I was initially pleased with the sound of my new ES5s, but after listening for a few days, something didn't seem quite right, so I ran a frequency sweep through both earpieces.
To my surprise I discovered a significant dip in the left earpiece centred at around 2.3 khz (the right is fine) and another lesser dip in the right at 4.3 khz (the left is fine). At first I thought it must be my ears or the signal generator, but after switching to other phones, it is clearly a dip is in the earpieces themselves.
I have a call and email into Westone to see what they have to say about this rather disappointing discovery.