To answer your question, the Sionics cans came in a number of iterations, some worked much better than others. As example the Sionics patented D.G. Thomas' "Perf Spiral" would be a gross under performer by today's baffle standards. As would the gas valve (SS/MAW), as would the original primary mentioned above.
But your question is "were they quieter than today's designs" and the answer is "depends on what your compare it to today."
Suppressor design has to take into account WHAT you are using your suppressor to accomplish. Suppressing 650 rounds per minute is vastly different than suppressing 10 rounds per minute.
The vast majority of suppressors we see today breakdown into three categories (we set aside all rimfires as that is a whole different discussion):
1. Pure junk designs (and there a great number of them).
2. Well designed for low rate of fire, high precision, rifle caliber centerfire cartridges.
3. Well designed for high rate of fire, low precision (<100 yards), pistol caliber centerfire cartidges.
1. Pure junk. Poor construction, poor suppression, poor accuracy.
2. Low rate of fire precision cans. Almost without exception they ALL far surpass any SIONICS series (S-1, S-2, S-3 often referred to as the MAWs)
3. High rate of fire cans. And here we can have a discussion. When one designs for pistol caliber, centerfire, full auto the design parameters are vastly different than for a low rof precision rifle can. The task is to provide tactical CQC suppression levels (quite low) for as long as possible before heat soak sets in.
Remember the rate of fire for the MAC10 was designed in part to provide bullet placement when fired perpendicular from a moving vehicle.
There the actual designs specifications focus on materials, VOLUME and baffle design. The typical MAC subcan were being highly modified by aftermarket providers even while MAC was operating out of Glover Street. In other words, back in the day MAC SIONIC cans were seen as being able to be greatly improved.
Wipes touched projectiles (not good), wore out (not good), leading and particulate build up was frequent as these were non-purging designs (not good), aluminum envelopes (not good), Perf Sipral or even the then superior punched replacement baffles as opposed to later fully faced cones ( not good), prone to backing off barrel thread (not good). etc. etc. etc. But, volume can do wonders for suppression, and some of the SIONIC cans were monsters....and they were and are to this day remarkably quiet.
Even leaving the primary untouched, if one dumped the original Perf Cone, timed the chambers with even the simplest of machine faced cone baffles and replaced the early leather wipes with neoprene or even last gen close tolerance "permanent" finals, using subsonic calibers (.45acp) they sounded like a hammer beating on mud, bolt was the loudest.
Not knowing what you heard/saw, what was actually inside the can, what rounds were used, if any ablatives (then called "dips") were in play, my answer to your question would be "could have been quite impressive, even by today's standards.....for 50 continuous rounds."
Having said that, a well designed subgun only has to be quieter than the MAC's bolt slam to beat the SIONICS can. Remember SIONICS was a pioneer in subsonic rounds.
WerBell closing the deal. Order room service, wait until the knock on the door, set 5 go into a stack of phone books infront of the buyer (11), open the door and see if the staff looks concerned. Never did.
Compare the size of that Sionics with the late model monsters (10).
