Extremely Loud and Incredibly Close: Mixers at NHRA Finals Deal With 165 dB

The National Hot Rod Association (NHRA) is closing in on its season finale, the AAA Auto Club finals Nov. 8-11 at the Auto Club Raceway in Pomona, CA. And if you haven’t heard top-fuel dragsters up close, then you don’t know what loud really is.

“Massive [sound-pressure levels]. One hundred sixty-five dB. It’s like standing next to an explosion; it rattles your internal organs.”

At the AAA Auto Club finals, as many as 26 microphones are placed at key points along the 1,000-ft. strip.

That’s Tim Record speaking about what it’s like to the A1 mixer for ESPN’s broadcasts of the NHRA Full Throttle Drag Racing Series, which has held 23 events since February, leading up to next month’s finals. “The sound can be deceiving, since so much of it is felt rather than actually heard,” he continues. “It hits you right in the chest. That’s one of the challenges of the sound for drag racing.”

Another is how to capture the sound of top-fuel dragsters and Funny Cars that hit speeds in excess of 300 mph over a 1,000-ft. strip (down from the historic ¼ mile [1,320 ft.], in order to limit top speeds and increase safety in the wake of a number of driver injuries and deaths). The numbers are jaw-dropping: they approach and sometimes exceed 165 dB, exponentially beyond (on the logarithmic deciBel scale) the 116 dB recorded at Cameron Indoor Stadium at Duke University during a game against Wake Forest in 2009 or even the 127 dB worth of vuvuzela horns at the World Cup in South Africa. According to an article on ESPN’s Go.com, the NHRA once let the network bring some seismologists out to the starting line, where two top-fuel dragsters registered a 2.3 on the Richter scale, the scale used to measure earthquakes.

Record relies on field technician Mason Armstrong to place a series of 26 microphones at key points on the strip. These include two Audio-Technica ATM 250 large-diaphragm microphones in each lane at the staging area/starting line — aka the launch point — just aft of the cars themselves to catch the engine roar of the takeoff, as well as two pairs of Sennheiser 416 shotgun mics attached to the “Christmas tree” array of lights that acts as the countdown to the start of the race.

Two robo-cams are lined up at the starting line with Audio-Technica BP4027 stereo shotgun microphones attached. These catch the initial departure sounds of the cars as they head down the track. A series of strategically placed shotgun mics are taped to the track sidewalls — isolated with foam from the wall itself to reduce mechanical-coupling vibrations — and pointed almost exactly parallel to the wall and facing up and down the track to pick up the cars as they traverse the course over the next 4.5 seconds.

“These microphones are synched with the cameras along the track, so they have to be opened very precisely and very fast,” says Record.

That task falls to submixer Rusty Roark, working a Yamaha MC7L console in the C unit of the Crosscreek truck that has followed the series since the beginning. Record mixes from the truck’s A unit on a Calrec Sigma console.

“Rusty has eight fingers on the faders at all times, and he’s opening them as the cars pass each camera,” explains Record, who has been mixing NHRA off and on since the 1990s and regularly since 2005. “He’s gotta be quick, and he is.”

There are more microphones at the end of the track, including shotguns attached to camera 5 at the 1,000-ft. finish line. A dedicated “chute” mic — Shure ECM-77 electret — located near the 1,600-ft. point on the track picks up the sound of the cars’ parachutes as they deploy to slow the cars at the end of the run.

Record says microphones are sometimes casualties to the excessive SPL, especially around the launch point, where engines do occasionally blow up before the race begins. “We’ve lost a few diaphragms to that,” he says nonchalantly. “Microphones just aren’t built to withstand that kind of SPL.” Microphones are also occasionally lost as cars hit the wall and, in some cases, are grabbed by the parachute’s fluttering edges.

“It seems that, when they hit the wall, they hit it far away from a microphone, or else they take a mic with them,” says Record. “I’m still waiting for one to hit the wall close enough to pick up the crash sound but still leave the mic intact.”

RF and Low Frequencies
Other audio sources include driver/crew radios, with RF services provided by BSI on-site. Record says the mixers recently began isolating the RF audio, hard-patching that to deeper EVS tracks not available in the router, in order to be able to call it up for replays. Crowd noise is also a big part of the background ambience. However, quick and frequent cuts between track action and announce talent in a booth can make for jarring audio contrasts. So Record created a nine-minute loop of previously recorded ambience that is always available on its own fader and is mixed in lightly to provide context for talent-shot cutaways.

NHRA broadcasts are done in discrete 5.1 surround. What sets these shows apart from the typical live broadcast is that, because the six-hour event is compressed into a two-hour time slot, each show is essentially posted on the fly. The effects tracks are encoded prior to the program mix and recorded on isolated tracks. This way, they are archived as Lt/Rt for future use as 5.1.

The full program mix is separately encoded Lt/Rt. “This makes it possible to edit on the fly because the edit facility is based in stereo audio and can not handle discrete 5.1,” Record explains.

But the biggest challenge remains capturing the true effect of the low-frequency component of the sound. Record likens it to hearing gunshots live, then listening to recordings of them, which rarely capture the full impact of the reports: a “boom” reduced to a mere “pop.”

A combination of large-diaphragm microphones and equalization — usually rolling off some of the upper frequencies — produces good results. Outdoor events in potentially windy environments usually call for rolling off some low end on the source microphones to minimize low-frequency wind rumbling, which means that some of that is added back with EQ as well, says Record. But he’s still looking for a way to adequately convey the visceral aural impact that a 9,000-hp top-fuel engine can inflict when it detonates.

At least, he says, he has lots of opportunities to experiment: “If you don’t blow up a few engines every race, you’re not really trying.”