how can audio be any louder than 100 % modulation
Without adding distortion to the intelligence of the original audio signal you are absolutely correct in asking such a question and the answer is: there is no way.
Of course distortion is all relative to what we hear or think we hear as long as the actual bandwidth of the signal is modulated properly to negative and positive 100% (less negative in reality to keep the carrier from pinching off completely, usually -95% to be safe and avoid splatter and harmonics).
The problem is there are too many people out there that think over-modulation is the answer without understanding how that causes splatter or more occupied bandwidth to sound "loud" when in reality all they are doing is causing interference and reducing their total contact reach (more bandwidth = less transmit range at same RF power output).
The answer should be to restrict your radios to only 100% positive and 95% negative like they were probably designed to be as close as possible from factory. Running a power mic probably only overloads the built in automatic mic level limiter which will make you sound distorted and splatter over other channels.
You can use higher than 100% modulation as long as negative never goes below -95% but you are only adding distortion or what you call positive swing which is nothing more than a myth in the respect of increasing your range comparing PEP output of positive swing to zero swing at the end of the day.
In other words adjusting carrier level does nothing to increase range when going below zero swing.
Reducing average carrier to modulation (aka: positive swing) only does two things and two things only.. it introduces negative peak distortion (or round-off, roll-off to neg. portion) to your audio and allows your signal to drop under other stations at great distances for quieting or "blanketing " via carrier. This DOES not increase range.
This is an absolute fact and regardless what someone tries to tell you or even if you believe otherwise yourself you are only being fooled from real science of AM itself.
The proper way to get loudness, not occupy more than 1 channel (no splatter), and get the most out of your RF output for range is to run the radio the way it is meant to, or clip the built in limiter but ONLY IF/AND you are running outboard processing and know how to properly measure modulation levels on an oscilloscope.
That processing should be setup to run the mic into a compressor, then an audio limiter, then the limiter into a final audio clipper to sheer off what the limiter missed, and finally into an audio low pass filter to limit bandwidth to 10kHz or less and finally into your radio.
This is exactly how broadcast AM stations do it to get maximum loudness while still remaining in channel and in regulations except things get more complicated for them when introducing pre-emphasis required for AM broadcast radio.
Luckily with CB and Ham radio you do not need to worry about that extra headache.
BTW my first post, sorry for the info overload :laugh:
