Now that we are on this topic, I figure I can share a bit more about the engineering idea behind C9's performance and capability.
A while ago, I had a discussion in Michael's thread with gler about why there is the need to have C9 for IEMs. The common argument is any modern DAP will have plenty of power to drive most of the IEMs, so a better, even independent Amp is no need. However, this certainly does not explain why we see the performance differences between TOTL DAPs and mid-tier DAPs, even from the same brand. Hiby R8 performs better than R6 2020, even though on paper R6 has plenty of power. Also, this difference is clearly not just a tuning thing, but rather an elevation in lots of technical aspects such as soundstage, details, imaging, among many others.
So, I brought this question to Cayin's Wechat group: Why does C9 work with IEMs? If it is not just power, why can a better amp/DAP improve IEM performance? I posted these questions in the group and requested an answer in a non-technical language so that I can understand. I got warm feedback from both their general manager Mr. Liang and several engineers from other brands who happen to be in that group, and I think they explained this well.
According to Mr. Liang, in designing a good amp (or the amp inside a DAP), the focus is no longer just on increasing the max power. Instead, it is in managing
transient. What does this mean? He gave an example using cars. So, now the focus is no longer on increasing the max horsepower from the car. Instead, it is in controlling the speed of the car, such that it can accelerate/decelerate precisely as we command. In driving an IEM, the key in music reproduction is those
drivers should move in a manner exactly as we want them to be. Achieving this is difficult and requires lots of engineering effort, and this is the design goal behind C9: managing the trainset in a better way.
This in fact may explain why C9 can work with ultra-sensitive IEMs like Andromeda and Zen. For those sensitive IEMs, as I understand it, it is very easy that those units are moving in an undesirable manner (because they are just so sensitive to power). When the units are not moving in the way/frequency we want, the sound gets messed up and the clarity in the music is destroyed.
This also explains why "driving it loud' is NOT the same as "driving it well" - again, it is not about the max output power, but about managing the transient. For this point, I also refer to an excellent explanation offered by another sound engineer
@Liberatus in a
post in Diana V2's discussion thread.
Certainly, there is still an element of synergy among C9, the source gear, and IEMs. Not all IEMs and DAPs can benefit from C9, although I have found most of them do. Here I just want to offer some interesting background for the design idea behind C9.