Swift-III  (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This article may not be published in part or full without the express permission of AmpsLab.

Vifa XT25TG30-04

Fig 1 - Vifa XT25TG30-04 Impedance

In Swift-III, the tweeter has been upgraded to a Vifa XT25TG30-04. This tweeter is also a Dual Ring Radiator, similar to the smaller XT25SC90 but with a lower Fs centering at 470Hz, a more desired frequency.

Summing of Swift-III

Fig 2 - Frequency Response of Swift-III (ZA14 + XT25TG30)
1 meter - tweeter axis

Fig 2 shows the acoustic slopes of the ZA14 and the XT25TG30 crossing at 2,300Hz. What is really interesting is the highpass of the XT25TG30. The slope is virtually a straight line, resembling a textbook electrical filter.

In the all critical crossover region, no summing anomalies are seen. From 1kHz-4kHz, summing is smooth. No peaks or cancellations. Judging from the plot, the XT25TG30-04 is a better match for the ZA14 at 2,300Hz.

Frequency Response of Swift-III

Fig 3 - Frequency Response of SWIFT-III
1 meter - tweeter axis

Fig 3 above shows the summed response of the ZA14 and the XT25TG30 with a full passive crossover.

Disregard the measurements below 200Hz as they are affected by the room. The deep notch at 150Hz is attributed to a cancellation node caused by a sound wave bouncing back from the floor below the speaker.

Dispersion Measurements

Fig 4 - Frequency Response of SWIFT-III at various angles
1 meter - tweeter axis

Swift-III Horizontal Polar Response

Fig 5 - Horizontal Polar Response of SWIFT-III
Normalized Flat at 0 degrees curve

Swift-III Harmonic Distortion

Fig 6 - Harmonic Distortion of SWIFT-III
Blue trace consists of combined 2nd, 3rd, 4th and 5th Harmonics
0.7% at 2.7kHz (blue trace)
1.4% at 95Hz (blue trace)

Swift-III Passive Network

Fig 4 - SWIFT-III Passive Network (18dB/oct)

The crossover components are shown in Fig 4. Recommended types 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 Non-Polar Electrolytic Capacitors.

Swift-III Passive Network Impedance

Fig 5 - SWIFT-III Impedance (18dB/oct)

Swift-III Impedance

Swift-III's impedance is an insane load. The drastic dip to 2 ohms at about 2.7kHz is sure to stress most solid state power amplifiers. At such a low impedance, there is a strong probability that power amplifiers' over current protection circuits will be triggered.

After listening to Swift-III for a couple of days, it's apparent that there's distortion somewhere. My guess is my power amplifier's protection circuit was activated during certain parts of the music. To test my theory, a slight modification was made to the crossover. The next version shall be Swift-IIIa.


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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