You can use your players' intuition that the sound of battle should be important without squashing their imagination of the dungeon, while also serving your GMing need to keep the whole dungeon from going "on alert" and dogpiling them at the first clash of swords. You do this by making sound weird in these strange, underground halls, and then telegraphing to your players how sound works in this dungeon by describing what they hear.
There are two standard ways to hint that fight noise will not normally carry, without simply revealing the man behind the curtain and showing that it's just a game and they "shouldn't" care about this.
The dungeon deadens sound
The hush of the tomb is expected, but there's something more to it. As you proceed down the corridor, you realise you don't even hear your footsteps echoing back at you. Conversation from the tail of your marching order sounds like thin, unintelligible whispers only yards away at the head. The very air itself seems to swallow sound.
Variations on this have been mentioned in various comments: muffling tapestries, loud or white ambient noise that masks the sounds of the party's incursion (machinery, noisy rituals, rushing water or air), and the like. Deadening sounds comes in a variety of forms, but they all have in common that a brief description of how the environment interferes with the party's hearing will let them know that fight noise is not going to travel as far as they would normally fear.
The location's acoustics confound the ability to tell where sounds come from.
This takes a bit more work. The best way to show (not tell) this is to insert random noises, screams, and whispers into the game. Creating a list and randomly rolling on it every in-game chunk of time is the traditional means.
For example:
Atmospheric Dungeon Sound Events Table
Roll 1d8 every 30 in-game minutes:
- A scream, suddenly cut off, echoes from somewhere deep in the dungeon.
- Mutterings that sound right behind your shoulder that slowly fade away.
- The noise of battle, seemingly coming from directly in front of the party, where they can plainly see there is nothing.
- The sound of dripping water, as if from very far away, but it follows the party without growing louder or fainter for several minutes.
- Growls echo down the hall (1–3: ahead, 4–5: behind, 6: both)
- A strong but quiet winds blows, but it seems to snatch away any attempt at conversation, carrying the party's words who-knows-where.
- No event
- Roll twice and combine, rerolling results 7–8.
(This is just am example. Expand as necessary before, between, or even during sessions.)
By giving a dungeon unusual acoustic properties, you can leverage how your players are already intelligently thinking about sound, making them aware in a natural way that the sounds of battle can't easily be used to locate them, unless the listener is already very close (and perhaps even not then). You also reward your players' engagement with the world by responding with in-world details about something they've shown interest in, making their investment deeper rather that fighting against it. As a bonus, it gives your dungeon more character and makes it a more unnerving and unnatural environment.
No. It is not necessarily centered on the caster (though it can be).
A cube is not a burst power (to borrow a 4e term). The origination point of the cube is anywhere on a face, not necessarily the center. The term face when referring to a cube means the entire square comprising a side.
So you could feasibly center it on yourself, or place yourself in any other point of the cube's effect (and no, you don't have to attack yourself unless you want to).
I wanted to map this out real quick, just so we're all clear. Let's assume we have a 15' cube spell, and let's also use a grid just so we have a bit of clarity, and a limited set of points to operate from. There are 18 possible origin points for a 15' cube, representing two different 3x3 areas (the top and bottom face of a cube). For both of these the graph is the same, but the results are different. If you select the top face, the spell targets the 8 squares in your plane, and the 18 immediately below you. If you choose the origin as the bottom of the cube, then it targets the 8 in your plane and the 18 above you. Now which square is the origin:
XXX
XXX
XXX
Basically, you can be standing in any of the squares that are X and have the burst be those 9 squares. Let's look at a few more examples (Caster is C):
XCX
XXX
XXX
Here you step to a side and have it radiate to your left, right and two rows forward of you.
XXX
XCX
XXX
Here you center it on yourself.
CXX
XXX
XXX
Here you take a corner of the spell and cast it to your left and forward, and radiates out. It seems you should be able to be outside teh area too:
CXXX
XXX
XXX
Since you're adjacent (and heck that could be the middle of a face or the bottom or the top of it. (See the caveat below, this particular form falls much more into the "point" point of origin argument and may or may not be valid in all games.
CAVEAT: There are at least two camps developing around the term "point of origin" used in the text, and depending on which system you came from you may immediately interpret that differently. I have used in this response the version of the term influenced by my 4e experience, which infers that the point of origin is an entire square (this makes a ton of sense when you play with gridded combat as the default, which I do in my 5e games). However, there is a camp that comes from a different point of view that interprets "point of origin" as a singlular point (with an undefined diameter, likely just the part of the cast casting the spell...not sure, I'll let them speak for themselves). This POV would have the caster included in the spell if you cast in the ways that I describe above where the caster is fully within the Xs.
It's important to note that right now both of these interpretations are equally valid and subject to DM interpretation. I'll be using the "point is a whole space unless you don't want it to be" version, feel free to use whichever is most useful in your game (just be consistent about it).
Best Answer
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.