Ohm Question... (1 Viewer)

[Quintron]

I have an PA system 4 Ohm v 8 Ohm question thats been buggin' me.
I'm not gonna bother askin it until someone here can tell me that they can explain it (ie. Ohms Law-Speaker Configurations, etc ad nausa) in ultra laymans terms...Techno babble is all I've read on the net.
Anyone out there?
Cheers
Ken.

 

[damien]

the amp's ohms should be equal to or less than the speakers ohms. but if you have two speakers/cabs at 16 ohms each then the amp needs to be 8 or less ohms to handle them. and if you have 2 8ohm cabs the amp must be 4 ohms, etc. thats about as technical as i get.

 

[GlennStoneOcean]

I have an PA system 4 Ohm v 8 Ohm question thats been buggin' me.
I'm not gonna bother askin it until someone here can tell me that they can explain it (ie. Ohms Law-Speaker Configurations, etc ad nausa) in ultra laymans terms...Techno babble is all I've read on the net.
Anyone out there?
Cheers
Ken.

Well Ken to the best of my knowledge the lower the ohm the better lower end frequencies come through.

Hope that helps

Glenn

 

[sparse]

Well I recently bought a Fender Bassman head that produces 4 ohms output, is it going to be effected/damaged if I put it through an 8 ohm cab? (Or should I rewire it in parallel just to be safe? 2x12).

 

[damien]

everything i've ever heard on the subject has stated that as long as the head's ohms are less than or equal to the cabs, you're fine. i played an 8ohm head through a 16ohm cab for 50+ gigs and it was grand.

 

[GARYXKNIFEDX]

what Damo said,but also keep in mind that if the amp says 8 ohms,and you are using two cabs,the cabs must be 16 ohms each.
Also,if the amp is old,you may want to find out if it has been "fixed",one of my Marshall's is 4ohm's and it can't be changed by the switch on the back.

 

[Quintron]

Cheers lads.. This admittedly simple Ohm thing causes a mental block for me..

What I have is a 1400w amp which is rated at [FONT=Tahoma,Arial,Helvetica][SIZE=-1]2x700 W/4Ohm or 2x450W/8Ohm.
[/SIZE][/FONT][FONT=Tahoma,Arial,Helvetica][SIZE=-1]
[/SIZE][/FONT][FONT=Tahoma,Arial,Helvetica][SIZE=-1]Now I running that amp to 2 passive speakers, each at 400watts 8Ohm.
That means that I'm running the amp at 8Ohm? So consequently the max the 1400w amp will put out is 450watts per side? (Not much amp/speaker headroom there I think..)

Now if I add two more passive speakers at 8Ohms each to my existing pair...they would each run at 4ohm putting out a max of 350watts per speaker....? 350watts x 4 = 1400w.
My question is.... does any of the above make sense? Am I correct in my assumptions above?

Another example. One of my monitors blew last week.. I'm going to get new ones.. so I went looking on thomann for something cheap.
I saw the MA1220 here: http://www.thomann.de/thoiw6_the_box_ma1220_aktivmonitor_prodinfo.html
Looks fine for what I need..
(As a BTW my blown JBL monitor was rated at 140w RMS and 800w peak..thats a hell of a peak overhead! - These Thomann monitors are 120w with a 160w peak..big difference.. Is this a primary reason they are so cheap I wonder..)

Then I saw these other cheap yokes and the Ohm question was raised again:
http://www.thomann.de/the_box_sm100_aktivmonitor_prodinfo.html?iwid=6#fpix

They are 100w RMS at 4Ohm..but to make them 4 Ohm you have to hook up a passive speaker via the link channel.. So with the active and passsive speaker linked they run at 4Ohm so each monitor would get 50w..?
I have a 100w passive monitor lying around (M12e) so I figure these two monitors linked would make a nice parallel pair around say, a drum kit...50watts aside.. That again is assuming my calculations are accurate and I actually have a slight clue what I'm talking about..
Any clarification on the above by the Ohm meccas appreciated!
Cheers again,
Ken.

PS
[/SIZE][/FONT][FONT=Tahoma,Arial,Helvetica][SIZE=-1]I also have a 600w amp rated at [/SIZE][/FONT][FONT=Tahoma,Arial,Helvetica][SIZE=-1]2 x 300 Watt 4Ohm so 2 x 150w 8Ohm..
Most of the PA speakers I have seen run at 8Ohm so I suppose they think you are going to hook at least 4 speakers up to the amp?...2 x left and 2 x right or else get 4Ohm PA speakers like these I suppose..?
[/SIZE][/FONT][FONT=Tahoma,Arial,Helvetica][SIZE=-1]http://www.thomann.de/thoiw6_the_box_pa215_fullrangebox_prodinfo.html
[/SIZE][/FONT][FONT=Tahoma,Arial,Helvetica][SIZE=-1]Again though 90% of the PA speakers I have seen are 8Ohm ...so there must be a reason for this..Anyone?[/SIZE][/FONT]

 

[Anthony]

how do you find out the ohmage of your cab?
a

 

[Quintron]

Hey Anthony.
It should be written somewhere on the back of the cab or at least on the speaker horn. If not you could check your cab model on the internet and see what its rated as there.

 

[sparse]

Hey Anthony.
It should be written somewhere on the back of the cab or at least on the speaker horn. If not you could check your cab model on the internet and see what its rated as there.

What if you have non descript old spakers that have no writting on them like mine?

 

[kings lead hat]

http://www.the12volt.com/ohm/ohmslaw.asp

heres ohms law
just fill in the gaps you know already

 

[Quintron]

Cheers for the link kings lead hat.
But that is double dutch to me I'm afraid....

I just want to know if my theories are correct in the previous post ....and then I'll happily live on in total ignorance of Ohms Law

 

[Seamy ALB]

Well Ken to the best of my knowledge the lower the ohm the better lower end frequencies come through.

Hope that helps

Glenn

This is not true!!

Ohms are a measure of resistance to the output of an amplifier. Most amps cannot handle 2ohm operation the minimum load should be 4ohm.

To work out the load that an amp is driving into you add together the speaker cab ohm rating and divide by 4, eg 8 0hm + 8 0hm = total load of 4 ohm.

The reason why it is not safe to run amps into low loads is because the resistance is so low more current runs through the amp increasing heat and therfore chance of amp failure or literally melting the amp.

 

[Quintron]

To work out the load that an amp is driving into you add together the speaker cab ohm rating and divide by 4, eg 8 0hm + 8 0hm = total load of 4 ohm.

So running 2 x 8 Ohm speakers together (eg Left and Right) runs the amp at 4 Ohm? I thought it was slaving one speaker off another that caused a 4 Ohm load per side...