For earmoulds used with BTE (behind the ear) hearing aids and In-ear monitors, the quality of tubing is very important. For high powered aids the tubing should be thick-walled with a hole diameter of 2mm. Use of standard tubing on high powered aids may cause feedback.
Earmoulds need to be re-tubed regularly. Replace the earmould tubing as soon as it begins to harden.
It is surprising how much the tubing can affect the sound quality.