Checking speaker with a meter?

[KiOgon]

I have a 12" speaker - Celestion Truvox 1220 with no other markings of power handling or impedance. It measures 5.6 Ohms with my multimeter so is it most likely a 4 or 8 Ohm impedance wise?

I know you can't actually measure impedance with a meter - but as a guide - will the meter read lower or higher?

BTW the speaker works fine, I just want to know before I try it on another amp.

Cheers,
John

[The Bass Doc]

Meters read low so 8 ohms it will be.

[geoffbyrne]

What ^he said!

G.

[KiOgon]

[quote name='The Bass Doc' post='775102' date='Mar 15 2010, 12:03 PM']Meters read low so 8 ohms it will be.[/quote]
Many thanks Bass Doc & G for replying while I was typing
Cheers

Edited March 15, 2010 by KiOgon

[SteveO]

IIRC its because impedance increases in coils as the power increases, so with the tiny measuring current of your meter you will get a nominal value, but the impedance will increase when it's under normal operation.

/nerd

[Mr. Foxen]

[quote name='SteveO' post='775181' date='Mar 15 2010, 01:18 PM']IIRC its because impedance increases in coils as the power increases, so with the tiny measuring current of your meter you will get a nominal value, but the impedance will increase when it's under normal operation.

/nerd[/quote]


Not quite. The meter measures resistance. The impedance is affected by frequency, and also by other factors such as capacitance, so the nominal value is a normalised average over a range. You have to put quite a lot of power into it before the heat in the coil shifts it too much, when you are hitting power compression territory.

/bigger nerd

[SteveO]

[quote name='Mr. Foxen' post='775200' date='Mar 15 2010, 02:30 PM']Not quite. The meter measures resistance. The impedance is affected by frequency, and also by other factors such as capacitance, so the nominal value is a normalised average over a range. You have to put quite a lot of power into it before the heat in the coil shifts it too much, when you are hitting power compression territory.

/bigger nerd[/quote]
Ahhh thats right, its frequency that affects AC impedance. I was thinking of the increased impedance from the effects of the magnetic field generated in a DC coil (which is proportional to power). Obviously thats irrelevant in an AC speaker coil. I will have to stop chipping in with these 20-yr-old-badly-remembered-o-level-physics comments

[flyfisher]

As the previous posts correctly state, everything about speaker impedance is 'nominal' as it varies with frequency and other factors and is not very easy to measure without a bunch of specialised test equipment.

However, you could try this rough-and-ready approach:

[i]If you just want to find out the nominal impedence of the speaker e.g. ist it 4, 8 or 15 ohms then there is a rough & ready way. Just use your multimeter to measure the DC resistance of the voice coil i.e. across the speaker terminals (with nothing else connected) and multiply the answer by 1.3. So if the DC resistance is say 6 ohms then the speaker is nominally 8 ohm impedance. [/i]

So, the OP measured 5.6 ohms with a DC ohmmeter x1.3 = 7.28 = 8 ohms impedance.

From: [url="http://www.epanorama.net/documents/audio/speaker_impedance.html"]http://www.epanorama.net/documents/audio/s..._impedance.html[/url]