An efficient speaker will convert 5% of the amplifier power into sound.

95% of the amplifier power is wasted as heat, etc.

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If you put 40 watts into a speaker,
most of the 40 watts will be wasted as heat, etc
so the loudspeaker should get about as hot as a 40 watt light bulb !

Your loudspeaker NEVER gets as hot as a 40 watt light bulb.

So, you NEVER put 40 watts into your speakers !