Even when no audio signal is present, the idling signal from a class-D amplifier will constantly deliver significant power to the speaker if the impedance is not high enough. A class-D amplifier modulates the duty cycle of a rail-to-rail square wave. When there is no audio signal, the duty cycle is near 50%. Therefore, a square wave can be used to calculate the idle current of a class-D amplifier, applying the impedance curves shown previously. At a switching frequency of 400 kHz, a typical value for in-ear wearables, the dynamic driver current consumption is five times higher compared to a Balanced Armature driver. Additional power savings can be realized by using higher impedance Balanced Armature drivers. The design flexibility possible in Balanced Armature coils allows for impedances of even hundreds of ohms. Commonly used in hearing health devices, high impedance coils reduce the audio-related current through the battery and amplifier. This in turn reduces the power dissipation in these devices, improving efficiency even more.