There is another kind of microspeakers whose electro-acoustic parameters stay between those of receivers and typical microspeakers. The near field speakers are similarly sized as microspeakers, miniature and round or rectangular, for example 12*6mm, 15*8mm or 25*8mm. This category of speakers is used in glasses and very near field applications.

Earphone receivers are often 1mW and microspeakers possibly 1W, while the near field speakers are usually rated 100mW or 0.1W. The sound output level is of course in between. The earphone receivers here refer to traditional electro-dynamic ones with plastic diaphragms. When measured in pressure field such as IEC 711 couplers, they usually range between 110dB~ 130dBSPL in bass frequency. On the other hand, microspeakers are measured in free field on baffle and/or with closed box. Near field speakers are sometimes measured at 1cm, 3cm or similar distances. This considers the fact that they are often placed near but not against the ear or temple.

It’s worth mentioning that receivers can be further divided into telephone use and earphone/ headphone use. Telephone usually uses bulky receivers of diameter around 13mm, and tested in high leak condition. Earphone and headphone use much thinner receivers, with earphone ranging from 5mm to 12mm in diameter, headphone from 30mm to 40 diameter. They are tested in low leak condition that assumes very fit contact with ear.

Balanced armature is a special family of receivers. It uses armature and metal diaphragm to squeeze out air through a narrow and thin chamber, and out from a spout. The efficiency is high so that large sound output can be attained with lower voltage. Due to its frequency response characteristic and electrical parameters, balanced armature are mainly used in hearing aids and high-fidelity In-Ear Monitors (IEMs).