Recording a Tesla Coil (or 5) - Gear and Setup Question

[andrewpdupuis]

Hi y'all,

I've been a lurker here for a while, but finally have a situation where I really could use some assistance. I'm working on a music video shoot with an electric violin controlling 5 musical tesla coils, and am seriously struggling with tone and phase interplay. I have a photo of the staging attached - the coils can't go in my usual recording space due to EMI issues (and fire safety, since each puts out about 6ft bolts of lightning), so we're stuck with the big warehouse-type room for safety reasons.

Im also attaching an audio file of the current draft audio for context on the rest of this if you've never heard these things before. http://www.filehosting.org/file/details/750000/Palladio%20Second%20Mix.mp3

The big issues I could use some help with:

- Tesla coils sound weird - they're close to a trumpet in timbre, but even more aggressively resonant. The large coil in the center back of the image is the "bass" coil (down an octave and a half at its nicest tone), but the other four all operate in the trumpet bandwidth. I wanted to mic them with my SM57s since they're so loud (120-135db SPL max - we're in hearing protection while using them), but the 57s are sounding dead and I wanted to move to condensors perhaps? The recording above was with the small diaphragm condensers on the Zoom H4n i had for scouting.

- The space is very live as you can hear in the recording. Ideas for shutting some of that down with micing? Maybe some temp foam installs?

- FInally, how would you mix and mic? I was considering mic-ing each coil and running the midi parts of the show, then mixing in post once I'm back at my desk. I don't even know how i'd accurately monitor something so loud.

Thanks in advance for any input!!

[Hugh Robjohns]

I feel desperately sorry for the violinist who has to stand in the middle of all that noise!

Your best bet on controlling the room acoustic is to hire heavy theatrical drapes and hang them on a scaffold frame around the walls.

My concern with moving to capacitor mics -- aside from finding models with a suitably high SPL rating, of course -- is going to be of EMI interference... but you'll just have to try and see.

I think my approach would be to set up a stereo array a safe distance from the coils and record the whole thing as an ensemble in the room -- rather than close mic stuff. That approach will minimise the RFI and SPL issues, and capture the scale and power of the thing rather better than individual close miking, I think.

H

[Martin Walker]

Hi andrewpdupuis, and welcome to the SOS Forums!

I can't add anything to Hugh's already excellent advice, except to agree that moving back to get an overall sonic picture rather than attempting to more closely mic makes perfect sense and will minimise your interference problems.

I've just downloaded your in-progress audio version, which sounds great, but doesn't have any real feelings of 'power' from those Tesla coils, and none of the real low-end I was expecting.

However, do keep us updated - as a sound designer myself, I'd love to hear/see the final version when it's released!

Martin

[BJG145]

Awesome, I've just been looking at Tesla kits lately. Look forward to seeing the video. Stay safe!

[andrewpdupuis]

@Hugh - luckily she knew what she's getting herself into haha - she's one of the tesla coil builders, and we've got some decent hearing protection on her. Re: the room, I was thinking draping may be the only way. May not be in the budget - however, after talking to the tesla people we might be able to get away with running single coils in a much smaller space (ie: somewhere where we need 20 feet of draping not 200 ft). We still don't want this anywhere near our normal studio setups - I like my computer equipment non-crispy.

Having done some more testing last night, I tried mic-ing all the coils at about 6ft (the closest safe distance), and that ends up being OK from an EMI perspective but there are 1/100ths of a second where even the sm57s are blowing out. We think its because the actual sound from the coils comes from the lightning creating an envelop of air along the lightning's branching. This means the sound pressure is rapidly shifting (50-60x per second) around the mic's axis, which I think is creating high pressure dynamic loading around the membrane. I also tried a cheaper large diaphragm (MXL V67i) at 10ft since it's rated for 140db. But you're dead on the money - we're grabbing a ton of EMI with the large diaphragm.

I think y'all are right that a distance stereo array will be the right call - we tried a few takes with mics outside the room, as well as some on the roof, and some outside the windows of the room (to my back in the image). The room is resonating so strongly with the sound that anything beyond its boundaries loses some of the tinniness.

@Martin and Hugh, I'm definitely struggling to capture the power of the setup. A big part is that the low end is almost non-existent - even in person these things live pretty high up. However, the room itself is definitely adding some good low end. I just wish there was some 60-200Hz low bass 'crackle' and rumble instead of the kazoo feeling - its hard to capture something that's not quite there irl. Or I'm missing it because the dominant frequencies are just so dang loud.

@bjg - thanks! If you have questions let me know! The group this is for has done a ton of building and testing with coils, and definitely have some of the most experience in the field with both performance and safety. Its funny that almost no one has done 'real' recordings of the things though!

PS: As a fun side note - if I unplug all my mics, am 60ft away, and touch my finger to the input of my mic preamp, we get (surprising decent) audio - because I am a good enough antenna for the amount of EMI in the room to become a microphone. Which is always fun.

[Sam Spoons]

WRT the lack of bass it it unacceptable to supplement the low end artificially with appropriate synthesised bass? I realise that it may go against the artistic principle of the thing but......

[Folderol]

I think one problem may be that you're mentally comparing the Tesla coils with real lightning. To get anywhere near that you would need some form of delay line and low pass filter.

[Martin Walker]

WRT the lack of bass it it unacceptable to supplement the low end artificially with appropriate synthesised bass? I realise that it may go against the artistic principle of the thing but......

FathomFive: Build this bass-enhancer into an aux on your mix to generate controllable tape-like fullness and bass depth.

I'm currently exploring FathomFive (from Chris Johnson aka Airwindows), and am mightily impressed with the way its low shelving EQ and Suboctave contributions combine to reinforce the low end without sounding artificial, and it's a free download (although I'm one of the many musicians who now support Chris via a tiny monthly donation to his Patreon account, because his plug-in range is stunning).

Find out more and download it here: https://www.airwindows.com/fathom-five/

Martin