The sound guide tube is not only a channel for sound propagation, but its shape and thickness changes will also affect the frequency response.

1.What is a sound tube?
A plastic sound tube made of special materials, about 35-45mm long, usually connected to the ear hook at one end and the ear mold or ear plug at the other end, mainly used for sound transmission.

2. What are horn sound guide tube and anti-horn sound guide tube?
If the inner diameter of the sound tube changes from thinner to thicker from the outside of the ear canal, it is called a horn sound tube; if the inner diameter of the sound tube changes from thicker and thinner from the outer side of the ear canal, it is called a reverse horn sound tube . The horn sound tube can improve the effective transmission of high-frequency energy, thereby increasing the gain and output of the high-frequency part.

However, the increased high-frequency region depends on the length of the horn sound tube and the inner diameter of the beginning and end of the sound tube. In general, the longer the horn sound tube, the smaller the frequency range affected.

3. What are the common types of sound guide tubes?
1) 13 sound guide tubes:
13 The sound guide tube is a conventional sound guide tube type with an inner diameter of about 1.9 mm and an outer diameter of about 2.9 mm.

2) Libby Horn:
There are two common specifications of the horn sound tube, which are the Libby 4 mm type and the Libby 3 mm type.

Libby 3 mm is suitable for small ear canal of children or adults, it can increase 8-10 dB for high frequencies above 2K Hz; Libby 4 mm type can extend high frequencies to 8K Hz, and the frequency response curve is smooth, and the peak appears at At 2.7K Hz, the resonance characteristic of the external auditory meatus just happens to be compensated.

3) C.F.A. sound guide tube (Continuous flow adapter)
C.F.A. sound guide tube needs to be used in conjunction with a specific ear mold hook, divided into horn type (CFA #2 horn) and stepped type (CFA #3 stepped bore). This type of sound guide tube prevents extra formants due to improper connections.

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