Shotgun Microphones - frequency response plots and comments

R

rob aylestone

Moderator
Not sure if shotgun mics have any interest here - but I've got quite a few and it's very common for people to like/dislike the sound of individual mics, and to appreciate that longer is more directional. I thought I'd try to tie it down a bit - so I hit on a test idea. Line up 4 mics of different lengths and put them on a T bar, so they can rotate. Point them at a speaker with pink noise, then record all 4. Look at the meters and record the meter levels in a spreadsheet. rotate the bar and repeat the readings, then keep doing this for the 180 degrees. I then thought that I'd filter the pink noise to produce a fairly wide range of more focussed noise - so remove all bar 63Hz, then 250, then upwards to the top. Do the spin and record the levels for all this and then plot the results on a graph. The results were quite informative and not quite what I expected. It was easy to see the slope on the graphs - as the mic went off axis, the longer mics rapidly reduced in level. The shorter ones were far less sharp on the angle changes in level. What got me was the Sennheiser 416 - the sort of standard 'go to' shotgun mic is not really much of a shotgun at all at the middle-ish speech frequencies. It's drop-off was quite gentle. It has a neutral tone and I wonder if the popularity is simply because it's forgiving. The longer shotguns clearly need much more careful aiming.

With our music recording, I wonder why we rarely do multiple frequency response plots? We compare X against Y and never think about the changes that happen as you go off-axis? I wonder if our liking for certain mics on say guitars or pianos might well be because they change their response with angle more than we think? Point a mic at the neck joint gives more HF we know, but if the directivity at the bass end means the sound hole is covered too that might sound good. Point another with less off-axis bass response and we might discover this is less nice. Looking back at old mic posts - we constantly just talk about one frequency response plot. AKG and Neumann sometimes do their plots on a circular graph and reveal different frequencies, but they're quite rare.

 
That was great, Rob. I wasn't sure I'd be able to follow along with all the measurements and graphs but it all clicked together nicely.
 
It just had me think that when we all talk about our mics, maybe the same thing is what makes one mic appeal and us dislike another. It also perhaps suggests why the mic modelling ones, where mics can 'pretend' to be something else fail - they can't change the results - you might switch the mic to U47 sound, but it would perform exactly the same in the graphs. I guess the tone would change, but the multiple traces would always track up and down in the same way? The angle effect would be missing if they just used a sort of EQ curve across the board. Trying to do it with electrical boost or cut wouldn't work? because the real acceptance angles would be missing? It's taxing my brain to be fair.
 
Your testing rig is quite fascinating. My approach to searching for a mic is very low tech and I think similar to many. Read reviews, buy mic, test mic, sell mic, and repeat until I find one that works. I'm fairly happy with what I have currently so I haven't bought any in a while but even with the small collection I have I am still learning new ways to use them.

Regarding the shotguns, I have never used one but I have read about famous rock singers using them to get a specific sound on a recording.
 
Some of the older ones actually had vocals listed in the original manuals and specs. Now I think everything has pigeon holes of virtual rules!
 
Rob, appreciate the review.

I have a pair of the short Audio-Technica AT875 mics and for the money, they are quite versatile. Frequency-wise they need a bit of EQ air on top, but other than that, they work decently, and they are sturdy enough that you can just toss them in a bag.
I had to have a client do a voice-over on location in a small, somewhat noisy office, and with the right positioning the 875 brought in a quiet, close-mic'ed track that edited very well.
For sound-effects/ambient sound gathering for smaller projects, a pair of them is a good budget option until you can move up the ladder.
C.
 
I must say that I've never thought of them as a budget choice - just a practical one. A short shotgun for short shotgun stuff. It did surprise me that the directionality changes with angle were quite so gentle - it sounds more directional than it really is. I'm intrigued by how it works - I have not opened it up but I wonder, if - as it doesn't have the usual slots - it is a dual capsule design? Audio Technica made one of those years ago with two cardioid capsules one in front of the other and this gave it a more shotgun pattern, without the usual slots? I've not pulled it apart. Have you looked in yours?
 
I have never had mine apart, but I know what you are saying about the consistency of the pattern.
For sound effects, using them on a T-bar at a 35 degree "fan", they do quite well to pick up, say, passing cars L-to-R or the ambience of a forest, with a solid frequency spread across the sound image.

C.
 
I'll remember that - if I see another second hand I might get another - I like the tone - but a stereo pair could be good - I also wonder if it would be any good as a drum overhead?
 
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