#1
I have a Marshall 1960 4x12 that has seen a few different speaker combinations come and go. I am settled with two v30's and two 75's, all of which are 16 ohms. The 75's are from an 80's Marshall combo and ever since I have put them in the impedance reads strangely. When I use a multimeter to measure the impedance, via speaker cable, the 16 ohm jack reads 12-13 ohms. I have read that it is normal for a multimeter to read about 3/4ths of a load instead of the full load due to air/crimp wires/etc.

Back to the point... The 4 ohm jack changes impedance when i measure it. It could read anywhere from 4.5-6.5 ohms.

Looked inside and even measured the individual speakers and rechecked the wiring. Not sure what the problem is or if its even anything to worry about.

I play a marshall jcm 800, which aren't exactly known to handle mismatches well....
Last edited by andyhatescrass at Oct 9, 2013,
#2
Your fine.

Lots of older Celestions were not 16 ohm but are 15ohm, but the little` mismatch is fine on the amp. If it were a lower reading the you need to be careful
2002 PRS CE22
2013 G&L ASAT Deluxe
2009 Epiphone G-400 (SH-4)
Marshall JCM2000 DSL100
Krank 1980 Jr 20watt
Krank Rev 4x12 (eminence V12)
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Morley Bad Horsie 2
MXR Smart Gate
Last edited by Robbgnarly at Oct 9, 2013,
#3
You're probably reading DC resistance, not AC impedance.

While they are related, they are not the same.
“Ignorance more frequently begets confidence than does knowledge.”
Charles Darwin
#4
The DC resistance of a speaker will always read less than the impedance. It's got nothing to do with air/crimp wires/etc or any other such nonsense. It's a mathematical certainty.
To explain it as simply as I can without getting into complex phase math, there are two elements to impedance - resistance and reactance. Resistance is impedance to the DC component and reactance is impedance to the AC component.
It can be represented as a right triangle with resistance on one side, reactance on the other and total impedance on the hypotenuse. The hypotenuse is always bigger. If you ever read DC resistance higher than total impedance your test equipment is busted. The resistance setting on a multimeter is reading the DC component only.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band
Last edited by Cathbard at Oct 9, 2013,
#5
Quote by Cathbard
The DC resistance of a speaker will always read less than the impedance. It's got nothing to do with air/crimp wires/etc or any other such nonsense. It's a mathematical certainty.
To explain it as simply as I can without getting into complex phase math, there are two elements to impedance - resistance and reactance. Resistance is impedance to the DC component and reactance is impedance to the AC component.
It can be represented as a right triangle with resistance on one side, reactance on the other and total impedance on the hypotenuse. The hypotenuse is always bigger. If you ever read DC resistance higher than total impedance your test equipment is busted. The resistance setting on a multimeter is reading the DC component only.


I'm pretty sure the meter isn't the problem. It works fine on everything else. The 4ohm jack is the one thing that doesn't read a little less than the total impedance.

Is it possible that it could be a problem with the cab somewhere?
#6
It's a low impedance. Maybe you are just seeing errors because of the conductivity between the probe and whatever you are touching.
#7
Quote by fly135
It's a low impedance. Maybe you are just seeing errors because of the conductivity between the probe and whatever you are touching.
Yep. When measuring that low a resistance, filth and corruption on the contacts will do it, so will touching it with your fingers. Try giving everything a decent clean and try again, it should be about 3 ohm, give or take.
It could also simply be that your meter isn't up to the task of accurately reading something as low as 3 ohms.
Gilchrist custom
Yamaha SBG500
Telecasters
Randall RM100 & RM20
Marshall JTM45 clone
Marshall JCM900 4102 (modded)
Marshall 18W clone
Fender 5F1 Champ clone
Atomic Amplifire
Marshall 1960A
Boss GT-100


Cathbard Amplification
My band