The world is currently flooded with reverb plugins and just about all of them are usable with a few that are truly fantastic. That said, most are based on the impulse response of either some excellent sounding recording environments, or early hardware reverb gear. What you don’t see much is some truly natural spaces, especially caves.
A cave has a possibility of being a great source for a naturally smooth reverb, but one problem is getting permission (usually from the federal or state park service) and other is actually getting the equipment necessary there to record the impulses.
Acoustician Yuri Lysoivanov of Flashpoint Chicago Campus of Columbia College Hollywood set out to change all that starting with some impulses from Mammoth Cave in Kentucky, which he described to a meeting of the Acoustical Society of America in Victoria, Canada recently. Mammoth was an excellent choice since it’s the longest cave network in the world at 400-miles long and filled with a wide variety of spaces within the system.
Most spaces that are sampled for reverb are wood or tile and we certainly have grown to like that sound. This particular cave has limestone and sandstone walls with a large number of naturally formed odd angles. This provides a warmth and diffusion that you just can’t find in manmade environments, which is what makes it so attractive as a reverb source.
Lysoivanov and his team only had permission to be in the cave for one day, so they could only record the impulse response of 4 spaces within the cave system. Surprisingly, the decay time was relatively short at 1.5 and 4 seconds, which is actually totally in the range for working with music. The responses also had a rather warm sound with the most energy at between 100 and 200Hz with a fairly steep rolloff starting at 300Hz to 8kHz.
Cave reverb is an untapped resource and may be a missing link in our search for the “perfect wave” when it comes to reverb. I hope these samples show up in an impulse library somewhere soon. I have a feeling that a lot of us will want to use them.