Swift
Ultima-II
(Linear Phase)
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This article may not be published in part or full without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.
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Vifa XT25SC90-04 re-visited
Though
the XT25TG30 and the XT25SC90 look similar, they are actually
quite different. This is reflected in the frequency responses
in Vifa datasheets. The TG30 (Fig 34) has a flatter response
whereas the SC90 (Fig 35) has a peak in the lower treble
followed by a depression at 3.5kHz. |
click
picture to Enlarge
Fig
34 - VIFA XT25TG30 |
click
picture to Enlarge
Fig
35 - VIFA XT25SC90
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In
Fig 36, the Black trace is the RAW response of the SC90.
It can be seen this response mimics the saddle in Fig 35.
The Violet trace is the SC90 with the Ultima High Pass network.
The Red trace is the SC90 with a new network that's optimized
for the Ultima-II. |
Fig
36 - XT25SC90 Frequency Response
(mic 1 meter Tweeter Axis | 5ms Impulse Window | 1/12 oct smoothing)
Swift
Ultima-II Frequency Response
Fig 37 is the response of the Ultima-II. There's a slight
dip at 3.5kHz, which is consistent with the RAW response
of the SC90. This does work in our favor as it'll tame
the sibilance in some recordings.
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Fig
37 - Swift Ultima-II Frequency Response
(mic 1 meter Tweeter Axis | 5ms Impulse Window | 1/12 oct smoothing)
Swift
Ultima-II
linear phase loudspeaker
The Impedance and Phase plots of Ultima-II (Fig 38) vary
slightly from the Ultima. Above 500Hz, Phase is well controlled
within a 18 degree window. Attempts at a tighter window
were discarded in favor of better sound quality. Impedance
is a healthy 6 ohms from 5kHz - 20kHz.
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Fig
38 - Swift Ultima-II Impedance/Phase Response
Swift
Ultima-II Dispersion
Fig 39 is the Horizontal Dispersion with curves taken
at 15 degrees intervals. At 10kHz upwards, it is obvious
that as the angle is increased, the ultra-high frequencies
drop off. For best response, the Ultima-II placement should
not exceed +/- 30 degrees from central axis (top three
traces).
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Fig
39 - Swift Ultima-II Horizontal Dispersion
(mic 1 meter On Axis with XT25SC90 | 5ms Impulse Window | 1/12
oct smoothing)
Swift
Ultima-II Distortion
The frequency response of the Ultima is shown in Fig 40.
Overall, distortion is low, averaging 0.2% THD in mid-band.
However, there's a minor peak of 1% THD at 4kHz comprising
of 2nd harmonics. This particular distortion is inherent
in the SC90 tweeter. Fortunately, the distortion is benign
as I failed to pick up any distortion during auditioning.
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Fig
40 - SWIFT Ultima-II Distortion
(mic 20 ins On Axis with XT25SC90 | 5ms Impulse Window | 1/12
oct smoothing)
Swift
Ultima-II Tone Energy Storage
Fig 41 is the Tone Energy Storage of the Ultima-II. Since
drivers are motional mechancial devices, they do not instantly
come to a stop after they are excited. The blue slices
indicate the stored energy released after receiving a
signal (think of it as "Ringing").
Less
Ringing = less Smearing = better Clarity.
Generally,
the Ultima-II is quite well controlled. There's a tiny
amount from 6kHz-15kHz which is inaudible.
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Fig
41 - Swift Ultima-II Tone Energy Storage
(mic 1 meter On Axis with XT25SC90 | 5ms Impulse Window)
Swift
Ultima-II Crossover Network
The network for the ZA14 remains the same as in the Ultima.
For the XT25SC90, the inductor is lowered to a 0.18mH
and the L-pad is removed.
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Fig
42 - Crossover Network of Swift Ultima-II
auditioning Swift Ultima-II
The
Ultima-II has the same character as the Ultima. Vocals are
clear, void of any veil and yet not shouty. There's the
right amount of treble without any hint of brightness. Supported
with the right subwoofer, the system is indeed impressive.
Subwoofers should be crossed at 85Hz-100Hz (24dB/oct) for
best performance.
Sep 8, 2013
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