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Speaker Asylum: Re: From another posterabout the B&W 700 series design flaws... by John Ashman

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Re: From another posterabout the B&W 700 series design flaws...

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Quote:

This is a problem, by the way, that plagues all current 2-way Kevlar,
metal, or carbon-fiber loudspeakers ... at the current state of the art,
the 6.5" or 7" drivers are forced to operate right up to the edge of their
working ranges in order to meet the tweeter in a moderate-distortion
frequency range.

If you lower the crossover frequency, tweeter IM distortion skyrockets,
resulting in raspy, distorted high frequencies at mid-to-high listening
levels; if you raise the crossover frequency, the Kevlar breakup creeps in,
resulting in a forward, aggressive sound at moderate listening levels, and
complete breakup at high levels (unlike paper cones, Kevlar, metal, and
carbon fibers do not go into gradual breakup).

This presents the designer with a tough choice: rough sound in the entire
treble region, or the characteristic Kevlar forwardness, which can at times
actually give a snarly sound to the speaker system. At the present, the
best choice is a fourth-order (24dB/Oct.) crossover with a sharp notch
tuned to the Kevlar resonance.

Rigidity means accelerations from the voice coil are accurately translated
into cone or dome acceleration over the entire driver surface; this
translates to ruler-flat frequency response, fast pulse risetime, low IM
distortion and a transparent, "see-through" quality to the sound.

[unquote]

What B&W does is incorrect according to Lynn - They use shallow crossovers WAY too high in the frequency band for Kevlar. And an FST design with flexible Kevlar can't transmit a signal accurately throughout the entire cone. Therefore, you get a strange sound and, apparently, a very beamy sound. Maybe you should try reading Lynn's article. And see this picture of Kevlar -


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Topic - Why are the B&W 700 series less used than the CDM NT series? - bluesky 20:03:00 11/30/04 ( 34)