what does this tweeter impedance curve mean?

[jimk04]

Playing around with some 4" KEF coax from 1st gen Eggs. Aluminium cone mids and a black (mylar?) tweeter. Here is the DATS curve of the tweeter, and I dont really undrstand where the FS is or why it looks like this?


I measured two of them and both are pretty much identical.

 

[planet10]

Ferroflui?

dave

 

[jimk04]

I was wasndering how to interpret your reply Dave , do you mean the tweeter is measuring thus due to sticky ferro fluid

 

[Ken Newton]

Dave surely is referring to ferrofluid damping the tweeter’s Fs to the degree that it is no longer visible on the plot. Even so, the low-frequency roll-off still should be visible. Not the response showing flat down to 20Hz. Puzzling.

 

[planet10]

Ferrofluid can often completely flatten out the impedance bump, you curve looks typical.

dave

 

[rayma]

Can you measure a different driver? There may be a problem with your test setup.
Or could there be a parallel resistor connected to the tweeter hidden somewhere?

 

[jimk04]

the tset was for two tweeters. can do another pair

 

[daqvin_carter]

Do they make sound? Can you run a sweep at roughly 1 watt? Not seeing a FS peak would make me think stuck voice coil. If the Ferrofluid hardened it might do that. Another option is a pole piece shifted and the coil is stuck.

 

[SBA_SLOB_GUY]

Hi there,

i have taken some impedance measurements of a pair of KEF SP1632 some time ago, here:

the coax tweeter impedance is very flat - extremely low Qts value

 

[jimk04]

Thanks for all the input. Yes they make a sound when doing a sweep with DATS. Haven't measured FR yet or played music thru them. Doubt you'd get into them to check the ferrofluid. Look well sealed!

 

[WhiteDragon]

Seen small 3/4" or .75 to .8 tweeters with light mylar or polycarbonate cones and impedance peak is almost un seen.
But is a wide impedance bump from 700 to 1300 Hz. Be misleading if less visible thinking crossover could be low.
Just assume towards the top of the peak when seen.
This ones practical non existent but would assume towards the 1100 / 1200 Hz bump and you would cross it high
just like any other small tweeter 2.5 to 3k

Some Visaton small polycarbonate tweeters can surprisingly go pretty low without distortion at normal levels.
KEF might be the same.