Headphone Reviews

I wrote several issues back that my first high-end headphones were Koss Pro4AAs, which I bought in 1972 following a positive review in the British magazine Hi-Fi News. Although that review didn't mention that the Pro4AAs were relatively fragile (footnote 1), I nonetheless loved their sound. They were the best headphones I'd heard—until, a couple years later, I was playing bass on some sessions for record producer Tony Cox. Tony had a pair of signal-energized electrostatic headphones, Koss ESP-6es, which were heavy and clunky—but they opened my ears to the sound quality that could be obtained from "cans." I didn't hear better until after I'd moved to Santa Fe, in 1986, and J. Gordon Holt loaned me his review samples of the Stax SR-Lambda Pros.

Koss's ESP-6 model is long out of production, but its descendant, the ESP/950, is still available, and is reviewed by Herb Reichert elsewhere in this issue. So when I heard that Shure had introduced a pair of electrostatic headphones, the KSE1500s, I didn't need my arm twisted to ask for a review pair. But in my haste, I didn't immediately notice that the KSE1500s are not conventional headphones but in-ear monitors. And they're not only headphones—for $2999, the purchaser gets not just the IEMs but a D/A headphone amplifier and energizer unit, and a plethora of adapter cables and accessories.

Technology
IEMs typically have armature drive-units—basically, a metal reed fixed at one end, with the other end set vibrating by one or two voice-coils. But an electrostatic driver? I shouldn't have been surprised. An IEM doesn't need a big diaphragm; in fact, conceptually, it could be considered a capacitor microphone in reverse, and Shure has considerable experience with such designs. Their SM81 cardioid capacitor microphone, for example, has long been one of my go-to mikes for recording acoustic guitar and piano.

The reality is little more complicated than that, however. Microphones typically use a permanently polarized diaphragm, called an electret. By contrast, the KSE1500 drive-unit features a virtually massless diaphragm suspended between two back plates, with a polarizing voltage across the plates of ±200V. When fed an audio signal of sufficiently high voltage—according to the KSE1500's specifications, 200V—the diaphragm vibrates, producing sound, which is coupled to the user's eardrum via a small tube, over which fits a sleeve to seal the ear canal and provide isolation from external sounds.

Because of their need for both a high signal voltage and a polarizing voltage, the KSE1500s can be used only with their dedicated amplifier. A Kevlar-shielded cable terminated with a six-pin Lemo connector delivers both signal and the DC bias voltage to the earpieces. The amplifier is housed in an elegant, black-anodized enclosure a little smaller than an iPhone. On its top end are the Lemo connector, an analog line-in jack, a battery-status LED, and a recessed, knurled volume knob; on the other end are a Micro-B USB port and a slide switch to choose between the analog and USB inputs. The USB input will handle 16-, 24-, and 32-bit data with sample rates of 44.1 to 96kHz; the analog input can either be fed straight to the output amplifier, or digitized in order to be operated on by the amplifier's DSP-based equalizer. The USB interface can accept data from PCs and Macs, but also from iOS and Android devices.

The front of the amplifier is where the action is. In normal use, a tiny, color-LCD panel displays the input selected, level meters, battery level—the amplifier is powered by an internal rechargeable 3.6V Li-ion cell—and the volume, both as a number from 0 to 25 and as a colored dial. Two clicks on the volume knob display a menu that can be navigated by further clicks and twists of the same knob, along with presses of one of the two buttons on the enclosure's left side. (The other button locks the controls.)

The first Menu screen offers a choice among Audio, Utilities, and Equalizer functions. Audio offers a choice of 0, –10, or –20dB pads for the analog input mode, controls an analog-domain limiter, and displays the sample rate of the incoming data. (The manual says that it also allows the amplifier to be set to low or high output gain, but that didn't appear to be available on the review sample.) Utilities grants access to battery, hardware, and firmware information, as well as a Factory Reset and the ability to turn off battery recharging via USB—necessary for use with some portable sources. (Battery recharging is reinstated the next time the amplifier is turned on.)

Equalizer offers four adjustable four-band equalizer presets—Low Boost, Vocal Boost, Loudness, and De-Ess—and four four-band parametric equalizers, two offering a peaking filter and two a high- or low-pass shelving filter, all with adjustable center/turnover frequency, bandwidth/Q, and gain/cut of up to ±6dB. The Equalizer can be bypassed—when the DSP is not in use, battery life is claimed to increase from 7 to 10 hours.

Use
Like all IEMs, the KSE1500s' earpieces are inserted in the ear canals with a twist-and-push motion that takes a bit of practice. (The left and right earpieces are respectively indicated with blue and red dots.) Shure's excellent manual was a help with this, as was the fact that the cables have bendable sleeves that allow them to be twisted into place over the outer ear, or pinna. But as supplied, the earpieces themselves were a sloppy fit. I had a similar problem when I reviewed Shure's E3c in-ear headphones in May 2004: none of the sleeves fit my wider-than-average ear canals. And without a good seal between sleeve and canal, the bass rolls off significantly.

The KSE1500s come in a smart black case, with a drawer on one side for storing the accessories. These include Soft Flex rubber sleeves in small, medium, and large, yellow Soft Foam sleeves, and Triple-Flange sleeves. Fortunately, the largest rubber sleeves supplied with the KSE1500s were a good fit—I had no problems getting excellent bass extension. However, after a week or so of use, I felt I needed a little more bass than the Shures were offering—I've found in the past that I prefer headphones with more low frequencies than is strictly natural, perhaps to compensate for the fact that my chest cavity is not being excited, as it is with loudspeakers and natural sounds. After some experimentation, I set one of the user-defined equalizer presets to boost by 3dB all frequencies below 125Hz.

There was plenty of gain available. I tended to have the KSE1500s' volume control set to "14," which produced comfortably loud listening levels. Apple's USB Prober utility identified the KSE1500 amplifier as "Shure KSA1500" from "Shure Incorporated," and reported that the USB interface operated in the optimal isochronous asynchronous mode.

Listening
As the KSE1500 is a closed system and I don't have the necessary dummy head to perform acoustic measurements, this review comprises only my listening impressions. Those impressions were good. I began with test-tone files ripped from Editor's Choice (CD, Stereophile STPH016-2). Even without my preferred EQ, the KSE1500s played the low-frequency, ¹?₃-octave warble tones cleanly and with full weight down to 32Hz. The 25Hz tone was shelved down a little, and the 20Hz tone was very quiet. One problem with dynamic IEMs is that they have limited dynamic range at low frequencies, but here the Shures excelled—I could hear no "doubling" (second-harmonic distortion) on the lowest-frequency tones. The half-step–spaced tonebursts on Editor's Choice also spoke cleanly and evenly throughout the bass and midrange, and the sound of my Fender bass guitar in the Channel ID and Phase tracks was powerful and clean.

It was the combination of clarity and low-frequency weight that first sold me on the Shures. Whether it was Jack Bruce's fuzzed, overdriven bass in "Spoonful," from Cream's Fresh Cream (ALAC file ripped from CD, Atco), the subtly woody character of Jerome Harris's Taylor bass guitar in "Only Then," from his Rendezvous (ALAC file ripped from CD, Stereophile STPH013-2), or Anthony Jackson's drop down to his low B string on the line "negotiations and love songs are often mistaken for one and the same" in "Train in the Distance," from Paul Simon's Hearts and Bones (ALAC file ripped from CD, Warner Bros.), the characters of the instruments were both readily apparent and maximally distinct from one another. And from this fussy Fender bass player, that is praise indeed.

The pink-noise track from Editor's Choice sounded as even through the midrange as the Ultimate Ears 18 Pros, but the Shures were cleaner below 40Hz on the warble-tone track. Neither the Shures nor the Ultimates could match the bass impact of the over-ear Audeze LCD-Xes, but both the Shures and the Audezes had a touch more energy apparent in the brightness region than the Ultimate Ears. The KSE1500s also had slightly more top-octave energy than the UE 18s.

Jazz drummer Billy Drummond is one of the most inventive top-kit players I've heard; the varied characters of his cymbals in the drum solo in "Followthrough," from Harris's Rendezvous, were laid bare by the Shures, sounding like brushed and struck bronze rather than the shaped and textured white noise typically heard through cheap earbuds. This clarity was evident even with lossily compressed recordings; the subtle acoustic surrounding the acoustic guitar in Sabrina Dinan's cover of "Certain Surprise," from Johnny Boy Would Love This . . . A Tribute to . . . John Martyn (256kbps AAC file, Liaison), was readily audible.

Whether it was Esperanza Spalding's funky, multitracked soprano in "Rest in Pleasure," from her Emily's D+Evolution (24/96 FLAC from Pono Music, Concord 723828), or the creamy mezzo-soprano of Lorraine Hunt Lieberson in Brahms's song "Unbewegte laue Luft" (ALAC file ripped from CD, Wigmore Hall Live 0013), women's voices were reproduced with superbly natural tonalities. And again, the Shures' clarity impressed—I could hear deep into the mix of the stacked vocal harmonies in "We've Only Just Begun," from the Carpenters' Singles 1969–1981 (download from Acoustic Sounds), even with the Antipodes downsampling the file on the fly from DSD to 24/88.2 PCM.

On the Go
I used the KSE1500 on my subway commute, feeding it data from my iPhone 6S with the supplied Micro-B to Lightning adapter cable and securing it to the phone with one of the supplied rubber belts. The sound isolation was excellent, better even than my usual traveling companions, the Ultimate Ears 18 Pros. In his review of AudioQuest's Red and Black USB headphone amplifiers, Art Dudley had been a bit sniffy about using an iPhone as a source, but I felt that the sound quality using my iPhone's Lightning port was not significantly worse than what I hear from the mighty Antipodes server.

I also used my PonoPlayer to feed the KSE1500 amplifier's line input. When using an analog input source, bypassing the equalizer maintains a 100% analog signal path. In theory, this would be better than using the equalizer to provide the 3dB bass boost I mentioned earlier, as the Pono's intrinsic sound quality is superb. But pragmatism won out over purity: I mostly kept the EQ in-circuit.

Summing Up
I had two problems with the KSE1500 amplifier. The first is that while having inputs and outputs on opposite ends of the case makes for a logical circuit layout, it means that it can't comfortably fit in a shirt or jacket pocket. Second, though the short lengths of cable connecting each earpiece to the yoke aren't armored with the Kevlar that covers the rest of the cable, they're stiffer and heavier than those of normal IEMs. Even after several weeks of use, I would find the right earpiece, which I always inserted first, trying to remove itself as I screwed in the left earpiece, even though I'd looped its cable over my pinna. However, once both earpieces were inserted, they would stay seated in place; I could listen for two to three hours without discomfort.

Those are minor quibbles—Shure's KSE1500 is the finest-sounding in-ear monitor system I have experienced. The combination of clean lows, a palpably natural, transparent midrange, and—especially for in-ear headphones—extended highs makes it a winner.

It's fair to note, however, that at $2999 the KSE1500 system has some serious competition from more conventional headphone systems. The combination of the Audeze LCD-X planar-magnetic headphones ($1699) and Ayre Acoustics Codex ($1795) is not significantly more expensive, and as much as I enjoyed the in-ear experience offered by the Shures, I still prefer over-ear headphones for listening at home. But that doesn't mean the Shure KSE1500s don't belong in Class A of "Recommended Components." They undoubtedly do.

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Footnote 1: Ironically, when I interviewed Koss founder John Koss for the same magazine, by then called Hi-Fi News & Record Review, in November 1982, he told me that the Pro4AAs were their first "blow-up proof" headphones.