Thursday, April 5th, 2012 | by Randy Coppinger
Highly directional mic patterns do a pretty good job of capturing on-axis sources while minimizing off-axis sounds. Or to put it less technically: they hear more of what you point them at. Some smart guys figured out that they could put a mic element inside a tube and cut slots on the sides to further kill off-axis sounds, using phase cancellation. Known as an “Interference Tube,” this design makes a mic look kind of like a firearm, hence the name “shotgun.”
[Read more about How a Shotgun Mic Works on Randy's website. --Ed.]
These highly-directional mikes are often used for location recording. Neumann says of their KMR 81i shotgun: “Typical applications are film and video recordings, where the microphone should not appear in the picture.” Several other mic companies make shotguns too. I wanted to know how they compared — inspiration to investigate.
I had the following mikes at my disposal: Sennheiser 416, Sennheiser 415, Rode NTG3, and Neumann KMR81i. I hung two at a time to record the same performance with both microphones. This made it easier to hear sonic differences rather than performance differences. It seemed to me that the 416 was the most commonly used of the group so I decided to compare each of the other mikes to it.
The signal path: GML 8304 mic pre-amplifier > 192 IO. Since the 415 is T-powered, a custom built T-power to phantom power conversion box was used for that mic only. Microphones were placed above the head pointing down at a distance of roughly 18 inches from the mouth.
Recordings were level-matched by ear in ProTools after the recording session.
I prefer to record with professional actors, but this opportunity came together on short notice so I volunteered my own voice. I’m not as consistent as people who do this for a living, so forgive the differences between sets. I gave three different reads:
- Standard – A conversational volume level.
- Intimate – A quieter read. This forces recording with more gain, which can reveal issues of noise floor and room acoustics.
- Projected – Basically shouting. Recording gain must be reduced, which can reveal issues of clipping and room acoustics.
Give a blind listen to these samples, form your own opinions, then click to identify the mikes and read on.
[Audio files are presented in pairs, with two mics recorded simultaneously. The order of reads presented below for each mic are: standard, intimate, projected. Files are 160kbps mono MP3s; find 48kHz 24-bit WAVs here.]
415 vs 416
There are several obvious differences between these two mikes. Yes, the 415 is silver and the 416 is black, but that shouldn’t be audible. The electronics are different: the 415 is T-powered and the 416 is phantom powered. If I had used a pre-amp that supported T-power we might expect a difference but add to the situation the phantom to T-power box my friend built for the 415 and we should expect to hear even more of a difference.
Despite the variations these microphones sound quite similar. Though there are noticeable differences, I would be comfortable using them interchangeably on the same project.
NTG3 vs 416
At roughly 70% the cost of a 416, the NTG3 aims to deliver similar results at a more affordable price. I was surprised how good the mic sounded. The 416 is already a fairly bright sounding microphone. To me the NTG3 goes too far trying to get the same kind of sound. The Rode seemed slightly more hyped, to the point of being strident. My voice doesn’t make a very good test for sibilance, so I’m interested to hear the NTG3 on some voices that would better reveal the issue. It was also slightly thinner sounding than the 416. The trade off — sonics for price — seems fair.
KMR 81i vs 416
According to Neumann, the KMR81i “has been specifically designed for electronic news gathering.” Another stated design goal, and something that’s difficult to accomplish with an interference tube, is a relatively flat off-axis frequency response. But the frequency response charts on the website don’t seem to support that claim. [Like many shotgun mics, the KMR 81 i has a supercardioid pattern below 1kHz, and a lobar/clover-leaf pattern at higher frequencies, with significant narrowing of the polar response above 16kHz. --Ed.]
The KMR81i was warmer than the 416. We can also hear more room mode response and room noise, especially on the intimate read. This seems to be a symptom of the better low frequency response of the Neumann. Overall it sounds more realistic, more true than the other microphones. But the lack of hype is kind of boring too.
Rather than declaring a “winner,” I’m glad to better understand the relative strengths and weaknesses of each mic. It’s nice to have options.
Clearly these recordings indicate more that needs to be done. Not only should I use a professional actor next time, I also need to include some more microphones. I’d also like to test how well the microphones reject off-axis sounds by recording in reflective and noisy situations. Interference tubes are notorious for sounding “phasey” off-axis, so it would be nice to have an actor move off-axis to compare this effect from mic to mic.
Thanks to Charlie Gondak for recording me and additional encouragement/support from Dave Appelt, Charlie Campagna, Peter Zinda, Chip Beaman and Justin Langley.