8ohm JBL driver measuring 4.5 ohms, is it normal?

[Embryos]

Hello all,
I was looking to purchase a pair of JBL 2213h woofers for my 4312bs. The woofer is an 8 ohm speaker, but the reading provided by the seller is 4.5 and 4.6 respectively. From my research, Ive read that a 6-8 ohm reading is normal for an 8ohm speaker, so 4.5 ohm seems low. Do you think these speakers are faulty? Or us thus lower reading normal for an 8 ohm speaker? The seller claims they are in excellent condition. What do you all think?
Thanks for any help or info you can give!

 

[damacman]

That's DCR - not impedance. They're fine.

 

[WaynerN]

The 8 ohm rating is an "averaged" rating. The tweeter's impedance varies at different frequencies. As @damacman stated, measuring the coils resistance with an DMM is not really its impedance.

 

[sregor]

http://www.jblproservice.com/pdf/Thiele Small Parameters/Theile Parameters.pdf
On the fourth page the line for the 2213H says RE is 4.4, so you are good to go.

 

[Tronk]

That's DCR - not impedance. They're fine.

The 8 ohm rating is an "averaged" rating. The tweeter's impedance varies at different frequencies. As @damacman stated, measuring the coils resistance with an DMM is not really its impedance.

I have a sub that's marketed at 4-8 ohms and have wondered what it actually is. Does it mean that the impedance varies and it's only at 4 ohms some of the time?

 

[guest139]

I have a sub that's marketed at 4-8 ohms and have wondered what it actually is. Does it mean that the impedance varies and it's only at 4 ohms some of the time?

The nominal impedance of a driver is an average based on the frequency range of said driver. Impedance varies with frequency. If you measure the impedance of a driver while the voicecoil is at rest you are measuring the DC resistance(Re). If you have a DMM hooked up to a driver to measure the DC resistance you can see the impedance fluctuate if you were to move the cone with your hand. That is why it is important to measure the driver’s DC resistance while it is on a steady surface free of vibrations.

 

[rothwellaudio]

I have a sub that's marketed at 4-8 ohms and have wondered what it actually is. Does it mean that the impedance varies and it's only at 4 ohms some of the time?

Not so much "some of the time" as "at some of the frequencies". Here's a picture pulled at random from a google search:

As you can see from the graph, the impedance is about 18 ohms at 40Hz and 100Hz, is about 8 ohms at 70Hz and drops down to about 5.5 ohms at 200Hz.
What you measure with a multimeter is the impedance at 0Hz, ie DC resistance.

The graph is taken from this page if you want to read the accompanying article:
https://www.aperionaudio.com/blogs/aperion-audio-blog/the-truth-about-speaker-impedance

 

[Tronk]

I was mostly wondering because I bought this 4-8 ohm speaker for my home theater system because the amp is 8 ohm. My question is not so much how many ohms the speaker actually is, but what does the amp see with this speaker on a channel and the load on the amp due to not actually being specified as an 8 ohm speaker.

Sorry for hijacking this thread with my question, I really should have started my own thread.

 

[rothwellaudio]

My question is not so much how many ohms the speaker actually is, but what does the amp see with this speaker on a channel and the load on the amp...

I'm not quite sure I understand the question. The impedance the amp sees is frequency dependent and will be similar to that shown in the graph. If you want to know exactly you will have to find a published graph for your sub or measure it yourself.

 

[toxcrusadr]

Looks like sregor nailed the OP's original question. Wherever you were seeing 6-8 ohms DCR for that driver, appears to be incorrect. JBL is pretty good about their technical specs so I would trust the spec sheet.

 

[Tronk]

I'm not quite sure I understand the question. The impedance the amp sees is frequency dependent and will be similar to that shown in the graph. If you want to know exactly you will have to find a published graph for your sub or measure it yourself.

If I hooked this 4-8 ohm speaker in parallel with a different 4 ohm speaker on the same channel, would it be a 2 ohm load?

 

[toxcrusadr]

It's probably got an area in the bass range where the impedance dips near 4 ohms, but most if it is closer to 8, so they fudged by calling it 4-8 ohms.

I take it this is not a self-powered (amplified) subwoofer? Because if it has its own amp it doesn't matter, the internal amp is the only one that will see the load.

If you are thinking of hooking it up on the L or R channel of your regular amp, that's probably not a good idea for an amp rated at 8 ohms. Even if the sub was really 8 ohms, that would still be a 4 ohm load in the bass region for that channel when the regular speaker is also connected.

 

[Tronk]

It's probably got an area in the bass range where the impedance dips near 4 ohms, but most if it is closer to 8, so they fudged by calling it 4-8 ohms.

I take it this is not a self-powered (amplified) subwoofer? Because if it has its own amp it doesn't matter, the internal amp is the only one that will see the load.

If you are thinking of hooking it up on the L or R channel of your regular amp, that's probably not a good idea for an amp rated at 8 ohms. Even if the sub was really 8 ohms, that would still be a 4 ohm load in the bass region for that channel when the regular speaker is also connected.

No, it's not a powered speaker, I use it with a TPA3116 amp rated 2-8 ohms and intended on wiring a 4 ohm bass shaker in parallel with the speaker.

 

[toxcrusadr]

OIC.

You'd probably just have to try it. If the amp is rated down to 2 ohms you don't have a lot to lose. But take it easy till you see how it responds.

 

[Tronk]

OIC.

You'd probably just have to try it. If the amp is rated down to 2 ohms you don't have a lot to lose. But take it easy till you see how it responds.

I don't listen to anything loud, my old ears can't take it and my wife would tell me to turn it down anyway.

And you're right, if it would smoke the amp, I'm only out less than 20 bucks so I don't have much to lose, and I'd get another and go a different route.