Looking to find Le of a driver

[mikee55]

Hello, I need to find Le of my driver. How do I go about this,please?


Cheers Mike

[hooha]

Hi Mike,

Not sure what you mean, you already have a reading - its 0.00

To get proper Le ratings it is best to use an LCR meter or bridge. Even then, these devices usually measure Le at a frequency that is far, far out of the passband of any sub (1kHz).

IMO, Le is an overrated measurement and should be taken with a grain of salt when dealing with subs.

Mark

[ocool_15]

I assumed you got a answer in your other thread "Measuring a Tweeter" where richie00boy(Post #21) was going to let you know how. I measure it similar to the way I measure a speakers impedence.

Basically you find the impedence at a high frequency(1k to 12k) and minus the DcR. Then calculate it like you were making a 6dB/oct low pass filter.

Example:

Say you measured the impedence of the woofer at 12.2 ohms at 1khz. you minus the DcR of 6.7 ohms for 5.5 ohms impedence caused by the inductance.


bcae1 link 91. on the left
enter the 5.5 ohms as "Low Freq. Impedance" and 1000Hz as the crossover frequency. On the left "Inductor value" will indicate .88mH(.875mH more specifically). That is the inductance value of your speaker.


Note: The calculated value will vary somewhat by frequency when using a speaker. I suspect it is due to the amount of metal around the inductor as it is not an air core but am uncertain.
I have seen the calculated value at 12K being less then at 1kHz by about 4.4%

[ocool_15]

btw you have a Re of 6.7 and a z of 10 ohms. Are you sure thats not a 8 ohm driver?

[hooha]

Interesting. Inductance becomes a more worthy parameter when dealing with midranges and tweeters, but I don't know many folks who listen to their subs at 1kHz.

Mark

[Svante]

Originally posted by ocool_15
I assumed you got a answer in your other thread "Measuring a Tweeter" where richie00boy(Post #21) was going to let you know how. I measure it similar to the way I measure a speakers impedence.

Basically you find the impedence at a high frequency(1k to 12k) and minus the DcR. Then calculate it like you were making a 6dB/oct low pass filter.

Example:

Say you measured the impedence of the woofer at 12.2 ohms at 1khz. you minus the DcR of 6.7 ohms for 5.5 ohms impedence caused by the inductance.


bcae1 link 91. on the left
enter the 5.5 ohms as "Low Freq. Impedance" and 1000Hz as the crossover frequency. On the left "Inductor value" will indicate .88mH(.875mH more specifically). That is the inductance value of your speaker.


Note: The calculated value will vary somewhat by frequency when using a speaker. I suspect it is due to the amount of metal around the inductor as it is not an air core but am uncertain.
I have seen the calculated value at 12K being less then at 1kHz by about 4.4%

This is not the way to do it.

First, if one assumes a simplified model of the voice coil inductance as frequency independent, the current and voltage of the inductance will be 90 degrees out of phase. This would mean that in your example, the reactance of the voice coil would be sqrt(12.2²-6.7²)=10.2 ohms. At 1 kHz that corresponds to (from |Z|=2*pi*f*L) L=|Z|/(2*pi*f)=10.2/(2*pi*1000)=1.6 mH.

Second, the voice coil inductance is not frequency independent. This in turn leads to that the phase shift between current and voltage is not 90 degrees, but typically 60-70 degrees, and the impedance is not proportional to the frequency, but rather to f^0.7 (typically)