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[email protected] dpierce.cartchunk.org@gmail.com is offline
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Default More than 30W per chanel Class A transistor amps

On Monday, March 4, 2019 at 4:47:15 PM UTC-5, Trevor Wilson wrote:
On 5/03/2019 7:11 am, Peter Wieck wrote:

Um. Not so much. Back in the day, AR made a huge point on
the power-handling capacity of their speakers, and used
"magic" such as ferro-fluid and so forth for heat dissipation.


Back in "which" day? Ferrofluid was not commonly used until the
1980's, long after the original AR days, and more like into
the Teledyne/Acoustic Research era and later.

**Ferro-fluid is used only in HF drivers and some mids and,
except for NEAR drivers, not in bass drivers


Quite correct. Some tweeters used it, very few midranges used and
not a single bass or wide-band driver of any commercial viability
used it. It's use or non-use is well correlated with the maximum
excursion capability of the driver: it's completely unsuitable
for drivers with large excursions (typically greater than 0.5mm)
because it literally is pumped out of the gap.

And it is the bass driver that limits
the maximum thermal limits of a speaker system.


For the most part, the actual data from the field contradicts this.
Looking at data from many of the clients I have dealt with over
the years, power-related (either thermal or mechanical) speaker
failures by far are dominated by thermal failure of tweeters,
while the remainder are mechanical failures of woofers. For certain,
there are overlaps (e.g., mechanical tweeters failures and thermal
breakdown in woofers), but, based on field data across a very large
number of systems, these latter are very much in the minority.

Except for some pro drivers, few domestic bass drivers can cope
with sine wave power levels of more than 50 Watts or so.


It's not so simple a relation as that. For sure, one can say that
if the voice coil is subject to sufficient input such that you're
dissipating the vast majority of the input power as heat in the voice
coil, that's largely true.

But consider the following: all other things being equal, for what
might be the output voltage of the amplifier that would result in
50 watts being produced at, say, lower midrange frequencies would
produce MUCH less power (and thus thermal dissipation) at below
100Hz or say at 2000 Hz, where the impedance is substantially higher.

Especially on the low bass, where the impedance is dominated by the
resonant peak from the woofer, and combined with the fact that the
excursion of the woofer gores as the inverse square of frequency,
the thermal problems a secondary compared to the mechanical limits.

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