Mockingbird-XT2 (the Final Cut)


It was 3 years ago that I did the Mockingbird-XT. In this final version, I tidied up the crossover, in particular the Peerless XT25TG30-04 tweeter. With this update, I expect the frequency response to be flatter than before.

Fig 1 – Fountek FW-168 RAW Response • Baffle Width=8-1/2″

The RAW response of the Fountek FW168 is in Fig 1. We see a sharp peak when the cone breaks up. This is typical of aluminum cone woofers. Fortunately it’s at 7.5kHz, so it’s not that difficult to deal with.

Fig 2 – Fountek FW168 with Low Pass Filter (LPF)

The Blue plot in Fig 2 is the FW168 with a 2nd order low pass filter. Instead of using a notch filter to remove the 7.5kHz peak, I adjusted the filter to lower it by -20dB.

Fig 3 – Blue plot=Fountek FW168 with LPF • Peerless XT25TG30-04 with HPF

Fig 3 shows the FW168 and the Peerless XT25TG35-04 crossing at about 1.8kHz. I normally avoid crossing a HiFi tweeter at such a low crossover frequency but if I cross the FW168 higher, I would end up using a notch filter for the 7.5kHz peak.

Fig 4 – Mockingbird-XT2 Passband

No cancellations are observed in the Mockingbird-XT2 crossover passband (Fig 4). This indicates the two drivers are summing properly.

Fig 5 – Mockingbird-XT2 Frequency Response

The final frequency response of the Mockingbird-XT2 is in Fig 5. It is a much better response than the XT. There is a light depression at 2kHz which may work in my favor because our ears are most sensitive at exactly that area. There is a bit of extra energy after that, from 3kHz to 10kHz. This will result in a slight emphasis in the treble. I don’t think this will cause problems because at a listening distance of 6ft to 8ft, the treble will be softer, so it’ll kind of balanced out.

Fig 6 – Mockingbird-XT2 Null Response

Fig 6 is the Null Response of the Mockingbird-XT2. Even though the lowest point is at about 1.7kHz, the lack of a sharp null indicates the two drivers are over-lapping. Whether this is objectionable can only be verified in the audition.

Fig 7 – Mockingbird-XT2 Step Response

Fig 8 – Mockingbird-XT2 Waterfall 

Fig 9 – Mockingbird-XT2 Toneburst Energy Storage

Fig 10 – Mockingbird-XT2 Spectrogram

The plots in 7,8 and 9 do not flag any anomalies in the Mockingbird-XT2. The Spectrogram in Fig 10 shows some excess energy at 1kHz and 1.3kHz but they die out by 6 msec.

Fig 11 – Mockingbird-XT2 Harmonic Distortion

The Total Harmonic Distortion (THD) is about -45dB below the fundamental. The 2nd and 3rd harmonics reside lower at -50dB.

Sound of Mockingbird-XT2

I struck the jackpot with the Fountek FW168. This is exactly the sound I was looking for.

The Mockingbird-XT2 is “fast”, as in lively. Midrange clarity is outstanding. Vocals are well isolated and focused. And the bass….. what can I say except that I totally didn’t expect this quality from the FW168. Fast, tight, detailed and with texture are the kind of words that best describe the bass character.

Listening to UFO (Bela Fleck and the Fleckstones) is out of this world. In Magic Fingers, the sustain in the bass can be clearly heard. In the middle of the track when the bass went lower, there’s just the right amount weight. Nowhere did I hear the over-amplified bass that anti-bass reflex listeners complain about.

As for the treble, I had to pad it down by 1dB. Otherwise, the tonal balance in the Mockingbird-XT2 is a bit off. Makes listening tiring after a while.

The Mockingbird-XT2 ranks beside the Cardinal-XT2 as the must build 6-1/2″ 2-way.

Crossover is available on request. Free for DIY. Not for Commercial use.
Unless otherwise stated, all measurements were made with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.