Frequency response of the Amps HD, in the left channel (blue trace) and right channel (red trace)
Frequency response of the Amps HD driven by 5-ohm (blue trace) and 75-ohm (green trace) output impedance.
Isolation of the Amps HD, right channel, medium-sized tip. Negative dB numbers indicate a reduction in leakage of interior sound into the headphones. Actual results will vary with tip choice and ear shape/size.
Total harmonic distortion of the Amps HD at 80 dBA average output (purple trace) and 100 dBA average output (orange trace).
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.
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.
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.
Brett,
I am extremely happy to see S&V providing measurements as well as listener reviews. I would not purchase these earphones because I listen mostly to acoustic music - classical and jazz - but I could see where the bass freak would love these. Did you say that 0.179 volts rms at the earphone's stated impedance is a milliwatt? And, given that you measured the impedance as 16 ohms, 0.179 volts rms is really 2 dB higher than a milliwatt.
So this leads to the question of do we put in a milliwatt (or a watt for loudspeakers) at a voltage that is based on the spec or on the measurement of impedance we've already taken? I don't have the answer. Do you.
Last, any indication of what the highest play level would be possible with these earphones before they reach distortion levels that are intollerable to most of us (say enoghh to cause austachien.
Thanks
John Franks
Hi, John. Great questions!
You're right that 0.179 Vrms isn't actually 1 milliwatt into a real set of headphones - it's 1 milliwatt into a 32-ohm load resistor, which I consider to be broadly representational of a typical headphone. Just as 2.83 Vrms isn't actually 1 watt into a real speaker - it's 1 watt into an 8-ohm load resistor, broadly representational of a typical speaker.
Thus, in both cases, I'm actually measuring voltage sensitivity, not power/wattage sensitivity. In both cases, the watts reference is outdated and imprecise. But I keep using it because it's the industry standard. When I do measurements, I try to conform with industry standards or common practice whenever possible, whether or not I agree with them.
There really should be a CEA committee to update/tighten/improve measurement techniques for sensitivity of speakers and headphones. As you can see from the work of all the guys who measure this, we're all just doing our own thing in the absence of a good standard - i.e., coming up with a sensitivity measurement technique that is reasonable, accurate and repeatable. Which I think everybody has done (unless they're measuring with pink noise, which isn't accurate or repeatable), but still, our measurements are at best roughly comparable with each other and the manufacturers.
Highest play level possible (i.e., under a certain distortion threshold) is complicated and subjective. I'm hoping that showing the distortion curve at 100 dB (same technique as used by Tyll Hertsens at Inner Fidelity) gives you some idea of that, but yeah, we really need something that gives a better representation of max volume.
I did this in my recent Bluetooth speaker review. But while my technique was reasonable and did let me rate the products against each other in a relative way I think was accurate and repeatable, the absolute levels I cited were totally subjective and not in any way accurate or repeatable. You'd need research into what levels of distortion at what frequency the average listener finds intolerable - and it seems to me that research would have to be done separately for IEMs, on-ear/over-ear 'phones, and speakers.
Oh, for the days when a technical editor could make a living by writing two reviews a month and thus have time for research projects....
Thank you for your accurate review. Your comments on the treble were particularly useful, insightful and accurate. I purchased the AMPS HD earphones after reading your review. Here's my comments which I have posed on SOL Republic's Facebook page:
OK, I just visited JB Hifi in Sydney Australia and bought myself a pair of AMPS HD earphones, after comparing with the V10 headphones. Two comments:
(i) The AMPS HD earphones are the best earphones straight out of the box that I've ever heard, and I've owned much more expensive stuff like triple armature exotica. I let three people have a listen to it playing Gangnam Style and they were blown away. It's on their shopping list now. These headphones have a good strong bass that's not overwhelming, and a very smooth high that may seem a little flat but you'll appreciate it when you turn the volume up because the treble will not cause fatigue. Thank you SOL Republic for these fine earphones - they provide a WOW factor I haven't experienced for a long time. The only other pair of earphones I have heard that sound a lot better are the Sony XBA 4 which has four armatures and a recommended retail price over $400.
(ii) Luckily JB Hifi had a pair of V10 headphones which I was able to connect to my iPhone and test out. They were shit. The iPhone does not have enough power to drive them. Just no power at all from the iPhone.