Gun noise between floors

[thalcos]

I'm trying to put together some quick and dirty rules for a Die Hard-like scenario, where gun noise on one floor of a big skyscraper can attract baddies, but lots of floors separation probably won't. Curious if anyone has any feedback? (My dB science is rudimentary at best)

Most guns are in the 150 dB range. From what I can tell, a "typical" mixed-use building cuts noise by about 40-50 dB between floors. This means that anyone one or two floors away will pretty much always hear a gunshot.

Three to four floors away seems like a Per roll to pick up on gunfire, probably at a bonus if there's not a lot of background noise on those floors, or if the gunfight is an extended firefight.

Five floors away seems like when you're not going to really notice anything unless everything is quiet and you.

Does this sound about right? Or am I underestimating gunshot noise vs. modern building material?

[AlexanderHowl]

That depends a lot on where the shot occurs. Modern skyscrapers have shared structural elements between floors that can transmit sound, as can elevator shafts, stairwells, and ventilation systems, so I would say that a 40 dB drop/floor is realistic in individual offices, with a 20 dB/floor drop being realistic for hallways that connect to elevators and stairwells. In a stairwell or elevator shaft, the dB drop would be only 10 dB/floor, so someone on the 15th floor of a stairwell would hear a shot on the 1st floor of a stairwell, though it would drop by 20 dB/floor for connecting hallways and 40 dB/floor for offices.

[Anthony]

Assuming a fixed number of db drop between floors isn't really physically accurate; some of the dropoff is because it has to go sideways and echo up, and it can do that up multiple stories almost as easily as up one story.

[khorboth]

I can only offer personal experience, but it's something. When workers were doing construction on my middle school with a small caliber firearm, it was easily audible in the whole school. The farthest point was one floor down and about 30 yards away. The building was mostly concrete construction.

[Eukie]

Originally Posted by thalcos

Most guns are in the 150 dB range. From what I can tell, a "typical" mixed-use building cuts noise by about 40-50 dB between floors. This means that anyone one or two floors away will pretty much always hear a gunshot.

You can shave off 16-26 dB because a gunshot is a very short impulse, meaning it's harder for a human ear to detect. Say 20 dB for convenience. Through two floors, that's another 90 dB or so. This means the dB SPL (loudness) before distance is a mere 40 dB, which should be about -5 on a hearing roll at two storeys distance. In real world terms, it's probably another 16 dB reduction, for a loudness of 24 dB, which should be difficult to hear against any background noise.

Even at one floor it should be 80, requiring an unmodified hearing roll at less than 4 yards distance (about a storey), or have a dB SPL of about 70, which can be difficult to hear over regular conversation.

And this is for a dB SPL of -45 per floor. Thicker or sound insulating floors can probably up to double this.

As others have noted, it can be louder if there's an "easier" path for the sound to travel through. This can be a bit troublesome to model but the simplest way is probably to make note of where elevator shafts and stairwells are, and calculate the Range along the path through the vertical spaces, taking into account all walls/doors that block the sound.

[dcarson]

Add in possible background noise. A phone bank with 30 people making or receiving sales or support calls or programmers that like music while they program can drown out sounds.

[thalcos]

I completely forgot about the effect elevator shafts might happen on loud noises. This makes a cool addition, where PCs with good tactics skills can think about this ahead of time and then adjust their plans. Neat!

[AlexanderHowl]

Reducing sound by 90 dB between floors is nearly impossible without massive sound dampening redesign. That would be sufficient to turn an instantly lethal sound (200 dB) into merely a loud concert (110 dB).

[MrFix]

High Tech has rules for these under Suppressors section of gun accessories. HT159.

For intervening terrain of concrete, it's -1 to hear the shot through it, so -1 per floor is appropriate. What -1 means is that effectively the distance at which the shot is heard at Per+0 is halved.

Normally, most firearms are heard at Per+0 at 512 yards away. Let's say a sentry is 10 floors above the gunman. Assuming floors are at least 3 yards tall, that puts the gunman 30 yards away. This is 4 lines closer than 512 (512/2/2/2/2=32), so the sentry hears the gunshot at Per+4. But since there's 10 layers of concrete(and similar materials used for building housing), he has -1 times 10, so -10 to hear it, for total of Per-6.

For someone only 1 floor away (3-5 yards), the roll is Per+7 (7 lines closer than 512). Since there's only 1 layer of concrete inbetween, it's just -1 so he hears it at Per+6

Using a good suppressor (-4 Hearing), with subsonic ammo (-1 for pistols, -2 for PDW/Rifle), firing bolt action/slide lock weapon (-1), that's an extra -6 or -7 for total of Per-12 or Per-13 to hear a gunshot through 10 floors OR walls.

Since you seldom will be firing straight up towards the sentry, that's another -1 for being outside of gunfire's cone.