohms

Joe.

8. steveksux

Mar 23, 2005
Detroit area, Troy, MI
Also easier formula could be (R1xR2)/(R1+R2). Since the first 2 8's = 4 (easy enough to do in your head) just do (4x8)/(4+8)=32/12=8/3=2.67.

For combining equal impedance cabs, i.e. all 8 ohm, the formula breaks down to just ohms/# cabs. 3 8 ohm cabs = 8/3 ohms. 4 8's = 2 ohm (8/4).

Randy
P.S. The formula above (R1xR2)/(R1+R2) does NOT expand to more than 2 cabs. You can't do (R1xR2xR3)/(R1+R2+R3).

The formula mentioned earlier post (1/(1/R1+1/R2+...1/Rn) )can be expanded to add as many cabs as you want.

9. seanmI'd kill for a Nobel Peace Prize!Supporting Member

Feb 19, 2004
Ottawa, Canada
Actually the formula is really simple if *all* are the same ohms:

R/n

Where n is the number of cabs So 8 / 3 = 2.67.

Jul 3, 2004
Pasco, WA
Nice!

Joe.

11. xring

Sep 16, 2003
Ohio
OK guys, this is sort of related and I'm not quite sure. I have an Ampeg B4R head and the ratings are this:
(2 ch. amp)
500w X 2 @ 2 ohms
350w X 2 @ 4 ohms or
1000w Bridged @ 4 ohms.

On the 500 X 2, is that 2-2ohm cabs or 2-4ohm cabs? Makes a big difference in my application. I totally get the bridged application (2 8 ohm cabs= 4 ohms), but I lose it going seperate channels.
I believe the parallel vs series difference applies here, thus my total lack of understanding.
Thanks for the help, Randy
ps: I realize now that I can't daisy chain the 3 8 ohm cabs bridged as I can only go as low as 4 ohms bridged.

12. LowtonejoeSupporting Member

Jul 3, 2004
Pasco, WA

Each side of your amp can go down to 2 ohms in any speaker configuration.

It's easy...when bridged, you have one amp that can go down to 4 ohms. When operating with two channels you have two amps. Each one can go down to two ohms.

Not sure what you mean about parallel/series. That has to do with speakers, not amps.

Joe.

13. LowtonejoeSupporting Member

Jul 3, 2004
Pasco, WA
AND...if you want to use all three cabs use two cabs on one side (4 ohms) and one cab on the other side (8ohms). That is perfectly o.k....as long as you are in 2 channel mode, NOT bridged.

Joe.

14. xring

Sep 16, 2003
Ohio
Great. I think I've come away from this a little wiser. Nevermind the series/parallel question.
It's a bummer though. I was hoping to get max wattage stereo with 4 ohms per side, but that ain't 'happenen!
I think 2 cabs per side at only 350w won't let the cabinets speak as they are rated at 1700w rms per side!
Much appreciated.

15. LowtonejoeSupporting Member

Jul 3, 2004
Pasco, WA
Yeah, bummer. Max wattage per side is definitely 2 ohms.

But...max wattage bridged is 4 ohms. You can run 2 8ohm cabs and get max wattage.

What cabs are you using? That sounds real high. Are you sure you are not referring to peak wattage instead of RMS wattage?

If your peak wattage is 1700w then your rms wattage will be anywhere from 425 to 850w depending on how the manufacturer measured it. Commonly it would be 425w

Or are these custom cabs?

Joe.

16. xring

Sep 16, 2003
Ohio
Well the cabs are the Avatars. B212 Delta is rated 1000w rms. Also a B210 Delta for 700rms. I was going to get another cab for tonal options, but since that wouldn't really be feasible, I considered getting two more cabs for a monster rig. It would require more power for that, and realistically, I don't need it. I already do bridge them for the 1000w, but the B4R offers so many hook up options, I just got to thinking. (I ought not do that!)
I could run a separate power amp in at say...2500watts, but I think I'll pass!

r

17. IvanMikePlayer Characters fear me...Supporting Member

Nov 10, 2002
Middletown CT, USA
i think i'm gonna unstick the FAQ and all the threads linked in it like the OHMS FAQ because apparently, no one reads them.

18. xring

Sep 16, 2003
Ohio
Don't unstick it on my sorry account. I just blew it and will shut up now...
Randy

19. Plain Old Me

Dec 14, 2004
Man, I don't really wana calculate how many watts each speaker would get in those set ups...