AMPLIFIER RECOMMENDATIONS
As compared to
most
electrostatic loudspeakers, the
Spectra 1100 possesses
good
efficiency and
is
rela-
tively easy to drive. However, compared to traditional
magnetic loudspeakers, the 1100 possesses only
medium efficiency, andcanoccasionallyposedriving
difficulties at high frequencies where impedance can
dip to as low as
2
ohms.
Therefore, when choosing a power amplifier, a few
factors must be considered. The recommended
minimum of 75-1
00
watts per channel will yield good
results,
but
will
not realize the speakers' full potential,
especially in larger rooms. Amplifiers as large as
200
watts per channel may be used, as bng as good
common Sense
is employed: the speaker/a,plifier
should not
be
pushed to the limit of distortion. The
Spectra 1100
is very rugged, and the electrostatic
panel itself cannot be damaged by excessive drive,
but
the interface electronics and woofer system do
have finite power handling capacity. The advantage
inusingalargepoweramplifieris not so much to allow
the system to play much louder, but rather to allow for
unrestricted dynamic headroom. In bi-amping con-
fgurations, the power requirementsforeach amplifier
can be somewhat lower.
In addition to the
8
ohm power rating of the amplifier,
the amplifier's ability to drive low impedances should
be
considered. Despite the speaker's rating
of
2
ohms at highfrequencies, the ampliiier does not nec-
essarily have to be rated for
2
ohms, since this
minimum occurs over only a very narrow frequency
range. However,
to
yield optimum performance from
the loudspeaker, the amplifier should be ratedtodrive
4
ohm loads, and/or be advertised as being a 'high
current" design.
Acoustat does not generally recommend the used of
mono-bridged amplifiers with Spectra loudspeakers.
When a stereo amplifier is bridged into mono, each
17
half of the amplifier "sees" only half the bad imped-
ance. Therefore, that
2
ohm minimum then becomes
a
1
ohm minimum, which can cause overheating or
instabiliiy in some amplifiers. At the very least, very
few
amplifiers can deliver more power at
1
ohm: most
deliver considerably less.
The choice of amplifier device technology (transistor,
MOSFET vacuum tube, etc.) is an entirely personal
one. Acoustat does not favor one technology over
another. Each amplifier must be evaluated on
its
own
particular merits. The
same comments hold true for
the choice of speaker cable.
THEORY
&
PRACTICE OF SPECTRA OPERATION
Spectra 11
00
represents a very high state of perfec-
tion of electrostatic hybrid loudspeakers.
Theintedacetechniques allowing the Symmetric Pair
Electrically Curved Transducer (SPECTRA) mode
of operation were only perfected in late 1986.
At that time Acoustat made a quantum leap in the
productof STEP-UP EFFICIENCY and BANDWIDTH
which allowed for fhe first time a combination of
traditional Acoustat high pedormance with the half-
century old ideal of VARIABLE GEOMETRY opera-
tion.
This breakthrough solved the long standing impasse
which had not allowed high SPL electrostats to have
optimum behavior at all audio frequencies.
You will find Spectra has wide, pleasant dispersion at
all frequencies, razor-sharp high-frequency time
alignment, and clean low bass.
Spectra achieves this by effectively changing size
and shape at different frequencies. Spectra
is about
3"
wide
at
highest frequencies and about 9" wide at
middle frequencies. The lowest frequencies are
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