Swift-IIIa  (HD)
(High Definition Series)

5 inch 2-way
13 Liters Bass Reflex Satellite

by Michael Chua

This design is free for DIY. Not for Commercial Use.
This article may not be published in part or full without the express permission of AmpsLab.

Swift-III Impedance

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.

Swift-IIIa - Distortion Corrected

Fig 8 -Swift-IIIa Distortion

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.


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.


next > Swift | Swift-II Hybrid | Swift-II Passive | Swift-II Music
  Swift-III | Swift-IIIa | Swift-IIIb | Swift-IIIc | Swift Ultima | Swift Ultima-II


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