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This article may not be published in part or full without the express permission of AmpsLab.

ZA14W08 up-close

Swift-II is designed as a no-compromised Monitor. When supported with a Subwoofer, the performance will rival speakers costing many time more.

Before we proceed further, let's take a closer look at the ZA14. Fig 1 is the manufacturer's SPL/FRQ plot. The most obvious anomaly is the sharp peak centering at about 9kHz. This kind of peak is cone breakup due to the use of extremely stiff cone material, in this case, aluminum. What is less obvious is a +3dB hump at about 2kHz. Bear in mind that this response plot is with the ZA14 mounted on an Infinite Baffle.

Fig 2 is a SPL sweep with the ZA14 mounted onto a box with a baffle of 8.5" width. Disregard the region below 300Hz. The measurement is inaccurate due to room interaction.

The cone breakup correlates to Fig 1. However, the rise in the mid frequencies is now greater. We can see clearly the climb starting from 400Hz and peaking at about 1.4kHz. The difference between these two points is +6dB. This is the classic case of Baffle Step at work. If this effect is left uncorrected, it will result in a response with heavy emphasis in the mid-range, leading to speakers that some describe as "shouty".

click to Enlarge

Fig 1 - Manufacturer's SPL/FRQ Plot

Fig 2 - SPL Sweep of ZA14 in 13L Box

taming the ZA14

Fig 3 - ZA14 Response at 2.25kHz Crossover (active 18dB/oct)

The Blue trace in Fig 3 is the raw response of the ZA14. The Violet trace is with the Synergy crossover set at 2.25kHz. Lastly, the Red trace is with Baffle Step Compensation (BSC) applied. Attenuation is -6dB. The cone breakup peak has been attentuated by -50dB. I seriously doubt it will cause any problems when it's buried this much.

XT25SC90 re-visited

Fig 4 - XT25SC90 Response at 2.25kHz Crossover (active 18dB/oct)

The plots in Fig 4 are of the Vifa XT25SC90. The Blue trace is the raw response of the tweeter, that is without any crossover. As can be seen, the XT25 has a healthy bandwidth, extending from 1kHz to 20kHz. Though the response is flat within a 5dB window, there is a hump at 8kHz. Normally, one would correct this for flat but since it's there, I shall take advantage of this high frequency emphasis.

The Red trace is with the Synergy active crossover set at 2.25kHz. The effectiveness of a steep crossover is clearly visible. At 1kHz, the attenuation is -20dB. Judging from the plots, this tweeter can easily be crossed at 2kHz or even 1.8kHz. Whether distortion stemming from crossing so low is acceptable is another matter.

Summing of the ZA14 with XT25 with Hybrid Crossover

Fig 5 - Frequency Response of SWIFT-II ( 2.25kHz | 18dB/oct)

Fig 5 shows the summed response of the ZA14 and the XT25. This response is a Hybrid, that is the crossover is active (18dB/oct) while passive components, a 1.5mH in parallel with a 15 ohm resistor, were used for BSC.

From the frequency response of the Swift-II, we can see there is an upper treble boost at 8kHz. This helps to compensate slightly our hearing deficiency at high frequencies (Fletcher-Munson).

In Fig 6 below, the Red trace is of the Swift-II without BSC. The rise in the mid-range response is clearly visible. The Blue trace is with BSC. The step response created by mounting the ZA14 onto a relatively narrow baffle has been corrected.

Fig 7 shows the passive components for the Blue trace. No components are necessary for the XT25.

Response without BSC vs with BSC

Fig 6 - SWIFT-II without BSC and with BSC (1.5mH//15 ohms)


Hybrid network of Swift-II

Fig 7 - SWIFT-II Hybrid Network with BSC (1.5mH//15 ohms)



next > Swift | Swift-II Hybrid | Swift-II Passive | Swift-II Music
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