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Shotgun Off-Axis Rejection


Paul F
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I'm looking to add to my microphone collection. I have an MKH 415.  Assuming equal performance other than off-axis rejection, which one of these would you choose for a shotgun microphone? It's not clear to me that a tighter rejection is always better. Thoughts?

 

6db, 8db, or 14db?

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If you’re looking for off axis rejection in a short shotgun the Sanken CS3e is indeed worth looking at. Not my favorite sound but in a really loud environment I’m less picky.

 

I’m a big fan of the Sennheiser 8060. Fairly directional and very punchy. Cuts through kind of like a 416 does.

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  • 4 weeks later...

Off-axis rejection in any shotgun mike is highly variable as a function of both frequency and the specific angle of sound incidence. That's the nature of the interference-tube technique, which is based on phase cancellation created by path-length differences. At one off-axis angle you might find 10 dB variation in response across a given octave or two of the frequency range (a degree of variability that wouldn't be tolerated in any other type of microphone). If you move the source or the mike just 10 degrees relative to the main axis, that entire response curve will change; its hills and valleys will occur at different frequencies from before, and the distance from the highest peak to the deepest valley will also change.

 

As a result, no one overall decibel amount can possibly characterize a microphone's behavior in practical situations. If you graph the microphone's directivity factor vs. frequency, then you start to say something--but the sound quality in practice will still be affected significantly by factors that the graph doesn't reveal.

 

The length of the interference tube determines three interrelated effects. One is that a shorter tube generally causes less violent ups and downs in the frequency response for any given angle of off-axis sound incidence. A longer tube causes a greater degree of variation or deviation from flat response, depending on the angle.

 

Second is that, at any angle at which a given frequency is being (relatively) suppressed, a longer tube would generally suppress it more--though that's not an airtight statement, since the frequencies of maximum suppression at any given angle are also a function of the tube length, so it's true only in the aggregate.

 

Third--and this is something that I'm surprised that people seem to forget so often, even in this forum sometimes--is that the length of the tube determines the frequency at which the tube begins to have any effect on off-axis sound pickup at all. For any given length of interference tube, there's a frequency below which the tube is transparent to sound and has no effect on the pattern. It's inversely proportional to wavelength. A longer interference tube will begin to narrow the microphone's pattern at a lower transition frequency than a shorter interference tube will do.

 

(As an aside: The little microphones that have come onto the professional market recently, with slotted tubes only two or three inches long, can't possibly have any narrowing effect except on the highest sound frequencies. From their polar diagrams it's clear that the narrowing occurs above the range that matters most, and that the degree of suppression is also quite limited, as one would expect from their principle of operation. Yet people's wishful thinking seems to take over, like "Wow! A miniature shotgun microphone! Why didn't someone think of this sooner?" The answer is that the interference tube principle can't be miniaturized and isn't being miniaturized, since it depends entirely on sound wavelengths--and the slotted tubes on these little microphones are more for show than for real, no matter whose brand is on the microphone.)

 

--best regards

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1 hour ago, DSatz said:

 

(As an aside: The little microphones that have come onto the professional market recently, with slotted tubes only two or three inches long, can't possibly have any narrowing effect except on the highest sound frequencies. From their polar diagrams it's clear that the narrowing occurs above the range that matters most, and that the degree of suppression is also quite limited, as one would expect from their principle of operation. Yet people's wishful thinking seems to take over, like "Wow! A miniature shotgun microphone! Why didn't someone think of this sooner?"


I‘m pretty sure that most of the more experienced members here are very aware of that. That’s a reason why most of us have or had short and long shotgun mics, of various kinds.

I have never tried one if the really short shotguns, but also personally love the DPA4017, which is 8 inches long. 
Just for the fun of it I just compared its graphs to that of the Sennheiser 8070. The polar pattern graphs actually look surprisingly similar, but when you look at the attenuation graphs at a given frequency the picture if quite different, of course. Nonetheless, the shorter DPA still manages about 10dB attenuation at 100Hz, so not too bad, but nothing compared to about -34dB of the 8070 - both at 90 degrees. 
But that is for me why the 4017 sounds so pleasing. It’s a well balanced compromise between a natural off axis sound and rejection. It also means the mic sounds far more natural indoors in rooms where the 8070 would sound absolutely horrible. The 4017 feels more like super cardioid. 
 

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From my listening tests, the Sanken CS-M1 (which is a likely candidate as one of the mics referenced in DSatz' commentary above) behaves similar to a Schoeps sporting an MK41 supercardioid capsule, but with an exaggerated high end.

 

From low to midrange frequencies, the directionality of a supercardioid is comparable to that of a shotgun microphone, but its off-axis pickup is much more uniform.

 

I've never considered the CS-M1 to be a shotgun mic. At best it's a sawed off shotgun, but that's illegal in the states.

 

 

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Microphones are our tools. I am very happy with my CS-M1, but I have a dozen more. To be honest, I have used the little Sanken a lot the last 10 months. Very convinient tool for a very fair price, very well balanced with the Cosi.

 

It is between words in my opinion, a vey good compromise though. Outside usually I will reach for something longer with better wind protection.

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