Shotgun mics and frequency response

[debuys]

I'm an audio guy evaluating a rode VM and I have noted there's an over hyped low mid and under represented high mid and what amounts to a low pass filter at 12k. In general it is a pleasing sound almost like a proximity effect, but more synthetic in a bad way. I have no experience with shotgun mics since it isn't something I have found much use for. Is this characteristic of shotgun mics or just the RVM?

[Angelo Baby]

there's an over hyped low mid and under represented high mid and what amounts to a low pass filter at 12k.

Are you sure? This is from the Rode website:

http://www.rodemic.com/images/mics/videomic_freq.jpg

[debuys]

Yes, I'm quite certain. I did some measuring myself, less scientific (no pink noise) and came to two conclusions 1) It is proximity effect. 2) I didn't understand the difference between a shotgun and a condenser with a tight polar pattern. It makes sense now and after talking to a salesperson I decided to keep it and not step up into something nicer.

I have seen the diagram above. It's BS like all manufacturer supplied performance data.

There's a dip around 6k, a small bump around 1k, the equivalent of a low pass at 12k and pretty stiff compression under 500. All of which is somewhat normal with low end shotguns I've been told. At first I was thinking it was little tricks to diminish small room reflections picked up by a typical condenser. Or worse, a defective mic.

I understand the why this type of mic isn't used much in audio studio environments and as such remained a mystery to me. Now that I understand shotguns better I think the RVM is pretty cool and I'm glad to have it in my arsenal in spite of the flimsy plastic. I still have a couple of weeks to return to B+H if I can justify an upgrade.

[ejolson]

I didn't understand the difference between a shotgun and a condenser with a tight polar pattern.

What is the difference between a shotgun and a condenser with a tight polar pattern?

[debuys]

The short version is a shotgun uses acoustic techniques putting the mic diaphragm at the end of a tube precisely slotted to cause phase cancellation of off axis sound. In a hyper and super cardioid mic there isn't cancellation, there's just rejection.

The technique used by shotguns (conjecture here) should cause significant phasing issues when multiple shotgun mics are used on the same source. In other words, a single shotgun might mix nicely with additional mic pair for stereo ambiance, but not with another shotgun pointed at the same source. I wouldn't think an XY stereo rig implemented with shotguns is advisable.

Still learning

[DrDave]

Some frequency graphs supplied by the manufacturer are accurate, done for each individual microphone and signed by the technician. If your mic did not come with a unique frequency graph, there is no guarantee that it will be the same as the idealized one printed in the booklet, although an honest company will specify the variance from the ideal graph as plus or minus 3dB or so.