Slater
Headphoneus Supremus
ZS6: sources / impedance adapters, foam
Following @HiFiChris suggestions about using sources with higher output impedance, or impedance adapters (with any source) to tame the excessive treble peaks (without altering other frequencies), I've made some new measurements.
This effect is possible thanks to impedance features of ZS6 (ZS5 & ZS6 impedance curves).
If you try this with ZS5 v1, for example, the effect is just the opposite (harsher upper-mids and treble), due to their impedance characteristics.
Graph of ZS5 and ZS6 frequency response variation when using a higher impedance source (example: GhostAudio miniA1 amplifier, output impedance 15Ω):
Now, the result frequency response of ZS6 when using an impedance adapter of 75Ω on a <1Ω source (with "stetotip" -thick silicone- and with foam tips) compared to same source without adapter, and to ZS5 v1.
(Note: closed sub-bass vent hole in ZS6 measurements; this explains the sub-bass difference with ZS5).
The treble with Z adapter + foam is very near to ZS5 v1 level.
Of course, you'll have to apply more voltage (raise volume pot) to get same sound level than before.
Nice finding. Should be easy to open the ZS6 up and solder in a 75Ω resistor. Then, no adapter needed.
You could also do an adjustable pot, or an externally accessible "socket" for on the fly changes:
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