I measured the RBH Sound HP-2s using a G.R.A.S. Model 43AG ear/cheek 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. I moved the headphone around to several different locations on the ear/cheek simulator to find the one with the most bass and the most typical average response. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.
This chart shows the HP-2s’ frequency response, which suggests that their tonal balance will be fairly neutral. It’s a fairly by-the-book response, with nothing to indicate that these headphones will have major idiosyncrasies. There’s perhaps a little more energy than usual between 7 and 10kHz, but the peak between 2 and 3kHz is at a typical level relative to the bass and midrange, which is probably why I found the headphones’ treble emphasis subtle and unobjectionable.
Adding 70 ohms output impedance to the V-Can’s 5 ohms, to simulate the effects of using a typical low-quality headphone amp, has only a subtle effect on the HP-2s’ response, kicking up the bass below 60Hz by about 1dB.
This chart compares the HP-2s with three other midpriced closed-back models: the NAD Viso HP50s, the Oppo Digital PM-3s, and the Bowers & Wilkins P7s. The response of the HP-2s is pretty close to that of the Viso HP50s, with a little more bass and a somewhat bigger peak between 2 and 3kHz.
The HP-2s’ waterfall plot looks clean above 1kHz, with no significant resonances. The resonance visible in the bass is typical of closed-back headphones.
The total harmonic distortion (THD) of the HP-2s is generally low. It gets up to around 1.5% in the bass at the very loud listening level of 90dBA. That’s probably inaudible -- a subwoofer routinely hits higher numbers in normal use without producing audible effects. Distortion exceeds 4% in the bass at the extremely high level of 100dBA, a typical result for closed-back headphones of the HP-2s’ size and price.
In this chart, the level of external noise is 75dB SPL (red line); the numbers below that indicate the level of attenuation of outside sounds. Here, the HP-2s achieve essentially the same result as their competitors. For reference, I added the result from the Bose QC25s, which have the most effective noise canceling of any over-ear headphones now on the market.
The impedance magnitude of the HP-2s is pretty much flat, running between 35 and 40 ohms; the impedance phase is also essentially flat.
The sensitivity of the HP-2s, measured between 300Hz and 3kHz with a 1mW signal calculated for the rated 32 ohms impedance, is 106.6dB. That’s high -- you won’t have any problem getting adequate volume from any source device I know of.
. . . Brent Butterworth