[Arny Krueger]

"Andrew Haley" wrote in
message

Arny Krueger wrote:

Hyper-clean watts are cheap. High powered, low
efficiency speakers that sacrifice efficiency for size
are the way things are now being done.

Persumably, this means that the big problem now is
cooling the voice coils of the low efficiency speakers.

Not the problem or even the most intractable problem. High temperature
voice coils are commonplace.

Traditional room acoustics are the still the major problem that remains to
be overcome.

For example a large audio system that I recently help set up used 4 18"
woofers, each with 30 mm linear travel. Each of the two 2 ohm voice coils
for each driver were attached to a channel output of a 1250 wpc/2 ohm stereo
power amplifier. This system measures flat to well below 10 Hz, and can
generate SPLs at that frequency well in excess of 115 dB with low
distortion. In actual use I saw about 1/3 of the available linear travel
being exercised.

Wrong again. In a world of signal processing computers
and DSPs, capacitors and resistors are vanishing from
signal paths. For example even the coupling capacitors
on headphone amps are being replaced with
servo-reference voltage sources because the size and
performance of coupling capacitors need not be
tolerated.

Ah, thanks. That answers a question that was mystifying
me: why bother with all these servo designs I keep seeing
whjen all you need is a little cap? :-)

The coupling caps for a headphone amp seem small enough until one tries to
fit an entire stereo receiver, music library, and music player into
something with the approximate footprint of a comemerative stamp and maybe
1/4" thick. In this day and age high performance op amps can be so small
and take so little power that one or more of them form a less costly and
more effective alternative to two audio coupling capacitors for a 16 ohm
headphone load.