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[Corey Scogin]

I have owned (4) EV QRx 115's for 6+ years now.  These were purchased in pairs at different times.  I just noticed that one pair lists the LF as a 4 ohm load whereas the other lists it as 8 ohm.  I have been unable to find any documentation from EV that shows a 4 ohm LF on the QRx 115.  I called EV tech support and the person I spoke with was unable to tell me anything useful.  The 4 ohm pair was purchased new around 2006.

Does anyone know if this speaker does have a 4 ohm LF section or if this is just a typo? (see the attached image)

Testing the DC resistance directly on the driver shows ~4.8 ohm.  I did not think to measure the DC resistance of the driver in one that lists 8 ohms.  I'll do that tonight.

[Greg_Cameron]

Testing the DC resistance directly on the driver shows ~4.8 ohm.  I did not think to measure the DC resistance of the driver in one that lists 8 ohms.  I'll do that tonight.

If the DCR is greater than 4 ohms, then it's likely the driver is actually 8 ohms. I'll be curious to see what the other driver measures.

[Dennis Wiggins]

Testing the DC resistance directly on the driver shows ~4.8 ohm.  I did not think to measure the DC resistance of the driver in one that lists 8 ohms.  I'll do that tonight.

You disconnected one of the leads to the crossover before measuring, right?  Usually an 8 ohm driver has "roughly" 6 ohms DC resistance, and a 4 ohm driver has about 3.   4.8 seems a little odd.

-Dennis

[Corey Scogin]

Testing the DC resistance directly on the driver shows ~4.8 ohm.  I did not think to measure the DC resistance of the driver in one that lists 8 ohms.  I'll do that tonight.

I pulled apart one of my older boxes that lists 8 ohms on the back plate.  It reads ~4.7 ohm across the driver.

You disconnected one of the leads to the crossover before measuring, right?  Usually an 8 ohm driver has "roughly" 6 ohms DC resistance, and a 4 ohm driver has about 3.   4.8 seems a little odd.

Yes, I pulled one of the leads off when measuring the DC resistance.


I'm guessing that this is simply a typo on the back plate.  I don't have an easy way to test the impedance of the driver across the frequency spectrum so I'm going to trust my assumption.

[Tim Perry]

Check the calibration of the Ohmmeter by measuring a known resistor.  Also check zero by shorting the test leads.

[Geoff Doane]

Check the calibration of the Ohmmeter by measuring a known resistor.  Also check zero by shorting the test leads.

I just checked a nominal 4Ω speaker here with a Fluke 79III digital meter.  On the regular autorange ohm scale, it reads 0.5Ω with the leads shorted, and 4.9Ω across the coil.  On the low ohms scale (0-40Ω), it reads 0.0Ω with the leads shorted, and 2.7Ω on the coil.

I tend to believe the low ohms scale on this meter, since it's giving the expected answer.  But this is a tricky measurement that most of us aren't properly equipped to do.  At least any meter should give you a relative reading between the different speakers, but an absolute measurement is trickier.

And as already mentioned, these are only DC resistances, not impedance.

GTD

[Greg_Cameron]

After looking again at the picture of the backplate on the cab in question, I would also concur that it's a typo. Since in full range mode they list 8 ohms, it would be the same for the LF driver in biamp since the LF driver is usually the determining factor for impedance with a passively crossed box. That's definitely confusing.

[Corey Scogin]

Check the calibration of the Ohmmeter by measuring a known resistor.  Also check zero by shorting the test leads.

Testing against a loose 10 ohm 5% resistor, the meter reads 10.1
Shorting the test leads, the meter reads 0.2

After looking again at the picture of the backplate on the cab in question, I would also concur that it's a typo. Since in full range mode they list 8 ohms, it would be the same for the LF driver in biamp since the LF driver is usually the determining factor for impedance with a passively crossed box. That's definitely confusing.

Good point. 

I sometimes use one daisy-chained off of another when in a wide venue.  They are powered by a QSC PL236 which is stable down to 2 ohms so it shouldn't be an issue either way.  I have not noticed a difference in the sound of the two when arrayed next to each other.  I'm assuming the LF on the 4 ohm box would be a bit louder if it were indeed 4 ohms.

[Greg_Cameron]

I'm assuming the LF on the 4 ohm box would be a bit louder if it were indeed 4 ohms.

All things being equal as far as sensitivity between a 4 & 8 ohm driver of the same model, The 4 ohm version would be 3dB louder since it's sourcing twice the current of the 8 ohm version. That would mean twice the wattage dissipated yielding 3dB more output.

[Ryan Grandusky]

It is an 8ohm LF driver, the 4ohm is a misprint on the box itself I have several of the QRX115 cabs and one set has the 4ohm rating on the back same as in your picture. I have confirmed this with Electrovoice.

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