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Parent Category: Products

Category: Headphone Measurements

Created: 01 March 2022

Reviewed on: SoundStage! Solo, March 2022

I measured the Meze Audio Liric headphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 QC audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. For most measurements, the headphones were amplified using a Musical Fidelity V-CAN amplifier; I used a Schiit Magnius amplifier for distortion measurements. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the Lirics’ frequency response. Looks pretty normal, with maybe a little more midrange than usual, and with a little less bass than usual.

Here we can see the difference in the headphones’ response when a high-impedance (75 ohms) source is substituted for a typical low-impedance source (5 ohms). Normally with planar-magnetic headphones, the difference is at most 0.5dB, usually in the bass. But here the difference is substantial—a drop of about 1.5dB in the bass and lower midrange, and a boost of 1 to 3dB in the upper midrange, between 1.2 and 2.8kHz. So these headphones will sound noticeably brighter when used with high-impedance source devices, like some older (and even a few newer) solid-state amps, some pro amps, and many tube amps.

This measurement shows how sensitive the headphones’ response is to their position on the ears. The black line shows the curve I used above. Normally I pick a curve that’s somewhere in the middle, but it’s pretty clear that the one with the most treble response is “right.” Notice how the treble response falls a few dB when I moved the headphones off their optimal position? This indicates that the quasi-two-way design of the Rinaro diaphragm really works—although it also suggests that you should move the headphones around slightly when you put them on to make sure you’re getting optimal treble response.

This chart shows the Lirics’ right-channel response compared with a few other open-back models (including the Dan Clark Audio Æon 2s with perfed pads, which are the planar-magnetic headphones I’ve found come closest to the Harman curve). The Lirics are well in the ballpark of normal, with a little more midrange energy and a little less bass than Harman-curve headphones.

The spectral-decay (waterfall) response of the Lirics is very interesting. All those very-high-Q resonances you see are typical of open-back headphones, especially planar magnetics; I think it’s part of what gives them a more spacious sound. But here, the resonances cover a much broader part of the audio spectrum than usual, and are lower in magnitude than usual. Something interesting is going on here—maybe it’s that Phase-X thing at work.

This chart shows the total harmonic distortion, measured at 90dBA and 100dBA (both levels set with pink noise). The distortion is low—not the near-zero distortion I’ve measured with many planar-magnetic headphones, but it should be well below audible levels for headphones.

In this chart, the external noise level is 85dB SPL (the red trace), and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. The Lirics’ isolation is typical for headphones in this class, although a little better than most below 1kHz.

Most planar-magnetic headphones have a dead-flat impedance curve, or close to it. Not these. The impedance is generally flat, at about 22 ohms, through most of the audio range, but there’s a huge peak up to 89 ohms at 1.9kHz, with an accompanying phase swing, too—confirming that these headphones’ sound will be unusually sensitive to the output impedance of the source device.

Sensitivity of the Lirics, calculated for 30 ohms rated impedance and averaged from 300Hz to 3kHz, is 95.9dB, so you’ll need something with a few dB more oomph than a smartphone or tablet to get good performance from them.

Bottom line: Other than that funky impedance curve, and the resulting tonal balance shift with high-impedance sources, the Lirics are well within the range of normal for high-end, closed-back headphones.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 20 February 2022

Reviewed on: SoundStage! Solo, February 2022

I measured the Grado RS2x headphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 QC audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. For most measurements, the headphones were amplified using a Musical Fidelity V-CAN amplifier; I used a Schiit Magnius amplifier for distortion measurements. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the RS2xes’ frequency response. It’s quite unusual. There’s not much bass. There’s an unusual cancellation/reinforcement peak in the 250Hz region, although its bandwidth is narrow enough that it probably won’t be very audible. Now up to the treble—we’d normally see something like a broad peak centered somewhere around 2.5 to 3kHz, followed by a narrower peak centered at maybe 6 or 7kHz. But here we see narrow, high-Q peaks at 2.2 and 4kHz, followed by a broad lift between 7 and 10kHz. What’s that sound like? Hard to say without having heard more headphones that measure like this, but it’s definitely going to be trebly.

Here we can see the difference in the headphones’ response when a high-impedance (75 ohms) source is substituted for a typical low-impedance source (5 ohms). There’s about 4.5dB more bass in the 70Hz region with the high-impedance source, so I’m guessing these headphones would sound especially nice with a tube amp.

This new measurement shows how sensitive the headphones’ response is to the headphones’ position on the ears. The black line shows the curve I used above, which I found to be most typical; the other curves are taken with the headphones moved about 5mm up, down, and to each side. As expected with open-back headphones that use highly porous earpads, positioning of these on the ears isn’t very critical.

This chart shows the RS2xes’ right-channel response compared with a few other open-back models (including the Dan Clark Audio Æon 2s with perfed pads, which are the planar-magnetic headphones I’ve found come closest to the Harman curve). Clearly, the RS2x headphones have more overall treble energy and a lot less bass than the others.

That “hash”—a series of very high-Q resonances—between 2 and 4kHz is pretty standard for open-back headphones; I think it’s part of what gives them a more spacious sound. Notice also the big resonance around 250Hz—the same spot where that cancellation/reinforcement dip/peak appears in the frequency response. Maybe that peak and dip are more audible than I expected.

This chart shows the total harmonic distortion, measured at 90dBA and 100dBA (both levels set with pink noise). The distortion here is very high in the bass; I normally don’t get too concerned about distortion, but I wouldn’t recommend these for anyone who listens to music with lots of deep bass, or who likes to play their headphones loud.

In this chart, the external noise level is 85dB SPL (the red trace), and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. Like most open-back headphones, the RS2xes don’t offer much isolation.

The impedance runs between 40 and 45 ohms through most of the audio range, but with a peak at the driver resonance at 82Hz. There’s a big phase swing at that frequency, too. That’s why the bass response changes so much with a high-impedance source.

Sensitivity of the RS2x headphones, calculated for 38 ohms rated impedance and averaged from 300Hz to 3kHz, is 107.1dB, so any source device should be more than ample to drive these.

Bottom line: If you’re technically minded when it comes to headphones, there are some red flags here—a treble-heavy, bass-shy frequency response and a lot of distortion.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 10 February 2022

Reviewed on: SoundStage! Solo, February 2022

I measured the Sendy Audio Apollo headphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 QC audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. For most measurements, the headphones were amplified using a Musical Fidelity V-CAN amplifier; I used a Schiit Magnius amplifier for distortion measurements. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the Apollos’ frequency response. It’s extremely unusual; I don’t think I’ve seen a curve like this before with a set of headphones. There’s not much deep bass, the usual peak at 3kHz (which is generally thought to give headphones a sound more like that of speakers in a room) is entirely absent, and there’s a very strong, high-Q peak centered at 5.7kHz.

Here we can see the difference in the headphones’ response when a high-impedance (75 ohms) source is substituted for a typical low-impedance source (5 ohms). As is almost always the case with planar-magnetic drivers, there’s effectively no difference (maybe 0.5dB more bass with the high-impedance source) because the load is almost purely resistive.

This is a new measurement I’m adding, to show how sensitive the headphones’ response is to positioning on the ears. The black line shows the curve I used above, which I found to be most typical; the other curves are taken with the headphones moved about 5mm up, down, and to each side. Because of the wide, soft earpads, the seal of the headphones is consistent, so bass response really doesn’t vary at all. The variance in the higher frequencies is normal—high-Q resonances that shift in frequency with position, and aren’t very audible.

This chart shows the Apollos’ right-channel response compared with a few other open-back models (including the Dan Clark Audio Æon 2 headphones with perfed pads, which are the planar-magnetic headphones I’ve found come closest to the Harman curve). It’s obvious that the Apollos are way off the norm.

The “hash” above 1kHz in the Apollos’ right-channel spectral-decay plot is common for open-back planar-magnetic headphones, although its bandwidth is broader—which suggests to me these might have an unusually open and ambient sound. However, there’s a very strong resonance between 5 and 6kHz that corresponds precisely with the big peak in the frequency-response measurements, and I’d guess that’s audible, depending on the high-frequency content of whatever you’re listening to.

Here’s the THD vs. frequency chart, measured at 90dBA and 100dBA (both levels set with pink noise). The distortion here is very low and totally inaudible even at high levels.

In this chart, the external noise level is 85dB SPL (the red trace), and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. You can see that the Apollos’ isolation is typical for large, open-back headphones. I included the Dan Clark Audio Æon RT Closed headphones so you can see how a closed-back model compares.

The rated impedance of the Apollo headphones wasn’t published at the time I did these measurements, but it’s basically dead-flat at 16 ohms with very little phase shift.

Sensitivity of the Apollos, calculated for 16 ohms impedance and averaged from 300Hz to 3kHz, is 95.8dB—high enough that you can get a useable volume from most sources, but low enough that you’ll want to use a DAC-amplifier or a portable music player to get the best performance from them.

Bottom line: The frequency-response plot shows that the Sendy Apollo headphones are going to have a distinctive and unusual sound. Otherwise, these measurements are fairly typical for open-back planar-magnetic headphones.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 01 February 2022

Reviewed on: SoundStage! Solo, February 2022

I measured the Mark Levinson N⁰ 5909 headphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 QC audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. I used a Reiyin WT-04 USB Bluetooth transmitter for Bluetooth measurements, but did most of the measurements with the supplied 3.5mm-to-USB-C cable. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the N⁰ 5909s’ frequency response, measured using the cabled connection with ANC set to High. (Measurements made using Bluetooth were very similar.) There are some interesting things going on here. First is a few dB more treble energy than I expected from a Harman curve headphone, stretching out over a broad band from about 3 to 12kHz. Second is less bass than I expected, with a resonant peak centered very low, at about 18Hz, where it will have a fairly negligible effect. Most unusual is the boost in the mids, from about 600Hz to 1.5kHz. It showed up consistently with ANC on, no matter how I did the measurements. A boost in this region is unusual, and not part of the Harman curve.

Here we can see the difference in the headphones’ response in three of the available modes: ANC off, ANC High, and passive (cabled, power off). Notice how the bass response diminishes a bit with ANC off, and a lot in passive mode (neither is an uncommon result), and how that midrange bump (or lower-midrange dip, depending on how you look at it) disappears, too.

This chart shows the N⁰ 5909s’ right-channel response in ANC High mode, compared with a couple of other high-end noise-canceling models (Bowers & Wilkins PX7 Carbon Edition and DALI IO-6 headphones) and the AKG K371s, which are—or were?—said to be very close to Harman curve. Obviously the N⁰ 5909s have a lot of treble energy relative to all the other headphones—even the K371s, which in theory should measure about the same as the N⁰ 5909s, right? Having put in countless hours using the K371s for recreational listening and audio production; having mixed a CD going back and forth between the AKG K371s and my JBL 305P MkII studio monitors (also designed in accordance with Harman guidelines); and having heard reaction from another very experienced reviewer who likes the K371s but thinks the N⁰ 5909s sound too bright, I have to say—I have a hard time seeing the N⁰ 5909s as a particularly faithful representation of the Harman curve.

The N⁰ 5909s’ right-channel spectral-decay plot looks pretty clean. Those resonances at about 600 and 800Hz and 1.5kHz are unusual, but they’re fairly high-Q so I doubt they’d be readily audible.

Here’s the THD vs. frequency chart, measured at 90dBA and 100dBA (both levels set with pink noise). There’s no audible distortion here.

In this chart, the external noise level is 85dB SPL (the red trace), and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. You can see that the N⁰ 5909s’ noise canceling isn’t quite up there with the Apple AirPods Max headphones, but it’s competitive with the Bose NC700s (which, by the way, measure almost exactly the same on this test as the Bose QC45s do), and worlds better than the DALI and Bowers & Wilkins models also included on this chart. I hope Harman’s accomplishments in this area will inspire its fellow high-end competitors to put a little more effort into their noise-canceling technology.

This chart shows the effects of all the different noise-canceling and ambience/transparency modes included in the N⁰ 5909s.

Connected to the Reiyin WT-04 USB transmitter (which has aptX Low Latency), the N⁰ 5909s average about 33ms latency, low enough that it won’t cause lip-sync problems when you’re watching videos.

Bottom line: The basic engineering is very solid here, and the noise canceling is excellent, but if these headphones closely track the Harman curve, then it would seem other headphones I’ve been told track the Harman curve don’t actually track the Harman curve.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 20 January 2022

Reviewed on: SoundStage! Solo, January 2022

I measured the Soundcore Frames using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, an Audiomatica Clio 12 QC audio analyzer, and a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. I placed the Frames on the ear/cheek simulator in the same position they’d be in when used on an actual human ear. Note that because this product is physically much different from headphones or earphones, these measurements, for the most part, cannot be directly compared with our usual headphone measurements. In fact, due to the Bluetooth connection and the unusual configuration of the product, some of our usual measurements (including spectral decay and isolation) were impractical or pointless to perform. If you’d like to learn more about what our measurements mean, click here.

This chart shows the Frames’ frequency response, measured with pink noise. At first glance, this doesn’t look good. But after measuring the Frames’ response with two different real-time analyzers and with a sine sweep on the Clio 12 QC, and seeing similar results, it dawned on me that comparing this product’s frequency response with that of headphones or earphones does not reflect its performance, as the Frames do not interact with the pinnae in the same fashion. Acoustically, they work more like speakers, which is why . . .

. . . I decided to compare them with speakers, specifically a Revel Performa3 speaker (one of the flattest-measuring speakers you can buy) measured in-room at a distance of 2.5m—but using the GRAS 43AG instead of a measurement microphone. I also threw in a good set of earphones, the Meze Rai Pentas, for comparison. Now the Frames’ response doesn’t look so wacky. In fact, the Frames aren’t far off the Revels’ response, except that they don’t have any bass.

This looks different from our usual distortion chart because I couldn’t get the Clio 12 QC’s sine analyzer to track the Frames, perhaps due to the latency, or some other factor. Normally we do this measurement at 90dBA and 100dBA, but the Frames wouldn’t play that loud. Instead, I measured them at 80dBA and 75dBA. Not surprisingly considering the size of the drivers, distortion is fairly high in the bass, but I think you’d only notice it in the 200Hz range—lower than that, and the distortion harmonics are well outside the human ear’s range of maximum sensitivity, so the distortion doesn’t usually become audible until it tops about 10%. Above about 500Hz, distortion is actually pretty low.

Latency with the Frames averaged around 53ms when fed signals from a Reiyin WT-04 USB Bluetooth transmitter. That’s surprising, considering that the Frames include no low-latency Bluetooth codecs, only SBC and AAC.

One more note: I measured the Frames’ maximum volume using the same technique I use to measure max volume of kids’ headphones—with -10dBFS pink noise playing full-blast, measured in dBA. I got 86.3dBA, which is about what I typically measure from kids’ headphones that limit volume as they’re supposed to (many do not). So that means the Frames play loud enough for casual listening, but not loud enough for any kind of focused, attentive music listening.

Bottom line: I assume this is the first set of measurements published for Bluetooth glasses, so we have no paradigm by which to judge the Frames. However, they’re designed with what seems to be a theoretically appropriate response for a product like this; their glaring flaw is that the tiny speaker drivers don’t play very loud or low.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 10 January 2022

Reviewed on: SoundStage! Solo, January 2022

I measured the CCA C10 earphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. The headphones were amplified using a Musical Fidelity V-CAN amplifier. I used the supplied medium-sized silicone tips for all measurements because they fit best in the ear simulator. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the C10s’ frequency response. Nothing really remarkable here; it’s unlikely anyone would find the sound of these earphones idiosyncratic. I had worried that, given their very low price, we might see a significant mismatch in the response and sensitivity of the left and right earphones, but they match very well, never varying by more than about 1dB.

This chart shows how the C10s’ tonal balance changes when they’re used with a high-impedance source, such as a cheap laptop, some tube amps, or some professional headphone amps. As usual with balanced armatures, we see some significant differences, although in this case they’re not major—the high-impedance source produced about 1.5 to 3dB less output between 6 and 15kHz, which listeners will hear as a mild softening of the sound, but not as an unnatural coloration.

This chart shows the C10s’ right-channel response compared with various earphones, including the AKG N5005s, which are said to be the passive earphones that come closest to the Harman curve. The C10s are safely in the ballpark of “normal,” and in the mids and treble, they’re close to the Harman curve. They’re a little different in the bass, though, with 2 or 3dB more energy in the upper bass, between about 80 and 250Hz, and about 2 or 3dB less energy in the lower bass, below about 70Hz.

The C10s’ spectral-decay plot looks pretty clean, with no significant resonances in the mids and treble, and just a bit of bass resonance from the dynamic driver.

The C10s’ total harmonic distortion is pretty close to zip.

In this chart, the external noise level is 85dB SPL, and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. In the 43AG ear/cheek simulator, the C10s didn’t offer quite as much isolation as some similar models with over-ear cable routing, but they still did fine, and better than most earphones with conventional, “hang from the earphone” cable routing.

The C10s are a little unusual for earphones with balanced armatures. Normally with balanced armatures, we’d see a rise in impedance in the treble, but above about 5kHz, the impedance falls quite a bit, which is why we see the treble reduction with high-impedance sources. (The electrical phase swing is pretty mild, though.) Interestingly, the impedance is just about dead-flat up to a little over 1kHz, which leads me to guess that the dynamic driver is active up to at least 1kHz, maybe higher.

Sensitivity, measured between 300Hz and 3kHz, using a 1mW signal calculated for 32 ohms rated impedance, is 115.8dB, which means the C10s will deliver loud volume from any source device.

Bottom line: No red flags here, which is rather shocking considering the complexity and low price of this design.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 01 January 2022

Reviewed on: SoundStage! Solo, January 2022

I measured the Campfire Audio Holocene earphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. The headphones were amplified using a Musical Fidelity V-CAN amplifier. I used the supplied medium-sized silicone tips for all measurements because they fit best in the ear simulator. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the Holocenes’ frequency response. It’s definitely idiosyncratic, especially for earphones—mainly in that it’s much flatter than we normally see. Instead of a rise in the bass response below about 200Hz, the bass gradually rolls off. Instead of a strong, octave-wide, 10dB-ish peak somewhere between 2 and 4kHz, there’s a two-octave-wide bump of just 2 to 4dB. The strongest response is in a peak centered at about 9.5kHz.

This chart shows how the Holocenes’ tonal balance changes when they’re used with a high-impedance source, such as a cheap laptop, some tube amps, or some professional headphone amps. As expected with balanced armatures, which have very non-flat impedance curves, there’s a big difference in tonal balance with the high-impedance source—it gets a lot more trebly. So I wouldn’t use these earphones with, say, a tube amp, and if I used them in the studio, I’d only do so with a headphone amp that has an output impedance of 1 ohm or lower (sadly, though, the output impedance of headphone amps is rarely specified).

This chart shows the Holocenes’ right-channel response compared with the Campfire Mammoth and the AKG N5005 earphones, which are said to be the passive earphones that come closest to the Harman curve. You can see how idiosyncratic the Holocenes’ response looks, and how “normal” the Mammoths’ response looks.

This chart shows the Holocenes’ right-channel response compared again with the AKG N5005 earphones, plus the Meze Rai Pentas and the Audeze Euclids—two high-end earphones I like a lot. It’s easy to see how idiosyncratic the Holocenes’ response is. The only earphones I can recall that measure anything like the Holocenes are the Sennheiser IE 300 earphones, which I thought were pretty great for their price. Because I didn’t bring my lab computer with me on my holiday travels, I couldn’t include that measurement here, but you can see it by clicking here. As you’ll see, the IE 300s’ curve looks much like the Holocenes’ curve, but with a lot more bass.

The Holocenes’ spectral-decay plot looks clean, with no significant resonances.

The Holocenes’ total harmonic distortion is very low, especially for balanced armatures—it never rises to even 1%.

In this chart, the external noise level is 85dB SPL, and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. With the foam tips installed, the Holocenes deliver outstanding isolation, so good that I had to lower the floor of the chart from 40dB SPL to 30dB to show the curve. Even in the upper bass, where many earphones deliver little or no isolation, the Holocenes averaged about a 20dB noise reduction. If you’re on a plane, you’ll still hear some low-frequency rumble, but this is actually better isolation than most noise-canceling headphones offer—and without the boost in noise above 1kHz that many noise-canceling headphones suffer.

As usual with balanced armatures, the Holocenes show a big impedance swing—from 3 ohms in the bass up to about 18 ohms at 7.2kHz. The electrical phase shows a correspondingly large swing, which is why the Holocenes are sensitive to the output impedance of the source device. Stick to a low-impedance source device with these; I’d seek out something with 0.5-ohm output impedance or lower.

Sensitivity, measured between 300Hz and 3kHz, using a 1mW signal calculated for 5.4-ohms rated impedance, is 111.9dB. That’s very high, so the Holocenes will deliver loud volume from any source device.

Bottom line: I liked these earphones a lot, and I liked the somewhat similar-sounding, similar-measuring Sennheiser IE 300 earphones, too, so maybe this type of frequency response is a viable alternative to more typical earphone responses? Tough to say without a lot more research. Other than their idiosyncratic frequency response and their sensitivity to the output impedance of the source device (which is common with balanced armatures), the Holocene earphones appear to conform to standard engineering practice and show no technical flaws.

. . . Brent Butterworth
brentb@soundstagenetwork.com

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Parent Category: Products

Category: Headphone Measurements

Created: 20 December 2021

Reviewed on: SoundStage! Solo, December 2021

I measured the Monoprice Monolith AMT headphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 QC audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. For most measurements, the headphones were amplified using a Musical Fidelity V-CAN amplifier; I used a Schiit Magnius amplifier for distortion measurements. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

This chart shows the AMTs’ frequency response. It’s definitely idiosyncratic. Had you shown me this curve and not told me what kind of product it is, I’d have guessed it’s a single-driver speaker with a whizzer cone, rather than headphones, because it’s essentially flat up to about 1.2kHz, gets a little ragged in the mids, and gets very hashy in the treble. With open-back headphones, we’d typically see a similarly flat response to about 1kHz, then a large peak, roughly +10dB centered somewhere between 2 and 4kHz. It’s the lack of this peak that causes the de-emphasis of vocals I heard in the AMTs.

Here we can see the difference in the headphones’ response when a high-impedance (75 ohms) source is substituted for a typical low-impedance source (5 ohms). As is almost always the case with ribbon drivers, there’s no difference because the load is almost purely resistive. So other than needing a lot of power (which we’ll discuss below), the AMTs will sound consistent no matter what source device you choose.

This chart shows the AMTs’ right-channel response compared with a couple of other open-back models (including the HEDD Audio HEDDphones, which also have AMT drivers) and the AKG K371 headphones, which are said to be very close to the Harman curve. It’s clear that the AMTs are far off the norm, with much less upper-mid and lower-treble energy—although they are fairly close to the Audeze LCD-X headphones, but the LCD-Xes are also somewhat idiosyncratic.

The AMTs’ right-channel spectral-decay plot looks messy. There’s a bit of upper-bass resonance, but an unusual and strong resonance peak at 1kHz. We also see the “hash” between 2 and 6kHz that’s typical of open-back headphones, especially planar-magnetics (which use a different type of ribbon driver)—and even some hash way down around 1kHz, where I can’t remember ever seeing it before. I associate this hash with spaciousness rather than a specific tonal coloration; perhaps the extra hash in the mids is what makes these headphones sound so spacious.

Here’s the THD vs. frequency chart, measured at 90dBA and 100dBA (both levels set with pink noise). There’s no audible distortion here—I’d guess that the few little bumps that you see in the curves are just external noise and vibration leaking through the driver.

In this chart, the external noise level is 85dB SPL (the red trace), and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. You can see that the AMTs’ isolation is typical for large, open-back headphones. I included the Monoprice Monolith M565C headphones so you can see how a closed-back design compares.

The impedance magnitude, rated at 32 ohms nominal, is as flat as I’ve ever seen, right on 30.5 ohms through the whole audioband. Electrical phase is similarly flat.

Sensitivity of the AMTs, calculated for 32 ohms impedance and averaged from 300Hz to 3kHz, is just 89.9dB—so you’d better have a pretty strong amp to drive these.

Bottom line: The frequency response and spectral-decay plots indicate that the AMTs are definitely going to have their own sonic vibe.

. . . Brent Butterworth
brentb@soundstagenetwork.com