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