A solution to the problems associated with IEC 711 and 0.4cc couplers is to display earphone response curves using a hybrid of both. Knowles publishes reference design earphone response curves using only the 711 coupler below 5 kHz and both the 711 and 0.4cc coupler responses above 5 kHz. This allows one to identify the treble output free of artificial peaks while still depicting the accurate bass and midrange. Because the 0.4cc coupler response will not be identical to the response in the ear, the perceived response may actually be something between the two (and different for each listener). That is why both coupler measurements are shown in the treble range.