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.
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.
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.
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.
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.
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.
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
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
brentb@soundstagenetwork.com
To measure the Focal Spirit Classic headphones, I used my usual rig: 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): roughly, the point in space where your palm intersects with the axis of your ear canal when you press your hand against your ear; and, roughly, the place where the front of the driver grille will sit when you wear the headphones. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. I experimented with the positions 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.
Although there’s still no broad agreement on what measurement of headphone frequency response would correspond to a perceived flat response, the Spirit Classics’ measured response pretty much squares with what I’ve found most people to perceive as flat. There’s a typical response bump at 3.1kHz, to accommodate the natural resonance of the human ear canal, and a strong measured response out to 9kHz. Only the bass looks a bit deficient, but this curve is actually quite similar to measurements I’ve taken of several respected audiophile models.
Adding 70 ohms to the V-Can’s output impedance of 5 ohms, to simulate the effects of using a typical low-quality headphone amp, produces no significant difference in response. Considering that the Spirit Classics’ sensitivity is fairly high, you should be able to get plenty of output and decent sound from anything with a headphone jack.
Compared to the ADL H118 and Bowers & Wilkins P7 headphones (both shown in the accompanying chart), the Spirit Classics have a little more bass and a little less treble, but their tonal balance looks flatter than either competitor’s.
The Focals’ spectral decay (waterfall) plot shows a very strong resonance at 800Hz -- which happens to correspond with a dip in the measured frequency response right at that frequency. However, this is a fairly narrow resonance, so I suspect it would be only occasionally audible.
Total harmonic distortion (THD) is practically nonexistent, even at 100dBA.
The spectrum of a 500Hz sinewave shows that the most audible distortion artifact at 100dB is the third harmonic (1500Hz), at about -56dB (about 0.16%).
The Spirit Classics attenuate external sounds pretty well for passive, closed-back headphones, reducing outside noise by -14dB at 1kHz and by as much as -32dB at higher frequencies. There’s no reduction in the “jet-engine band” below 200Hz, though.
The Focals’ impedance is mostly flat, averaging 33 ohms below 10kHz.
The average sensitivity from 300Hz to 3kHz at the specified impedance of 32 ohms measures 104.8dB with a 1mW signal.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the Audiofly AF140s 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 employed. I used the medium-size silicone tips supplied, and also tried the medium-size foam tips. There was only a slight difference in response, so except for the isolation measurement, I stuck with the silicone tips.
Compared with other earphones I’ve measured, the Audiofly AF140 has a relatively (but not grossly) strong peak at 2.5kHz, and a little bit (relatively speaking) of a dip in the mids at around 800Hz, but overall, the response looks fairly flat.
Adding 70 ohms to the V-Can’s output impedance of 5 ohms, to simulate the effects of using a typical low-quality headphone amp, has a big effect on the AF140’s performance. While the balance of bass to treble is pretty much flat with a low-impedance (i.e., high-quality) source device, the tonal balance will radically change if a high-impedance source (e.g., a cheap smartphone, tablet, or computer) is used: the sound will become much bassier and much duller in the highs. This is due to the big impedance swing you can see elsewhere in these measurements.
This comparison of the AF140 with the NuForce Primo 8 (a multidriver, balanced-armature earphone) and the Sony XBA-H1 (a hybrid design with one dynamic and one balanced-armature driver) shows that the Audioflys’ overall tonal balance looks fairly flat; their only real anomaly is that midrange dip.
Except for a long but very low-level resonance at 4kHz and a fairly strong but brief resonance at 13kHz (which also shows up in the frequency-response curves), the AF140’s decay looks pretty clean.
The AF140s’ total harmonic distortion (THD) at 90 and 100dBA is relatively high. Granted, these are very loud levels, but most of the earphones I’ve measured produce no more than a few percent THD on these tests. Even at 90dBA, a loud but still realistic listening level, the distortion hits 3% at 800Hz. This will be very audible, given that the main distortion harmonics will be at 1.6 and 2.4kHz, where human hearing is very sensitive. At 100dBA -- a level impracticable for listening but that, in these measurements, does tend to separate great from so-so products -- the distortion hits 14% at 800Hz.
The spectrum of a 500Hz sinewave confirms that AF140s’ distortion is relatively high. Even at the loud but not crazy-loud level of 90dBA, the levels of second- and third-harmonic distortion are almost equal, at about -28dB.
In this chart, the external noise level is at an SPL of 75dB; the numbers below that indicate attenuation of outside sounds. The AF140s don’t deliver much isolation in the “jet engine” band down low, but their isolation is fantastic at higher frequencies. Between 100Hz and 1kHz, the reduction ranges from -5dB at 100Hz to -17dB at 1kHz. But look at the 4kHz result: down -45dB! So while the AF140s probably won’t do a lot to damp the drone of jet engines, they’ll definitely block much of the hissing of the ventilation system, and probably help quiet screaming kids (for you, at least).
The AF140s’ impedance curve is a wild ride. That’s not uncommon for balanced-armature earphones, but still, dropping from 74 ohms at 20Hz to 16 ohms at 11kHz is a pretty big swing. However, the impedance phase is fairly flat.
The AF140s’ average sensitivity from 300Hz to 3kHz at the rated 38 ohms measures 106.2dB -- enough to play loudly with practically any source device.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the performance of the Audeze LCD-X 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 your palm intersects with the axis of your ear canal when you press your hand against your ear, and the place where the front of a driver grille sits when you wear the headphones. This is a “flat” measurement; no diffuse-field or free-field compensation curve was used. I experimented with the positions 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.
The LCD-X’s frequency response is about what I’m used to seeing from planar-magnetic headphones: dead flat from about 50Hz to 1.2kHz, with a peak at around 2.5kHz, which is typical. The only anomaly is that the treble response is a little less than I’m used to seeing from planar magnetics. Note the difference in bass response between the right and left channels: Each represents the best measurement I was able to get in more than a half-dozen tries; however, because slight differences in the seal of the earpads against the ear/cheek simulator can have huge effects on the measured response, I have no way of knowing if this represents an actual imbalance or a measurement artifact. Regardless, I didn’t notice any difference in the sounds of the left and right channels in my listening to the Audezes.
Because planar-magnetic drivers have an almost purely resistive (i.e., flat) impedance curve, their tonal balance rarely changes with different source devices. I simulated a change in source device by adding 70 ohms output impedance to the V-Can’s 5-ohm output impedance, for a total of 75 ohms, which is typical of the low-quality headphone amps built into laptops and cheap MP3 players. As you can see, there’s no significant difference in the Audezes’ response.
This chart compares the LCD-X with Audeze’s top model, the LCD-3, and with Oppo Digital’s new PM-1 planar-magnetic headphones. You can see that the LCD-X and LCD-3 headphones are practically identical up to 7kHz, but that the LCD-3s have 4 to 6dB more output between 7 and 9kHz. This should, at least in theory, give the LCD-3s a slightly brighter sound, and probably an enhanced sense of “air” and spaciousness. The Oppo PM-1s have a flatter response, but less energy in the lower treble.
The spectral-decay (waterfall) plot shows a couple of mild resonances in the vicinities of 800Hz and 1.4kHz, but their duration and bandwidth are so low that you probably wouldn’t notice them.
This plot of the LCD-Xs’ total harmonic distortion vs. frequency is one of the cleanest I’ve seen. The orange trace is taken at 100dBA, a higher level than most people could stand to listen to for more than a few seconds; even so, distortion is practically nonexistent.
This spectrum plot of the distortion harmonics, again taken at very loud levels, provides still more evidence that these are super-clean-sounding headphones.
Open-back planar-magnetic headphones provide little or no isolation from outside sounds, and the LCD-Xs almost none at all -- along with your music, you’ll hear everything going on around you.
The LCD-Xs’ impedance magnitude is essentially flat at 22 ohms (which matches the specification), and the impedance phase shift is near zero.
The LCD-Xs’ average sensitivity from 300Hz to 3kHz, at the rated 22 ohms, measured 101.5dB, which is very high for planar-magnetic headphones.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the NAD Viso HP20s 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 employed. Except as noted, I used the HP20s’ medium standard eartips. I experimented with the fit of the eartips and earpieces by inserting and reinserting them in the RA0045, and settled on the positions that gave the best bass response and the most characteristic result overall.
Earphones don’t always sound like they measure, but the HP20s sure seemed to. (It probably helps that designer Paul Barton and I use similar measurement gear.) There’s a mild bass boost centered at 40Hz -- exactly as I heard -- and a lot of energy between 4 and 6.5kHz, which is surely why I occasionally perceived the sound as bright.
Adding 70 ohms to the V-CAN’s output impedance of 5 ohms, to simulate the effects of using a typical low-quality headphone amp, had no effect on the HP20s’ response above 25Hz. So as you plug them into, variously, your smartphone, your laptop, and your high-end headphone amp, the HP20s’ tonal character shouldn’t change.
This comparison of the HP20s with Bowers & Wilkins’ C5 and RBH’s EP-1 suggests that, at least alongside those esteemed competitors, the HP20s’ response is relatively flat, with a more even balance of bass and treble than the two other models. Note the RBHs’ extra bass, and the B&Ws’ relative lack of energy in the treble.
The spectral-decay (waterfall) plot shows a fairly strong resonance at 5kHz and a weaker one at 6kHz, both of which correlate with the response peak in the treble.
The HP20s’ total harmonic distortion (THD) at 90 and 100dBA is very, very low
The spectrum of a 500Hz sinewave suggests that if you push the HP20s really, really loud, you’ll get a roughly equal mix of second- and third-harmonic distortion. But if you play the HP20s at levels high enough to make it audibly distort, you won’t have much hearing left for long.
For reasons I can’t explain, the HP20s delivered superb isolation at the lower frequencies of the audioband, where it really matters (and where jet engines roar): from -10 to -28dB, up to 4kHz. At higher frequencies, however, their isolation was less than the norm.
The HP20s’ impedance magnitude was effectively flat at 16.5 ohms; the impedance phase was also effectively flat.
The HP20s’ average sensitivity, from 300Hz to 3kHz at the rated 16 ohms, measured 106.9dB.
All things considered, nothing in these measurements suggests even the slightest reason for concern.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the performance of the Audeze LCD-3 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 your palm intersects with the axis of your ear canal when you press your hand against your ear, and the place where the front of the headphones’ driver grilles will sit when you wear them. This is a “flat” measurement: no diffuse-field or free-field compensation curve was used. 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.
The LCD-3’s frequency response is textbook for planar-magnetic headphones, with essentially flat response below 1kHz, a strong response peak at 2.8kHz, and minor response peaks at 6 and 8.5kHz. This generally conforms to the typical diffuse-field equalization used in many headphones.
Thanks to the resistive impedance of the planar-magnetic driver, 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 had zero audible effect. I could measure a difference only below 20Hz.
This chart compares the LCD-3 with another highly regarded planar-magnetic headphone, the HiFiMan HE-6, and a respected, new dynamic open-back headphone, the AKG K712. The responses of all three are similar below 1kHz, but between 3.3 and 6.5kHz the HE-6 has a lot more output than the LCD-3, which should make it sound brighter than the Audeze. The K712 should sound substantially different from its planar-magnetic competitors, with less output in the octave between 2.5 and 5kHz.
The spectral-decay (waterfall) plot shows a series of strong but narrow resonances between 2 and 4kHz.
For logistical reasons, I was unable to run a 90dB SPL distortion measurement on the LCD-3, but considering that the 100dB measurement shows near-zero distortion, the 90dB result could only be better.
The LCD-3 being an open-back planar-magnetic headphone, it provides almost no isolation from outside sounds. There is no significant attenuation below 2kHz, and only -5dB of isolation at 5kHz.
The impedance magnitude is essentially flat at 47 ohms, and the impedance phase is at 0 degrees through almost the entire audioband, rising to +5 degrees at 20kHz.
At its claimed impedance of 45 ohms, the LCD-3’s average sensitivity from 300Hz to 3kHz measured 94.5dB.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the Sony XBA-H1s using a G.R.A.S. RA0045 ear 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 drum reference point (DRP): the equivalent of a headphone’s response at the surface of your eardrum. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed. Except as noted, I used the XBA-H1s’ medium standard tips. I experimented with the fit of the tips/earpieces by inserting and reinserting them in the RA0045, settling on the positions that gave the best bass response and the most characteristic result overall.
For an earphone, the XBA-H1s’ frequency response looks pretty flat overall, with perhaps a slight excess of energy between 3 and 5kHz. (Almost all headphones have a peak or two somewhere in this region.)
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, tilts up the XBA-H1s’ response, dropping their bass output -1dB at 80Hz and kicking up the treble +5dB at 10kHz. Given my perception that the XBA-H1s sounded ever-so-slightly bright, even with the low-impedance output of my iPod Touch, I’d recommend using these headphones only with Apple or higher-end Android products, or with a separate headphone amplifier that has a low output impedance, preferably under 20 ohms.
Above 500Hz the XBA-H1s are fairly similar to the Audiofly AF78 hybrid and the RBH EP1 dynamic earphones, but the Sonys’ bass response looks much more neutral.
The spectral-decay (waterfall) plot looks very clean, with no notable resonances.
Total harmonic distortion (THD) at 100dBA is quite moderate overall, but with a little 10% peak centered near 3kHz; this drops to 3% at 90dBA. Considering that the first and second distortion harmonics of 3kHz are at 6 and 9kHz, respectively, your sensitivity to this distortion will vary inversely with your age, and more so if you’re male. (Translation: Your ability to hear higher frequencies decreases with age, especially in males.)
The spectrum of a 500Hz sinewave shows that the second and third distortion harmonics are nearly equal in level. It’d be nicer to see more second and less third, because odd-order harmonics are more objectionable, but the distortion is moderate anyway, so no big deal.
There’s not much isolation in the bass -- only about -8dB at 100Hz -- but it improves dramatically as the frequency rises: to -20dB at 1kHz, and about -30dB from 2.5 to 8kHz. That’s with the standard tips. The noise-isolating tip didn’t make a big difference, at least not when used in the cold-steel cone of the RA0045 ear simulator. It gave me an improvement of -8 to -15dB, but only at high frequencies: from 3 to 14kHz. I wonder how the results vary when the tips are inserted into a soft, warm ear canal.
The XBA-H1s’ impedance rises dramatically with frequency, running about 32 ohms below 1kHz, then rising to 186 ohms at 20kHz. The impedance phase rises similarly; it’s right near 0° at low frequencies, but jumps to +65° at 20kHz. Impedance swings at high frequencies are common in balanced-armature drivers, but I’d never before seen one so extreme. This causes the shift in tonal balance when the XBA-H1s are used with source devices that have a high output impedance.
The Sony XBA-H1s’ average sensitivity from 300Hz to 3kHz at the rated 40 ohms was very high, at 109.3dB.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the performance of the ADL H118 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) -- roughly, the point in space where your palm intersects with the axis of your ear canal when you press your hand against your ear, and the place where the front of the headphone’s driver grille will sit when you wear the headphone. This is a “flat” measurement; no diffuse-field or free-field compensation curve was used. 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.
The H118s’ frequency response shows the strong peak centered at 2.8kHz that’s often found in headphone response measurements, as well as a broad, strong boost between 6 and 10kHz. This is similar to the typical diffuse-field equalization used 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 produced a slight increase (about +1dB) in bass response between 40 and 90Hz.
You can see in the chart above that the ADLs’ tonal balance and overall response are quite similar to those of the B&W P7s -- which most reviewers liked. Compared with PSB’s M4U 1 headphones, which some consider to be a reference for a $300 passive design, the ADLs have notably less bass, a little more energy in the 3kHz range (i.e., closer to the classic diffuse-field curve used for many headphones), and less energy in the 8-10kHz range (so probably a bit less “air” than the PSBs).
The spectral-decay (waterfall) plot shows a very clean decay above 500Hz, with no noticeable resonances.
The H118s’ total harmonic distortion (THD) at 100dBA is rather high in the bass, measuring 5 to 8%, and 2 to 3% at 90dBA. You’d probably notice this if you play music with lots of bass at high volumes.
The spectrum of a 500Hz sinewave shows that the distortion is primarily third harmonic (-55dBFS), with a strong presence of second harmonic (-66dBFS) -- it shouldn’t sound terribly objectionable.
Isolation is a tad less than average for over-ear headphones: -4dB at 1kHz, and typically -20dB at higher frequencies.
The impedance runs about 72 ohms, and the impedance phase is essentially flat.
The H118’s average sensitivity from 300Hz to 3kHz, at the rated 68 ohms, measured 103.9dB.
. . . Brent Butterworth
brentb@soundstagenetwork.com
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