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Accuphase Basic Engineering Policy
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We seek, through audio technology, music that's exciting and inspiring, that moves our hearts and enriches our lives. This is the idea behind our slogan "Enrich Life through Technology". It is the basic guiding principle behind all Accuphase audio components whose high grade can even be considered to be extravagant. We intend, however, to avoid non-audible frills, and concentrate our engineering on how best to reproduce the musical contents of program sources. If "Accuphase tone", as such, should come to be accepted, it would a manifestation of our interpretation of sound as it should be, and its hallmark would be its very special degree of transparency and clarity. To this end, we are re-educating our engineers in music, to increase further their knowledge and appreciation of this art which we are dedicated to re-creating.
OUR VIEWS CONCERNING SPECIFICATIONS
It is our policy concerning specifications to avoid listing meaningless figures. Rather we stress the characteristics most important to best music reproduction, and consider each figure very carefully as to what it means in terms of good music. Our specification figures are then rated very conservatively, and represent what we can guarantee the user for continuous, long-life performance. We acknowledge that specifications are an important factor in determining the quality of audio components, but believe that what lies behind the figures is even more important.
Some ultra wide-band proponents maintain that frequency response from DC to 100kHz is necessary from the standpoint of transient response. However, the truth is that no program source goes beyond 20kHz. Moreover, if a square wave (a sine wave with countless harmonics) is recorded on a highest quality 15-inch tape recorder, only the fundamental sine wave can be recorded beyond 7kHz. Even at 7kHz, the fundamental wave plus the 3rd harmonic (21kHz) forming a composite wave with a single dip at the crest is all that can be recorded. The range for the speakers is about the same. While the upper range for human hearing is 20kHz, most people cannot distinguish the higher harmonics beyond 7kHz. To them a 10kHz square waveform on an oscilloscope would be meaningless from a hearing standpoint. We believe therefore that a frequency response from 20Hz to 20kHz is sufficient. What is more important as far as characteristics in frequencies beyond human hearing are concerned is phase characteristic to prevent overshoot distortion and vibration with input pulses within the audible range. This problem extends up to several hundred kHz, so we cannot be content with a flat frequency response characteristic that is only wide.
The ratio between signal and noise levels is referred to as S/N ratio or S/N. We regard at least a 50dB rating as a necessary minimum, more than 60dB for good quality and over 70dB for high quality audio equipment. Moreover, 10dB should be subtracted from S/N ratio ratings for FM tuners since they are normally measured at 100% modulation while the average broadcast signal level is about 10dB less. In the case of power amplifiers, there should be absolutely no residual noise under "no signal" conditions. This level is measured against the output to determine its S/N ratio, so this ratio will vary at different powers. Minimum S/N requirements for output powers should be 10W: 79dB, 20W: 86dB, 100W: 89dB and 150W: 90,8dB. Noise can be expected with anything less than these ratings.
Different checking standards for total harmonic distortion (THD) in relation to loudness, frequency, etc, have resulted in different ratings which were often meaningless from a comparison standpoint in the past. However, re-examination of methods is being regarded as necessary by top experts today, with its improved equipment and more discriminating listeners. Since we regard S/N 50dB as the bare minimum requirement against noise, we believe that -50dB (about 0,2%) should be considered the maximum standard for THD. When two signals enter an amplifier with THD distortion, intermodulation distortion (IMD) results and sound becomes muddy. Both THD and IMD are caused by non-linear amplifiers and have a mutual relationship, IMD occurring at within 1 to 6 cycles of THD, and increasing sharply past the clipping level. The tolerance level of IMD has been regarded as to 2 to 5% for years, but our tests show that it should be held from down to less than 0,5% in high quality amplifiers.
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