As promised, here are some sounds from a dyno run.
What you’re hearing here is a Zoom H4n’s onboard mics, uncovered, with the mic level set to 0.5! Normalization in post only required +6 to +8 dB of gain, so consider for a moment how loud that really is — and these weren’t even particularly loud cars.
So, for those of you who have never seen or heard a dynomometer, here’s an idea of what we are dealing with. First off, the room the cars are in is rectangular cinderblock. There are lots of fans to vent exhaust out. The wall behind the camera is an open garage door for getting cars in and out. The window on the right lets users see a computer monitor showing RPM, Torque, and Horsepower readouts. The cars are lined up with the wheels on a big drum, and then strapped into place. The dyno works by using a known resistance on the drum, which calculates torque. Using the handy formula of (Torque x Engine speed) / 5,252 = Horsepower, the dyno can then calculate the power put down by the car at the wheels. Cool, right?
If you’re trying to record a legitimate dyno pull such as the one above, the technician strives to get the car into a gear with as close to a 1:1 ratio as possible (usually 3rd). This gives the most accurate numbers, but also means that at the top of that gear the wheel speed could be upwards of 100 mph! Aurally, this means the sounds of the dynomometer itself (like the screeching and humming you hear when then the car shuts down) are much more pronounced than when in a lower gear. So, if you have the option, do the pull in the lowest gear possible to improve audio quality.
Another thing, is get your mics as close as possible while avoiding fans! As you can see in the video, there are lots of fans placed in front of the car. This is because the car is designed to be air-cooled by the wind generated by the speeds it thinks it’s moving at. However, because the car is actually stationary while on the dyno, there wouldn’t be any air moving which would cause it to overheat. Hence the big fans. Keep them in mind when placing mics, especially around the front of the car. You’ll also hear in the vid that this particular dyno room was exceptionally reflective. Nearly every dyno you encounter will be in a similar facility — thus to combat the reflection, increase your signal-to-reflection ratio by getting your mics close. Mr. Caviezel outlines this in one of my recent posts.
If you have questions or comments, be sure to leave them below.