DC signals also affect the movement of the speaker cone which may result in a reduction of audio quality, although low level DC doesn’t damage the speaker. If you were to apply more than a little DC power to speakers, this will cause the voice coil to heat up significantly, which would likely cause damage. A considerable DC through the speaker element can quite quickly fry the speakers.
The basic requirement of a speaker protector requires that any potentially dangerous DC flow to the speakers should be interrupted as quickly as possible.
Many hi-fi amplifiers and professional power amps (and loudspeaker systems) provide some of protection, either to protect the speakers from an amp fault, and/or vice versa. Some of these are implemented at a very basic level and some are better. In hi-fi amplifiers typical circuit has a relay with a delay that turns on few seconds after amplifier is powered up to to stop any popping when the amp is turned on and with a detection circuit that disengages a relay if the amplifier goes wrong and sends DC current to the speaker. DC protection uses a relay to disconnect the speakers if any appreciable DC appears at the amplifier output. Typically that is in the range -/+ 1.5 to 3 volts.
Here are some links to speaker DC protection circuit designs I found on-line:
https://sound-au.com/project33.htm
http://www.geofex.com/article_folders/ampprot/dcprot.htm
http://tolisdiy.com/2019/02/16/enhanced-dc-protection-circuit/
https://sound-au.com/appnotes/an017.htm
http://tolisdiy.com/2019/02/16/enhanced-dc-protection-circuit/
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candy clicker says:
Right? Aim for numerous achievements