Confidence limits
Purpose
Because the headphone is re-seated on the artificial ear between each of the 10 measurements of each capsule's frequency response, small disparities in headphone positioning result in each response being somewhat different. Similar variations are likely to be experienced in normal use. This measurement shows how large the variability was for each casule of the tested headphone, and where in the audible spectrum it was greatest/least. We can be 95% certain that had a very large number of response measurements been made, their mean would lie within these limits.

Method
The 10 frequency responses obtained from each capsule are statistically analysed to determine 95% confidence limits for the mean (averaged) response across the entire measurement frequency range of 20Hz to 20kHz.

Measurement parameters
Test signal:                                                        pink-spectrum periodic noise
Sampling frequency:                                       96kHz
Bit-depth:                                                           16-bit
FFT length:                                                        32,768 points
Frequency resolution (measurement):         2.93Hz
Frequency resolution (graph):                        1/100th octave
Re-seats on the artificial ear:                          10 per capsule
Measurement averages:                                 10 per re-seat