# Ohms and impedence

Discussion in 'Amps and Cabs [BG]' started by acor1016, Apr 3, 2002.

1. ### acor1016

Jul 16, 2001
Hey everyone. Today a friend and I were talking bass and just music in general when we both came across the question of what exactly is impedence. i know its the resistance and ohms is how it is measured, but how would say a 4 ohm speaker/amp relate to say an 8 ohm speaker/amp and so on. This question is not just for bass but for other speakers as well. any response is welcome, nothing is too general or specific. im just curious and wanted to find out all i could, thanks alot for your time

Acor

2. ### JimK

Dec 12, 1999
Resistance = Ohms
...only resisitors in circuit.

Reactance = Ohms
...caps &/or inductors in circuit.

Impedance = Ohms
...resistors + caps &/or inductors in circuit.

Imagine a typical 90 degree triangle-
a = the base
b = the right side
R = the hypoteneuse

a = Resistance or "R"
(Real Power = Watts)

b = Reactance or "XL - XC"
(Imaginary or Phantom Power = VARS(Volt-Amp Reactive)

R = Impedance or "Y". "Y" is the resultant of the 'sum of the squares' rule found in basic Trig.
R = the square root of "R-Squared" + "(XL - XC)-quantity Squared".
If-
a = 3 Ohms(Resistance)
b = 4 Ohms(Reactance)
R = 5 Ohms(Impedance)

Power for Impedance is measured in Volt-Amps(called Apparent Power)...

As far as Bass & cabinets & amplifiers go-
FME & IMO, I prefer the total load to = 4 Ohms...if you're like me & only like taking ONE cabinet out, it needs to be a 4-Ohm cab.
If you like taking out, say, 1x15 = a 2x10...each cab 'should' be 8 Ohms. Both cabs working together, IN PARALLEL, yields a total of 4-Ohms.

Gotta go...

3. ### miktitSupporting Member

Apr 15, 2001
Denmark
How can I decide what impedance my cab is, if nothing is listed on it.
I have a Kustom 15" cabinet with no indication on the impedance. I'm just afraid of combining it with say a 4x10" and get below 4 ohms wich would make my amp go smoke.

Mikkel Tiedt - Copenhagen - Denmark

4. ### embellisherHoly Ghost filled Bass PlayerSupporting Member

Even though this is a general query, the guys in Amps can tell you so much about ohms and impedance that it will make your head spin!

So, I am moving this thread to Amps.

5. ### Bob Lee (QSC)In case you missed it, I work for QSC Audio!Gold Supporting MemberCommercial User

Jul 3, 2001
Costa Mesa, Calif.
Technical Communications Developer, QSC Audio
Hi Mikkel,

If you can find out from the manufacturer or from some sort of reliable documentation, that's the best way. Usually a single large driver is 8 ohms, but not always.

You can measure the DC resistance with an ohmmeter. That's usually a reliable indicator, but again, there are exceptions that can lead you to an erroneous estimation. If you measure about 5 to 6 ohms resistance, it's most likely an 8-ohm cabinet. If you measure about 2.5 to 3 ohms, it's probably a 4-ohm cab.