Headphones

As I commented in the main text, the Sundara is unusually insensitive for a modern, medium-impedance headphone. We recorded a voltage sensitivity – averaged for the two capsules – of 105.7dB for 1Vrms input at 1kHz, which is the sort of figure we saw from the first of the new-generation planar magnetic headphones seven years ago [eg the Audeze LCD-2 at 106.0dB; HFN Mar '13]. Since then we've seen a leap in the sensitivity of the most advanced isodynamic designs, to 115.2dB for the Audeze EL-8 open-back [HFN Oct '15] and 114.6dB for the Oppo PM-2 [HFN Feb '15]. Being off the pace by 9-10dB is significant.

As we've become used to seeing from planar magnetic headphones, the Sundara has a pretty flat response trend below 1kHz [uncorrected responses, Graph 1 below], its output only falling to –6dB (re. 200Hz) below 20Hz. Above 1kHz the response is also typical of planar magnetic designs in that, while there is a peak in output around 3kHz, there is insufficient lower presence band output generally to deliver what is conventionally considered necessary for a neutral tonal balance. These two features are reflected in the diffuse-field corrected response [green trace, Graph 2] which displays only mild low frequency peaking but a big 'hole' in perceived output between 1kHz and 4kHz. Together these suggest that the Sundara will evince a lower-mid and upper-bass warmth accompanied by a softening of the low treble – a view echoed by our reviewer.

Also typical of isodynamic drivers, the Sundara's impedance is virtually constant, varying by a minuscule 0.4ohm (20Hz–20kHz). So, its frequency response will not be significantly affected by the headphone preamp's source impedance. However, wiggles in the impedance trace beginning just above 400Hz coincide with irregularities in the frequency responses, suggesting the presence of diaphragm resonances, confirmed by a CSD waterfall which shows high-Q modes particularly in the treble. KH