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A few PCs in my group have used Thunderwave quite liberally. I recently realised that it emits a boom audible up to 300 feet. When one of these booms happens, does the GM:

  1. Do nothing?
  2. Roll to determine whether a nearby (≤300 ft) group of enemies heard it and begins to approach the party?
  3. Determine that a nearby group of enemies definitely heard it and starts to move towards the party?
  4. Something else?

I'm currently running “Greenest in Flames” from Hoard of the Dragon Queen, which, by design, already has a large group of enemies running around — true, there is noise/chaos due to the attack, but these booms are bound to attract attention.

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There are not precise mechanics for this, so take the action that best enhances the narrative.

Looking at scale on the map of Greenest, 300' is actually a pretty large area relative to the size of the town. Also, the adventure recommends rolling for a random encounter for every 100' travelled in town. Looking at the encounter probabilities, it seems almost certain that there would be some groups of raiders within that radius.

Despite the general chaos in the town, a booming clap of thunder should be loud and distinct enough to be noticeable. How the raiders would react to it isn't clearly spelled out, however. They might be inclined to investigate, but there are various reasons that they might choose to ignore it instead, such as assuming it's the dragon's doing, being too focused on the looting they are doing, or assuming that someone else will deal with it.

As a GM who has recently run this adventure for a party with both a Druid and Bard who know Thunderwave, this is how I handled situations where it was cast.

The spell was first cast to save a group of townsfolk before the party even made it to the keep. I picked one of the more intimidating random encounter groups (with a drake) and had it approach the location of the battle. I had forewarned the party that the spell might draw attention, and they managed to spot the approaching group before it spotted them, so they ran away and hid, stumbling upon some more hiding townsfolk in the process. Responding to the thunderclap in this way added to the tension of the scene and helped maintain momentum after the battle.

The second use was against the ram at the front of the temple. The spell took out most of the encounter group and destroyed the crude ram, but it also drew the attention of the wild patrol around the temple. The party used this to their advantage, letting the patrol chase them away from the temple, leading them away long enough for those trapped within to escape. Responding to the thunderclap in this way rewarded the players by allowing their creativity to overcome a very difficult obstacle.

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    \$\begingroup\$ Good point about there being dragon activity in the area. Especially because it's a blue dragon, thunder might draw less attention than it otherwise would. \$\endgroup\$ – Bradd Szonye Oct 15 '14 at 0:38
  • \$\begingroup\$ I like your answer a lot since you used your own experience. And with your examples you give the asker some good ideas how to solve his/her problem. \$\endgroup\$ – Tijnkwan Oct 15 '14 at 6:58
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“Greenest in Flames” provides a random encounter table for parties who travel in the open (or who fail at stealth). If the players take action that specifically draws attention to them, like cast thunderwave, I would make an additional roll on the encounter table. If they persist in drawing attention to themselves, I might even make the random encounter automatic, or roll for more than one at a time.

In situations where there are known enemies nearby (like the episode’s “Sanctuary” mission), you can use passive Wisdom (Perception) checks for the enemies to see whether the sound has drawn their attention. I recommend DC 5 (very easy) to notice the booming of thunder, although in the noise and chaos of Greenest I also recommend making the checks with disadvantage, so some groups may overlook the noise.

Once you’ve determined who notices the noise, you can determine who responds to it and how. Sentries, guards, and foes who are looking for a fight are likely to respond, unless they have a reason to call it somebody else’s problem. Other foes may take defensive action like locking doors and watching out for trouble. In this case, there is blue dragon activity in the area, so foes might pay less attention to lightning and thunder than they otherwise would.

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    \$\begingroup\$ The last paragraph reminds me how the lack of Reaction rolls (and Morale rolls) in 5e is a disappointing oversight in the designers' incorporation of older editions' best ideas. The Reaction table is the highest play-effect:rule ratio ever packed into three column inches and would have been so easy to include. \$\endgroup\$ – SevenSidedDie Oct 14 '14 at 23:28
  • \$\begingroup\$ @SevenSidedDie Reaction and Morale may be in the DMG. Until the DMG actually releases, we won't know for sure. \$\endgroup\$ – aramis Oct 15 '14 at 3:48
  • \$\begingroup\$ @aramis That's quite true. The developer blogging up to now has ignored the concept though, and it's absent from the MM (where I'd expect individual morale ratings to appear) and the Starter Set's DM material, so I'll be surprised, pleasantly, if the DMG proves me wrong. \$\endgroup\$ – SevenSidedDie Oct 15 '14 at 4:40
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I would do #3, but the result would surprise you in the case of Thunderwave. The short explanation is that something "audible at 300ft" is actually really not that loud. Imagine someone hitting two twigs together a football field away from you in silence - it would be "audible". The real question is whether or not your baddies might recognize the sound as out-of-place at the volume level that they perceive it, I would guess "it depends".


Here's a breakdown of why Thuderwave is not loud at distance:

it emits a boom audible up to 300 feet

I checked what "audible" means - 10 db according to a google search result.

Then I used this calculator to get a reference for something that would fade to ~10db at ~300ft.

The result is disappointingly quiet - at 1m (~3ft) you're already down to 50db which is described as "Quiet" with "light auto traffic [at] 100ft" as the example.
At 30ft it's down to 30db - "soft whisper"

If you interpret "audible" as "quiet" and bump the 10db up to 50, that bumps the 1m rating to 90db - "Heavy truck (50 ft); City traffic; Very annoying; Hearing damage (8 Hrs)"
At 30 ft it's down to 70db - "Noisy restaurant"
At 90 ft it's down to 60db - "AC unit; conversational speech"

AFAIK this is all in open air. It wouldn't be so loud in a dungeon with walls. Someone on reddit did a simulation of that.

As you can see, inverse square does a pretty good job of keeping things quiet, even if you consider the generous interpretation of "audible". What this tells me is that Thunderwave is extremely loud throughout the target 15ft cube, which is not how noise normally behaves - in real life it's closer to point-source.

tl;dr: If you're trying to imagine how loud thunderwave is from outside of the target cube imagine light traffic at 100ft, that's how loud it is 1m away. Not loud at all - "audible at 300ft" means just that.

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    \$\begingroup\$ This is so close to a quality answer that it hurts. The Question-and-Answer format of StackExchange doesn't lend itself well to extended comments or discussion. Rather, an answer should be just that: an answer. Adding just a couple of lines to directly answer the Question (and summarizing the Reddit post, in case that link should stop working for some reason) would turn this into an excellent answer. \$\endgroup\$ – minnmass Jul 21 '17 at 13:42
  • \$\begingroup\$ You're right, not wanting to waste that effort I added an explicit answer. =) \$\endgroup\$ – Vasiliy Sharapov Jul 21 '17 at 14:18

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