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The acoustics
The theory behind the LS1‘s acoustical design originates back to the 1930s and ‘40s.
Cabinets in those days were flat but wide, which moved the baffle-step frequency below
250 Hz. Above that frequency sound is radiated hemispherically. Psycho acoustics says
that the ear is sensitive to phase errors down to approximately 250 Hz. The wide baffle
helps to attenuate interfering reflections throughout this whole range.
Of course progress since the 40‘s has learned that edge diffraction of the cabinet deteri-
orates the stereo image, hence the sides of the LS1 cabinet are strongly rounded by the
legs. As a bonus, the shallow cabinet moves the lateral resonance inside the box signifi-
cantly above the cross-over frequency of the low frequency driver. This avoids boxiness
before any electronic correction is applied.
Next step in the design phase was the driver selection. We settled on an outstanding pair
of Seas units. The tweeter’s exceptionally low distortion in the mid range allows a fairly
low cross-over frequency that benefits vertical dispersion. Its small constant directivity
horn ensures an even spread of high frequency energy.
Even dispersion is also helped by the lack of cone breakup effects in the magnesium
woofer. The woofer’s long excursion permits generous sound pressure capability down to
40Hz for the two way configuration. Adding the LS1s takes performance up a notch by
extending the response down to 20 Hz and further increasing attainable loudness.
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