Beyerdynamic T 51 i and T 51 p On-Ear Sealed Headphones Measurements
Raw frequency response plots show a 10dB bass hump centered at around 120Hz, and extending upward to 300Hz. This is the predominant artifact in listening as the bass blees excessively into the midrange and makes for a bass heavy listening experience.
Midrange 300Hz to 2kHz slopes downward 4dB, which is continued by a slightly too short concha peak at 3kHz. There's good argument for a -5db warm tilt overall on a headphone, but this is significantly steeper than that as can be seen on the diffuse field compensated curve above. A treble notch 5-8kHz ensures this headphone never sounds piercing, but warm tilt goes away here; above 3kHz plot contours are about right for a flat treble response, but for a slightly bright 10kHz peak. This tends to give a little sparkle to the otherwise warm response.
30Hz square wave shows significant sway back from lack of extension and phase shift below driver primary resonance, which can be seen as the peak at 12Hz in the impedance plot. This results in a loose and distorted bass below 100Hz, but is quite understandable in a headphone of this size and type. For me, the bass bleeding into the midrange was more of a problem.
The slight upward rise of the 300Hz square wave is indicative of it's midrange warm tilt. initial transient should be higher and is somewhat misshapen with noise. This probably evidences the grainy sound heard in listening.
Impulse response too shows a low initial transient and relatively high amount of subsequent noise. Noise appears quite periodic so is likely due to the resonance at 10kHz seen in the Raw FR.
Other than a moderate and likely not too audible bump at 2kHz, distortion is fairly low. Increases in bass distortion below driver resonance in this type of headphone is the norm; this headphone looks a bit better than average.
Impedance plots shows a significant primary driver resonance at 120Hz, and a fairly strong resonance at 2.5kHz. Nominal impedance is around 40 Ohms.
Isolation is slightly above average for a headphone of this type at -22dB broadband.
Needing 35mVrms to achieve 90dBspl at the ear this headphone will be driven to solid levels by a portable device.