Why a round magnet is used in a speaker?

It is used , because around it is a wire wound coil , which reacts aganst the magnet when

power /current is applied , its round to allow the cone to move freely ,

It's actually an electro-magnet and inside there's a coil. When the amplifier reacts to the music a electrical current is sent which compresses the speakers coil and then releases it to create sound.

The speaker's permanent magnet is round in order to produce the maximum external magnetic field, and therefore force to the electromagnetic speaker coil that is encircling it.

The speaker coil is round, to maintain the best strength, and also to create the strongest electromagnetic field area, which has been created by the turns in the coils. These coils are inside the magnetic field generated by the permanent magnet.

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