Hawk-II (HiVi L6-4R with Vifa D27TG35-06)


In this 2nd version of Hawk, I went all out to control the HiVi L6-4R. The network for the L6-4R is quite elaborate. Apart from a second order filter, there’s a shelving network for baffle step and a conjugate network to tame the cone breakup peak ar 2.5kHz.

Fig 1 –  Frequency Response of HiVi L6-4R  •  Baffle Width=10″

Fig 1 shows the RAW response of the HiVi L6-4R. My targeted crossover frequency is 2.5kHz. Unfortunately, this is exactly where the cone breakup peak is. It would be easier to use the natural roll-off and cross at 3.5kHz with a planar tweeter like my RT1C-A but where’s the challenge in that.

Fig 2 – HiVi L6-4R RAW and with LPF

The Blue plot in Fig 2 is the final response with my network in place. Note the absence of the peak at 2.5kHz. That’s important, otherwise it will interfere with the summation when I cross it with a tweeter.

Fig 3 – HiVi L6-4R with LPF  •  Vifa D27TG35-06 with HPF

The Red plot in Fig 3 is my vintage Vifa D27TG35-06 with a high pass filter. This tweeter is another Vifa classic. It is now manufactured by Scanspeak under their Discovery label, model D2606/9220. Tymphany also manufactures it as a Peerless D27TG35-06. However, I’m not sure how close the Peerless is to my original D27 because the frequency response doesn’t look the same. I will likely buy the Scanspeak and Peerless version later to compare them to my original D27. 

Fig 4 – Crossover Passband

The Black plot in Fig 4 is the summation of the the HiVi L6-4R with the Vifa D27 tweeter. There are some loss on the right side of the passband, about -3dB from 3kHz to 5kHz. Nothing too serious. It will help to tame recordings that are too sibilant.

Fig 5 – Hawk-II Frequency Response

The Hawk-II response (Fig 5) is exceptionally flat except for the depression mentioned earlier. Due to my room limitations, measurements below 500Hz are in nearfield.

Fig 6 – Null Response

Fig 6 is the Null plot when I flipped the tweeter wires around. The notch is not very deep but it does center on my targeted frequency of 2.5kHz.

Fig 7 – RAW and Nearfield Responses

To check on my BSC, I included the Black plot below 500Hz. This measurement includes my room reflections. Disregard the chunk of frequencies missing from 100Hz~200Hz. It’s an anomaly caused by a floor bounce.

It can be seen that my upper bass (100Hz) is about -3dB less than the midrange. This is exactly what my BSC is intended to do. I didn’t want to bring the bass up to the same level as the midrange because when the Hawk-II is used in a smaller room or against a back wall, the bass will be louder.

Fig 8 – Step Response

Fig 8 is the Step Response of the Hawk-II. The HiVi L6-4R woofer is slightly slower than the Vifa P17WJ-00-08 that is in the Honeycreeper. The peak registered 400 microsec whereas in the Honeycreeper, it’s 300 microsec. Not that we can hear any difference. 

Fig 9 – Waterfall

The Waterfall plot in Fig 9 shows some artifacts in the treble. Though they are recorded, they are not audible. My time window is highly magnified at 1.5 msec.  

Fig 10 – Spectrogram

This Spectrogram in Fig 10 shows the artifacts in the treble are insignificant. The most prominent extension is at 1.5kHz. It will not cause any harm because the energy is dissipated by 6 msec.

Fig 11 – Impedance

The Hawk-II is a difficult load. At 2kHz, it dips to 3.2Ω. During playback, I didn’t detect any issues with my power amplifier but it may trigger some amplifier’s over-current protection circuitry. Fortunately, the electrical phase at 2.5kHz is at zero. That reduces the demand on the amplifier. 

Sound of the Hawk-II

Once in a while in designing speakers, something magical happens. The Hawk-II is one of them.

When I first heard the Hawk-II, it sounded like any other competently designed speaker. After a few days, I tweaked the crossover to see whether I can extract more out of it. Suddenly, the music jumped out. I knew I hit the sweet spot. Now the music sounds realistic and lifelike.

Another aspect that’s exclusive to the Hawk-II is in the harmonics. This speaker really shines with acoustic guitars and horns. It is during the end of the notes that the richness in the harmonics are heard. Kenny G’s saxophone has never sounded this heavenly. So does Ben Webster.

For guitars, I had on Acoustic Highway by Craig Chaquico. The guitar took on a new dimension with the harmonics. It’s never been that expressive before.

But the Hawk-II doesn’t excel in instruments only. In My Sweet Lady, John Denver’s voice projected out of the Hawk-II and pierced my heart. This is a very sad song about a 20 yr old young mother who died of bone cancer.

After all that’s said and done, the Hawk-II exceeded my expectations. I never expected this sound quality from drivers that are moderately priced.  It only goes to show you don’t need to spend a fortune to get good music.

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.