Source of this impedance abberation

[AllenB]

Any suggestions on what is causing this?

[Ron E]

cone breakup

[AllenB]

I decided to get to the bottom of this so I pulled a driver and ran some plots. I found three resonances in this area which I could only pick on the phase plot (first plot). I used blue-tak on the spider, the surround, and on seven concentric levels of the cone itself.

The resonance above 500Hz went when I damped the spider. Damping the surround and cone mostly made things more complicated (e.g. second plot). There was a location 3" in from the cone edge where the impedance seemed to come together (third plot). I assume from the phase in this plot that this was a good thing.

Now I know that adding weight to this location will do this, how should I approach a permanent fix? Doping, weighting, felt pads?

[AllenB]

...and should I limit the treatment to only the cone region which showed the desired effect?

[speaker dave]

The odd thing is that your impedance wiggle doesn't really show up in the response (acoustical) curve.

Usually the first big resonance just above the piston band (the frequency range where the whole cone really does move as a piston) is a surround antiphase resonance, sometimes called an edge hole. Your wiggle is about the right frequency for it but I don't see any acoustical evidence of it. A second possibility is always a box resonance (panel or internal dimension related) because the frequency range is about right.

Edge resonances sometimes respond to damping of the surround. Manufacturers would apply a gooey treatment but for experimentation you might try gentle pressure with a layer of foam in contact with any suspect areas. Hanging mass can give you added resonances, as you see.

Heretical question: If it doesn't show up in the response can we just ignore it??

David S.

[AllenB]

Originally Posted by speaker dave

Heretical question: If it doesn't show up in the response can we just ignore it??

Hehe. Back when I first began to discover what went on behind the response, I thought I'd discovered the secret treasure...but now I feel like I've gone full circle.

Did I make it clear that my plots were impedance magnitude and impedance phase? I found that the location of the blu-tak affected the frequency contribution and the mass was critical. Up to 10g was an improvement. 20g stopped helping and created new problems.

I picked up some 2mm felt and various craft glues today. It will take 24cm x 30cm to reach 10g but I am not happy with any of the glues I have here, especially as one has glued the test paper to my desk