Fig
6 - Swift-III Impedance
Swift-III
Distortion
Fig
7 - Swift-III Distortion
If there's one thing that really bugs me, it's a kind
of irritation in my inner ear when I listen to music.
Swift-III did exactly that.
In
Fig 6, Swift-III's impedance dips to an astounding 2 ohms
at 2.7kHz. Correspondingly, there is a distortion peak
at the same frequency (Fig 7). Eventhough the THD at 2.7kHz
is only 0.7%, the distortion is not benign as they consist
mainly of odd harmonics.
To
resolve this issue, all it took was a 2.2 ohm resistor
right at the beginning of the High Pass Network. By simply
raising the tweeter's impedance to 4 ohms (Fig 9), the
distortion peak at 2.7kHz disappeared completely (Fig
8). This is undeniable proof that my amplifier's protection
circuitry was guilty of the distortion.
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Swift-IIIa - Distortion Corrected
Fig
8 -Swift-IIIa Distortion
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Though
the 2.2 ohm resistor removed the distortion, the music lost
some of it's sparkle. It sounds rather "dull",
unexciting, certainly not the kind of intimacy that I yearn
for. To restore the speaker to her former glory, the EQ
network was re-tuned.
Now
the Swift-IIIa really SINGS. This is the version I recommend.
Use the crossover in Fig 11 below and you'll be immersed
in musical bliss.
Enjoy.
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Swift-IIIa Impedance
Fig
9 - Swift-IIIa Impedance
Minimum Impedance at 4 ohms at approx 2.6kHz
Swift-IIIa
Frequency Response
Fig
10 - Frequency Response of SWIFT-IIIa
1 meter - tweeter axis
Swift-IIIa Passive Network
Fig
11 - SWIFT-IIIa Passive Network (18dB/oct)
Fig
11 is the crossover for Swift-IIIa. Note the addition of
a 2.2 ohm at the front of the High Pass. If one intends
to play loud, use a 20 Watt. The resistor in parallel with
the 3uF is now a 4.7 ohms.
Recommended
types of components are Polypropylene Capacitors, Air-Core
Inductors (minimum 18 awg) and preferably Non-Inductive
10 Watts resistors. To save cost, the 50uF and 170uF can
be replaced by Non-Polar Electrolytic Capacitors, subject
to their quality of course.
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