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I measured the Oppo PM-2s using a G.R.A.S. 43AG ear/cheek simulator, a Clio 10 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. Measurements were calibrated for ear reference point (ERP): i.e., roughly the point where the axis of your ear canal intersects with your palm when you press a hand flat against your ear. This is a “flat” measurement; no diffuse-field or freefield compensation curve was used. I experimented with the fit of the earpieces by moving them around on the plate of the ear/cheek simulator, and settled on the positions that gave the best bass response and the most characteristic result overall.

Frequency response

The Oppo PM-2s’ response is similar to those of most of the planar-magnetic headphones I’ve measured, with one noteworthy difference. Most planar-magnetics are flat to about 1.5kHz, above which frequency their response begins to rise. The PM-2s’ response starts rising gradually at about 500Hz, which means that their midrange should sound +3 to +5dB fuller.

Frequency response

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 significantly affect the PM-2s’ response. Thus, its tonal balance will be the same from any source device. That’s especially good for these headphones, which are designed to be used with portable devices.

Frequency response

This comparison shows that while the PM-2s produce considerably less treble energy than the HiFiMan HE-560 or HE-400i headphones, compared to the PM-1s they have roughly +2dB more treble from 2 to 3kHz, and +3dB more from 6 to 8kHz. The PM-2s seem to strike the most even tonal balance of all four models.

Waterfall

The spectral-decay (waterfall) plot shows slight resonances around 2kHz. However, these are so low in level, at about -40dB, that there’s little chance you’ll hear them, especially considering that external sounds leaking in through the open backs of the earpieces will likely be much higher in magnitude.

THD

Distortion at 90dBA from the PM-2s was almost nonexistent, except for a rise to 2% at 400Hz. At 100dBA -- an extremely loud listening level you probably couldn’t tolerate for long -- the distortion rises to 4% at 400Hz and 3% at 230Hz. (Both of these peaks correspond with peaks at the same frequencies in the impedance measurement.) I heard no distortion when I was testing the PM-2s.

Isolation

For open-back headphones, the PM-2s deliver better isolation than average. There’s no isolation below 1.5kHz, but it’s -5 to -15dB from 1.5 to 10kHz. However, most closed-back models deliver isolation in the -10 to -30dB range.

Impedance

The PM-2s’ impedance is almost flat, with a magnitude of 31 to 32 ohms and negligible phase shift. There are a couple of small impedance “bumps” that correspond to the peaks noted in the high-level distortion test.

The PM-2s’ average sensitivity from 300Hz to 3kHz at the rated 32 ohms measures 103.7dB. That’s +2.1dB more than Oppo’s PM-1s, and roughly in the average range of over-ear headphone sensitivity -- very impressive for planar-magnetic headphones.

. . . Brent Butterworth
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I measured the NuForce Primo 8s using a G.R.A.S. RA0045 ear simulator, a Clio 10 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. Measurements were calibrated for drum reference point (DRP), the equivalent of the headphones’ response at the surface of the eardrum. This is a “flat” measurement; no diffuse-field or free-field compensation curve was used. I used the medium-sized silicone eartips supplied.

Frequency response

The Primo 8s’ measured frequency response is unusual, and doesn’t correlate well with my perception of its tonal balance. The response below 1kHz is exceptionally flat, much like what I’ve measured from planar-magnetic headphones such as the Audeze LCD-3s -- most other earphones have a bump in the bass response. There’s a relatively mild peak at 2kHz, and above that the response rolls off quickly. Just goes to show that you need to be careful not to judge a set of headphones too strongly by its measured frequency response.

Frequency response

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 a large effect on the Primo 8s’ measured response. The peak at 2kHz disappears entirely, and the treble rolloff becomes more severe by about -7dB. These earphones really demand a source with a low output impedance, at the very least a higher-quality smartphone such as an iPhone or a Samsung Galaxy S; an even better idea would be a separate headphone amp.

Frequency response

Compared to the Audiofly AF140 (a design with one dynamic driver and two balanced armatures) and the Sony XBA-H1 (one dynamic driver and one balanced armature), the Primo 8s show a much flatter response up to about 5kHz, but much less treble response.

Waterfall

The decay of the Primo 8s might look a tad messy, but this is an excellent result. First, see how clean the response is from 500Hz to 1kHz. That’s rare: Few other earphones I’ve measured can stop on a dime at frequencies between 500Hz and 1kHz. There are some long resonances at 6, 8, and 14kHz, but they’re very narrow and very low in level; there’s little chance they’d be audible.

THD

The Primo 8s’ total harmonic distortion (THD) at 90 and 100dBA is modest. There’s a little, but this is an average to above-average result. At the loud-but-not-crazy-loud level of 90dBA, the THD below 1.5kHz is about 1%. Even at the very high level of 100dBA, THD is never higher than 3%.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the level of attenuation of outside sounds. Probably because of the occlusion of the G.R.A.S. ear simulator by the Primo 8’s relatively large driver enclosure, the NuForces deliver outstanding isolation. They should substantially reduce jet-engine noise, considering that they attenuate outside sound by -28dB at 100Hz and -33dB at 1kHz, and by even more between 2 and 10kHz.

Impedance

The impedance plots of balanced-armature headphones usually show pretty wild swings, and the Primo 8s are no exception. You can see here that they peak at 59 ohms at 550Hz, then fall to just 6 ohms at 20kHz. Phase response is also extreme: flat through much of the audioband, but dropping to -67 degrees at 1.35kHz. All the more reason to make sure you mate the Primo 8s with a high-quality source device.

The Primo 8s’ average sensitivity from 300Hz to 3kHz at the rated 38 ohms measured 116.6dB. That’s very high, and indicates that the Primo 8s will play loud as hell from even the cheapest, crummiest MP3 player.

. . . Brent Butterworth
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I measured the Level Ins using a G.R.A.S. Model RA0045 ear simulator, a Clio 10 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. Measurements were calibrated for drum reference point (DRP), roughly the point at the center of the listener’s eardrum (or, in this case, the center of the measurement microphone). I used the Samsungs’ medium-size memory-foam eartip because that’s what fit the RA0045 best. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.

Frequency response

The Level Ins’ response clearly shows the cause of the bright tonal balance I heard. The rise in the bass centered at 130Hz is normal, as is the peak centered at 3kHz (if perhaps a tad high), but the relative amount of energy between 5 and 9kHz is extremely high. My guess is that the balanced armature Samsung uses as a tweeter is set for a level about 5dB too high.

Frequency response

Adding 70 ohms output impedance to the V-Can’s 5 ohms, to simulate the effects of using a typical low-quality headphone amp, usually has a large effect on earphones with balanced armatures. With the Level Ins, the effect is not large in magnitude, but it kicks the treble of an already bright-sounding headphone up another 1.5dB.

Frequency response

The Level Ins’ response is quite similar to that of Sony’s XBA-H1s, which I love so much, except that the Samsungs’ output between 6 and 9kHz is 5 to 10dB higher than the Sonys’. The Audiofly AF140s show more of a “boom’n’sizzle” response than either the Samsung or Sony earphones.

Waterfall

The Level Ins have one of the cleanest spectral-decay plots I’ve seen in any type of headphone or earphone, with near-zero resonance. I redid this measurement three times and got the same result every time; other headphones measured in the same session gave me more typical results.

THD

The Samsungs’ total harmonic distortion (THD) is fairly average at 90dBA: typically, around 1%. But at 100dBA -- a very loud listening level -- the distortion is pretty high, and consistently so through much of the audioband, running 3 to 5% below 2kHz, then rising to 9% in a narrow peak centered on 4kHz.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the attenuation of outside sounds. The Level Ins’ isolation is very good for universal-fit earphones, reducing noise at 1kHz by about 15dB, and reducing noise by 35dB or more between 2.2 and 11kHz at higher frequencies. Between 5 and 12kHz, the isolation is 5 to 10dB better with the memory-foam tip than with the silicone tip.

Impedance

The Level Ins’ impedance is low overall, remaining below 10 ohms up to 1.5kHz, but is flatter than usual for earphones with balanced-armature drivers. The impedance phase response is also close to flat.

The sensitivity of the Level Ins, measured with a 1mW signal calculated for the specified 16 ohms impedance, is 98.2dB. That’s enough to get you a reasonable level from a portable audio player, but most of the earphones I measure deliver 6 to 10dB more output from the same signal.

. . . Brent Butterworth
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I measured the Brainwavz S5s using a G.R.A.S. Model RA0045 ear simulator, a Clio 10 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. Measurements were calibrated for drum reference point (DRP), which is roughly the point at the center of the eardrum (in this case, the center of the measurement microphone). I used the largest silicone eartips because those best fit the RA0045. This is a “flat” measurement; no diffuse-field or free-field compensation curve was applied.

Frequency response

The S5s’ frequency response shows that they’re something a little different. See that big peak in the response centered at 6.8kHz? Move it down to about 3kHz, drop it by about 5dB, and you’d have a totally normal, “by the book” earphone response. But as you can see, the response is very smooth through most of the audioband, and the average amount of treble energy pretty well balances the average amount of bass energy.

Frequency response

Adding 70 ohms to the V-Can’s 5-ohm output impedance, to simulate the effects of using a typical low-quality headphone amp, has the completely insignificant effect of elevating the S5s’ bass response by 0.5dB at 10Hz.

Frequency response

It’s interesting to see how similar the response of the Brainwavz S5s is to that of the NAD Viso HP20s, the earphones that so closely resemble it. But there are differences: the NADs have a little more bass, a little less treble. The Sony XBA-H1s have a flatter overall response than either competitor, but considerably less treble energy above 5kHz.

Waterfall

The S5s produce an extremely clean spectral-decay plot, with no significant resonances except a couple of very well-damped ones at 9.5 and 13kHz, which correspond with the response peaks that show up in the frequency response.

THD

The S5s’ total harmonic distortion (THD) is very, very low. At 90dBA, the distortion basically disappears into the noise floor at frequencies above 100Hz. At 100dBA, it rises to about 2.2% at 20Hz -- still exceptionally low, especially considering that 100dBA (measured with pink noise) is an extremely loud level.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The S5s’ isolation is outstanding for universal-fit earphones, reducing noise at 1kHz by about 30dB, and reducing noise at about 3kHz by as much as 47dB. Note that your results may not be as good, depending on the size and shape of your ear canals and on the eartips you use.

Impedance

The S5s’ impedance is fairly low, running almost dead flat at 17 ohms. The impedance phase response is essentially flat up to 10kHz.

The sensitivity, measured between 300Hz and 3kHz with a 1mW signal and calculated for the rated impedance of 16 ohms, is 105.1dB. That’s about average, and should be plenty enough to get you ample volume with any portable device.

. . . Brent Butterworth
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I measured the Oppo PM-1 headphones using a G.R.A.S. 43AG ear/cheek simulator, a Clio 10 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. Measurements were calibrated for ear reference point (ERP), which is roughly the point where the axis of your ear canal intersects with your palm when you press your hand flat against your ear. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. I experimented with the fit of the earpieces by moving them around on the plate of the ear/cheek simulator, settling on the positions that gave the best bass response and the most characteristic result overall.

Frequency response

The PM-1s measure much like the other planar-magnetic headphones I’ve tested. It’s common for headphones to have a peak at 3kHz, which is thought to make headphones sound more like speakers in a real room -- but this peak is mild, at about +6dB (a lot of them are more like +12dB). Another mild, and very narrow, peak occurs at 8.8kHz.

Frequency response

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 real effect on the PM-1s. That might not be a big deal with most planar-magnetics -- few are designed to be driven by portable devices -- but it’s important with the PM-1s. It suggests you won’t hear a change in tonal balance when you switch from a good high-end amp to a portable source device.

Frequency response

In this comparison with two other planar-magnetic headphone models, Audeze’s LCD-X and HiFiMan’s HE-6, the PM-1s have the flattest-looking response, which suggests they will probably have a fairly flat sound and won’t be an outlier.

Waterfall

The spectral-decay (waterfall) plot shows no major or troublesome resonances.

THD

The PM-1s’ total harmonic distortion (THD), at 90 and 100dBA, is generally very low, which is the norm for planar-magnetic headphones, although there is a little band of distortion between 200 and 300Hz. The important number here is the 90dBA result; that’s a usable (if quite loud) listening level, and there the distortion is just 2%, which is barely audible. At 100dBA, a level useful only for measurement comparisons, the distortion is 6%.

Isolation

For what it’s worth, the PM-1s deliver better isolation than any other open-back planar-magnetic I’ve measured: -16 to -20dB above 4kHz. Still, though, as with all open-back ’phones, there’s no attenuation of sound below 1kHz.

Impedance

The PM-1s’ impedance is effectively flat, with a magnitude of 32 ohms (same as the spec), and negligible phase shift.

The Oppos’ average sensitivity from 300Hz to 3kHz at the rated 32 ohms measures 101.6dB. That’s excellent for a planar-magnetic, although about -2 or -3dB below what typical over-ear headphones might deliver.

. . . Brent Butterworth
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I measured the KEF M200 earphones using a G.R.A.S. RA0045 ear simulator, a Clio 10 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. Measurements were calibrated for drum reference point (DRP), the equivalent of a earphone’s response at the surface of your eardrum. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. I used the medium-size silicone tips that I received with the review samples. Because of the large diameter of the M200s’ sound tubes, I had to press lightly with a fingertip to get a good seal in the ear simulator.

Frequency response

There’s some disagreement about what constitutes a good frequency-response measurement for earphones, but I think all experts would agree that this one looks unusual. That dip in the midrange centered at about 900Hz is fairly common, but here it’s about -6dB lower than I usually measure. The treble response above 4kHz is cleaner than I’m used to seeing, with just one strong, narrow peak at 8kHz instead of the usual multiple, spread-out peaks.

Frequency response

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 affect the M200s’ performance, but only in a band of about one-third of an octave centered at 13kHz, where the response drops about -4dB with the high-impedance source. This would be audible to most people, although whether you’d perceive it as an improvement in or a degradation of the sound would depend on your hearing and taste.

Frequency response

This comparison of the M200s with NAD’s Viso HP20 and Bowers & Wilkins’ C5 earphones suggests that the KEFs are the least likely to be perceived as having a flat response, thanks to that big midrange dip. To my ears (and those of many other reviewers), the Viso HP20s sound fairly flat, the C5s a little on the bassy side.

Waterfall

The spectral-decay (waterfall) plot looks clean except for one very strong resonance at 4.8kHz. But given the narrowness of this resonance, I expect it would be audible only with certain pieces of music, and then only fleetingly.

THD

The total harmonic distortion (THD) at 100dBA is a little high relative to the best earphones I’ve measured, hitting about 3% at 1kHz, but given that 3% isn’t such a high distortion level in transducers, and that 100dBA is an extremely loud playback level, I doubt you’d encounter this flaw in normal listening.

Isolation

In this chart, the external noise level is 75dB SPL; numbers below that indicate the degree of attenuation of outside sounds. Thanks probably to its big, fat 6.8mm sound tubes, the M200s deliver good isolation from outside sounds. In the key band between 100Hz and 1kHz, the reduction ranges from -11dB at 100Hz to -27dB at 1kHz, and even better at higher frequencies.

Impedance

The impedance magnitude is almost dead flat (if unusually low) at 12.5 ohms; the impedance phase is also almost entirely flat.

The M200s’ average sensitivity from 300Hz to 3kHz at the rated 12 ohms measures 96.7dB, which is -7 to -10dB lower than I measure with typical earphones. That’s because of the big midrange dip. With the M200s, you’ll probably need to turn your smartphone up to nearly maximum volume.

. . . Brent Butterworth
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I measured the performance of the HP50 headphones 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. Measurements were calibrated for ear reference point (ERP), which is roughly the point in space where, with your hand pressed against your ear, your palm intersects the axis of your ear canal, and roughly the place where the front of the headphone’s driver grille will sit when you wear the ’phones. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. I experimented with the position of the earpads by moving them around slightly on the ear/cheek simulator, and settled on the positions that gave the best bass response and the most characteristic result overall.

Frequency response

The HP50s’ frequency response shows a strong peak centered at 2.8kHz (as one often finds in headphone response measurements), and a broad, strong boost between 6 and 10kHz. This is similar to the typical diffuse-field equalization employed in many headphones. 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, produces a slight increase (about 1dB) in bass response between 40 and 90Hz.

Compared with most of the headphones I’ve measured, the HP50s’ response looks pretty flat. The treble does show some boost, but it’s slight -- typically, 1 to 2dB relative to the bass -- and very broad, covering the entire band between 2 and 8kHz. So the treble should be pretty much uncolored, and that rise could have the result of making the HP50s sound a tad bright (or the bass a tad damped). Note the slight difference in bass response, probably due to the fit of the different earpieces on the ear/cheek simulator; these are the best results I was able to achieve.

Frequency response

When I tried increasing the source impedance from 5 to 75 ohms, to simulate the effect of using a low-quality source device such as a typical laptop computer, there was no notable change in frequency response.

Frequency response

You can see from the chart above how similar the HP50s are to Paul Barton’s other model of passive over-ear headphones, the PSB M4U 1. The HP50s produce a bit more low bass, but the difference you’ll probably notice most is the HP50s’ roughly -3dB dip in response around 1kHz. According to Barton, this results in not an audible dip in midrange sound, but an increased sense of the headphones sounding like real speakers in a real room. In comparison, the Bowers & Wilkins P7 headphones produce less bass but have a relatively strong peak around 2.8kHz, which means they should sound somewhat brighter, with less bottom-end kick.

Waterfall

The spectral-decay (waterfall) plot shows a couple of strong but very narrow (and thus probably inaudible) resonances, at 1.8 and 2.9kHz.

THD

The total harmonic distortion (THD) is extremely low at 100dBA, and remains less than 2% at 20Hz. 

THD

The spectrum of a 500Hz sinewave shows that, even at 100dB, all of the distortion harmonics are well below -70dBFS (0.03%) and are thus inaudible.

Isolation

For passive headphones, the HP50s do a great job of attenuating external sounds. They reduce external noise by -15dB at 1kHz, and by as much as -40dB at 8kHz. They won’t do much for you on a plane, though; as with most passive closed-back headphones, there’s no significant reduction of noise below 200Hz, which is where jet engines produce most of their noise.

Impedance

The impedance averages 37 ohms, and the magnitude and phase are both close to flat.

The HP50s’ average sensitivity from 300Hz to 3kHz, at the rated impedance of 32 ohms, measures 106.3dB with a 1mW signal.

. . . Brent Butterworth
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I measured the Bowers & Wilkins P7 headphones using a G.R.A.S. Model 43AG ear simulator, a Clio 10 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. Measurements were calibrated for the ear reference point (ERP) -- roughly the point in space where, with one palm pressed against your ear, the axis of your ear canal intersects with your palm. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.

Frequency response

The P7s’ frequency-response curve correlates fairly well with what’s generally accepted as a subjectively flat headphone response. There’s a little extra energy at 2.3 and 7kHz, corresponding to the lower and mid-treble regions, which suggests that the treble response will be strong; you should get a heightened sense of detail.

Frequency response

Adding 70 ohms of output impedance to the V-CAN’S 5-ohm output impedance, to simulate the effects of using a typical low-quality headphone amp, has a noticeable but mild effect on the P7s’ response: a slight bass boost (typically, +1.5dB) when the P7s are used with a higher-impedance source device, such as a typical laptop computer or cheap smartphone. This will result in slightly more perceived bass, and probably a slightly softer, smoother treble response. But considering the P7s’ comparatively strong treble, they should sound good even with low-quality sources.

Frequency response

Compared to two well-regarded over-ear headphones, the ADL H118 and the Focal Spirit Classic models, the P7s have a flatter response below 1kHz, but a notably stronger treble response.

Waterfall

The P7s have a nice, clean decay, the only significant resonance showing up in the vicinity of 900Hz. And even that’s at -30 to -40dBFS, and lasts only about 10 milliseconds.

THD

The P7s’ total harmonic distortion (THD) at 90 and 100dBA is generally fairly low, but, as with many headphones, it rises below 100Hz, reaching 8.5% at 20Hz at 100dBA. Note, though, that this is a very loud listening level.

Isolation

In this chart, the external noise is at an SPL of 75dB; the numbers below that level indicate the attenuation of external sounds. For an over-ear, sealed-back headphone, the P7s’ isolation is a little better than average, reducing noise at 1kHz by about 14dB, and by 25 to 30dB at higher 

Impedance

The P7s’ impedance is basically flat, with a little rise in the bass. That’s why its bass response in the 5 vs. 75 ohms response chart shows a slight bump upward with high-impedance (75 ohm) source devices. The impedance phase response is also close to flat.

The B&W P7s’ sensitivity, measured with a 1mW signal calculated for the rated 22 ohms impedance, is 101.7dB. That’s moderate, suggesting that the P7s will play loud, but not real loud, from most smartphones and portable audio players.

. . . Brent Butterworth
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