3 Key Qualities to Superior Loudspeakers
|The importance of a flat, full bandwidth amplitude response cannot be overstated. Although a linear response alone will not guarantee an excellent loudspeaker, it is the bedrock on which everything else is built. Careful selection of high quality drivers is the first step for achieving a flat response. No single driver, nor any two drivers, can adequately cover the entire audible spectrum. Driver size is also important since it effects dispersion and off-axis response. Dispersion and acoustic interference are effected by the size of the driver's surface area relative to the wavelength produced. Drivers should be crossed over at or below the point at which their off-axis dispersion begins to narrow. The distance between drivers should likewise be restricted to less than one half wavelength at the crossover frequency. Because all drivers have a limited bandwidth of linear operation, none should be asked to work outside their optimal range. A speaker's polar response needs to be linear also. Without off-axis linearity, the reverberant field, a composite of direct and off-axis reflected sound, will be tonally out of balance.
High quality drivers are also necessary for low distortion operation at realistic sound pressure levels. Interference patterns are minimized by reducing the shared frequency overlap between drivers through the use of a high order crossover, 24 dB per octave or greater. Cumulative Spectral Decay is also lower with quality drivers. Stored energy from the cabinet and inside the enclosure needs to be minimized.
Dynamics and transients are what make live acoustic music sound alive. All too often, to get the full impact of live music, the volume keeps getting inched up, little by little, in a futile attempt to simulate that live punch which says, "This sounds real." In reality, all this does is make it less real because the soft passages are no longer really soft and the spikes still don't pop out from the average volume. It all sounds just loud, not truly live. Great efforts by audiophiles are put into the quality of the signal path, from the source to the preamp to the amp and into the speaker cables. But after all the effort, that pristinely amplified signal is dumped it into yet more circuitry : a passive crossover. It's not just jarringly counterintuitive, it's bafflingly inane. The two main obstacles getting in the way of reproducing the recording as accurately as possible are 1) a passive crossover, and 2) drivers that can't handle the power required for dynamic peaks and transient spikes. The use of an active crossover eliminates the inefficiencies and monstrous obstacles presented by passive crossovers. This sidestep in turn reduces the compression of dynamics and transients caused by post-amplification processing of the signal. An active crossover also allows for needed equalization. Most importantly, a separate amplifier for each range (low, mid, high frequency ranges) only has to deal with the limited bandwidth, power draw and impedance curve of a single driver. Each amp takes direct control over each driver. Clipping, distortion, and especially intermodulation, are greatly reduced.
The Parallel Audio system achieves these qualities by a number of means.
Drivers have been selected for their smooth frequency response, low distortion, high power handling, and short cumulative spectral decay. The subwoofer and midrange are crossed over below the point where the driver's dispersion becomes directional. Each uses the flattest, cleanest part of its bandwidth. The tweeter, midrange, and subwoofer are less than one half wavelength apart at the crossover frequency—effectively a near acoustic point source that provides a wide, even dispersion pattern for a linear polar/power response. A high order Linkwitz/Riley 48 dB per octave active crossover is used to minimize the shared frequencies between drivers and reduce interference patterns.
Both the subwoofer and the midrange are in sealed acoustic suspension enclosures optimally damped to reduce the back wave from returning through the driver membrane. The enclosures are cylindrical to eliminate the panel resonances of boxes. There are essentially no baffles to cause diffraction or baffle-step issues. The low Qs of the drivers and the enclosures keep stored energy extremely low for delivering clean transients, less resonance.
The active crossover, tri-amplification and high quality premium drivers insure that dynamics and transients are delivered to your ears unhampered. Separate amplification of each bandwidth also reduces intermodulation and eases the load on the amps. Nothing but wire comes between each amplifier and driver to allow maximum control and damping for high resolution throughout the audible spectrum. All these factors sum together to realize superior performance.
Designs that cannot accomplish some or all of these key qualities (some may excel in one area at the expense of another) are all types of passive crossover, single driver, line source, d'Appolito configuration, horns (front or backloaded), bass reflex/passive radiator, transmission line, ribbons, and panel transducers of any kind. That leaves very few choices, and strikes out many very well respected loudspeakers.
If you'd like to listen to a pair, see the Auditioning Loudspeakers page.
See this link on the Relationship between Measurements and Preferences.
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