YAHAT: Tested the resistance on my JBL bookshelf speakers with a multimeter

[Shawn]

One was 4.7ohm and the other one was 5ohm. They are rated at 6ohm. Doesn't that seem a little low? My rear speakers were both 8 ohm like they are supposed to be. I guess that would explain why my reciever runs so hot?

 

[saltedeggman]

good job !!

 

[quakefiend420]

yeah that would probably do it...as long as your reciever is rated to handle it though, it should be fine...

 

[ArmenK]

no, impedance is not the same as resistance... impedance changes with frequency so your DMM won't measure that

Edit: Read this

 

[dighn]

Originally posted by: ArmenK
no, impedance is not the same as resistance... impedance changes with frequency so your DMM won't measure that

speakers are inductive so the impedance should go up with frequency

ok maybe a little more complicated than that

 

[quakefiend420]

Originally posted by: ArmenK
no, impedance is not the same as resistance... impedance changes with frequency so your DMM won't measure that

impedence changes with frequency?

so a 4 ohm speaker is rated at 4 ohms of resistance, but the impedance will vary?

this is a new one to me

 

[Eli]

Originally posted by: quakefiend420

Originally posted by: ArmenK
no, impedance is not the same as resistance... impedance changes with frequency so your DMM won't measure that

impedence changes with frequency?

so a 4 ohm speaker is rated at 4 ohms of resistance, but the impedance will vary?

this is a new one to me

Something like that.

Look at this graph for an example.

 

[dighn]

Originally posted by: Eli


Look at this graph for an example.

but which value do they use when they quote a single impedence number?

 

[95SS]

Originally posted by: dighn

Originally posted by: Eli


Look at this graph for an example.

but which value do they use when they quote a single impedence number?

IIRC, the quoted spec is the nominal impedance.

Originally posted by: ArmenK

Edit: Read this

Very good read. :thumbsup:

 

[OS]

Originally posted by: quakefiend420

Originally posted by: ArmenK
no, impedance is not the same as resistance... impedance changes with frequency so your DMM won't measure that

impedence changes with frequency?

so a 4 ohm speaker is rated at 4 ohms of resistance, but the impedance will vary?

this is a new one to me

Yes, a speaker is actually constructed similar to an inductor, a bunch of wire coiled around an iron core. Capacitors/inductors have a frequency response you can write an equation for based on a number of physical parameters. So the circuit/element looks different to waveforms of different frequencies.

So using a DMM may not represent the impedance correctly since DMMs typically use DC current to find the resistance. However, audio frequency is about 20 hz to 20 khz so they are on different parts of the frequency response.