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