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I measured the RBH Sound EP3s using a G.R.A.S. Model RA0045 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 amplifier. I primarily used one of the smaller Comply foam eartips supplied with the EP3s because it fit the simulator well, and I figure it’s what most listeners will prefer. For comparison, I also include a measurement taken with one of the supplied silicone tips. This is a “flat” measurement; no diffuse-field or free-field compensation curve was employed.

Frequency response

This is the frequency response of the EP3s using the smaller of the supplied Comply foam eartips. There’s a little more bass and treble output (or a little less midrange output) than I’m used to seeing.

Comply to silicon comparison

This chart shows the EP3s’ frequency response with the Comply foam tip (green trace) and the medium-size silicone tip (purple trace). The slight difference is perhaps enough to cause the EP3s to sound slightly brighter with the silicone tip. Because the shapes and sizes of ear canals vary, so may the actual results you get with these tips.

Frequency response

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 zero audible effect on the sound of the EP3s.

Frequency response

You can see from this chart that the EP3s (blue trace) have stronger bass and treble output than RBH’s EP1s (red trace), and that both have much less midrange energy than the PSB M4U 4s (green trace). The Sennheiser IE 800s -- which I included because they’re well-regarded earphones that also have ceramic enclosures -- have much less lower-treble response, but a stronger 10kHz response than any of the other headphones measured here.

Waterfall

Resonance in the EP3s is mild and well damped, other than the bass resonances that have shown up in almost every set of earphones I’ve measured.

THD

The EP3s’ total harmonic distortion (THD) is low. At the loud listening level of 90dBA, the distortion will almost certainly be inaudible. A narrow THD peak at 2.7kHz rises to about 3.5% at 100dBA, but it’s probably not troublesome, considering that: 100dBA is way louder than most people would ever listen; the peak is narrow; and the first three distortion products will be at the high frequencies of 5.4, 8.1, and 10.8kHz.

Isolation

In this chart, the external noise level is 75dB SPL; the numbers below that indicate the degree of attenuation of outside sounds. The EP3s’ isolation is fantastic with the supplied eartips of Comply (shown) or silicone (not shown, but almost exactly the same result). They reduce ambient noise in the “jet-engine band” of 100-200Hz by 17-20dB -- better, even, than most noise-canceling headphones can achieve.

Impedance

The EP3s’ impedance magnitude is essentially flat at 16 ohms, as is the phase.

The sensitivity of the EP3s, measured between 300Hz and 3kHz with a 1mW signal calculated for the rated 16 ohms impedance, is 105.2dB, which is above average; the EP3s should play quite loudly, regardless of the source device used.

. . . Brent Butterworth
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