Tactical Sound Detection Rules

[swaghauler]

This recently came up in my campaign because my PCs have now acquired enough suppressed weapons that I needed better rules for sound detection.

What I'm currently using is a system where I determine the background noise in Decibels (using commonly available charts online) and I subtract this "background noise level" from whatever noise level my PCs are generating and apply it to this chart to determine the chance of hearing that activity with a PERCEPTION check (my Observation skill)...

MODIFIED DECIBELS CHART (after subtracting activity noise from ambient noise)

0 Dbl or less = IMPOSSIBLE TASK
10 Dbl = FORMIDABLE TASK
20 Dbl = DIFFICULT TASK
40 Dbl = AVERAGE TASK
80 Dbl = ROUTINE TASK
160 Dbl = EASY TASK
161+ Dbl = Automatic detection, no roll needed.

For Silencers, I go a little "Hollywood" because games should be fun. The chance to be detected becomes one level harder for EACH RANGE BAND the weapon is away from the person listening to it. So if a suppressed 9mm pistol has a rating of 130 Dbl (down from 160), It is an EASY task to hear it at Short range. A ROUTINE task at Medium range, an AVERAGE Task at Long range, and a FORMIDABLE task at Extreme range to detect that pistol.

I also add...

- 10 Dbl of Suppressor reduction for specialty ammo designed for suppressed guns.
- 10 Dbl of suppression for a locked action (where the gun doesn't cycle to release noise from the action/chamber).
- 10 Dbl of suppression for light fluid in the Can (suppressor) like water and 20 Dbl for heavy fluid in the Can (for wipes or grease).
- Earplugs are good for from 20 Dbl to 30 Dbl of sound reduction.

For those wondering, here are my background noise levels...

0 Dbl (true 0 not modified Dbl) = Beyond the range of human hearing.

10 Dbl = Normal human breathing at rest.

20 Dbl = Silent walking, whispered speech

30 Dbl = Light rain, walking in the woods on twigs.

40 Dbl = The typical noise in a family home or in a quiet social gathering.

50 Dbl = Steady medium rain with wind, typical noise in an apartment complex at rest.

60 Dbl = Normal Conversation, typical social setting (office, upscale restaurant, etc...)

70 Dbl = A hard rain or very windy moderate rain, typical social setting (busy office, restaurant, command post, etc...), light traffic in the background.

80 Dbl = Fresh gale, A chaotic social environment (a typical city fast food joint, warehouse, or very busy office), heavy traffic in the background.

90 Dbl = A SHOUTED Conversation, train station, heavy (diesel) commercial traffic, warehouse with heavy equipment in the background.

100 Dbl = Subway platform, light construction, port facility, stadium crowd, a fistfight in a bar. *At this level, prolonged exposure to the sound will cause hearing loss after 15 minutes of exposure.

110 Dbl = Power tools, Rock concert, turbo-prop aircraft, high-speed train passing, melee weapon combat.

120 Dbl = Jackhammer, Siren at 100ft, power hammer on steel, turbofan aircraft, muscle car headers,

130 Dbl = Heavy industrial machinery, military ducted jet engines running. At this level, even short exposure to this sound can cause hearing damage.

140 Dbl = Comercial jet taking off, small caliber or low-charge black powder firearms under 750 ft/sec.

150 Dbl = Black powder firearms over 750ft/sec, firearms under 1,000ft/sec.

160 Dbl = Most rifle rounds under .40 caliber and under 3,000ft/sec, singer shattering a glass.

170 Dbl = Most rifle rounds over 3,000ft/sec (5.56mm m193 ball is 165Dbl)

180 Dbl = Larger (.50 cal & elephant guns) rifle rounds, artillery firing, explosions, the LRAD's "warble" used to disperse protesters.

190 Dbl = Major explosions. Above 195 Dbl, sound becomes a shockwave that can cause damage to all physical objects.

Barriers CAN affect ambient (background) noise with paper-thin apartment walls absorbing 5 Dbl while typical doors and walls reduce it by 10 Dbl. Well-built structures, fire doors, and security doors could decrease sound by 20 to 30 Dbls.

So how do you handle suppressed weapons and sound perception in your games?

* over the course of months or years, not immediately.