clay wrapped around voice coil

[SWhite]

I removed the dust covers in preperation of redoing the surrounds on a pair of woofers and found a substantial amount of clay wrapped around the voice coils.

I've never seen anything like that before and was curious what you thought.

I'm going to leave the dust covers off for a while and see how much difference there is with out clay and then decide which I prefer. I could use the increase in sensitivity.

[Vikash]

Nice pic. I can only think that it is used to add mass to the cone and you would thus reduce efficiency and fs, and extend low end response. It would be strange not to just use a heavier diaphram though, so maybe it's a way for the manufacture to fine tune the same basic driver slightly. I'm just stabbing in the dark here.

The only other ring you would put around the top of the VC is a shorting ring, but it wouldn't be clay.

Or maybe the clay somehow aids heat transfer away from the aluminium former.

Depending on how much the clay weighs and consequenctly affetcs T/S params, it may change box requirements so you should keep that in mind. Worse still, if it is used to keep the VC cool, you could be reducing its power limits.

[sreten]

The clay will impact the high frequency response of the driver.

The upper frequency limit of a driver is when the voice coil
effective mass = the effective massloading of the cone, the
clay here is being used to limit high frequency response.

sreten.

[Svante]

Originally posted by sreten
The clay will impact the high frequency response of the driver.

The upper frequency limit of a driver is when the voice coil
effective mass = the effective massloading of the cone, the
clay here is being used to limit high frequency response.

sreten.

??? I have never heard this, could you elaborate on this a bit?

[sreten]

Originally posted by Svante


??? I have never heard this, could you elaborate on this a bit?

Just something I've known for a long time, can't remember
the source, but its certainly the main purpose of the clay ring.

Its accepted the effective radiating diameter of a cone decreases
above a certain frequency with frequency, and at some point the
mass of the voice coil will begin to dominate the response.

Hence a short coil in a long gap driver will have more treble than
a long coil in a short gap approach. I've also seen Tannoy 0.5
way bass drivers fitted with a large central plastic slug, this may
be extra mass loading and control of roll-off in the midband.

sreten.

[Salas]

Just mass loading, with the usual affect on HF too.

[Svante]

Originally posted by sreten


Just something I've known for a long time, can't remember
the source, but its certainly the main purpose of the clay ring.

Its accepted the effective radiating diameter of a cone decreases
above a certain frequency with frequency, and at some point the
mass of the voice coil will begin to dominate the response.

Hence a short coil in a long gap driver will have more treble than
a long coil in a short gap approach. I've also seen Tannoy 0.5
way bass drivers fitted with a large central plastic slug, this may
be extra mass loading and control of roll-off in the midband.

sreten.

I don't understand how added mass could affect the FR. I can see that if the effective surface decreases, the radiated power will too. But that effect would be the same with and without the clay, right? I can see that the effectve mass of the cone decreases as the effective surface does, and that this would compensate to some extent the drop due to loss of area. Do you mean that the relative mass drop is smaller if clay is added and that this compensatory effect is reduced?

[pinkmouse]

Originally posted by Svante



I don't understand how added mass could affect the FR. I

The added mass will reduce the resonant frequency of the driver, however it will also decrease the efficiency as well, as the coil has to work harder to move the cone.

[Svante]

Originally posted by pinkmouse


The added mass will reduce the resonant frequency of the driver, however it will also decrease the efficiency as well, as the coil has to work harder to move the cone.

Yes, of course, that I understand, but here the issue was the rolloff at high frequencies.

[pinkmouse]

Sorry...

Well, as far as I understand it, the compliance of the cone material acts to damp higher wavelengths from propagating out from where the VC joins the cone. This is why higher frequency drivers tend to be both smaller, and use thinner cone material than lower order drivers.