Module 2

Styles & Components

What is inside a hearing aid, the family of styles from behind-the-ear to completely-in-canal, and how the device couples to the ear.

The signal chain inside every aid

Every hearing aid, whatever its shape, contains the same chain: one or more microphones convert sound to an electrical signal; an analogue-to-digital converter feeds a digital signal processor (DSP) that applies gain, compression and other processing; and a receiver (the miniature loudspeaker) converts the processed signal back to sound in the ear canal. A battery — increasingly rechargeable — powers it all [1].

sound inMicrophonesound → electricalDSPgain · compressionReceiverelectrical → soundto ear canal
Every hearing aid, whatever its style, runs this chain: microphone → DSP → receiver, powered by a (often rechargeable) battery.

Styles

Styles trade size against power, features and handling. Behind-the-ear (BTE) aids house the electronics behind the pinna and deliver sound through tubing to an earmould; they are the most powerful and flexible, suiting all ages and the most severe losses. Receiver-in-canal (RIC) aids move the receiver into the ear canal on a thin wire, giving a discreet device with a wide fitting range — now the most commonly fitted style. In-the-ear (ITE), in-the-canal (ITC) and completely-in-canal (CIC) aids are custom-moulded to the ear; they are cosmetically appealing but smaller batteries and limited space cap their power and feature set [1].

CICCompletely-in-canalmost discreet · mild–moderateITCIn-the-canalcustom · mild–moderateITEIn-the-earcustom · mild–severeRICReceiver-in-canalmost common · mild–severeBTEBehind-the-earmost powerful · all lossessmaller / less powerful → larger / more powerful (down)
Size trades against power and features. RIC is the most commonly fitted style today; BTE remains first choice for the most severe losses and for children.

Coupling: moulds, domes and the occlusion effect

How the aid couples to the ear shapes both comfort and sound. A custom earmould seals the canal for maximum gain without feedback — needed for severe losses. Open domesleave the canal vented, letting low-frequency sound pass naturally and the wearer’s own voice escape; this reduces the boomy occlusion effect and suits milder, high-frequency losses, at the cost of available gain before feedback. Matching the coupling to the audiogram is a core fitting decision [1].