SOL Republic Amps HD Headphones

After hearing the enthusiastic sales pitch from SOL Republic, one of the latest of many new entrants into the headphone biz, I was disappointed when I heard the company's first model, the Tracks $99 on-ear. While the Tracks is beautifully made and incredibly comfortable for an on-ear model, its extremely bass-heavy balance made me feel like I was locked in the trunk of a Honda Civic with two 12-inch woofers and the complete works of Deadmau5 cranked way up.

When I received the company's first in-ear monitor (IEM), the $99 Amps HD, I wondered if the company would be able to achieve the blend of design and sound quality it originally promised - or if it'd be another well-crafted but sonically intolerable product.

The Amps HD has an unusual but attractive design, with a big SOL logo plate (available in black or silver) and a clear plastic strain relief. Rubber tips in four sizes are provided (and if you register your Amps with SOL Republic, they'll supply you with replacement tips for the life of the product), along with a case. The angled earpieces give it a fit our testers described as "good" or "great." (though S+V Web editor Michael Berk found the housings too large to find a comfortable fit) We also loved the flat cable, which minimizes tangles at the slight expense of somewhat increased handling noise.

An in-line mic/control is provided. SOL Republic says the mic/control is compatible with Apple and most Android and Blackberry phones, but it gave my Motorola Droid Pro fits, causing the sound to mute briefly every few seconds. You can check your phone's compatibility here.

SOL-ful sound?

Besides my own listening impressions of the Amps HD, I got the opinions of fellow S+V contributing tech editor Geoff Morrison and L.A.-based voice actress/singer Lauren Dragan. All of us listened first through a high-end setup using a Rane HC 6S professional headphone amp and a Denon DVD-2900 DVD/SACD/CD player.

I then checked out the Amps HD using my Motorola Droid Pro cell phone and various laptop computers. I found that with my phone, it plays just loud enough, but if your phone has less output or you really like to crank the sound up, you might want an IEM with higher sensitivity.

Geoff and I both reacted instantly and enthusiastically to the Amps HD's sound. "I like these!" he exclaimed. I, too, liked the tonal balance right off. The bass is powerful and punchy and grooving, but not overwhelming as it is with way too many of today's headphones. It's pretty close to a just-right amount of bass - in our opinion, it's a level that a few serious audiophiles might find a bit much, but that most people would find perfect.

The treble may be more of a point of contention for some. Geoff and I both found it exceptionally smooth and never fatiguing. However, because the treble sounds slightly tame, the Amps HD doesn't sound quite as open and lively as some other IEMs we know of, especially many balanced-armature models. For Geoff and I, this was a totally OK - perhaps even welcome - trade-off. Lauren, probably possessed of the best high-frequency hearing of the three of us because she's young and female, found the sound a little too dull for her taste, though she still liked thought the sound OK overall.

That smooth sound made most voices sound great through the Amps HD. Surprisingly, even with the strong bass I never noticed bloating on male voices; most of them sounded right-on. A few lighter-voiced singers (James Taylor in particular) sounded a little small and recessed due to the mellow highs, but I think most listeners will find the voice reproduction about as good as it gets for a $99 IEM.

"Smooth" might not sound like the adjective to describe a great rock headphone, but the Amps HD is one of the best rock IEMs I've heard. I found I could listen to Soundgarden's Louder Than Love at a satisfying level with none of the fatigue and ear strain that many IEMs give me when I rock out. At the same time, it's an ideal jazz 'phone, with a just-right balance on everything I listened to, from guitarist Julian Lage's recent Gladwell CD to the 24/96 high-res download of Sonny Rollins' "St. Thomas" from the HDTracks/Sound+Vision sampler.

To sum up: The Amps HD sounds smooth, satisfying, and punchy, and it's great for pop, rock, jazz and hip-hop, which means we think most people will like it a lot. Those who crave an exciting, detailed, ambient sound probably won't be as enthusiastic.


I measured the Amps HD using a G.R.A.S. Type 43AG ear/cheek simulator, a Clio FW audio analyzer, and a Musical Fidelity V-Can headphone amplifier. I used the larger of the medium-sized tips, which seemed to fit the ear/cheek simulator's fake rubber ears the best, and experimented with slight differences in position of the IEMs to get the most representative results.

The Amps HD frequency response measurement seems to show a very bass-heavy, treble-deficient balance. However, the bass measurements and subjective tonal balance of IEMs are extremely fit-dependent; none of the panelists complained about excessive bass, so perhaps I got a much better-than-average seal with the 43AG's rubber ear. Adding 70 ohms output impedance to the V-Can's 5-ohm output impedance to simulate the effects of using a low-quality headphone amp produced almost no difference in frequency response: about +2 dB at 20 Hz, which you're unlikely to notice.

Distortion is very low. Total harmonic distortion (THD) at 100 dB rises a little below 100 Hz but hits just 3.5% at 20 Hz, and between 1.5 and 3.4 KHz there's a little increase in THD, to 2% to 2.4%. Judged against an amplifier, that may seem high, but it's low for a headphone driven to high volume. THD at 80 dB is so low it's not worth mentioning.

Impedance is almost dead flat, averaging 15.5 ohms. Isolation is typical for an IEM, reducing outside sounds from -10 to -30 dB between 1.3 kHz and 15.6 kHz. There's not much isolation up around 20 kHz but you'll never hear that. Isolation results will vary with the tips you choose, the shape of your ear, and how tight of a fit you like.

Average sensitivity from 300 Hz to 10 kHz with a 0.179 volts RMS signal is 95.4 dB.

To Amp or Not to Amp?

Overall, this is a well-made, nicely styled, very good-sounding IEM, one we can easily recommend. Like every other set of headphones, its sound will please some people more than others, but we think most listeners will be pretty thrilled with what the Amps HD delivers for $99.