Acoustat SPECTRA 1100 Owner's Manual
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AMPLIFIER RECOMMENDATIONSAs compared to most electrostatic loudspeakers, theSpectra 1100 possessesgood efficiency and is rela-tively easy to drive. However, compared to traditionalmagnetic loudspeakers, the 1100 possesses onlymedium efficiency, andcanoccasionallyposedrivingdifficulties at highfrequencies where impedance candip to as low as 2 ohms.Therefore, when choosing a power amplifier, a fewfactors must be considered. The recommendedminimumof 75-100 watts per channelwill yield goodresults, but will not realize the speakers' full potential,especially in larger rooms. Amplifiers as large as 200watts per channel may be used, as bng as goodcommon Sense is employed: the speaker/a,plifiershould not be pushed to the limit of distortion. TheSpectra 1100 is very rugged, and the electrostaticpanel itself cannot be damaged by excessive drive,but the interface electronics and woofer system dohave finite power handling capacity. The advantageinusingalargepoweramplifierisnot so much to allowthe system to play much louder, but rather to allow forunrestricted dynamic headroom. In bi-amping con-fgurations,the power requirementsforeachamplifiercan be somewhat lower.In addition to the 8 ohm power rating of the amplifier,the amplifier's ability to drive low impedances shouldbe considered. Despite the speaker's rating of 2ohms at highfrequencies,the ampliiier does not nec-essarily have to be rated for 2 ohms, since thisminimum occurs over only a very narrow frequencyrange. However, to yield optimum performance fromthe loudspeaker, the amplifier shouldbe ratedtodrive4 ohm loads, and/or be advertised as being a 'highcurrent" design.Acoustat does not generally recommendthe used ofmono-bridged amplifiers with Spectra loudspeakers.When a stereo amplifier is bridged into mono, each17half of the amplifier "sees" only half the bad imped-ance. Therefore, that 2 ohm minimumthen becomesa 1 ohm minimum, which can cause overheating orinstabiliiy in some amplifiers. At the very least, veryfew amplifierscan deliver more power at 1ohm: mostdeliver considerably less.The choice of amplifier device technology (transistor,MOSFET vacuum tube, etc.) is an entirely personalone. Acoustat does not favor one technology overanother. Eachamplifier must be evaluatedon its ownparticular merits. The same comments hold true forthe choice of speaker cable.THEORY & PRACTICE OF SPECTRA OPERATIONSpectra 1100 represents a very high state of perfec-tion of electrostatic hybrid loudspeakers.Theintedacetechniquesallowing the SymmetricPairElectrically Curved Transducer (SPECTRA) modeof operation were only perfected in late 1986.At that time Acoustat made a quantum leap in theproductof STEP-UP EFFICIENCY and BANDWIDTHwhich allowed for fhe first time a combination oftraditional Acoustat high pedormance with the half-century old ideal of VARIABLE GEOMETRY opera-tion.This breakthroughsolvedthe long standing impassewhich had not allowed high SPL electrostats to haveoptimum behavior at all audio frequencies.You will find Spectra has wide, pleasantdispersion atall frequencies, razor-sharp high-frequency timealignment, and clean low bass.Spectra achieves this by effectively changing sizeand shape at different frequencies. Spectra is about3"wide at highest frequencies and about 9" wide atmiddle frequencies. The lowest frequencies are18 |
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