Why Protect Amplifiers from Lightning Riding in on Outdoor Speaker Wires?

When you have an outdoor speaker system you have the potential for lightning to enter the home on speaker wires.   Systems Integrators can easily understand and explain that once this unwanted energy gets on the line it is going to go directly through the amplifier on its way to the earth ground of your house unless we divert it around the amplifier.  See an example design diagram here. Outdoor speakers are typically isolated from ground therefore it is not common to surge protect that end of the line in most installations.  But, the amplifiers that power the outdoor speakers are another matter.  Running speaker wire out to numerous outdoor speakers is like putting up a giant copper antenna and asking for nearby lightning to “hit me.”  It does not take a direct strike to inject surge energy into the speaker wires.  Strikes as far as one quarter mile away generate enough EMP energy for the surge to travel thought the air and inductively couple onto the speaker wire and travel into the home or other structure.  And, once lightning finds itself inside the home it can easily destroy the amp and migrate to other equipment in the rack or home.