Without a suppressor, you hear 2 things when firing- the gases being released and the sonic crack of the bullet (anything over ~1110 fps). These 2 together make the "bang". With a suppressor, you muffle the gases part to quieten it down, but still get the sonic crack (for full power ammo). The subsonic round takes away the crack, and has a low powder charge for less gases (or less bang). If you reduce the speed to around 2K fps, you reduce the powder charge also, which will reduce the bang some, but still have the sonic crack. Shooting this reduced load suppressed will quieten down the gases some, but maybe not enough to tell with the naked ear, unless you have a DB meter. Essentially, anything over the speed of sound (1110 fps) would have the sonic crack and the bang. The bang may reduce slightly with a lower speed round due to less powder. How much? I don't think you could tell unless you have a DB meter.