BillG
Major Contributor
Sure, any tip change could change frequency response, but a huge change in bore length and geometry like that will likely have an unpredictably larger effect than a normal 3rd party tip. If you can send your IEMs with these custom tips to get measured on industry standard gear you might be able to correct for this with EQ, but you might not, due to changes in bore geometry possibly introducing acoustic reflections and cancellations and so non-minimum phase behaviour that cannot be effectively EQed out. CIEM tuning is very difficult to get right due to these issues, so you can't expect an IEM to necessarily sound fine or even be easily correctable with EQ if you just slap it onto an ear mold.
I'm not talking about the extra weight of the ear mold, I'm talking about the weight distribution shifting to outside the ear canal entrance from the weight of the IEM (which is often not insignificant, sometimes made of metal) protruding out of the ear that I'd imagine would cause pressure points in the canal from the mold and so affect comfort, which is one of the major reasons to get custom-molded IEMs in the first place. I doubt they would just disappear into the ear and be almost unnoticeable like purpose-built CIEMs do. Of course, all these reservations could be confirmed or denied if you get some of these custom-fit eartips, try them out and report back
I suspect the manufacturers of these tips know a lot more about what they're doing then you seem to give them credit for. I'll listen to them instead.
Trust me, I know. I also know that I (now 53) need a different size of foam tips for IEMs than I did even 5 years ago.
