Speakers and ohms

[lhrocker]

When you put a meter on a speaker to measure the impedance, will the meter usually read higher or lower than the actual impedance of the speaker?

[shobet]

How far out are you?

[Cygnus X1]

Lower.
An 8 ohm (impedance) speaker measures around 7.2 (resistance).

I think shobet is referring to how long the leads are.
That will also affect the reading.

[lhrocker]

I have 4 8 ohms in series parallel, and i get a reading in the 5 ballpark. This is right off the actual speakers and connections - not from a speaker cable.

[Cygnus X1]

Are the speakers connected to the amp?

[Firebird V]

Did you zero out your meter before testing?

[lhrocker]

Cygnus - not while I was measuring it

FB - It's a digital meter, but I'll see if there's a way to do it on the fluke

[emperor_black]

are you saying that the 8 ohm speakers by themselves are only reading 5 ohms each? I remember getting somewhere in the high 7's for my 8 ohm celestion vintage 30.

[CharvelRocker]

You're doing better than me... I put mine on a multi meter and it reads 21 something on a 16 ohm speaker IIRC. Not a cheap meter, it's a top of the line Fluke. Never figured out what the deal was.

[Cygnus X1]

I would disconnect and measure each separated.
One or two may be out of spec in the upwards range.

[marcus]

Nominal impedance (what is usually quoted as the impedance of a speaker) and DC resistance (what you read with an Ohmeter) are only loosely related. The actual impedance of a speaker can vary by as much as 1/2-2x across the supported frequency range. 5 Ohms may very well be the specified DC resistance of your speaker.

[lhrocker]

Then I shouldn't match the amp setting to the metered reading, right? The speakers are a pair of 8 ohm Boogie Celestions and a pair of 8 ohm vintage 30's.

Nominal impedance (what is usually quoted as the impedance of a speaker) and DC resistance (what you read with an Ohmeter) are only loosely related. The actual impedance of a speaker can vary by as much as 1/2-2x across the supported frequency range. 5 Ohms may very well be the specified DC resistance of your speaker.

[marcus]

Then I shouldn't match the amp setting to the metered reading, right? The speakers are a pair of 8 ohm Boogie Celestions and a pair of 8 ohm vintage 30's.

Yes, you should match it to the impedance, not the DC resistance. I just looked up the specs for the vintage 30, and it says the DC resistance should be 7.3 Ohms. I am not sure about the Boogie Celestions (modified v30s?) but 5 Ohms is probably a little low. You may want to check the wiring of the cabinet, or, as Cygnus suggested, unwire them and measure each speaker individually.

[lhrocker]

Thanx guys - wouldn't wanna blow up my head...

[OnlineStageGear]

The resistance is usually a close reading to impedance like was mentioned and should only be used to get an idea of what you have. Measuring resistance is only one portion of what gives a speaker it's impedance. Four electrical quantities determine the impedance of a circuit: resistance, capacitance, inductance and frequency. Or an easier way to remember it is impedance is resistance plus reactance.

Matt