How BOOM built the world’s biggest explosion sound effects library

The sound effects team at BOOM really goes all-in when they do something, and their newest release is the biggest explosion sound effects library ever created.

The library was created in collaboration with the EA DICE Battlefield sound team - and uniquely, this one was captured in an actual urban environment, a setting where explosion sounds are often heard in movies and games. Here's the story on how they managed to do that, and the challenges and possibilities offered by such a special recording location - as told by BOOM Library's Axel Rohrbach:

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How did the idea for the Urban Explosions library come about, and how’s it connected to DICE’s Battlefield?
If you have a look at all sorts of media, explosions mostly happen in urban environments, be it computer games, movies or TV shows. However, you won’t find many source sounds of explosions recorded in such an environment, actually – for obvious reasons: it is very hard to find a place with lots of buildings which is not crowded and noisy, a place where it doesn’t really matter if another window bursts because of the shockwave of an explosion.

It is very hard to find a place with lots of buildings which is not crowded and noisy – a place where it doesn’t really matter if another window bursts because of the shockwave of an explosion

We indeed burst out most of the windows which were still intact when we arrived first. I met Bence and Andreas from DICE and told them about my plans. They were fond of the idea and to help out with their expertise on the recordings, so they joined the session to get fresh and custom material for the Battlefield franchise. We discussed what each party is after and split different acoustic tasks so that in the end we would have a wide variety of perspectives when all these tracks get combined in a session.
 

What did you want to do differently from the other explosion libraries out there?
Most importantly we recorded in an urban environment but we also captured different spots within these locations, to have a diversity in terms of reverb tails. Additionally we recorded something less urban sounding to be able to offer the most flexible set of tracks. In the end, this gives the user the possibility to work with the Construction Kit files to create explosion sounds for non-urban environments as well. Additionally, we were able to record indoors in many different sized and shaped rooms; another rather rare opportunity for us which helps making this library unique.
 

The launch trailer for the Urban Explosions library

What’s characteristic about explosions recorded in an urban environment – and how did you find a fitting location?
In general you will have much more distinct echoes rather than a reverberant and diffuse tail once you get straight walls. The more buildings, the longer the distinct echoes can be heard. We were able to place microphones in the streets, on upper floor balconies and close to walls outside of buildings. We also changed the detonation spots to create different sounding tails. The sonic characteristic in general is just much more diverse and flexible, especially because we did record distant explosions with microphones up to 200 meters away in an open field as well.
Finding the location was indeed a very difficult task. It is not enough to have two buildings with only one floor. You need as many buildings as possible to get a real urban feel.

We were able to place microphones in the streets, on upper floor balconies and close to walls outside of buildings. We also changed the detonation spots to create different sounding tails

Finding such a place without any surroundings like a highway, railroad lines, airports, farmers or neighbors who get either afraid or annoyed, that alone was a hard task. Add to this a place where it doesn’t really matter if you have a ton of craters on the property or, as stated before, if something like windows break – this makes it even harder. I talked to movie location scouts first. That turned out to be a dead-end as they normally only understand what a good picture is, not that much what the needs for a good field recording spot is. I talked to the military, to industrial places, to private people.

In the end our explosives supervisor, in cooperation with some location scouts he was working with beforehand, were able to find three more or less suited places. Another point that makes it more difficult to find locations for explosion recordings is that we were there for three days in a row. It is easier to get permissions for one firework that lasts for 30 minutes, or just a few bangs of explosives. But finding a place that allows for three days was hard.

How did you prepare for the actual recordings – and can you share some details on your recording setup?
We had a very diverse setup, basically we brought everything we had. Our main setup which is Sound Devices 744T recorders and the Sonosax R4+ recording 15 microphones was setup to record the main tracks. Several microphones ranging from mono dynamic mics over diverse stereo setups to ambisonic. In addition, we had handhelds set up all over the place, ranging from Olympus LS5 over Zoom H6 to Sony PCM100. These were meant as some kind of experimental addition.

In the end, we were surprised how well those performed on such loud sources. We had tons of microphone cables with us. Some things that need to be considered and stuff we always bring: duct-tape, enough drinking water, snacks to stay concentrated over the long and active days.

Also something we mostly bring is enough plastic bags to cover up each microphone and recorder in case of rain. On the second day, every half hour or so it poured for 5 minutes, so we had to rush, covering and uncovering everything to be able to go on as quickly as possible. Luckily that worked out without any issues, even with the Schoeps mics we brought ;-)
 

What are some of the highlights for you in the library?
In my opinion the flexibility is one of the absolute key highlights. With urban, open field and indoor bangs, you have a library that can be used not only for explosion sound design, but also to support gun shots or to design cannon shots. But even to create sweeteners for huge footsteps of dinosaurs, dragons or Godzilla, epic door slams, even percussion and trailer hits.

There are some experimental recordings like microphones placed inside a gully or metallic pipes which almost sound synthetic. The track count allows for mixing in diverse surround formats and also offers the possibility to create a sheer endless amount of different sounding bangs.
 

What was the biggest challenge in making the library? Any lessons learned from making it?
One challenge that popped up over and over again in creating this library was to explain to people what is important when recording sounds instead of picture. That started with the search for the right location (see above), but also required clarification with the explosives supervisor. Normally they’re looking for explosions that either look cool or destroy as much as possible – both mostly being as quiet as possible. We were after something that is highly controllable and destroys as little as possible and we were not at all interested in cool visuals (a.k.a. big fireballs, as we already have them in the trailer for our DESTRUCTION library :-). The explosives supervisor obviously is a professional in what he does, but it was a rather uncommon request.

Another challenge was the weather. In the end, everything worked out, but we were constantly afraid that we would have to stop because of rain. I think the biggest challenge was indeed to find a location that offered what we were after: quiet surroundings, many buildings; basically a ghost town with the possibility to get some kind of permission to do whatever you want.

Any tips for making the most of the library?
A general tip working with multi-channel recordings is to first look for one file that is as close as possible to what you have in mind and go as far as needed with EQing, compressing, distorting etc. Only then try to fill it up using more channels with distinct characteristics that might be still missing like a longer tail or a short bass kick. Try to avoid too much overlapping within the same character / frequency response. This helps to avoid creating a dense white noise sound and works for gun recordings, explosions, multi-channel car recordings or even drum-sets.

Other than that: the Designed versions are always a good starting point, being already pretty dense, loud, compressed. Use the Construction Kit to add unique flavor. The Construction Kit sounds are still pretty dynamic on purpose. You can highly process them or leave them as they are to get a more realistic character. If you do so, keep in mind that in reality these bangs are really very loud, so put this into context. Make sure that quiet stuff like footsteps or grass rustling surrounding the explosion are really quiet in a mix compared to the bangs to create this loud feeling.
 

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