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Evolution
of Sound Reproduction
Horns were mandatory at little
available power
Until about 1930 tube amplifiers and
useful moving coil speakers had spread.
To make the most out of the little
available amp power of less than 1 Watt,
horns were used to amplify the sound.
Big horns with high efficiency could
fill a cinema with sound, where enough
space for them was available. The first
3-way systems for high, medium and low
frequencies came up in 1931.
Moving coil speakers basically
remained same
Only moving coil speakers basically
remained the same and reproduction of
deep bass in homes could not keep up
with ever smaller electronic devices, at
the contrary, despite bass waves have
the lowest energy levels, generating
them became more and more inefficient
and commercial sub-woofers consume more
energy than ever, up to 10,000 times
more!
A speaker should reproduce all
frequencies as evenly as possible and
not prefer, discriminate, distort any or
create new sounds, otherwise it won't
work with the reproduction of the
original sound.
Horns have high efficiency
In the beginnings of sound reproduction
horns were always attached. There the
speaker diaphragm pumps air quickly back
and forth through the horn throat and
therefor the horn draws up to 50% of the
energy that flows until the end. The
waves expand gradually along the duct
and emerge at the mouth to the ambient.
At the backward side of the diaphragm
the air is free to escape in different
directions with little air resistance.
Therefor only little pressure builds up
and basically no bass is radiated.
Closed boxes were the death of deep
bass
But there was a dilemma, because
consumers always want smaller speakers
and horns cannot be made smaller without
serious losses of quality. Therefor
direct radiating mode came up. Without a
horn speakers can work down to their
resonant frequency. This worked fine for
mid and high frequencies, but for bass
the provided diaphragm areas were much
too small compared to those wavelengths
and also an acoustical short circuit
between both sides had to be prevented,
which could be done by a bigger flat
baffle that eventually was bent to a
smaller open 'U' or even closed to a
box, the smaller the cheaper. As a
downside bass radiation became
inefficient but that time wasn't much
bass recorded.
A well-kept secret for a
long time
This way closed boxes evolved to the
dominant enclosure type. The German
HiFi-Norm of 1966 therefor only required
40Hz as lowest frequency and until today
this is still often praised and ennobled
from sellers to impress customers, not
telling them that the lowest pitch of a
concert piano is 26Hz, the leftmost
pedal of a grand organ is 16Hz or even
deeper and it's not less with modern
music and video recordings, so more than
a whole octave of sub-bass notes cannot
be heard.
Very much power is wasted to produce
a little bit of bass
Nevertheless engineers are still
increasing the diaphragm excursions with
excessive amplifier power, trying to get
more bass out of closed boxes. Adversely
the air volume within the box creates
cushion forces that have to be overcome
but do not add to sound volume and all
the energy at the closed side is lost.
Any attempt to use some of it, needs a
phase shift that introduces resonances
and severe loss of quality. The other
side of the diaphragm is at free air as
shown before and as a result of improper
enclosure type, only very little bass
wave energy is radiated: at 40Hz a good
12"-speaker can radiate from a big
housing less than 0.35% of the amp power
as sound waves while 99.65% is converted
to waist heat and eventually
distortions. At 16Hz the efficiency
drops to only 0.01%. To produce one Watt
of deep bass sound, which equals the
sound energy of a loud orchestra, 10,000
Watt of amp power are required.
It can be different
Jet-Bass is a new horn type
especially developed for deep bass,
e.g. of about 60 Liter gross space
volume, where a 10"-speaker delivers -
out of an ordinary 30 to 40 Watt
amplifier - more bass than you will
want in your living room with
apparently no low frequency limit. You
may discover sounds, never before
heard from comparable speakers.
Because you have always been
told "this is impossible", I
understand that such bold claims call
for disbelief, that's usual with
unknown things, but now ...
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