How the Hawk came about
I liked what I heard during the auditioning of the L6-4R in an active bi-amped system. I believed that I finally found a woofer that I can design a 2-way bookshelf speaker that has sufficient bass, a clear midrange and treble that doesn’t assault you. And most importantly, I can achieve this without having to resort to any correction networks. No BSC, Zobel and LCR. Just a High Pass and Low Pass.
Fig 1 – HiVi L6-4R RAW Frequency ResponseDisregard the deep notch at 150Hz. It is caused by a “floor bounce”
The Black plot in Fig 1 is the RAW response of the L6-4R mounted onto a 13 liters bass reflex box with a front panel width of 8.5″. The Blue plot is with a 12dB/oct low pass filter that I adjusted to lower the rise in the mid-range caused by baffle step.
Fig 2 – Hawk Frequency Response
The Black plot in Fig 2 is the summed response of the HiVi L6-4R and Peerless XT25TG30-08 tweeter. I corrected the slope of the tweeter crossover (Red plot) to minimize the effects of Baffle Edge Diffraction. Bear in mind that the tweeter is surface mounted in my test box with sharp edges on all corners.
Fig 3 – Hawk Frequency Response with tweeter wired in Reversed Phase
The Violet plot in Fig 3 is the response with the XT25TG30 wired in Reversed Phase. It shows that acoustically, the two drivers are crossing at 2.6kHz. Come to think of it, this null looks very much like the one in my earlier audition when I crossed these drivers with a 24dB/oct electronic crossover.
Fig 4 – Hawk Harmonic Distortion
Generally, Harmonic Distortion is -50dB below the fundamental all the way up to 10kHz (Fig 4). The purpose of this measurement is not for the speaker to display the lowest distortion. Rather, if it registers high distortion, it tells me that something is not right. Perhaps some manufacturing defects with the drivers.
Fig 5 – Hawk Impedance
Fig 5 is the Impedance Sweep of the Hawk. Some solid state power amplifier’s protection circuits may be activated due to Hawk’s impedance.
It barely touches 4 ohms at 200Hz, which is expected from a 4 ohms woofer. What power amplifiers really dislike is at 10kHz. Here, it dips to 3 ohms. Fortunately, there’s not much energy up there. Owners of tube power amps may not face this issue because some output transformers have 2 ohm tap.
Though the impedance may be demanding at 200Hz and 10kHz, the Hawk’s Phase Response is quite friendly. From 200Hz to 20kHz, it is within a +/- 35° window. This helps to lighten the load on the amplifier, in particular at 200Hz and 10kHz.
|How does the Hawk sound like
It took me awhile to “voice” the Hawk the way I wanted. After making five versions of the crossover, I finally got the Hawk to “sing”. By that, I mean the music sounds “live”. Not like some “pipe-in-music” in shopping malls.
The Hawk’s mid-range is as clear and transparent as can be, making the all important vocals and instruments cut right through the mix. Female voices in particular, sound beautiful. No shrillness or glare and with just the right amount of crispness in the sibilance. Treble is smooth, no harshness. Mid-bass has punch and definition. The lower bass goes down to about 50Hz, enough to lend some weight to the “thud”.
All in, the Hawk offers fantastic performance at a ridiculously low cost. I am exceeding proud of this design.
September 13, 2017Projects