Author Topic: 2 Ohm, 4 Ohm, 8 Ohm?? (Read 376 times)

richbass939 · « **on:** August 13, 2006, 04:44:33 PM »

Once again I'll admit I don't know squat and ask a technical question.
I hear a lot about amps producing, say, 320 watts into 8 Ohm or 480 watts into 4 Ohm. I know that Ohm represents impedence but that's about all. Is there a performance or sound advantage of using 8 Ohm speakers? Why not use a 4 Ohm system and get more power? Will someone please give me an Ohm 101 lesson?
Thanks,
Rich

FC Bass · « **Reply #1 on:** August 13, 2006, 05:27:11 PM »

My Ampeg gives 275 watt at 8 ohm and 450 watt at 4 ohm. There should be no difference in sound, only in output. Some amps , for instance the Mesa 400+ have the same output at 2,4 or 8 ohm.
With my amp the volume difference between 4 and 8 ohm is minimal, far enough for most situations. Never go below the minimal impedence (4 ohm on my Ampeg) You'll fry your amp if you do! So I can use two 8 ohm cabinets or one 4 ohm cabinet (my mesa is 4 ohm)
Following examples are when the cabs are wired parallel, Most connections are wired this way:

Two 8 ohm cabs will result in 4 ohm
Two 4 ohm cabs will result in 2 ohm
Two 16 ohm cabs will result in 8 ohm
Four 16 ohm cabs will result in 4 ohm
Four 8 ohm cabs will result in 2 ohm

Please anyone correct me if I'm wrong or fill the gaps I left
This is just basic info, I'm not that technical also... I hope it's a bit usefull for you and I'm sure there are others here who will have a more technical answer...

Cheers!
F.C.

olieoliver · « **Reply #2 on:** August 13, 2006, 07:14:16 PM »

I believe you are correct Flip. Cabinets can be rewired to change the impendence too. Two 8 ohm speakers wired parallel should give you an 8 ohm cabinet while the same two 8 ohm speakers wired series should give you a 4 ohm cabinet.
(I believe, anyone please correct me if I am wrong).

bigredbass · « **Reply #3 on:** August 13, 2006, 07:30:00 PM »

There's other more-qualified members who can explain ohm-age properly than myself.

In the real world, pay VERY good attention to FC's chart.

Make sure at what minimum ohms YOUR amp operates: Virtually all bass amps (Ampeg, Eden, SWR, and on and on) and commercial power amps (the Crests, Crowns, Stewarts, etc.) will operate at a 4 ohm load. A lot of amps will operate at 2, and you occasionally find a very few that will not go below 8 (the old Yamaha P Series power amps from the 80s come to mind, and others). You also find (usually) tube amps that have a selectable output selector, so be sure that control matches your cab(s). If you run a power amp in bridged mode, remember that they often bridge at one ohm value only, even though in stereo they will operate fine at several different values. You want to obey the manufacturer's suggested spec, period.

As far as the cabinet side goes, the higher the impedance of the cab, the more of them you can run: You could run 2 8-ohm cabs (equals 4 ohms) instead of one 1 4-ohm cab off the same amp. This is a cheap(er) way to get louder, as you get the same bump in db level (+3db) doubling cabs as you would in doubling the power of your amp (500w to 1000w). This is why a Marshall stack with both cabs sounds so much louder than a half-stack. And why you can move earth with the original SVT setup (300w head and TWO 810 cabs) instead of simply rattling the bottles behind the bar with a single 810.

J o e y

lbpesq · « **Reply #4 on:** August 13, 2006, 08:31:52 PM »

I believe the formula is two 8 ohm speakers wired in parallel yields 4 ohms of resistance, wired in series yields 16 ohms of resistance. You can usually safely go up - for example an amp putting out a 4 ohm signal can push an 8 ohm speaker, but going down - an 8 ohm amp into a 4 ohm speaker will fry the speaker and/or amp. The folks at Boogie tell me that the 4 ohm out pushing an 8 ohm speaker is often a preferred tone.

Bill, tgo

keavin · « **Reply #5 on:** August 13, 2006, 08:47:18 PM »

I'm running two JBL 15's @200watts per chanell via a Carvin ProBassII bass amp which gives me pretty good flexibility for my situitations,but out doors i use my Hartke 350watts for my stage shaking alembic sounds!

marcky · « **Reply #6 on:** August 14, 2006, 01:48:53 AM »

You are right Bill, two 8 ohm speakers wired parallel gives a 4 ohm cabinet.
Use this impedance calculator for more wire options
http://colomar.com/Shavano/impedance_proc.php

richbass939 · « **Reply #7 on:** August 15, 2006, 05:06:03 AM »

Thank you, everybody, for the Ohm lesson. Very helpful.
Rich

lbpesq · « **Reply #8 on:** August 15, 2006, 06:22:24 AM »

Rich:

Now go sit cross-legged in a quiet tranquill place, close your eyes, empty your mind of the mundane thoughts of everyday life, visualize your dream Alembic and the appropriate matching dream rig, take a deep breath, and chant:

oooohhhhhmmmmmm, oooohhhhhmmmmmm, oooohhhhhmmmmmm!

You're welcome, grasshopper. LOL

Bill, tgo

olieoliver · « **Reply #9 on:** August 15, 2006, 06:29:22 AM »

As my daughter would say ...OOHHMMM you bought another bass, mama's gonna' kill you...

FC Bass · « **Reply #10 on:** August 15, 2006, 06:34:41 AM »

Olie:
Maybe your wife is responsible for the 'fraudulent' ebay listings?
-LOL-

richbass939 · « **Reply #11 on:** August 15, 2006, 04:53:01 PM »

Oh, is that what Ohm really means?
Bill, tgo, does it work if you set something on fire and stick it in your mouth before you do the deep breath part?
Thank you,
Grasshopperbass939

bigredbass · « **Reply #12 on:** August 16, 2006, 06:09:03 AM »

Or is this post an ohmage to impedance?

J o e y

gtrguy · « **Reply #13 on:** August 16, 2006, 09:39:15 AM »

OK, Question for the experts: I have a SWR Goliath senior cab 4x10 @8 ohms. I also have a Ampeg BXT115 cab at 4 ohms. I'd love to run both with my SWR 550 amp. I think I need both cabs to be at 8 ohms. Any solutions? Do I just need to sell the BXT115 and get another 8 ohm cab?
Bye, Dave

olieoliver · « **Reply #14 on:** August 16, 2006, 09:44:38 AM »

Dave, I believe you should be able to run both cabs. If you ran them in series it should bring you down to 6 ohms, which the SWR 550 should be able to handle just fine. ALL feel free to correct me if I am wrong though.