16 ohm speakers parallel want 4 ohm impedance

You can't, the best you can do is 8 ohms with those speakers. Will it really sound louder at 4 ohms? No, almost no difference at all. Why?
It takes 10 times the power to double the volume (an increase of 3 db)
Changing from 8 ohms to 4 only doubles the power, and that's why there is no real hearable difference.
Now hooking up 2 cabinets instead of one cabinet? You will get a bit more efficiency, because four speakers move more air than two speakers. And it will be running at 4 ohms with two cabinets, a bit of an improvement.
And running at 2 ohms? don't do that. It will overheat and destroy the amplifier.

Actually now that I think of it, there is a way to make it better if you only can use one speaker cabinet. Take the stock speakers out and install EVM or EVX, or even JBL speakers. Then it will be louder and sound much better, and you can use two 8 ohm speakers to get 4 ohms.

double the power to increase it by 3bd

double the loudness (10db) requires 10 times the power.

get 2 speakers that are playing at the same wattage. the SPL should have only increased it by 3db.

it requires double the power to increase it by 3db not 10 times more...

Typically, it takes ten times the power to double the volume from the speakers.
That is why there is almost no noticeable difference between a 50 watt amp and a 100 watt amp.
Double the power only increases the power 3 db, not the volume.

yes i know.

but u sed, it takes 10 times the power to increase it by 3db.

thats wrong

10 times the power is twice the increase in 'loudness' which is 10dB

increasing by 3dB, only requires twice more power, which is twice th acoustic output.

oh, lord....

my god...

These are good points that usually get lost in "how many watts" conversations. The types of speakers and cabinet build can make a much more profound difference.