I recently acquired the SoundField ST450 MKII Ambisonic Microphone and wanted to see how the unit responded to gun shots. As usual I was very excited to try a new piece of audio gear and rushed to get all the ingredients together for recording. Once I decided what I was going to test and how, I was off to the races! I placed the microphone in my driveway and recorded a 300 Blackout rifle along with a AK-47 and a AR-15 rifle. I used super sonic and subsonic ammunition along with a Gemtech ONE suppressor on the 300 Blackout. For the AK-47 and AR-15 I only shot supersonic unsuppressed. I did change the microphone postion and distance for the AK-47 and AR-15.
On the two days I recorded, the weather was perfect! It was very cold and there was absolutely no wind. As an added bonus the small barn swallows were taking a break from their usual winter songwriting seminar featuring chirps, chirps and more chirps.
I was unsure where to set the input levels on the control unit as I can only assume it has no input limiter. I started with the knob at “12” then “9” then “3”. Since I could not see the level meters while shooting I really had no idea how hot the signal was going in. During playback I could not hear any distortion or heavy pumping from a possible limiter. There is some type of “clipping prevention” going on which may be from the analog preamp circuit. (a guess)
300 Blackout rifle: ST450 MKII facing away from house, shots at 12 to 15 feet, side muzzle POV.
AK-47 rifle: ST450 MKII facing toward the house, shots at 25 feet, side muzzle POV.
AR-15 rifle: ST450 MKII facing toward the house, shots at 25 feet, side muzzle POV.
Included in this set of free sounds are the original four channel B-Format, 5.1 surround and stereo formats. In order to decode the B-Format sound files in post, you will need special software, either one of the free versions from various sources, or Soundfield’s own SurroundZone 2 which you may still be able to find on the web. I am not sure if I can hand out the SurroundZone 2 software but if you cannot find it let me know and I’ll see what I can do.
SoundField ST450 MKII
The ST450 MKII generates audio in any format including mono, stereo, M/S, 5.1 surround and beyond, without the need for more than one microphone and will generate both surround and stereo simultaneously via the external control unit that requires a 12v supply via a standard Hirose connector. The microphone’s control unit includes a built-in front-panel headphone monitor, bar-graph metering, and a fine degree of control over all microphone parameters. The ST450 capsules have built in heaters that help to combat the mic’s sensitivity to humidity.
SoundField’s unique B-Format
SoundField Technology is based on the principle that all acoustic events can be represented by four basic elements. These are ‘X’ which is front/back information (depth), ‘Y’ which is left/right information (width), ‘Z’ which is up/down information (height) and ‘W’ the central point from which the other three elements are referenced. Collectively, W, X, Y and Z are entitled SoundField B-Format. Because the SoundField capsule array captures three dimensional sound at the same ‘central point’, all phase related anomalies created by spaced microphones are eliminated. Once in B-Format the point of acoustic origin is defined and all output variations i.e. mono, stereo, M/S, 5.1, 6.1 etc. are derived from this same ‘central point’. Thus, surround recordings made with SoundField microphones can be collapsed to stereo or mono – without the phase cancellation and high frequency differences encountered when ‘summing’ multiple spaced microphones.
Download The Gun Test Sound Effects: 349.6MB ZIP File
Please Note: Since I had the microphone horizontally pointed at the sound source I had the End Fire mode selected on the control unit during recording. When decoding the B-Format sound files please do not enable End Fire mode in your decoder. The 5.1 sound file was processed with 12dB of gain with the Avid Pro-Limiter.
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