Theory:

Soundboard:
 
These are curved (concave) surfaces that are used in auditoriums and halls to improve sound quality. This board is positioned so that the speaker is at the concave surface's focal point. The speaker's voice is reflected to the audience, improving the sound quality heard by the audience.
 
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Curved surface in auditoriums
 
Ear trumpet:
 
An ear trumpet is a type of hearing aid that can help people who have trouble hearing. One end of this device is wide, while the other is narrow. The sound from the sources enters the wide end of the device and is reflected by its walls into the narrow end. This concentrates the sound, allowing it to enter the eardrum with greater intensity. This improves a person's ability to hear sound.
 
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Ear trumpet
  
Megaphone:

A megaphone is a horn-shaped device that is used to address a small crowd. It is wide on one end and narrows on the other. When a person speaks at the narrow end, the multiple reflections from the tube walls concentrate the sound of his speech. As a result, his voice can be heard clearly from a great distance.
 
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Reference:
https://www.stockvault.net/photo/255115/hand-holding-megaphone