Purpose
Frequency response is the single most important determinant of headphone sound quality. This test determines headphone frequency response as it might be measured at the DRP (drum reference point, ie. the eardrum) of a real human ear, although in practice that is highly variable between individuals. The responses are referred to as ‘uncorrected’ because they do not represent the headphone’s perceived frequency balance: for that a response correction must be applied (see Corrected responses).
Method
While it is possible to measure headphone frequency response using real human ears, that is a time-consuming process which requires repeated measurements with different individuals to account for natural variation. More normally, as here, measurement is made using a standardised artificial ear, ideally one that uses a realistically shaped pinna (outer ear) and incorporates an ear simulator which mimics the ear's acoustical impedance. Within this ear simulator is a microphone capsule which records the headphone response. Ten impulse responses (five in the case of some early legacy measurements) are measured separately for the headphone's left and right capsules, using left and right artificial pinnae, between which the headphone is removed from and replaced (reseated) on the artificial ear. This done to capture frequency response changes which occur due to slight differences in positioning of the headphone relative to the ear, and perhaps small differences in earpad sealing also. The individual IR measurements are then converted to frequency responses by FFT analysis using an adaptive window. The graphed uncorrected response is the mean of these; the extent of the variation between them is shown separately in the Confidence limits graphs. Both capsule's responses are normalised to 0dB at 1kHz.
Measurement parameters (wired headphones)
Test signal: pink-spectrum periodic noise
Sampling frequency: 96kHz
Bit-depth: 16 bits
FFT length: 32,768pt
Frequency resolution (measurement): 2.93Hz
Frequency resolution (graph): 1/100th octave
Reseats on the artificial ear: 10 per capsule
Measurement averages: 10 per reseat
Measurement parameters (Bluetooth headphones)
Test signal: pink-spectrum periodic noise
Sampling frequency: 48kHz
Bit-depth: 16 bits
FFT length: 16,384pt
Frequency resolution (measurement): 2.93Hz
Frequency resolution (graph): 1/100th octave
Reseats on the artificial ear: 10 per capsule
Measurement averages: 10 per reseat