AADE L/C iiB - what else?
I would have to rig up a bridge circuit or similar lash-up on the bench to measure at 1kHz - rather more work than a quick coffee time check-up with AADE and DMM.
piglet
** There are lots of elses !!!!!
The AADE is quite unsuited to measuring loudspeaker inductance.
The maker says the MINIMUM measuring frequency is 20kHz and the unit is NOT suitable for iron cored inductors.
All your figures for speaker voice coils are way off, many times under the value at 1kHz.
OTOH, the figures for the WW resistors look realistic.
Horses for courses.
.... Phil
True, but is was handy and would at least give a rough (or very rough) indication of whether speaker inductance is comparable to a wirewound resistor.
If the 1kHz inductance is actually higher then that just means a speaker is even *less* like a wirewound resistor than was suggested. I am now satisfied that a speaker has much more inductance than a wirewound resistor of similar rating. 1kHz measurement will be one of my "rainy day" projects.
piglet
I found a Belco BR-8 AC Bridge I bought back in 1977 - it is horribly fiddly to use with juggling ratio arm, meter sensitivity and loss balance controls but the AF source measured at 920Hz.
Here are the (low-precison) results:
a) Speaker 1. 17uH AADE (669kHz) -> 102uH at 920Hz
b) Speaker 2. 110uH AADE (444kHz) -> 165uH at 920Hz
c) Speaker 3. 37.6uH AADE (576kHz) -> 115uH at 920uH
So, yes - the 1kHz inductance is higher than the 100's kHz by factors from 1.5X to 6X. I guess that is due to construction and amount of air gap coil to lossy core stator.
The OP application was concerned with pwm class-D which I suppose uses frequencies between 30kHz to 300kHz so somewhat lower than AADE measurement freqs but above AF.
All I need now is a HiFi speaker to try :}
piglet
Done sooner - cracked apart reveals progressive wound inductor-like helix of NiCr (or similar) wire on a former with crimped end caps. Mnfr datasheet did not lie.
No doubt there are countless other constructions around too so it could be that I just stumbled on an a-typically low-L resistor.
piglet
** Congrats on getting it done right.
If you can afford to pull one of them apart and test the voice coil on its own - that would be instructive.
... Phil
** They rarely do.
Similar style resistors in higher vales ( ie over 100 ohms) are often spiral cut metal film types - but genuine WW types can tolerate large pulse currents that kill the film types - so are prefered in many apps.
** No you didn't.Even among WW types, there is quite a big variation in inductance for the same wattage and resistance value. The variable is the kind of resistance wire being used and its ohms per meter.
... Phil
Nope, You didn't miss a thing! :)
Jamie
As if Jamie were a reliable witness. He's so unreliable that he even thinks that his opinion is worth posting.
-- Bill Sloman, Sydney
Something like that is done in precision wirewound resistors e.g.
see p3 "construction"; the winding direction is reversed half way along the bobbin.
(Sorry not been following entire thread so may have missed some context)
-- John Devereux
** Which is nothing like what was claimed.
.... Phil
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.