The IEC 711 coupler is the most common one used to measure Balanced Armature driver frequency response. It provides a reasonable simulation of the ear’s response to about 8-10 kHz. Above that the coupler’s resonant frequency of about 13.5 kHz causes too much inaccuracy to be reliable. The presence of signal beyond 8 kHz can be seen, but not its level with any accuracy. A single coupler can be used to compare different drivers at higher frequencies by showing relative responses.