Stereo recording of an extremly loud race car

[mar-kus]

Dear collegues.
Next monday I have a recording to do I never did before.
My big hope is that someone can give me some good advice.
The goal is a stereo recording of a race car which is very loud.
The first thoughts came to my mind was using two sennheiser 441MDs
mounted on a stereo rig for a boom.
I should be able to walk around with mics on a boom (not extended only for handling) connected to my sound devices 788t.
I own a schoeps cmit and a Schoeps ccm8 for MS recording.
But I fear that the cars loudness will lead to a distorted sound with these mics.
Any ideas or advices?
Thanks a lot for your help guys.

Regards

Markus

[boojum]

DPA 4061's. Light, small and can handle volume levels higher than what will make you vomit: 144dB SPL Before Clipping

I believe that is louder than jet engine noise. They record music beautifully, too. Race engines, jet engines, the Rolling Stones and Haydn. What a package! ;o)

[hbphotoav]

Originally Posted by boojum

DPA 4061's. Light, small and can handle volume levels higher than what will make you vomit: 144dB SPL Before Clipping

I believe that is louder than jet engine noise. They record music beautifully, too. Race engines, jet engines, the Rolling Stones and Haydn. What a package! ;o)

Ditto. And you can gaff tape/zip tie/rig them to absolutely anything and dang near anywhere. Put them on a 1m piece of carbon fiber rod across a bike rack on the rear of the vehicle and you're there.

Unless it's a F1 car. There, you're on your own.

[Mark A. Jay]

You did not say at how many meters you would be recording, nor whether your mics will travel with the vehicle, or it will pull away / drive by.

Having worked in exhaust (for years) I can tell you that at 1 - 2 meters, a lightly-damped exhaust system can easily (under full load) produce 130 - 140 dB. Since it is a race car (yes?) you can count on the exhaust system being as low pressure drop as possible, and therefore, not likely to attenuate the exhaust signature all that much. ALso, do not forget that the induction system can also be very loud (though not as loud as the exhaust).

I recall when I worked at Tenneco, testing a four-rotor Mazda 792 (I think) IMSA GTP race car on the dyno, and later, on the test track. On the chassis dyno, we were using Bruel & Kjaer type 4190 microphones and had to (several times) move the mics back because we were overloading the digital recorder's front end. In the end, we ended up acquiring the data at about 4m from the exhaust as the vehicle was extremely loud (basically, it had no real exhaust system to speak of, and thus, no attenuation of the exhaust. If memory sevres, max SPL was around 140 dB SPL at 4m.

Granted, I have no idea how much specific output that the engine had as compared to what you will be recording, but it's not unreasonable to expect 130 dB at full power at approximately 1 meter from the tailpipe (again, for an exhaust system that does not have high insertion loss).

Can you (publicly) state the engine type, displacement, approximate brake horsepower (or kW)? Also, as I asked before, will you be recording it as it goes by you, recording it in-cabin, or recording it stationary?

Anyway, let me know if I can help.

[Petrus]

DPA 4062 version can take even higher SPLs than 4061, they are designed just for that. If the cars are dragsters the levels will be terrible. There is no way to monitor, either, have to run by the meters. You might need pads on the mic lines also. Remember also to use both earplugs and hearing protectors.

Using dynamic mics is one route, they can stand higher levels than condensers and might be easier on the pres (lower voltages).
-------------
edit: wrongly remembered model number corrected.

[boojum]

Petrus, do you mean the 4062 which is good to 154dB? The 4063 is rated to 138dB. Am I missing something in the DPA specs? And the 4061 goes to 144dB. Where am I off on this?

Anyway, the DPA 406n series will do the trick, for sure.

[Petrus]

My bad, I remembered the numbers wrong. DPA 4062 it is.

I corrected my post also.

[GuySonic]

My company has sold special very well matched stereo mic sets for actually placing inside the engine compartment and used for close to exhaust of unmufflered race cars/boats.

Rated to ~158 dB, run on powering module containing 2-nine volt batteries, and ALWAYS meant for LINE level input when recording super loud 'industrial' sources.

Much more natural sounding than any of the DPA 4060 series mics, precision full bandwidth stereo-surround useful matched, and with much deeper low frequency ability.

The custom built DSM-13 mics and have been used by some of the customers listed on my Film Credits page for major film resource sounds.

[mar-kus]

Dear collegues.
Thanks to all the advices you gave to me.
The projects is As follows:
I'll record the new Audi R 15 race car on track.
A Sound Devices 702t will be installed together with two DPA 4061 lavs.
The Audi will drive several rounds with that stereo setup.
Parallel to that A second stereo system will be built in front of the side window of a Audi RS6. It will consist of a Sound Devices 788t and a Schoeps CMIT & CCM8 MS setup.
With this AUDI RS6 we will drive near the AUDI R15.
All will Be synchronised to a HD-Cam with ambient timecode clockits.
It's for a highend cinema spot.
The second part is a scene at the pit lane.
This scene will be recorded with the Schoeps MS system from a distance to the R15 of about 3 to 4 meters.

As a second safety stereo system I will build 2 Sennheiser MD441 Dynamics on
a 30cm stereo bar and spread them to 35 degrees.
In case of the fail of the Schoeps System I'll use this Sennheiser system at the pit lane.

That's the project I have to handle next week.

[boojum]

Markus, my passport is up to date and you really need to mail me round trip tickets to this so that I can help and ride in the Audi, also. I am sitting at the computer now waiting for you to tell me where to tickets will be. LOL

Sounds like a fun project. You got a plum with this one. "Junge, dass ist Tempo!

All the best


Later - 10 cylinder diesel Rennwagen with 600 BHP and 700+ ft lbs of torque in a chassis hardly heavier than a supermarket basket. Pass gut auf! That is some ride!

[zoom]

Hi Markus,

what means 'extremly loud' translated in dB SPL?

This needs to be defined first and to do this correct, a SPL-meter would be very useful to rent or to borrow.
Always protect your ears! They will be damaged irreversible at such hight sound pressure levels...

the CMIT/CCM8 combination allows 132/134 dBSPL (the Fig8: 134 dBSPL addressed directly to the side) for a THD of 0.5%.

So I think -according the graph above- the Schoeps should do their work although you say this is 'extremely loud'... and the Preamps have to be set close to zero dB gain (limiters=on anyway, HP-filtering at the CMIT and recorder is also a good idea).
But I highly recommend to measure with one of these handheld SPL-meters (without A-weighting filter) at the location where the mics needs to be placed. This is easy - or not? :-)

Can you give us a short report of your result and how your different setups worked? This would be very intresting!



cheers
stefan

[Petrus]

What kind of wind protection are you planning to use in RS6? 70m/sec wind might be a lot to handle even for a full winjammer kit, only 3 times the official gale force... Not to mention the stress put on the rigging (might be thousands of newtons).

Actually I am doubtfull if meaningfull sound can be captured under those conditions. I hope it works, of course.

[mar-kus]

@boojum
you are crazy ;-)
I worry how I can handle this and you want to have a ride on it.
I would be happy to have you here for help but unfortunatelly I don't have to decide such things.
And of course I'm looking forward to this challenge.

@zoom
Unfortunatelly no further info is availlable about the loudness of this car.
So I'll take several different stereo setups with me for standby.

@Petrus
The mics of the RS6 won't be installed outside the car.
The rear side window will be opened and the stereo setup will be installed inside the car in the calm spot at the window completed with a full rycote shield.
That's the idea I have in mind.

Regards to all the great guys here.
Markus

[mar-kus]

@zoom
Thank you for the good advice to use a SPL meter.
I'll use one to find out the peaks.
The big problem is also that I have nearly no influence of what is allowed to install in the R15 and the engineers will have the last word of course.
Shure I will give you a short report how it worked.

Regards
Markus

[DannyL]

One more bit of advice:

Get a "speed shot"

As the car moves through a camera frame left to right, a stereo pair with the same l/r orientation and mounted 3 meters apart (Depending on the speed and the width of the camera shot 1.5 to 6 meters) will capture the sound and give the listener a very realistic impression of the speed of the vehicle.

Position the mics track-side either on a turn or straightaway. (Mics are outside of the vehicle. Camera position will dictate mic position) Press record.

All TV automobile race coverage includes speed shots. They are amazingly effective.

Best;
Danny

[Petrus]

Originally Posted by mar-kus

@Petrus
The mics of the RS6 won't be installed outside the car.
The rear side window will be opened and the stereo setup will be installed inside the car in the calm spot at the window completed with a full rycote shield.
That's the idea I have in mind.

Regards to all the great guys here.
Markus

Be prepared for very high level infrasonic frequences, which might overload the capsule. We all know the effect of having the rear window open at highway speeds, it of course depends on the aerodynamics of the vehicle.

[duaneadam]

Curious to know how this turned out. The previous generation Audi TDI race cars were super quiet, almost Prius like. Haven't heard the R15 yet but wondering if your session turned out as expected.

[tmcconnell]

microphones' diaphrams, like speakers, have to move a little before they are "happy". I don;t know how close you will be, but distance of course has a non linear impact. It could be you are well within the range of a lot of mics that will give a better impression of the sound at 130 db. Also, a little compression (in the mic) at big levels can not hurt since the compression will occur anyway downstream. I might suggest a cheaper, but an insensitive tube mic (GT?) that will be happy and compress a little close to its spl limit. There ain't no formula, and honestly, (and I expect to get flamed for this), a lot of folks who do this day in any day out realize that getting it about right every time is more important than getting a perfect read on every assignment. so, like, it all depends on your pov. I say experiment. Come prepared for several scenarios. t.