1. What is an In-Ear-Canalphone?
In-Ear-Canalphone, also known as canalphone, ear-canalphone, ear-canal headphone, or In-Ear-Monitor (IEM), is a type of Inter Aural headphone that is designed to be used where the user’s ear canal is sealed by the ‘phone. The seal generally serves two functions: 1) to block noise and 2) to form a sealed acoustic chamber in order to achieve a fuller sound. To create such a seal, the earphone’s nozzle along with its tip (or sleeve) is inserted into the front part of the ear canal. Many high end canalphones are custom molded to the user's ear for maximum comfort and a perfect seal.
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Is it a canalphone or an IEM?
Due to its great portability, high sound quality and noise blocking ability, specially tuned (and often custom molded) canalphones have long been used on stage by musicians and audio engineers alike. These canalphones are part of the In-Ear-Monitor-System (IEMS), which can be either wired or wireless. For ease of naming, canalphones used in such system are referred to as IEMs. Later, as canalphone manufacturer began to make high quality canalphones available for the general consumer (iPod generation), the word ‘IEM’ became popular thus replacing ‘canalphone’ as how we refer to all canalphones. Technically speaking, only canalphones on an IEMS should be called an IEM. However, there is no concrete definition of the word ‘IEM’ and it is easier for general consumer to use a simpler terminology. Sometime ‘IEM’ is also used only to refer to high quality canalphones. For the purpose of this article, we will refer to all canalphones as IEMs.
[Basic components of an IEM]
2. I thought IEM/canalphone is also called 'earbud'?
No, IEM and earbud each refer to two different kind of Inter-Aural headphones.
Inter Aural headphone, or in-the-ear headphone, is sometime known as earphone. It refers to headphones with a transducer small enough to be placed/worn in the ear. The two major types of inter aural headphone are earbuds and canalphones.
[Picture of various types of earbuds]
Earbuds are worn in the opening of the ear, often just outside of the opening of ear canal. They can have a headband or clip-on to increase comfort, but they do not form an air-tight seal in the ear canal as they are not intended to go into the ear canal.
[Picture of various types of IEM]
On the other hand, canalphones/IEM are intended to be partially inserted into the ear canal to create an air-tight seal (for reasons see first question).
The reason why so many websites mislabeled IEM as 'earbud' is simply because they don't understand the differences.