So, as someone who has a range of equipment: Icon Audio HP8 Mk II, Schiit Bifrost, Ultrasone Edition 8 Limited, Cypher Labs Algorhythm Solo -dB, RX Headphone amp, various other headphones, etc. I had been investigating CIEMs for a while, but you just can't know until you buy them and have them built and hopefully they arrive with a good fit.
I looked at Heir Audios, JH Audio, Etymotics, Shure, Frogbeats, etc.
I wanted the compact size, the sound isolation and the quality people say is there with them, but I tell you, after listening almost exclusively to my Ultrasone's for the last year, I was sceptical I'd get anything that I would be able to enjoy even if I had to accept it was a compromise.
Eventually, I opted for the Frogbeats C4. I like giving smaller companies a chance and some of the reviews were promising.
Yes, it's true, the company had been suffering from its ability to communicate in a timely fashion, yes, some of the build times were slower than stated, etc. When I did hear from David at Frogbeats he was open, helpful and did try to make the experience pleasant. Any problems are teething problems and the bottom line is I got the C4s, the quality of the build is good, I never had any doubt about whether they would turn up, I just had a vague fear they may take a while. Even this was unfounded.
While I was waiting I also ordered a custom cable from Plus Sound (http://www.plussoundaudio.com/iemcables.html). The C4s and the custom cable arrived the same day (Yay!).
The Plus Sound cable is amazing. Brilliant build quality, exactly as I specified. It just looks the business and will last for years.
In my mind there are loads of great reasons to get custom cables and only one of them relates to any perceived sound quality improvement. The other reasons: custom length(s) makes specific uses a lot easier, superior and longer lasting build quality, superior and custom looks as sexy looking hifi kit is a factor. To be honest, these is a definite improvement in clarity to my ears, but it is a relatively small difference and 99.99% of humans could be perfectly content without knowing which cable it was one way or another.
So, basically, I just wanted to say, the C4s are excellent. The treble and mids are crystal clear and the whole thing sounds dynamic and musical. The sound isolation is excellent. Now, as for bass. Initially, I thought there wasn't any... Then I realised I didn't have them fitted perfectly. The fit is critical.
If I twist them in a little more and press them deep the bass is excellent. If I am sitting down and relaxing somewhere I can enjoy a full sound spectrum consistently.
If I am on the move, the sound quality is still excellent, but from time to time I may have to reseat them in my ears to get the full range, particularly if the cable catches on something or gets a little tugged.
Overall, I am very impressed with the C4s. While they do not have the sheer dramatic stage presence of the Ultrasone 8s (almost nothing does) and they are a completely different type of listening experience, they rock well. They sing well, the dynamics are brilliant, the quality is up there and I highly recommend them.