Is there such a thing as a low RPM alternator

Like most of us, my Dart voltage drops below 12 volts at idle, but runs 14-15 at cruising speed. is there such a thing as an alternator that is designed to work at full capacity at lower rpms, or is there something else I can do? I do not use the factory ammeter. I disconnected it and connected both the wires together when I installed my custom dash and voltmeter. It's never been a problem, but I hate seeing such low voltage at idle.