ORTF Stereo Microphone

#1

Hi guys, sorry I didn’t do a terribly good job documenting this one. I’ve gotten a new camera recently with half an idea of getting back into doing some video work and thus found myself in need of some microphones. Obviously I could just buy them but I’m sure I don’t have to tell you bunch that it’s a lot more fun and a better learning experience to try and make something yourself.

Recently I’ve been following along with this gentleman’s excellent tutorials and while I can’t say I’m absorbing 100% of the technical aspect of why he makes certain design decisions, I am picking up a lot and the builds are so well documented I’ve managed to make what I consider to be quite capable microphones just by following along.

My most recent project was a ORTF Stereo Microphone designed to mount and plug directly into a camera. This arrangement uses two microphone capsules positioned 17 cm apart and at 110 degrees from each other, mimicking the position of ears on the human head. The result is apparently a realistic stereo effect (amongst other things) and my experience testing the mic confirms this.

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Jules provides files for the production of a bar with this angle and spacing set already, and one needs only slot in the microphone capsules in the appropriate notches. I opted to 3d print it at home as that is what I have on hand:

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He then suggests using some cheap plastic hair rollers to act as baskets for the microphone capsules, but I didn’t want to buy a whole pack of future landfill fodder so I designed little baskets myself to slide on:

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After soldering the capsules (I stuck with the ones he recommends) I carefully thread the cables through the baskets/fiddly bits and triple checked the left and right channels with a multimeter. It would not have been a huge deal to goof here as I could just flip the bar upside down, but the print had a “nice side” and I wanted to route the cords along the bottom. I then soldered the 3.5mm stereo connector and covered the capsule baskets with a layer of sheer nylon and faux fur for wind protection. I also added an adapter for the camera’s hotshoe through the hole in the centre.

Here’s the final result:

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I still have lots to learn but I’m chuffed with it.

8 Likes
#2

Awesome! How did the 3d printed baskets come out?

#3

Cool build !

I got to play with an original ORTF (made by RTF) a while back - they have a modified design that has an encoding box to produce Ambisonics signals for doing object based spatial audio.

I’ve always wanted to give that a go on my own 360 camera - might have to build one of these myself !

Are there any considerations for reducing handling noise (which I know can be an issue with these mic layouts)?

#4

It came out not bad! It didn’t occur to me to document the process until later so I stupidly glued everything together before getting a photo of it and the capsule in place. My printer is queued up for awhile but when I find a gap I’ll print another basket and post it here. I’ve recently frankensteined together a new extruder assembly and have been getting some really stubborn stringiness which I’m still trying to tune out. It definitely affected the aesthetic of the final print but, eh, we’ll call it bonus wind protection. It was, as you might expect a balancing act between making it structurally worthy and not too obstructive to sound, and took a couple of revisions.

#5

I got to play with an original ORTF (made by RTF) a while back - they have a modified design that has an encoding box to produce Ambisonics signals for doing object based spatial audio.

That’s super cool! I’m really interested in the history of the set up. The same gentleman I’ve been following along with has plans for an ambisonic microphone which uses four capsules in an array which I’ve thought about doing next after I make a couple of lav mics. While the lav mics are fairly justifiable in a practicability sense (maybe could be put to use for some induction videos…?), the ambisonic mic in my case is definitely a solution in search of a problem! I’m a game design lecturer so maybe recording some ambient audio in real world space and then mapping it to a recreation of that space in VR, or something.

Are there any considerations for reducing handling noise (which I know can be an issue with these mic layouts)?

You’re of course right to ask. Naturally the camera’s autofucus comes in randomly in the final audio sounding like a cement mixer. In the original build he sandwiched the stereo bar between two rubber gaskets. This may be sufficient but I’ve really been wanting to design a shockmount for awhile. I was thinking it will probably consist of a two halves of a cylinder clamping on the bar and joined using a bolt down the centre hole that’s already there, with a larger cylinder around that which connects to the hotshoe adapter. I was thinking of printing these with some holes for brass hooks on the cylinders and suspending the bar between them with some elastic hair ties threaded through the hooks.