Measurements

I measured the Tracks V8, Tracks HD V10, and Tracks Ultra V12 using a G.R.A.S.43AG ear/cheek simulator, a Clio FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and a Musical Fidelity V-Can headphone amplifier. As is often the case with on-ear headphones, I had to use the 43AG's clamping mechanism to get an adequate seal on the simulator's rubber ear. It's possible this may have slightly boosted the bass in the frequency response measurements.

Tracks

The Tracks' frequency response measurement suggests a sound that's heavy in the bass and midrange but perhaps a little soft in the treble. The bass response is broad and smooth, rather than the boomy resonant peak that many headphones produce. The peak at 1 kHz - a region where most headphones have a dip - suggests that the Tracks might emphasize midrange, particularly voices, somewhat. Adding 70 ohms output impedance to the V-Can's 5-ohm output impedance to simulate the effects of using a typical low-quality headphone amp does not affect frequency response.

Total harmonic distortion (THD) at 100 dBA is negligible at frequencies above 100 Hz. Below 100 Hz, there's some distortion, but not a whole lot for a headphone of the Tracks' configuration and cost: a max of 4.8% at 20 Hz. Impedance averages about 63 ohms, with a sharp rise to 88 ohms at 50 Hz. Isolation is typical for a passive on-ear headphone, with reduction of -10 to -30 dB above 800 Hz.

Average sensitivity with a 1 mW signal at 60 ohms rated impedance is 100.8 dB from 300 Hz to 10 kHz, 102.5 dB from 300 Hz to 6 kHz.

Tracks HD

The Tracks HD V10 frequency response measurement shows a powerful peak at 1 kHz, indicating that this headphone may have a midrange bias. It also has substantial bass response, with broad, flat output across the entire bass range. The treble response isn't real strong, but slight peaks at 2 and 5 kHz may even out the subjective tonal balance to some degree. Adding 70 ohms output impedance to the V-Can's 5-ohm output impedance to simulate the effects of using a typical low-quality headphone amp has no significant effect on frequency response.

Total harmonic distortion (THD) at 100 dBA is low for a compact headphone: insignificant above 100 Hz, and rising to an average of 2.8% from 20 to 80 Hz. Impedance is fairly flat, averaging 60 ohms and peaking at 70 ohms at 60 Hz.

Isolation seems to comparable to that of the Tracks and Tracks Ultra V12, with reduction of -12 to -30 dB above 1 kHz; the differences among the units are minor in this area and possibly due to slight differences in the positions of the earpieces on the ear/cheek simulator.

Average sensitivity with a 1 mW signal at 60 ohms rated impedance is 104.6 dB from 300 Hz to 10 kHz, 106.8 dB from 300 Hz to 6 kHz.

Tracks Ultra 

It appears from the frequency response chart that the Ultra V12 has a heavy emphasis on the midrange, with a huge peak centered at 1 kHz - right where most neutral-sounding headphones tend to have a large dip. There's also ample and very broad bass response, although without the usual peak around 2 to 3 kHz, the treble may sound a little muted. Adding 70 ohms output impedance to the V-Can's 5-ohm output impedance to simulate the effects of using a typical low-quality headphone amp has no significant effect on frequency response.

Total harmonic distortion (THD) at 100 dBA is very low for a compact headphone: almost unmeasurable through most of the audio band, rising to just 3.9% at 20 Hz. Impedance averages 57 ohms with a slight rise to 67 ohms at 50 Hz.

Isolation is typical for an on-ear passive headphone, with reduction of -9 to -30 dB above 1 kHz. These isolation results are slightly different than I measured from the standard Tracks. I don't know if the discrepancy is due to slightly different position of the earpiece on the ear/cheek simulator, or actual internal differences between the two headphones.

Average sensitivity with a 1 mW signal at 55 ohms rated impedance is 104.6 dB from 300 Hz to 10 kHz, 106.7 dB from 300 Hz to 6 kHz. - Brent Butterworth

Bottom Line

So which Tracks is for you? While the sonics weren't necessarily to my taste, aside from the Ultra, I can see the appeal for serious baseheads, and the design is appealing. And the price - especially for the Tracks and Tracks HD - is right, especially for the impressive build quality. Even for the pricier V12/Ultra model, the modular design means that it'll be easy to keep the 'phones going as parts wear out, perhaps lowering your overall headphone spending over the next couple of years.

I wouldn't necessarily say you're getting less for your money with the original Tracks - sure there's a pricing spread, but the three models seem, rather, just to be pitched at very different tastes. There's enough similarity in the sound signature otherwise. Want big bass? Hip-hop, modern pop, and electronic dance music more your thing? Go with the Tracks. Rock your thing? The Tracks HD might fit your needs. But if you're a jazz or classical fan, or really if you're mostly interested in acoustic or vocal music of any stripe, you're going to want to go with the Ultra. 

Does the top-end V12 driver mean the Ultra's an "audiophile" headphone? That's hard to say. It is absolutely not a basshead 'phone, with a sonic profile that tends to the mids, with reasonably good detail up top. I'm still not sure if it wins out at its price point and in its form factor, but if you dig the look, feel, and construction of the Sol Republic's 'phones, it's worth an audition.