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Author Topic: Another Question for HF driver Gurus  (Read 2517 times)

RYAN LOUDMUSIC JENKINS

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Another Question for HF driver Gurus
« on: June 30, 2011, 09:23:28 am »

If I measure the DC resistance of an assembled HF driver will it be different than the DC resistance of the diaphram when it is not mounted in the magnet?

I have some HF drivers that are measuring 12.1 ohms but my supplier has raw diaphrams that are measuring about 6 ohms.  He says his are 8 ohm nominal diaphrams.  Mine I believe to be 16 ohm versions.  I do not need a diaphram but I just want to verify just in case I need to replace diaphrams in the future.  Of course I have 12 years on the boxes without issues so it may never come up but you never know.

Thanks a bunch, Ryan
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Jim McKeveny

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Re: Another Question for HF driver Gurus
« Reply #1 on: June 30, 2011, 09:47:43 am »

Ryan-

DC resistance tends to be 15%-20% lower than rated impedance. 
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Peter Morris

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Re: Another Question for HF driver Gurus
« Reply #2 on: June 30, 2011, 10:15:29 am »

If I measure the DC resistance of an assembled HF driver will it be different than the DC resistance of the diaphram when it is not mounted in the magnet?

I have some HF drivers that are measuring 12.1 ohms but my supplier has raw diaphrams that are measuring about 6 ohms.  He says his are 8 ohm nominal diaphrams.  Mine I believe to be 16 ohm versions.  I do not need a diaphram but I just want to verify just in case I need to replace diaphrams in the future.  Of course I have 12 years on the boxes without issues so it may never come up but you never know.

Thanks a bunch, Ryan

The general formula for impedance is  -

Z = (( R2 + (XL - Xc)2)
When you measure the DC resistance you are only measuring the R bit.  You are not taking to account the reactance the X bits

Xc = 1/(2pi FC)
XL = 2pi FL

Soooo  the Z for a speaker is always a bit more when you add the bit that comes from the inductance / frequency.

Note - the inductance is effected by the mechanical behavior of the driver - that why there are peaks and dips in the impedance curve associated with mechanical resonances.
« Last Edit: June 30, 2011, 10:26:53 am by Peter Morris »
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Greg_Cameron

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Re: Another Question for HF driver Gurus
« Reply #3 on: June 30, 2011, 10:26:08 am »

If I measure the DC resistance of an assembled HF driver will it be different than the DC resistance of the diaphram when it is not mounted in the magnet?

The dc resistance with an ohm meter will be the same with the diaphragm sitting in or out of the magnetic gap. The only time this might not be true is if the diaphragm is vibrating due to external sound exciting it whilst in the driver motor.

Greg
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RYAN LOUDMUSIC JENKINS

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Re: Another Question for HF driver Gurus
« Reply #4 on: June 30, 2011, 10:58:04 am »

The dc resistance with an ohm meter will be the same with the diaphragm sitting in or out of the magnetic gap. The only time this might not be true is if the diaphragm is vibrating due to external sound exciting it whilst in the driver motor.

Greg

While the other responses are interesting and informative, this is what I needed to know.  The only easily made measurement to compare the HF drivers in my boxes to the diaphrams that are 300 miles away is for each of us to do a simple DC resistance measurement to compare them.  Since the drivers are Ferrofluid cooled, I do not want to take them apart if I don't have to.
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Ales Dravinec

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Re: Another Question for HF driver Gurus
« Reply #5 on: June 30, 2011, 04:01:43 pm »

If I measure the DC resistance of an assembled HF driver will it be different than the DC resistance of the diaphram when it is not mounted in the magnet?

No !!
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Guillaume Boda

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Re: Another Question for HF driver Gurus
« Reply #6 on: July 03, 2011, 08:30:36 pm »

In any case, you're right about the impedance of those spare diaphragms you measured:

12  ohm measured DC = 16ohm driver
6    ohm measured DC  = 8ohm driver
3.2 ohm measured DC = 4ohm driver
(approx. of course)

it's the same whether it's a HF driver or a woofer.
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ProSoundWeb Community

Re: Another Question for HF driver Gurus
« Reply #6 on: July 03, 2011, 08:30:36 pm »


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