DATS v3 questions

[adason]

Just gave myself a little gift for xmass.
Can anyone help me interpret some curves?
Basically just checking at first. Yes, i read some dayton brochures.

Here after hookup, i measured small aura fullrange, then four loose tweeters.

 

[adason]

First from right, tiny dayton dome. I like this dome, used it before. Nice extension to 20kHz, good dispersion due to small size.
Looks little over 6 ohm, with Fs around 2kHz.

 

[adason]

Second is onkyo tweeter from the box of 200 on sale. They sound decent. I used them in line arrays a lot.
I am puzzled by impedance curve, starts above 5 ohm, and only goes up, no Fs is observed. Why?

 

[adason]

Next is small planar, foster supertweeter. Great extension to 40kHz with uniform of axis. Used it a lot, as part of three speaker systems now. Its only supertweeter, i cross it very high, 10kHz.
As expected for planar, flat impedance, 8 ohm, with just tiny bumps between 2-5 kHz.

 

[adason]

Last but not least, we have big hivi planar. It sounds ok, but due to the size, its narrowing of axis on top.
Again, flat impedance at 8 ohm, with tiny bump at ~1.8kHz. But why is it rising aftewards?

 

[mboxler]

The inductance of the voice coil will create the rising impedance. For fun, if you have a 1 - 2uf capacitor, connect it across the driver terminals and remeasure. The impedance will not only level out but will drop as the value of the capacitor increases.

 

[adason]

I have literally thousands of capacitors
But what would be the point putting cap on terminals? In what crossover would you do that?
Typically cap is in serier with voice coil for tweeter, inductor on terminals.

 

[adason]

You can compensate increasing impedance with zobel, but that is not what you suggest.
You are suggesting shorting the highs.

 

[mboxler]

The experiment was to show how the voice coil inductance can be tamed. The B&C DE-120 has quite a rising Impedance, as well as a rising response curve. Here are plots of the tweeter in a circuit. White is no parallel capacitor, Blue is with a 2.2uf parallel capacitor.

 

[adason]

As i explained above, its a bad idea. Basically you are shorting highs.
But i did it anyway, to prove my point. This is what i got with 2uF cap on terminals. Impedance drops below nominal. If you like your amp to oscillate, its ok with me.

 

[adason]

My original question about those two tiny dome tweeters remain unanswered. Why is one showing nice Fs resonance, other does not.

I did not ask why its is rising afterwards, i know that. I asked why is impedance rising in planar, since it has no standard voice coil. Its aluminium foil etched on mylar membrane. It should be flat. But the rise is tiny, and i believe hivi shows it too, so no issue.

Was about to post impedances of small bookshelfs, but there seems to be no interest in dats.

 

[mboxler]

Sorry for misunderstanding your question. Could it be skim effect?

Here's a plot of a speaker cable. It too has rising impedance.

 

[NeonDriver]

Possibly the tweeter with no discernible Fs peak has a generous amount of ferrofluid damping, that can flatten an impedance peak. I've never seen one quite that flat, however. There is a tiny rise around 4K Hz.

The planar drivers still have some inductance, most every conductor does. This may be causing an impedance rise at the high end.

 

[adason]

No idea about ferrofluid, you may be right. I would not expect it in such a cheap tweeter.
Btw, i measuted few, since i have many, and they are very consistent. And sound good.
Thanks for info.

 

[planet10]

Why is one showing nice Fs resonance, other does not.

sx there FerroFluid? Althou even with those you usually see a t least a tiny bump.

dave

 

[planet10]

I would not expect it in such a cheap tweeter.

I have some 60¢ tweeters with FerroFluid.

dave

 

[1audio]

Can you measure past 20 KHz? Its concievable that the resonance is ultrasonic. if the suspension is stifff enough and the dome + VC light enough its possible.

 

[adason]

No, 20kHz is upper limit. I can lower lower limit to 1Hz though

 

[drewmc]

Adason, I am pretty sure the planar tweeters still have inductance, larger for the larger HiVi. True ribbons have vanishingly small inductance without a transformer, but the multi-turn planar have considerably more due to the longer coil and presence of the steel grid holding the magnets. why the little dome has no peak is a mystery. Maybe the ferrofluid is partially dried out so it is extremely damped?

 

[drewmc]

Do you have frequency plots for the small domes. I would bet the Onkyo tweeter has falling response below 6KHz.