Author Topic: 2 Ohm, 4 Ohm, 8 Ohm?? (Read 377 times)

lbpesq · « **Reply #15 on:** August 16, 2006, 09:57:09 AM »

I think if you run 8 and 4 ohm cabs in series, you wind up with a 12 ohm load. On my boogie I have 3 speaker outs, 8, 4, and 4 ohms. The folks at Mesa tell me I can use any of them, so long as the cab ohm rating is equal to, or greater than the amp outs. Thus, in Dave's situation I would plug the 4 ohm cab into the 4 ohm out, and the 8 ohm cab into either the other 4 ohm out or the 8 ohm out, whichever sounds better. Of course this is for a Boogie Mark amp. Your situation may be different.

Bill, tgo

olieoliver · « **Reply #16 on:** August 16, 2006, 10:01:35 AM »

I stand corrected, Bill is right. I meant to say parrallel would be 6 ohms.

lbpesq · « **Reply #17 on:** August 16, 2006, 10:07:56 AM »

Olie:

I was also about to opine that parallel would yield a 6 ohm load, but I tried it on the ohm calculator Marcky posted above and an 8 ohm speaker wired in parallel with a 4 ohm speaker yeilds 2.67 ohms. Then when I thought about it, it seemed to make sense. If two 8 ohm speakers wired in parallel yield a 4 ohm load, reducing one of the speakers to 4 ohm wouldn't raise the level to a 6 ohm load.

Bill, tgo

(Message edited by lbpesq on August 16, 2006)

olieoliver · « **Reply #18 on:** August 16, 2006, 10:23:21 AM »

I checked with SWR's web site and they show minimum load at 4 ohms. I believe the 2 spkr outputs on the rear are wired parrallel. And looks like Bill is right about the 2.67 ohms. So I probably wouldn't run these cabs at the same time through your 550.

dadabass2001 · « **Reply #19 on:** August 16, 2006, 11:06:53 AM »

Okay guys,
The straight formulae from physics class (jeez, I still remember taking physics class!) are:

For Series: R1+R2+R3 ... = R total
so 4+4=8; 4+8=12, etc

For Parallel: 1/R1+1/R2 ...=1/R total
so 1/4+1/4=2/4=1/2 total impedance= 2ohms;
but you must find the common denominator (ouch... math too!) 1/4+1/8=2/8+1/8=3/8=1/2.67 total impedance=2.67

I don't FEEL tardy... class dismissed!
Sorry
Mike

marcky · « **Reply #20 on:** August 17, 2006, 03:00:36 AM »

You are right again Bill, one 4ohm cab + one 8ohm cab = 2.67ohm.
I've just finished building two cab's like this for a customer of mine. His Aguilar power amp is set on 2ohm when he runs both cabinets.
Please everyone when you are not sure about connecting your cabinets use the ohm calculator posted above or send me an email to prevent any amp damage!!
Marcky Vanderkley

gtrguy · « **Reply #21 on:** August 17, 2006, 01:27:47 PM »

Thanks, it's not a good match for the SWR. anyone want to buy a mint Ampeg 1x15 BXT115-HL4 cab designed to Vic Wooten specs? It's got amazing tone. You can feel the air move right through you on the lows!

David Houck · « **Reply #22 on:** August 17, 2006, 03:57:29 PM »

Rich; when I bought my Eden 210 cabs, I went with 4 ohm, and here's why.

Two channel power amps put out more power per channel into 4 ohms than into 8 ohms. If I don't plan to carry more than two cabs to any gig, then I will make more efficient use of my amp if I get the 4 ohm version of the Eden 210 cabs rather than the 8 ohm version.

Of course if I play a gig where I want to use four cabs, then I'm going to be wishing they were 8 ohms cabs. (This of course ignores the fact that some power amps will operate with a 2 ohm load, but generally 2 ohm loads are to be avoided.)

Thus the decision whether to go with 4 ohm or 8 ohm cabs is difficult and involves anticipating your needs in addition to matching power amp output with cab power ratings.

As a generalization, the power amp output rating should be equal to or higher than the speaker cab rating.

richbass939 · « **Reply #23 on:** August 17, 2006, 07:31:36 PM »

Thanks again, everyone. I now have a basic understanding of impedence. I have a 115 combo and 210 cab (both 8 Ohm). That is plenty for the gigs I do. Dave, I don't see myself playing any gigs that would require a boatload of cabs. My rig is just fine right now. I don't need anything else. My wife is starting to seriously ask me, Don't you have enough stuff, already? The marital bliss could start to show some wear marks pretty soon. I think I'll stop the abrasive action.
Rich

David Houck · « **Reply #24 on:** August 17, 2006, 08:07:23 PM »

Yes, two cabs is all I've needed for the gigs that we play too.

elwoodblue · « **Reply #25 on:** September 07, 2006, 01:15:20 AM »

thanks rich for the thread,
I needed a reminder to check what impedence my custom cab is.
...when I was using a old 2 ohm peavey PA head the only worries I had was how to get rid of the honkiness .
Now I have a Stewart world 2.1 and I want to keep it working good for a long time.
The impedence calc will come in handy.

thanks all