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Hi Lew!

Likewise, nice to hear from you!

The design I'm contemplating would have an efficiency in the 93 dB ballpark, so even with the S-30 we'd theoretically be able hit 110 dB. Thermal power handling would be good (400 watts), so thermal compression - or more precisely thermal modulation - should be negligible at normal listening levels.

Which reminds me of an under-appreciated advantage of a Power Paradigm amplifier: As the voice coil heats up and its resistance rises, the wattage that the amplifier delivers stays essentially constant, thus negating the major source of thermal modulation. A Voltage Paradigm amplifier (typical solid state amp), on the other hand, delivers reduced wattage as the voice coil heats up (constant voltage into higher impedance = reduced wattage), so thermal modulation can become significant on peaks, reducing the power delivered to the voice coil on such peaks, thus robbing the music of dynamic contrast, and dynamic contrast = emotion.

I'm using the term "thermal modulation" to describe the effects of the virtually instantaneous heating of the voice coil when it gets hit with a lot of power. Considering that a woofer's efficiency is perhaps around 1%, a 100-watt peak is like touching it with a 99-watt soldering iron, and so it heats up immediately (and cools down more slowly). This rapid-onset thermal modulation is not well documented to the best of my knowledge, but smarter people than me believe that it is audibly significant (Earl Geddes for one).

The better-known thermal issue is thermal compression, which includes not only the increase in the voice coil's DC resistance as it heats up, but also the eventual heating of the entire magnet, which results in a loss of magnetic flux and corresponding loss of efficiency. I see that phenomenon in prosound a lot, where the musicians feel like their amps have run out of power on the last song of the set, but then everything is fine when they start the next set. It's not their amps losing power; it's the speaker magnets in their cabs getting hot and temporarily losing magnetic flux. It's probably rare for speakers to be pushed so hard in a home audio setting that the magnets heat up and lose flux, so I think that thermal modulation from the heat-induced rise in voice coil resistance is the primary culprit at home. Which Ralph's amps neatly deal with!


Me being a dealer makes you leery?? It gets worse... I'm a manufacturer too.



Edits: 05/03/14 05/03/14

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  • Hi Lew! - Duke 17:16:20 05/03/14 (0)

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