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The Caverns

Dan Daley • InstallationsSeptember 2019 • September 11, 2019

The venue has a capacity of 1,000. Photo by Michael Weintrob

This Rocking Venue Gets an Upgrade that Fred Flintstone Would Appreciate

Todd Mayo had never been inside a cave before Memorial Day, 2008. When he came out of the first one he’d ever been in — Cumberland Caverns, in McMinnville, Tennessee, about 50 miles southeast of Nashville — Mayo, a former marketing specialist from Memphis, had a spelunkogical epiphany: caves are great places to hear music in, and he was going to produce concerts in them. Ten weeks later, Mayo, who points out that he’d “never so much as booked a bar mitzvah” at that point had a lease on one of the caves, and within a few shows, had a commitment from PBS to air Bluegrass Underground, a series he co-developed and shot in front of a live audience in the cave.

This July, the show was about to tape its 10th season. This year, though, it’s the first complete season in a new cave. Not so much geologically new — the sedimentary Monteagle limestone that makes up most of the state’s 8,000-plus caves formed between 200 million to 240 million years ago, during the Carboniferous period. But this year, Mayo actually owns the cave, in Pelham, about 80 miles southeast of Nashville and formally dubbed The Caverns, a more generic moniker to reflect how the venues grew over time to include not only bluegrass but also rock, pop and even insert-adjective-here metal bands artists who, like Mayo a decade ago, felt some inexplicable but deeply resonant limbic kinship with a hole in the earth.

Rev. Sekou was among the artists that appeared at The Caverns for PBS’ Bluegrass Underground show.

‡‡         New Sound

In the process of transitioning from renter to owner, Mayo approved the acquisition of a new P.A. system for the venue. A major consideration was a new P.A. for the larger space, which can seat 750 or stand 1,000 patrons comfortably in an audience section created after several hundred-thousands of cubic feet of rock and dirt were excavated over the course of a year to create the venue. Six QSC WideLine 10 dual 10-inch line arrays per side create a pair of stereo hangs. There are two JBL VerTec 4880 subs, one placed on a kind of natural ledge that serendipitously is also the zero-reference point for the system’s time alignment. Powering is via 16 Crown I-Tech 12000HD amplifiers, split evenly between the P.A. and monitors. Eight Sound Image-branded G2 wedge monitors are available for the system, which is leased through and installed by Sound Image’s Nashville office.

Given the venue’s uniqueness, the sound system is carefully calibrated for it. Thus, the venue strongly recommends that touring artists not bring their own sound systems or insert-related gear (such as processors or EQ), although they are welcome to bring their own monitor systems — and those who do typically use IEMs. Visiting FOH consoles, though, are welcome, with The Caverns staffers nearby to guide mixers through the cave’s acoustical idiosyncrasies.

Like a firecracker in an ammo dump, even a little bit of sound can have major implications in an acoustical environment like a cave. Andy Kern, the avuncular staff FOH mixer who has been with the cave’s production team virtually since the beginning, says each performer and band needs to be evaluated on its own; electrified bands with drum kits can sometimes reach 95 dB before they’re even in the P.A. system. Sometimes, the entire band goes through the P.A.; other times, it might be just the kick and the vocals. The cave seems to decide the input plot, based on performers’ volume, attack and some mysterious combination of juju that includes a constant 56°F temperature year round and a barely fluctuating 90-percent humidity level that will express itself in ways such as moisture on the bottom of the line array hang.

At the end of last year’s concert season, the P.A. was sent back to Sound Image’s Nashville shop for a refurb that included brushing off calcium “rust,” spraying the boxes with silicon and powder-coating metal parts. The Yamaha M7CL FOH console is carefully positioned in the exact spot that doesn’t get an occasional drip from the ceiling. Kern, a Texas native who has also mixed PBS shows such as Music City Roots, says the venue allows him to build mixes in which certain instruments are heard only acoustically while others are in the P.A., but which all sound seamlessly integrated from the stage.

Billy Strings also made a Bluegrass Underground performance at The Caverns.

‡‡         Improved Logistics

The Caverns has a lot of other benefits over the venue’s previous iteration. Its larger size — about 530 feet from the mouth of the cave to the lip of the plank-floored 30-by-20-foot stage and a 20-foot ceiling over the seating area — allows trucks up to 24 feet long to back in on a poured concrete floor that extends the length of the cave. And under that concrete pad lie conduits with copper and Cat-5 cabling for audio and fiber for the cameras and recorders aboard the TNDV remote-production truck used for Bluegrass Underground and other shows.

The power here is also permanent, supplied by the local utility instead of having to rely on a portable generator, as they had to at the previous cave. The logistical advantage of the larger cavern allows more complex performances, such as the Flaming Lips’ New Year’s Eve show that included the band’s own laser-lights show as well as its own audio and lighting consoles. The venue now has full touring distro, with 60 amps for audio and 200 amps for lighting, which consists mainly of conventional PAR cans hung from four lateral trusses, installed by 4Wall, but with provisions for touring fixtures to be added as needed.

‡‡         Cave Acoustics

You’d expect that acoustics would be the primary challenge for sound in a cave, but you’d be wrong. Or at least… not right. Kern says keeping a lid on volume is job-one for front of house, as well as judiciously choosing to leave certain instruments out of the P.A. mix, when necessary. But the cave itself is remarkably accommodating for sonic behavior: rather than reflect sound, the cave interior’s many rock facets actually act as massive diffusors, keeping nodes from forming, while the cave mouth acts as a sort of bass trap, keeping LFE SPLs from accumulating.

These natural acoustical treatments help address the particular characteristics of the wider range of genres the cave now attracts. That extends to letting even some pretty loud performers come pretty close to 11 on their amps, such as the Seattle noise/black-metal band Sunn O))), known for a sound described as heavy, slow, and loud, and who played the cavern last April — six Marshall half stacks on the stage, but no rockslides. (Photos from that show in a Nashville paper suggest it was also an excellent visual pairing as well.) In fact, Kern adds, he consulted with an acoustician about possible commercial-type treatments early on, expecting (like most people) that a cave would be a reverberant space that required taming. But there was nothing on the market that could withstand the cave’s constant high humidity. “Absorptive materials aren’t going to work well if they’re always damp,” he says. “Plus, we didn’t want to have baffles possibly interfering with the sightlines — you want as little as possible to distract from the fact that you are in a cave.” As it turns out, the cave’s natural acoustical characteristics were best left as is, with attention paid mostly to keeping SPLs in check.

Swamp rock-funksters JJ Grey and Mofro rock The Caverns.

‡‡         A Perfect Match

In designing the sound system, Kern worked with Paul Fuerstenberger, a systems engineer at Sound Image in Nashville, who had also worked on the system at the previous cave. That venue, Fuerstenberger recalls, was wider and taller, and Sound Image’s own G5 boxes and Theater subs, which were rented in as needed, worked well in there ground stacked. But the new cave’s lower ceiling and longer throw distance called for a proper line-array design. After extensively measuring the cave’s dimensions, they ran those through several modeling software programs, including EASE’s Focus 3 array-modeling software, L-Acoustics’ Soundvision 3-D simulation and JBL’s Line Array Calculator, then applied the outcomes to several P.A. possibilities, including L-Acoustics’ Kara and JBL 4886 products. Fuerstenberger says they decided on QSC’s WideLine for its larger low-frequency drivers, which would let the boxes take more of the low-frequency work off of the subs.

“The room was already kind of low-mid heavy, and we needed to control some of that,” he explains. “This way, engineers wouldn’t have to push the subs as hard, especially since we only have one [sub] per side.”

Sound Image’s Paul Fuerstenberger spec’d the system.

Given that the space’s physical characteristics weren’t going to change anytime in the next million years or so, to stabilize the system’s performance they set the presets in the amps and locked access to them, installing a pair of Lake Mesa EQs, one to steer the main P.A. and the second for the subs and fills. These manage the main arrays and subs as well as the Sound Image 1160 front-fill speakers.

“We wanted to make it as easy as possible for the engineers who have to mix in there,” says Fuerstenberger. “The P.A. and the room are perfectly matched.”

The first time an artist came to play in the original cave, Kern says just the idea of being in a cave was novel enough. Now, artists are equally amazed at being underground and with sound and other staging elements that are on a par with what they experience elsewhere, albeit with more need to keep tuning acoustical instruments thanks to the humidity, which will also cause an occasional crackle in a mic cable connection or dampen a transducer (which the top-flight tech staff usually anticipates and quickly remedies). But once the house lights go down, a show there is almost like one played anywhere else. Except, yeah, you’re in a cave. A big, really nice-sounding cave.

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