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In the Forum: Horn-Loaded Speakers
In the Thread: Macondo’s Midbass Project – the grown up time.
Post Subject: Relationship between output impedance and diaphragm control.Posted by Romy the Cat on: 10/12/2010
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 jessie.dazzle wrote:
… I do not fully understand the relationship between output impedance and diaphragm control; also I don't know what you mean by "negative impedance". Your mid-bass drivers have 15 Ohm coils; from what you write, I assume you are driving them from 15 or 16 Ohm taps. Correct?
Jessie,

diaphragm control is the subject of output impedance. The negative impedance conceptually is way beyond of any 15 or 16 Ohm taps. What you have a SET and you change your taps from 4R to 8R or from 8R to 16R you change the way how you load your output tube, change the amp gain, very slightly change output impedance of the amp, change the amp‘s power. Well, with power it is a bit more complicated as proper change of taps possible only with proper change of plate current, but no one does it and let discard it. The negative impedance concept discards all of it. In the negative impedance world you drive your 15R woofer with amplifier that has -15R of output impedance (it was minus). In this scenario the impedance of voice coil and all reactance it might have is completely balanced out by the negative impedance of amplifier. They are in complete stateless mode and the driver diaphragm becomes infinitely damped. In fact you will not be able to move or press the cone of your woofer as it will be stiff as a wall, where all power or amp will hold it. The woofer in this configuration has absolutely no primary resonance as the amp juts cancels it out. Pretend that you have a shovel that you stick in the ground and that vibrates under gust of wind. No pretend that you attached your shovel to 7000 tons of freight train loaded with coal. Now if the shovel vibrates is not because the wind but because the vibration of the train. This is exactly how a diaphragm in negative impedance behaves only the function of train performed by amplifier.

The caT

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