I measured the Viso HP70s using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 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 amp. On the Model 43AG, I used the original G.R.A.S. KB0065 simulated pinna for most measurements as well as the new KB5000 pinna for certain measurements, as noted. For tests in Bluetooth mode, I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio 10 FW to the headphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The HP70s’ frequency response, shown here with noise canceling (NC) on in Bluetooth mode, looks mostly conventional. The squarish bump in the bass response below 150Hz corresponds pretty closely to the recommended bass response of the so-called “Harman curve,” which research shows is what most listeners prefer in headphones. The peak centered at 2.8kHz is standard for headphones because it makes them sound more like speakers in a room, though in this case it’s a little on the low side relative to the bass bump. Many headphones have a dip at about 5kHz, and another smaller peak centered somewhere around 8kHz, but the HP70s show a smoother, more gradual rolloff above the 2.8kHz lower-treble peak. This suggests that these headphones may sound a little on the mellow side.
This chart shows how the HP70s’ frequency response differs when in Bluetooth with NC on and off, and in wired mode with power off. The NC has very little effect on frequency response, which is an excellent and, sadly, rare result. Wired mode does change the sound, but it actually pushes the response closer to what I see in average headphones -- while it will sound different from the Bluetooth and/or NC modes, it probably won’t sound jarringly different.
This chart shows the HP70s’ measured right-channel frequency response with BT and NC on, measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I’ll eventually be switching to because it more accurately reflects the structure and pliability of the human ear. (I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I begin using only the new pinna.)
This chart shows that the HP70s are more or less in the same ballpark as their sister model, PSB’s M4U 8 (also designed by Paul Barton), and Sony’s WH-1000XMK2; here, the clear outliers are Bowers & Wilkins’s PXes. Note, though, that the HP70 is the only model shown that doesn’t have a dip in the 5-6kHz range.
This spectral-decay (waterfall) chart shows the results in wired mode; the latency introduced by Bluetooth prevented me from getting a reliable measurement in that mode. You can see some minor resonances at about 2, 4, 5, and 7kHz, but they’re well damped and shouldn’t be very audible, if at all. The little bit of resonance creeping in down around 200Hz may correspond with the bass bump below 150Hz.
Because of latency problems with Bluetooth, I had to measure the total harmonic distortion (THD) of the HP70s in wired mode. Distortion is negligible; even at the very loud level of 100dBA, there’s only about 3% distortion in the bass -- that might seem as if it would be audible, but the generally accepted threshold for the audibility of harmonic distortion in bass frequencies is 10%.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. Paul Barton told me that, compared with the M4U 8s’ NC chip, the HP70s’ NC chip is better at some frequencies and worse at others. This chart bears out that claim: the HP70s look better from about 90 to 150Hz, but the M4U 8s clearly outperform the HP70s from 150 to 1000Hz -- and approach the high standards set by the Sony and Bose models also shown here.
The HP70s’ impedance magnitude in wired mode is nearly flat in magnitude and phase, averaging about 38 ohms with negligible phase shift.
The sensitivity of the HP70s, measured from 300Hz to 3kHz with a 1mW signal calculated for 32 ohms impedance, is 110.3dB in wired mode with power off. They’re sure to deliver all the volume you could want if you’re watching a movie on an airplane and the battery runs down.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the ATH-ANC700BTs using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 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 amp. On the Model 43AG, I used the original G.R.A.S. KB0065 simulated pinna for most measurements as well as the new KB5000 pinna for certain measurements, as noted. For tests in Bluetooth mode, I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio 10 FW to the headphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The ATH-ANC700BTs’ frequency response, shown here with noise canceling (NC) on in Bluetooth mode, looks strange for a couple of reasons: the abrupt dip in the midrange and lower treble between 800Hz and 3.5kHz, and a lower/mid-treble response peak centered at 5kHz instead of the more usual 3kHz. It seems unlikely that this tuning would result in a natural, uncolored sound.
This chart shows how the response of the ATH-ANC700BTs differs when in Bluetooth with NC on, and in wired mode with NC on and power off. The responses with NC on don’t differ dramatically from Bluetooth to wired mode except in the bass, where there’s a peak at 65Hz. The wired mode with power off looks even stranger, with a huge peak centered at 500Hz -- something I’ve never seen before. Incidentally, measuring the wired connection with 70 ohms impedance added to the V-CAN’s 5-ohm output impedance produced a mild tilt in tonal balance, boosting bass and cutting treble by 1dB each.
This chart shows the ATH-ANC700BTs’ measured right-channel frequency response with BT and NC on, measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I’ll eventually be switching to because it more accurately reflects the structure and pliability of the human ear. I’m including this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I completely switch to the new pinna.
The ATH-ANC700BTs’ big midrange/lower-treble dip is put in perspective by this chart, which compares them with two other BT/NC models, the PSB M4U 8s and Sennheiser HD 4.50 BTNCs.
This spectral-decay (waterfall) chart shows the results in wired mode with NC on; the latency introduced by Bluetooth prevented me from getting a reliable measurement in that mode. There’s a lot of resonance below 1kHz, which corresponds with the shelf in the frequency response below 800Hz. There are also some unusual, extremely narrow (high-Q) resonances in the treble, but they’re so narrow, and so low in amplitude (-40dB), that I can’t imagine they’d be audible. (The black boxes in the lower left corner of the graph are there because the gating on this measurement reduces resolution at low frequencies.)
Because of latency issues with Bluetooth, I had to measure the total harmonic distortion (THD) of the ATH-ANC700BTs in wired mode; this measurement was taken with NC on. Distortion below about 150Hz is much higher than I’m used to seeing, even at 90dBA. I normally caution that, because my measurements are taken at loud levels, most of the distortion you see in the measurements probably isn’t audible at normal listening volume -- but I suspect that the bass distortion visible here might be audible. I measured a couple of other headphones at the same time and got normal measurements on this test. I also confirmed this result by shutting down and restarting the Clio analyzer, recalibrating the levels, and repeating the measurements, but the result was essentially the same.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. To interpret this, keep in mind that jet-airliner cabin noise tends to be loudest between 80 and 1000Hz, and the loudest part of that band is the low-frequency hum between 80 and 200Hz. The ATH-ANC700BT reduces noise pretty well, by about -15dB, between 80 and 200Hz, but doesn’t do much from 200 to 1000Hz -- which corresponds with Rad’s comment about the NC seeming to shift the noise up into the midrange.
The ATH-ANC700BTs’ impedance magnitude in wired mode averages 32 ohms with power off (full passive mode) and about 130 ohms with NC on. Phase is mostly flat in both modes.
The sensitivity of the ATH-ANC700BTs with a wired connection and NC off (full passive mode), measured between 300Hz and 3kHz with a 1mW signal calculated for the rated 35 ohms impedance, is 106.1dB. That should be plenty enough volume if you’re watching a movie on an airplane and the battery runs down.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the PSB M4U TW1s using a G.R.A.S. Model 43AG ear/cheek simulator plus RA0402 ear simulator/coupler and KB5000 simulated pinna, a Clio 10 FW audio analyzer, and a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio 10 FW to the earphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. Note that some of the measurements I usually perform are not included here; because the M4U TW1s have only Bluetooth input, my analyzer was unable to measure spectral decay; and, of course, impedance and sensitivity measurements are irrelevant for wireless-only earphones.
I was unable to get my Clio 10 FW analyzer to compensate for the M4U TW1s’ Bluetooth-induced latency, and so was unable to run the usual frequency-response sweeps. Instead, I fed the earphones pink noise and used the Clio’s FFT analyzer function to measure the frequency response. This changes the look of the curve quite a bit, giving the earphones the appearance of boosted bass. But if you were to turn the curve slightly counterclockwise, you’d see that the M4U TW1s have a very conventional frequency response for earphones, with a large, broad bass bump followed by a strong peak at 2.8kHz and a softer peak centered at about 7.8kHz. Incidentally, the reference level for this measurement was 94dB with a 500Hz sine tone, but this does not translate to 94dB with pink noise.
This chart shows the M4U TW1s’ right-channel frequency response measured with the stainless-steel coupler included with the RA0402 ear simulator, and with the addition of G.R.A.S.’s new KB5000 pinna, which I’ll eventually switch to because it more accurately reflects the structure and pliability of the human ear. (I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I begin using only the new pinna.)
This chart shows the M4U TW1s measured against the RBH EP-SB Bluetooth earphones and the Campfire Audio Comet passive earphones powered by a Musical Fidelity V-CAN amplifier, using the same pink-noise-plus-FFT-technique described above. You can see that all the curves are quite similar, with mild differences in tonal balance.
Because of latency issues with Bluetooth I had to measure the total harmonic distortion (THD) of the M4U TW1s using discrete tones in one-octave steps rather than swept tones, but the results should be comparable to my usual distortion measurements. The distortion is typical -- perhaps even a bit high -- for active earphones with dynamic drivers, hitting about 4% at 2500Hz at the extremely high listening level of 100dBA. I doubt this would be audible unless you really crank these up to the max, in which case the sound will likely make your ears hurt after a couple of minutes.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The isolation of the M4U TW1s is a little better than average for a conventional, dynamic-driver design, especially from 200 to 1000Hz, though not as good as a smaller design equipped with foam eartips.
The M4U TW1s’ range of Bluetooth operation was amazing: 47’, line of sight, and that’s through a window -- my house isn’t big enough for me to measure this entirely indoors. This result -- almost four times as far as some Bluetooth headphones and earphones can manage -- held true whether I used an iPod Touch or a Samsung Galaxy S9 smartphone as my source.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured B&O’s Beoplay H9i headphones using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 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 amp. On the Model 43AG, I used the original G.R.A.S. KB0065 simulated pinna for most measurements as well as the new KB5000 pinna for certain measurements, as noted. For tests in Bluetooth mode, I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio audio analyzer to the headphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The Beoplay H9i headphones’ frequency response (shown here with NC on in Bluetooth mode) is unusual. Note that the bass response rises to a narrow peak at around 20Hz; normally, it would rise to a broad hump centered at about 80Hz. The response peak that in most headphones is centered at 2.5-3kHz is shifted down to about 1.5kHz. There’s not much output in this measurement above 5kHz, although some of this reduction may have to do with the gating necessary to compensate for Bluetooth’s latency. I’m surprised that these headphones sound as normal as they do, given this unusual result.
This chart shows how the response of the B&O H9i headphones differs depending on whether they are in Bluetooth or in wired mode, and with NC on or off. It differs a lot -- you’ll likely notice significant differences in tonal balance as you switch among these modes.
This chart shows the measured right-channel frequency response in wired mode with NC on, measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I’ll eventually switch to because it more accurately reflects the structure and pliability of the human ear. I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I start using only the new pinna.
This chart makes it obvious how unusual the H9i headphones’ response is. You can see that the other headphones’ bass peaks at a much higher frequency, and that their upper-mid/lower-treble peaks are also much higher.
This spectral-decay (waterfall) chart was taken with the B&Os in wired mode; the latency introduced by Bluetooth prevented me from getting a reliable measurement in that mode. This is a pretty clean plot, with just a bit of resonance between 200 and 400Hz.
I had to measure the total harmonic distortion (THD) in wired mode because of Bluetooth’s latency problems. Distortion is fairly low, likely noticeable only in the bottom two octaves of bass, and only at extremely loud listening levels.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The isolation of the H9i headphones with NC on is among the best I’ve ever measured -- better even than the Bose QC35 II headphones, and in the same range as the Bose QC25s.
The impedance magnitude in wired mode is nearly flat in magnitude and phase, averaging about 32 ohms, with negligible phase shift.
The sensitivity of the H9i headphones, measured between 300Hz and 3kHz with a 1mW signal calculated for 32 ohms impedance, is 108.9dB in wired mode with NC off. Even if the battery runs down, they should deliver plenty of volume for watching a movie on an airplane.
. . . Brent Butterworth
brentb@soundstagenetwork.com
Reviewed: SoundStage! Solo, Brent Butterworth, July 2017
I measured the ATH-ADX5000s using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 ear simulator, a Clio 10 FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, a Musical Fidelity V-CAN amp, and an Audio-gd NFB-1AMP for distortion measurements. On the Model 43AG, I used the original KB0065 simulated pinna for most measurements as well as the new KB5000 pinna for certain measurements, as noted. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
Although the ATH-ADX5000s’ frequency response shows that its tonal balance is fairly similar to those of typical competitors, it does reveal some interesting idiosyncrasies. First is the midrange bump at about 1.3kHz. Then there’s the lack of the usual peak between 2 and 3kHz, which is generally considered necessary for headphones to deliver a sound approximating that of speakers in a room. However, there are strong peaks at 3.4 and 6.3kHz. I can’t remember seeing a response quite like this before, so I can’t confidently predict how it will sound, but if someone showed me a response curve like this and asked me to interpret it, I’d guess it would sound fairly flat but just a little bass-shy.
Note that this is the best match I was able to get between the left and right channels, after about 20 minutes of experimentation. Getting these measurements to match is always a challenge because slight changes in headphone position change the measured response, and the left and right simulated pinnae (which are based on averages of molds made from hundreds of human ears) aren’t perfect mirror images of each other (neither are your ears, for that matter). So I’m always reluctant to criticize headphones for channel matching. I didn’t notice a mismatch when listening, but still, this doesn’t impress me.
This chart shows the ATH-ADX5000s’ right-channel frequency response measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I’ll be switching to because it more accurately reflects the structure and pliability of the human ear. (I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until later this year, when I begin using only the new pinna.)
Here you can see how the ATH-ADX5000s’ tonal balance changes when they’re used with a high-impedance source, such as a cheap laptop or some cheap professional headphone amps. It’s not a big difference, largely because the ATH-ADX5000s’ high impedance means that changes in the source impedance don’t have as big an effect. But the headphones’ uneven impedance curve (see below) does result in a bass boost of about 1dB and a reduction of about 1dB in the lower treble, between 2 and 3kHz. Not a huge difference, but still an audible one.
This chart shows how the ATH-ADX5000s compare with several competing open-back headphones: the Audeze LCD-Xes, the HiFiMan HE1000 V2s, and the Sennheiser HD 800 Ses. While the overall balance is similar in all of these models, the ATH-ADX5000s’ competitors clearly have less energy between 1 and 2kHz, and more between 2 and 3kHz -- and that’s right in the “sweet spot” of human hearing, so the Audio-Technicas will certainly sound a little different.
The ATH-ADX5000s’ spectral decay (waterfall) chart shows no high-amplitude resonances, but many high-Q (i.e., narrow), very-low-amplitude (about -40dB) resonances between 1 and 5kHz. This is typical of open-back models; it doesn’t seem to affect their tonal balance, but I speculate that it’s part of what gives them a more spacious sound. Incidentally, I put 4” of denim insulation on top of the headphones when I take this measurement, so the resonances don’t represent room reflections of the sound coming off the back of the headphones.
The measured total harmonic distortion (THD) of the ATH-ADX5000s is low at any sane listening level. At 90dBA, which is quite loud, the THD rises to only about 1.5% at 20Hz. At the extremely loud level of 100dBA, it’s about 1.5% between 100 and 400Hz, and rises to about 4.7% at 20Hz.
In this chart the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. Like the other open-back models (the Audeze LCD-Xes and the HiFiMan HE1000 V2s), the ATH-ADX5000s provide no significant isolation. It’s interesting, though, to see how the ATH-ADX5000s and HE1000 V2s -- both of which have very open backs -- deliver less isolation than the LCD-Xes. If you want isolation, you’ll have to go with a closed-back model such as the Audeze LCD-XCs (also shown).
To the best of my memory, all over-ear and on-ear dynamic headphones I’ve tested have an impedance bump at the driver resonance (always in the bass); nonetheless, the ATH-ADX5000s’ is pretty extreme. The nominal impedance is about the same as the rated impedance of 420 ohms, but the impedance breaks 1400 ohms at 90Hz. Fortunately, because the overall impedance is high, this doesn’t cause major changes in tonal balance if a high-impedance source device is used. The phase response is pretty flat, though.
The sensitivity of the ATH-ADX5000s, measured between 300Hz and 3kHz with a 1mW signal calculated for 420 ohms impedance, is 101.8dB, which is 1.8dB higher than specified. This means that even though they weren’t designed for the purpose, the ATH-ADX5000s will work reasonably well with low-quality source devices.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the Marshall Mid A.N.C.s using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 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 amp. On the Model 43AG, I used the original G.R.A.S. KB0065 simulated pinna for most measurements, as well as the new KB5000 pinna for certain measurements, as noted. For tests in Bluetooth mode, I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio 10 FW to the headphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The Mid A.N.C.s’ frequency response (shown here with NC on, and a wired connection) looks fairly standard, except that the 3kHz peak found in most headphones is unusually strong. In my experience, that extra couple dB is likely to make headphones sound just a bit on the bright side.
This chart shows the right-channel frequency response of the Mid A.N.C.s measured in some of its various operating modes: wired passive (NC off), wired (NC on), and wired Bluetooth (NC on). They’re pretty close to each other, which is a good thing -- the Mid A.N.C.s should sound pretty similar no matter what mode you’re in. The Bluetooth mode looks as if it might sound a bit softer, but the gating required for the Clio analyzer to compensate for Bluetooth’s latency might be contributing to that effect in the measurement.
This chart shows the Mid A.N.C.s’ measured right-channel frequency response in wired mode with NC on, measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna (which I’ll eventually switch to because it more accurately reflects the structure and pliability of the human ear). I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I completely switch to the new pinna.
This chart shows the Mid A.N.C.s’ measured right-channel frequency response compared with three other noise-canceling headphones: the PSB M4U 8s, the Sony WH-1000X Mk.2s, and the Bose QC25s. Clearly, the Mid A.N.C.s have a little more energy between about 600Hz and 3.5kHz, with no extra bass to balance it out, so they’re likely to sound just a bit bright.
This spectral-decay (waterfall) chart shows the results in wired mode; the latency introduced by Bluetooth prevented me from getting a reliable measurement in that mode. While the resonance in the bass is unusually low, there’s a somewhat strong resonance centered at about 4kHz that doesn’t seem to correspond with the frequency-response measurements. Will this cause a slight brightness? Possibly.
Bluetooth’s latency meant that I had to measure the total harmonic distortion (THD) of the Mid A.N.C.s in wired mode. Distortion is a little higher than the norm, though the problem seems restricted to the bass; remember, most music has very little content below 40Hz.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The isolation of the Mid A.N.C.s is just about the same as that of another on-ear NC model I recently measured, the AKG N60 NC Wireless. Not surprisingly, neither can touch the over-ear Bose QC35 IIs, but they provide enough NC to make a plane ride much more pleasant.
The Mid A.N.C.s’ impedance magnitude in wired mode is dead flat at 38 ohms, with a nearly flat phase response. In active mode with NC on, it’s dead flat at 880 ohms, with flat phase response.
The sensitivity of the Mid A.N.C.s, measured between 300Hz and 3kHz with a 1mW signal calculated for the specified 32 ohms impedance, is 98.0dB in wired passive mode, and 102.2dB in wired active mode with NC on. They won’t deliver enough volume to blast out your eardrums, but you’ll have plenty enough for watching a movie on an airplane.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the HD 1 Frees using a G.R.A.S. Model 43AG ear/cheek simulator plus RA0402 ear simulator and KB5000 simulated pinna, a Clio 10 FW audio analyzer, and a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. I used a Sony HWS-BTA2W Bluetooth transmitter to send signals from the Clio 10 FW to the headphones. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. Note that some of the measurements I usually perform are not included here; because the HD 1 Frees have only Bluetooth input, my analyzer was unable to measure their spectral decay; and, of course, impedance and sensitivity measurements are irrelevant for wireless-only earphones.
The frequency response of the HD 1 Frees is normal in having peaks around 3 and 6.5kHz, but unusual in that the 6.5kHz peak is so much higher in amplitude than the 3kHz peak. Normally, it’s the other way around. Although it’s tough even for experienced technicians to know precisely how headphones or earphones will sound from their measurements, I speculate from these that the HD 1 Frees will sound a bit recessed in the upper midrange and lower treble, and unusually strong in the mid-treble. The broad bump in the bass is fairly standard for dynamic earphones.
This chart shows the HD 1 Frees’ measured right-channel frequency response with Bluetooth (BT) and noise canceling (NC) on, measured with the stainless-steel coupler included with the RA0402 ear simulator, and with the addition of G.R.A.S.’s new KB5000 pinna, which I’ll eventually be switching to because it more accurately reflects the structure and pliability of the human ear. I include this mostly for future reference rather than as something you should draw conclusions from; I intend to show both measurements in every review until I completely switch to the new pinna.
This chart shows how the HD 1 Frees differ from a few passive earphones I’ve reviewed. (I had no measurements of other Bluetooth earphones available.) Clearly, there’s a little extra energy around 50Hz and 6.5kHz, and a little less than usual around 3kHz.
Because of Bluetooth’s latency problem, I had to measure the total harmonic distortion (THD) of the HD 1 Frees using discrete tones in one-octave steps rather than swept tones; still, the results should be comparable to my usual distortion measurements. The distortion is very low, at less than 0.5% -- so low that I had to adjust my usual Y-axis scale down from its usual maximum value of 50%. Note that I tested a couple of other Bluetooth earphones at the same time, and got distortion numbers in the more usual range of 2-4% -- this measurement does appear to be genuinely excellent, not just a result of the different measurement technique.
In this chart, the level of external noise is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. Clearly, the isolation offered by the HD 1 Frees seems less than average; if this is a concern for you, I recommend replacing the stock eartips with Comply foam tips.
The HD 1 Frees’ range of Bluetooth operation was outstanding: I measured reliable line-of-sight reception at 33’ indoors -- three times farther than some Bluetooth headphones and earphones can manage.
. . . Brent Butterworth
brentb@soundstagenetwork.com
I measured the Campfire Comets using a G.R.A.S. Model 43AG ear/cheek simulator (including the RA0402 high-resolution 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 amplifier. I used the RA0402 as a direct coupler for most of the measurements, adding the Model 43AG plus the G.R.A.S. KB5000 simulated pinna for certain measurements, as noted. I used the included medium-size silicone tips for measurements with the coupler, and the large foam tips for measurements with the ear/cheek simulator. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The Comets’ response is unusual for earphones in that it’s much flatter than most; most have a broad boost in the bass and a stronger peak in the 3kHz region. That’s generally considered to give the most satisfying response, but headphones that don’t match that response can also sound great. The peak centered at 3.2kHz is narrower than usual, and followed by a much broader peak stretching from about 6.5 to 10kHz. That peak is probably why I perceived these headphones as sounding detailed and slightly bright, but not harsh or edgy.
This chart shows the Comets’ right-channel frequency response measured using only the RA0402 coupler (which has a stainless-steel tube into which earphones fit), and measured using the Model 43AG ear/cheek simulator with G.R.A.S.’s new KB5000 pinna, which I’ll be switching to eventually for my earphone measurements because it’s a more realistic representation of the acoustical environment presented by the human ear. (I include this for future reference; I intend to include both measurements until I completely switch to the new pinna.)
This chart shows the results of 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. As with almost all balanced-armature earphones, the Comets’ large impedance swings interact with the output impedance of the source device to change the response. So if you use a source with a relatively high output impedance (about 50 ohms or higher), such as a cheap laptop or smartphone, the Comets will likely sound substantially brighter.
This chart compares the Comets’ measured right-channel frequency response with that of two other multidriver earphones: the 1More Quad Drivers and the PSB M4U 4s. Both competitors have a large bump in the bass and much higher average treble energy compared with the Comets, but even that sort of response can sound balanced if the bass bump is in suitable proportion to the treble peak.
The spectral-decay (waterfall) chart shows that the Comets’ resonances are negligible.
The total harmonic distortion (THD) of the Comets is high for earphones. At 90dBA, it rises over a two-octave-wide midrange band to a peak of 2%; at 100dBA, it’s anywhere from 1.5 to 9%. (To be sure of the results, I repeated these measurements three times.) Note: These are extremely loud levels; I heard no distortion when I was auditioning the Comets; and scientific research shows that distortion in headphones is only rarely audible.
In this chart, the level of external noise is 85dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. I included measurements with the silicone and foam eartips because the choice of tip makes such a big difference with the Comets, probably because of the size of their earpieces. My guess is that the tiny earpiece lets the foam get farther into the ear canal, where it can form an exceptionally tight seal -- the best I can remember measuring from an earphone that doesn’t use over-ear cable routing or active noise canceling. My listening impressions match the measured result.
The Comets’ impedance, like that of almost every balanced-armature earphone, varies considerably with frequency, rising from 22 ohms in the bass to over 300 ohms in the treble. The phase shift is also large. I recommend using a low-impedance source with these; e.g., an iPhone, a higher-end Android phone, a decent portable music player, or a portable DAC-headphone amp.
The Comets’ sensitivity, measured from 300Hz to 3kHz with a 1mW signal at the specified 20 ohms impedance, is 107.8dB. You should get plenty of volume from them with any source device.
. . . Brent Butterworth
brentb@soundstagenetwork.com
The following categories containing listings of all product reviews published by the SoundStage! Network since 1995 from all of our online publications. The products are divided into categories and listed in descending order by date. There is no Search function within the listings, but you can search by bringing up the page with the appropriate list and using the "Find" command on your browser. (For Internet Explorer select: Edit > Find on this Page.)