Glad to help.
Yep, just like a beam antenna does only with db's of sound instesad of db's of rf energy. Concentrating it in one direction.
The Bulgy style attachments seem to concentrate the noise in the forward direction and lessen it proportionally in the others, particularly the rear.
So in total, the noise is the same, it is simply biased to the front which does not affect the operator whereas a true can actually internalizes and reduces the noise by expanding, baffeling and cooling the exhaust gasses.
It would not be hard for manufacturers to use a meter to make measurements for their devices and make comparitive gain plots for them so one device can be compared to another like is done for antenna's.