You cannot look at it like that. 10 decibel increase doubles the sound each time I believe, so the reduction of 21-26 dB would reduce the gunshot sound by approx 25-30% IMO. Then if the front door were closed or open there could be an additional reduction in noise. I believe neighbours thought it was fireworks being let off but I don't have links so this is IMO.
ETA A link re decibels might help. This seems to indicate 26 decibel reduction could reduce the sound of a .45 ACP to the sound of a .22 rifle.
How loud is your gun
From that link -
"How much noise does it make?
So you want to know which cartridge makes the louder bang?
Some technicalities are in order first.
Sound is measured in decibels (db), much like temperature is measured in degrees and speed in miles (or kilometers) per hour. Like most other units, the bottom of the scale or 0 db, is an arbitrary setting, which by convention is set to be the level of the sound that we can bearly hear, or our hearing threshold, as it is normally known.
One difference between the decibel scale and most of the other units we usually use in our everyday life, is the fact that the decibel scale is not linear, but logarithmic. In a linear scale, like velocity, if someone's car is moving at 100 mph, we know that he is moving at twice the speed of someone else who is doing 50 mph, i.e. 2x50 mph is double the velocity of the second car. In logarithmic scales a sound which is only 3 db higher than another, has twice the energy. For example, if you look at the table below, the 9mm Para cartridge at 160 db has twice the sound energy of the .45 ACP cartridge which is measured at 157 db.
Another complication is that the human ear does not hear linearly either. Although loudness is subjective, most people perceive one sound to be twice as loud as another, when there is a 10-fold increase in energy, or a difference of about 10 db. So a 60 db sound sounds twice as loud as a 50 db one, although there is 10 times more energy in it. Also, it is interesting to note that most people cann ot discern any difference in perceived loudness of less than 3 db. That means that the energy in the sound has to double, before someone can notice any difference.
After this technical jargon, here is a table of loudness.
db Environmental noise
0 Threshold of hearing
10 Normal breathing
20 Rusting leaves
30 Whisper at 30 feet
40 Quiet street
50 Interior home noise
60 Conversation
70 Crowded restaurant
75 Kitchen appliances
80 City traffic
85 Hearing damage possible
90 Lawn mower
100 Chain shaw
120 Threshold of pain
120 Siren
134 .22 LR rifle
140 Jet engine at take-off
150 .410 shotgun
152 .22 LR pistol
153 20 gauge shotgun
155 .223 rifle
155 .25 pistol
156 12 gauge shotgun
156 .30-.30 rifle
156 .308 rifle
156 .44 Special revolver
157 .22 Magnum pistol
157 .45 ACP pistol
158 .380 ACP pistol
158 .38 Special revolver
159 .30-06
160 9mm Para pistol
163 .41 Magnum revolver
164 .357 Magnum revolver
164 .44 Magnum revolver "