snip
Now AM works fine if you don't mind wasting power. This is because the audio is
carried only in the sidebands, not the carrier. And because the two sidebands
are mirror images of themselves, only one sideband is needed and the other is
wasted. If we eliminate the carrier and one sideband (resulting in the mode
called Single Sideband, or SSB), we are left with a 1 watt sideband that will
work just as well as if we burned 6 watts to transmit two sidebands and a
carrier. In other words, SSB is -AT LEAST- 6 times more efficient than AM. But
remember that average modulation is more like 30%, which means that a 0.3 watt
SSB transmission has the same effect as using 4.6 watts to transmit that very
same sideband using AM. Therefore, with normal speech, SSB is closer to 15 times
more efficient!
snip

You are wrong about SSB being 15 times more efficient. Your reasoning
is flawed in that.............................................. ......

If speech modulates a AM signal to a average of 30% then the same
speech will modulate a SSB to a similar reduced potential.
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On A.M. , with a 4 watt carrier at 100% modulation , we have 2 watts
of audio power used for the sidebands. One watt on each sideband.
This duplication of sidebands is not necessary to convey intelligence.

If we use the same transmitter and convert it to DSB ( double
sideband ) by removing the carrier , we can now have 2 watts per
sideband.

If we now remove the other sideband , and concentrate all of
the power into one sideband , we have a 4 watt sideband. With
this method of removing the carrier and one sideband we can
put 4 watts of intelligence out on SSB as compared to 1 watt on
A.M.. This makes a SSB transmission 4 times as powerful as its
A.M. counterpart.

In addition to the above transmitting advantage , the SSB
signal has a receive advantage also. Since only one sideband is
transmitted , only 1/2 the bandwidth is needed. This means that twice
the number of stations could operate in the same bandspace as A.M.. In
addition to this , because the bandwidth needed is only 1/2 of A.M. ,
only 1/2 of the atmospheric noise is picked up with the signal. This
gives you a 3db advantage over an A.M. receiver.

So when you add it all up you have 6db gain on transmit , and
3db gain on receive. That's effectively 9db of total gain.