At first I thought it was just the powder I was using as I had read power pistol is quite loud in testing.

I switched to 231 and it is much quieter but it almost rings my ears but not quite.  I think maybe the decibel level is lower but the pitch is much higher.  My Tirant 45 never even slightly offends my ears.

Anyone else have both and notice this?

What velocity are your rounds going?

What type of bullet, how long a barrel, and how much velocity are we talking about here? If you're loading 115gr bullet to supersonic (~1100FPS) velocities, the sonic crack will be much louder than any .45 ACP.

IMO most .45 cans I have heard on a 9mm *sound* quieter than the corresponding 9mm can.  I am sure with some type of analyzer you could see but the tone/pitch is must lower and therefore sounds quieter.

We ran a test one day at work with a HK USP 9mm with a gemtech mk-9 (or whatever the GIANT can is), a prototype short 300blk can (2" diameter) opened up for 9mm, TiRant 9, TiRant 45 and Osprey 9.

The two large cans (mk9 and 2" can) sounded much quieter to the ear, sounded like a baseball bat hitting a pillow.  TiRant 45 sounded similar but a little louder than those and the TiRant 9 and Osprey 9 sounded the loudest/highest pitched.

On the meter however it was exactly how one would imagine.  TiRant 9/Osprey/TiRant45/Protocan/MK9.  The two largest cans metered out towards 136-137 and despite the TiRant and Osprey being 10db lower you really couldn't tell unless you were the sound meter or downrange I guess.

147gr FMJ bullets just shy of 1000fps.  Probably averaging about 950fps out of my extended threaded EFK FNP barrel if my memory is correct.  The host is an FNX 9mm.