Fit
In-ear monitor fit identifies a universal shell or a custom shell made to match the individual wearer's ears.
Universal models use a standard shell with replaceable ear tips. Custom models are made from the wearer's ear impressions. Both rely on appropriate fit and sealing; the category alone does not establish comfort, isolation or sound quality.
Fit — Headphone
Fit affects whether an in-ear monitor sits securely and forms the intended acoustic seal. A poor seal can reduce bass and isolation. Universal models let you try tip sizes and materials, while a custom shell is shaped for its intended wearer rather than adjusted through ordinary tip selection.
Compare the version actually offered: mentioning an optional custom version does not make a universal model custom. Consider the fitting process and individual ear shape, without assuming that either approach guarantees comfort. This distinction applies to in-ear monitors, not over-ear pads, open earbuds or a headband's size adjustment.