I measured the Heritage HP-3s using a G.R.A.S. Model 43AG ear/cheek simulator (including the RA040X 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 Musical Fidelity V-CAN and Audio-gd NFB1-AMP headphone amplifiers. On the G.R.A.S. 43AG I used the original KB0065 simulated pinna for most measurements, as well as the new KB5000 pinna for some measurements, as noted. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.
The HP-3s’ frequency response is well within the norm for what researchers generally consider the most appropriate and realistic-sounding response curve for headphones. However, their bass response is quite different from that of most open-back audiophile headphones, which are often more or less flat up to about 1kHz.
This chart shows the HP-3s’ right-channel frequency response, measured with the old KB0065 pinna I’ve used for years and with 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 until I begin using only the new pinna, probably sometime this spring.
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. There’s effectively no difference in response, which means the headphones’ tonal balance shouldn’t change when you switch from driving them with a good headphone amp to driving them with a cheap laptop.
This chart shows the HP-3s’ measured right-channel frequency response compared with the Audeze LCD-X open-back planar-magnetic headphones and the Focal Clear dynamic open-back headphones. The HP-3s, despite their measured midrange dip, actually appear to be closer to what’s typically considered the most appropriate response curve for headphones, though they certainly produce more bass than most large, open-back audiophile headphones.
The spectral decay (waterfall) chart shows very low resonance overall, particularly in the bass, where most headphones are nowhere near as well controlled. There’s a resonance centered at 1.8kHz, but it’s down about 40dB, and its Q is so high (i.e., its resonance bandwidth is so narrow) that I can’t imagine it would be audible.
The HP-3s’ total harmonic distortion is a hair on the high side compared with the THD of large planar-magnetic headphones, but it’s typical for large dynamics, and in fact is similar to what I measured from the Focal Clear dynamic headphones. THD is negligible above 100Hz, but rises to 2.7% at 20Hz at 90dBA, which is a very loud listening level. The THD rises to 8.2% at 20Hz at the even louder level of 100dBA, but that’s extremely loud -- I’d never listen at that level for more than a second or two.
In this chart, the external noise level is 85dB SPL; the numbers below that indicate the attenuation of outside sounds. (Note that I recently switched to measuring at a level of 85dB instead of 75dB; this doesn’t change the way the isolation curves look, but an 85dB level allows me to get better measurements of noise-canceling headphones, which demand a lower noise floor.) This is an impressive result for semi-open-back headphones. The HP-3s deliver far better isolation than open-back models; their isolation curve looks more like that of large, closed-back models such as the Audeze LCD-XC than like that of an open-back model.
The HP-3s’ impedance magnitude stays mostly around the specified 25 ohms, with a slight bump to 28 ohms centered at 55Hz. Phase shift is negligible. This basically flat, relatively low impedance plays a big part in making the HP-3s sound good with smartphones.
The sensitivity of the HP-3s, measured between 300Hz and 3kHz with a 1mW signal at the specified 25 ohms impedance, is 97.1dB. This sensitivity, relatively high for a large audiophile headphone, means you should get a comfortable listening level from practically any source device.
. . . Brent Butterworth