Um... I'm not sure you really need to think about this quite so much. I mean, I would think most guys and gals don't pay overly much attention to the sound of each individual pee stream in a public bathroom. It's a case of get in, get emptied, wash hands and get out.
And... in the event you find someone who does hang around in public bathrooms long enough to develop, and make use of an expert ear for urination variation (at the very least enough to differentiate between several flows occuring at once)... well I'm not sure being gender ID'd should be your first concern, whoever you may be, and it might be wise to think about a speedy exit strategy.
And if someone goes so far as to be able to assume gender based on flow rate, bowl harmonics, accoustics, angle of attack, seat height and appliance model number... it might be time to pray for a stun gun or big stick, lol.