# Ohms????

Discussion in 'Amps and Cabs [BG]' started by FOE_Bass, Sep 5, 2000.

1. ### FOE_BassGuest

Jun 29, 2000
Grass Valley, CA
What the hell are ohms? I know that they are a unit of measurement, but what does it all mean Basil? <- Austin Powers. What's the difference between 4 ohms and 8 ohms (besides 4 ohms). What happens if you have two cabs, one that takes 400 watts at 8 ohms and one that takes 400 watts at 4 ohms powered by a head that puts out 350 watts at 4 ohms or 240 watts at 8 ohms. For clarification, I'm talking about a Hartke 4.5XL cab, 215B cab and a 7000 head. Thanx for the help.

2. ### White_Knight

Mar 19, 2000
USA
Ok, here goes:

1) Ohms are a way to measure resistance to the flow of electricity. 4 ohms and 8 ohms are the ammount of resistance to current flow that, say a speaker has.

2) What everything really depends upon is what your amplifier is rated at. If your amp is rated at 4 ohms then you can hook up either a single four ohm cabinent or two eight ohm cabinents (when two resistances of the same value are linked in parallel then the sum of the resistances is multiplied by 1/4) to get the four ohm total. You can go over the ohm rating of an amp (i.e. using a single 8 ohm cabinent with a 4 ohm amp), however you won't be getting the full power output of your amplifier.

3) I'd personally make sure that whatever load of speakers you hook up can handle the full output of your amplifier. Example: if you amp is 350 watts, either a single cab that handles MINIMUM 350 watts RMS or two cabs linked in parallel that will handle a MINIMUM of 350 watts total between them. Personally, I'd choose cabs that handle a bit higher, say around 400-450 watts 'cause then you aren't driving them so hard, but on the other hand you don't want to underpower the cabs either.

4) I wouldn't reccommend hooking up two four ohm cabs unless your amp can handle a two ohm load (or, if I remember correctly) or is a stereo amp (two power amplifiers in one case).

3. ### alternative roster

Aug 21, 2000
sounds right to me.

4. ### throbbinnut

Ohm's Law, just so you'll know it:

Voltage = Current * Resistance, or V=I*R

That is all you need to know to be a damn good electrical engineer. Add to that:

Power = Voltage * Current, or P=I*V

That's everything.

Chris

5. ### Luis Fabara

Aug 13, 2000
Is there a way to put 2 4OHM cabs toguether and make 8OHM??
YES.

You have to do a circuit. I mean every thing is a circuit.

The standard way of wiring your cabs is using the cables and just that. That method is Parallel Wiring. That rests the total resistance or impedance.

But you can do the oposite by wiring in SERIES.
Example:
How can you get a 4x10 cab with 8 OHM speakers..
I mean.. Thats 4 x 8, that would make 2 Ohms.. but actually every 4x10 is (ohms).
Manufacturers use a series/parallel combination for the wiring of the speakers.
I should suggest you dig of impedance in the internet so you can make your own special wiring.
I have to warn you, that the cabs will sound different with different wiring.

6. ### JimM

Jan 13, 2000
Northern California
One way to look at ohms,and the power they resist is to look at a completely different form of energy.take gasoline for example,Light a match to some raw gas and you get all the power in a very short time.probably no usefull work will be done by that.To do the same thing with ohms,(dont do this please)just connect the two wires coming from an amp to each other,you have a no load (0 ohms-the needle on the ohmmeter is all the way to the right)situation just like lighting a fuel source minus the lawnmower-you may have an instant burst of power,but it will FRY the amp.

On the other hand,if those same wires never find a path(through the speakers,for example)to each other,then its an infinite resistance or infinite ohms situation.like letting the gas evaporate.Here the ohmmeter needle hasnt moved and is on the left side of the scale.

Its a science to find the optimal relationship between power and load.The manufacturers have done most of the work by rating their amps and cabs etc.

P.S,I know you weren't asking for all this,I just wanted to have a little fun.

7. ### CROZ

Be Careful with the ohms, man. If you put two 4 ohm cabs together, believe it or not, you'll get less than four ohms and that will fry most amps. That's cuz' most amp speaker outputs and cabs are wired parallel.
Use your stereo outputs, not your bridged on the Hartke and you'll be OK.
Read Terry Buddingh's article in the August issue of Bass Player. It's got some good stuff in it.

8. ### Luis Fabara

Aug 13, 2000
Lets do some wiring.
THIS IS A Step-by-step procedure to make a SERIAL CABLE for 2 Enclosures.
This, will sum the Impedances (Or OHM ratings) of the cabs.
It works like this: 2 8OHM cabs = 16 OHM
2 4OHM cabs = 8 OHM

So lets begin.

First, you need (3) 1/4" Mono Plug Conectors and good speaker cable.

First you have to solder the positive and negative TIPS on the master plug. (The one that will be connected to the AMP)

Like this
___ + (Positive)
<====|______ - (Negative)

Now, the cable that was wired to the POSITIVE tip on the master PLUG must be soldered to the POSITIVE TIP in the PLUG NUMBER 1, and the cable that was wired to the NEGATIVE tip on the master PLUG must be soldered to the NEGATIVE TIP in the PLUG NUMBER 2.
Then , you must add another cable that will be hooked as this.

Solder one end to the NEGATIVE TIP of PLUG NUMBER 1 and the Other end to the POSITIVE TIP of PLUG NUMBER 2.

Then you can use this cable for any SERIES WIRING for your speakers. Now, you have to remember that ONLY the MASTER PLUG must be hooked to your AMP.

If you found this of any help, please make donations to:
"A Warwick Bass for "Luis Fabara" Foundation"

9. ### Joris

Do NOT put two DIFFERENT cabs in series. It'll sound like CRAP. I'm not going to explain, it's too complicated. But believe me. You don't wanna go there.