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Old 11th February 2004, 06:39 PM   #1
EC8010 is offline EC8010  United Kingdom
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Default Jordan JX92S impedance

Although the JX92 is nominally an 8 Ohm driver, it's really rather closer to 5 Ohms. Adding a Zobel network across it consisting of 4u7 in series with 8R2 (non-inductive) corrects the HF rise in impedance (red) and its 5 Ohmishness can clearly be seen (green).
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Old 11th February 2004, 06:51 PM   #2
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Default Re: Jordan JX92S impedance

Quote:
Originally posted by EC8010
Although the JX92 is nominally an 8 Ohm driver, it's really rather closer to 5 Ohms. Adding a Zobel network across it consisting of 4u7 in series with 8R2 (non-inductive) corrects the HF rise in impedance (red) and its 5 Ohmishness can clearly be seen (green).
Hi

The consequence of the rising impedance is that in the high frequencyes less current go thru the voice coil (if using voltage drive)...with the Zobel even less highs go thru the voice coil...

What you think of this??
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Old 11th February 2004, 07:59 PM   #3
sreten is offline sreten  United Kingdom
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A nominally 8 ohm driver indicates its average impedance,
consequenquently DC resistance is in the 5 to 6 ohm range.

Perfect Zobel compensation requires a resistor equal in value
to the DC resistance to give a perfectly flat impedance.

I believe the requirements for speakers are minimum impedance
which should be resistive should not be less than 1/root2 of the
nominal impedance.

This sets the DC resistance at 5.6R, common as is 2.7R for 4 ohm drivers.

Quote:
...with the Zobel even less highs go thru the voice coil...
With voltage drive this is entirely untrue.
Driver current is unaffected by the Zobel network.

sreten.
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Old 11th February 2004, 08:05 PM   #4
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Quote:
Originally posted by sreten




With voltage drive this is entirely untrue.
Driver current is unaffected by the Zobel network.

sreten.
Yes ...thats right... only with current drive that hapen!!
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Old 11th February 2004, 08:13 PM   #5
azira is offline azira  United States
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Quote:
Originally posted by Tube_Dude


Are you being serious???
Assuming the Zobel is in parallel with the speaker, he totally is. Think about it, with or without the zobel, it'll be the same voltage accross the speaker. That means same current. Doesn't matter what frequency.
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Old 11th February 2004, 08:16 PM   #6
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Quote:
Originally posted by azira


Assuming the Zobel is in parallel with the speaker, he totally is. Think about it, with or without the zobel, it'll be the same voltage accross the speaker. That means same current. Doesn't matter what frequency.
Yes ...i have remarked it so i have edited my previous post!!

Thanks anyway!
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Old 11th February 2004, 08:56 PM   #7
EC8010 is offline EC8010  United Kingdom
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Default Theory's nice, but nothing beats experiment.

Theory says that the Zobel resistor should be the same as the DC resistance of the voice coil. In practice, the matter is complicated by the fact that voice coil inductance is not pure inductance, but a transformer winding loosely coupled to a short circuit (the pole pieces). The figures I have given were determined experimentally, and I wasted a lot of time starting with a 5R resistor...
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Old 11th February 2004, 09:05 PM   #8
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Default Re: Theory's nice, but nothing beats experiment.

Quote:
Originally posted by EC8010
Theory says that the Zobel resistor should be the same as the DC resistance of the voice coil. In practice, the matter is complicated by the fact that voice coil inductance is not pure inductance, but a transformer winding loosely coupled to a short circuit (the pole pieces).
Yes!!...and there are also the motional voltage that also deviate from the pure inductance value...

Because of that , the impedance change when we put a hand in the speaker cone and don't let the speaker work freelly...
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Old 11th February 2004, 09:34 PM   #9
sreten is offline sreten  United Kingdom
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I may have misunderstood my theory, but I still can't see how
variations of the effective inductance affect the resistor value.

Resistances should be equal, seems to me its the capacitance
value you need to address for the problem you describe.

sreten.

edit :

according to Jordan DC resistance
is 4.5R and impedance is not given :
http://www.ejjordan.co.uk/JX92.html

By standard definitions this is a 6 ohm driver.
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Old 11th February 2004, 11:33 PM   #10
EC8010 is offline EC8010  United Kingdom
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Sreten, the impedance of the driver is a combination of voice coil inductance and resistance and the motional impedance. But it really doesn't matter what either of us think about theory. It was a combination of 8R2 and 4u7 that achieved the almost resistive 5R measured response above mechanical resonance.
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