Anomalies In Impedance Sweep - Need Explanation

[Trdat]

Attached is an impedance sweep of my Deltalite 2515 in a 120 litre cabinet. It is a ported box and the sweep up after the second impedance peak had these squiggly lines and I suspected it was resonances or maybe port resonances but after plugging them with port plugs to seal them the anomalie is still there. There isn't much on the net regarding problems with impedance sweeps but on youtube you do come across the idea that they are considered as resonances.

Is this theory correct? Should the sweep be a smooth line rising up?

How do I tell what kind of resonance it is and what is causing it?

And how do I fix them?

 

[DS23MAN]

Those are driver resonances.

 

[Vini darko]

Can you run the sweep again with just the driver in free air? That would narrow the search.

 

[DS23MAN]

It is a 15" light weight PA driver, no wonder you will see this anomalies.

 

[tomtoo]

In the data sheet it has a lot of impedance wiggels.

https://www.thomann.de/de/cla.html?tlfo=https%3A%2F%2Fimages.static-thomann.de%2Fpics%2Fatg%2Fatgdata%2Fdocument%2Fspecs%2F223101_deltaliteii2515.pdf&tsi=additionalContent&ta=download&tad[ourl]=https://www.thomann.de/de/eminence_deltalite_ii_2515.htm&tad[triggeredBy]=a&tad[triggeredByEvent]=click&tad[title]=Data%20Sheet&tad[pos]=sidebar

 

[Trdat]

Can you run the sweep again with just the driver in free air? That would narrow the search.

I was convinced that the free air sweep was smooth but I think your onto something.

 

[Trdat]

Thanks for your replies I have no idea why I was convinced that the spec sheet and my free air sweep had a smooth rise up. But upon a second look yes they are also on the spec sheet.

So I am presuming they are perfectly normal?

 

[DS23MAN]

Perfectly normal for a light weight 15" PA driver.

 

[Trdat]

Perfectly normal for a light weight 15" PA driver.

When you say light weight, are you impying that a ferrite magnet will not have these issues?

And a driver without these anomalies in a impedance sweep is a better one?

Just tyring to get my head around it.

 

[tomtoo]

When you say light weight, are you impying that a ferrite magnet will not have these issues?

And a driver without these anomalies in a impedance sweep is a better one?

Just tyring to get my head around it.

To complete driver corpus is light weight.

 

[Vini darko]

Thanks for your replies I have no idea why I was convinced that the spec sheet and my free air sweep had a smooth rise up. But upon a second look yes they are also on the spec sheet.

So I am presuming they are perfectly normal?

Im going presume what we are seeing is minor oscillation in the large paper cone. Wich is back feeding into the coil causing the wiggles in impedance. I have no idea as to the audibility of this. It may be entirely benign.
Edit: think ripples in a pond.

 

[tomtoo]

Would not make me crazy as long nothing bad is seen in the FR.

 

[DS23MAN]

When you say light weight, are you impying that a ferrite magnet will not have these issues?

And a driver without these anomalies in a impedance sweep is a better one?

Just tyring to get my head around it.

To complete driver corpus is light weight.

The cone is light weight.

 

[alex-z]

That driver is almost exclusively designed for high SPL from 80-200Hz, and the resonances are outside that range. So don't expect much audibility unless you are using a shallow crossover slope.