For future projects, a pair of 6600 and
7100 tweeters were acquired. The basic differences between these two
tweeters are the magnet system and the dome, where the 7100 has a ring
of damping glue to the dome. The ring neodym magnet of the 7100
tweeter provides a whopping 95+ dB sensitivity, suitable for fairly
high-efficiency systems where the 6600 does well up to 92 dB/2.8
volts. The 6600 display some inconsistency in sensitivity, around 1 dB
and although I don't regard this as a serious problem, a little
disappointing. Only two units were available for the 6600 tweeter. I
had another pair of 7100 for test, hence 4 samples on display below.
All of these are consistent in sensitivity and only display minor
differences between 15-20 kHz, probably due to the damping ring
applied. I wonder why SS added the damping ring as the 6600 display
less distortion in this area compared to 7100.
Both of these domes appear suitable for two-way systems with a very low point of crossover and from clients' project I know the 7100 can do well down to 1.5 kHz with a simple 2nd order crossover. The 7100 tweeter was tested in experimental designs and proved well down to 1.4 kHz, 12 dB/octave. Very impressive.
The 6640 Be dome was added later to my collection.
All measurements done with tweeters flush-mounted on 35 x 50 cm baffle, center placement and 20 cm from top. An IEC baffle may provide better low-end response.
The 6600 and 6640 tweeters present some challenges with regard to crossovers, because these tweeters go so low the can play midrange! The 7100 with its steeper low-end roll-off due to the very strong magnet system is easier. Taking the 6600 and 6640 down to 2 kHz and using a 12 dB/octave filter makes it necessary to apply impedance linearisation to render a smooth roll-off profile.
I don't think I've ever had a pair of so closely matched tweeters. The have outstanding performance in my Jenzen ATS speakers.