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Re: Supravox 215-2000EXC-OB differences.

Hi,

> So the OB version is beefed up and has changes in the pole piece
> and other areas. Many of these changes were designed by Thorsten
> Loesch and implemented by Guy LeCornec of Supravox France.

Actually, I suggested a few approaches to Guy, he choose what he felt best and changed the actual design. I understand it involves a longer airgap in the Magnet and changes to the voice coil. It results among other tings in a greater Xmax than the standard driver.

> Efficiency is definately compromised.

To relativate this a little. Many people do not understand how SPL, Efficiency and Qt relate.

A Cone driver is a mechanical resonant system. A given driver, with a given cone diameter, resonance frequency and equivalent volume (this is in effect a set of measures covering suspension stiffness and moving mass) will have a given SPL at the resonance for a given signal.

If I alter the Drivers Qe (and thus Qt) without altering anything else I do NOT alter the SPL at resonance!!!! I do alter the SPL above the resonance. The higher the Qe & Qt (and thus the lower the fieldcoil voltage) the lower the SPL above resonance ends up. Increasing the Fieldcoil Voltage increases the SPL above resonance and lowers Qe (& Qt).

To put this different, let us take a driver with an SPL of 94db/2.83V @ 50Hz Resonance.

If we adjust the Fieldcoil voltage so that Qt = 0.5 our midband SPL will be around 100db/2.83V (unless there is an additional MF/HF rise as observable for example with Lowthers).

If we adjust the Fieldcoil voltage so that Qt = 0.707 our midband SPL will be around 97db/2.83V.

If we adjust the fieldcoil voltage so that Qt = 1 our midband SPL will be 94db/2.83V with some response peaking above Fs.

In all three cases our SPL at 50Hz/2.83V is 94db.

I hope that illustrates the tradeoffs.

You can adjust the normal Fieldcoil drivers to similarly high Qt values, BUT at very low voltages the magnet system will operate outside saturation and will be less linear, hence my request to Supravox originally to adjust other driver parameters, to allow the fieldcoul to be operated near nominal voltage (and thus the magnetic flux at nominal levels) while increasing the Qt to > 0.5 at 12V Fieldcoil Voltage.

Ciao T

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