Mockingbird-V (Fountek FW168 with Peerless XT25TG30-04)

13 Liters Bass Reflex

The Mockingbird-V is a refinement of the Mockingbird-XT2. In this version, I went all out on the crossover. It cost more but the added expense is worth it. Now she sings like never before.

Fig 1 – Fountek FW168 RAW Frequency Response • Baffle Width=8-1/2″

Fig 1 is the RAW frequency response of the Fountek FW168 in a 13 liters bass reflex with a baffle width of 8-1/2″. The cone starts to breakup at 4kHz resulting in a nasty, sharp peak at 7.5kHz. Ignore the ugly notch at 150Hz. It’s a floor bounce that my mic picked up.

Fig 2 – Fountek FW168 with Low Pass network

The Blue plot is that of the FW168. This is what the response looks like after I tuned her for music. Obviously I was tuning with the tweeter connected but I’m showing just the woofer response first.

Fig 3 – Fountek FW168 with Peerless XT25TG30-04 (Flush Mounted)

The Red plot in Fig 3 is the Peerless XT25TG30-04 Ring Radiator tweeter. The crossover frequency falls at 2.5kHz for her to sound right. The tweeter must be flush mounted otherwise baffle diffraction will cause havoc.

Fig 4 – Mockingbird-V Passband

The Black plot in Fig 4 is the crossover passband. The summation looks good. The cone breakup peak at 7.5kHz did not cause any issues, so a notch filter was not necessary.

Fig 5 – Mockingbird-V Frequency Response

The final frequency response of the Mockingbird-V is in Fig 5. She is generally flat except for a 1dB rise from 1kHz~2khz. The treble actually extends to 20kHz.

Fig 6 – Mockingbird-V Null

The Violet plot in Fig 6 is with the tweeter wires in reversed phase. The null centers at 2.5kHz. It is not the prettiest but she’ll have to do. If I tweak the crossover any further, I run the risk of destroying the sound.

Fig 7 – Mockingbird-V Nearfield

The Blue plot in Fig 7 is the nearfield response spliced in at 500Hz. This is an approximation of the lower frequencies without any room reflections. The huge suck-out at 150Hz is not in the nearfield plot, confirming that that’s no defect in the woofer. 

Fig 8 – Mockingbird-V Port

The Brown plot (Fig 8) is the response of the port. Measurement is made with the mic inserted about 1/4″ into the mouth. From the peak, we can see the Mockingbird-V is tuned to 55Hz. The pipe resonance at 1.2kHz will not cause any honking since it’s -20dB below the fundamental.

Fig 9 – Mockingbird-V Step Response

The Step response in Fig 9 shows the FW168 transient is quite fast and smooth. There are no discontinuities all the way to the tip, hitting the apex at an impressive 250 microsec. This is one of the fastest transient in my collection of 6-1/2″ woofers.

Fig 10 – Mockingbird-V Waterfall

The Waterfall in Fig 10 recorded few artifacts in the treble. There is a longer decay at 1kHz which needs to be examine with the spectorgram.

Fig 11 – Mockingbird-V Spectrogram

The Spectrogram (Fig 11) shows a faint  streak at 1kHz. I did not detect any smearing during auditioning.

Fig 12 – Mockingbird-V Excess Group Delay

The Mockingbird-V recorded an astonishing 467microsec at 46Hz in her Excess Group Delay (Fig 12). This is one of the lowest I’ve ever seen.

Fig 13 – Mockingbird-V Box Modeling

The bass reflex alignment is in Fig 13. I did not want to over-damp the Mockingbird-V fearing I will lower the loudness of the bass too much. As it turned out, the bass loudness is about right. 

Fig 14 – Mockingbird-V Impedance

The Mockingbird-V is friendly on power amplifiers (Fig 14). Most of the time she’s above 10Ω, only dipping below after 1.5kHz. Even then she doesn’t go dangerously low, hitting 5Ω at 20kHz. The saddle on the left shows the box tuning at 55Hz. This is exactly what the port output showned in Fig 8. The electrical phase doesn’t deviate much except at 1.5kHz where it dipped to about -30°.

Sound of Mockingbird-V

The Mockingbird-V is all about musicality. Before this, I got a beautiful flat response but unfortunately, she sounded terrible. The music was compressed and had the life sucked out of her. I eventually threw out the crossover and voiced her by ear. 

And how does the Mockingbird-V sounds like? Well, I like her very much. This is one speaker I can listen to. The vocals project out and there’s excellent separation from the bass. There’s detail in the bass, even some texture. And the bass is dynamic. 

To test the bass, I played Stop, Look & Listen by Donna Summer. Man, she punches. And you can even make out some texture in the bass. Another track is Woman. Great dynamics. In Billy Ocean’s Love Zone, the bass came out punchy and tight.

As for the vocals, I had on My Sweet Lady by John Denver. His voice is crystal clear and sharply focused. And that lovely vibrato of his is just mesmerizing.

about the Fountek FW168

The Fountek is not an easy woofer to work with but sounds wonderful if you get it right. At $55, she’s about the same price as the Peerless 835025. She was unavailable for quite some time but she’s back in stock now at Parts Express. This is one woofer I can recommend. You’ll be surprised with her quality in the Mockingbird-V.

Unless otherwise stated, all measurements were made in Full Space (4 pi) with the mic at 36 ins, tweeter axis. Impulse Window=5ms. No smoothing applied.