The View Up Here

Random scribblings about kites, photography, machining, and anything else

Tascam DR-05 Micro-Wing

Posted by Tom Benedict on 17/06/2015

After sorting out the issues of protecting the microphones from wind and isolating them from rig and line noise, the biggest remaining technical problem with recording sound from a kite is distance: KAP (or KAS) rigs are rarely very close to their subjects. Trying to record stereo sound at those distances presents its own challenges.

Fortunately, field recordists have been working on this problem for decades. All manner of stereo microphone arrays have been invented over the years to address this. My own experimentation has only just begun, but I’m starting with a known design: the Olson Wing.

After ordering the bits for the EM-172 microphone array, it struck me how the arrangement of the built-in microphones on the Tascam DR-05 might lend itself to a simple experiment. I decided to build a micro Olson Wing around the DR-05 to see if I can get any immediate benefits in terms of spatial separation of the two channels. But first, a little background:

Curt Olson’s microphone array article describes the experiments he did that led him to his wing design. Vicki Powys’s articles describe her own microphone arrays, including her own take on Curt Olson’s wing design. They also have information on alternate construction materials. Curt Olson made all of his arrays out of wood, but Vicki Powys favors high density closed cell foam (pool floaties, yoga blocks, craft foam, etc.) Vicki found that the acoustic differences between foam and wood are small enough that it doesn’t have a huge effect. I’m sure someone more experienced with sound could tell the difference, but I know I won’t be able to. This is important because heavy wood construction isn’t ideal for kite payloads.

(As a quick aside, Zach Poff’s article on the EM-172 mics misses one minor, but important point: a wiring diagram. Vicki Powys’s first article describing her microphone arrays includes that diagram, along with information about ganging multiple microphones on a single channel in the same array.)

I had some 6mm craft foam left over from another project, so I grabbed a razor blade and a cutting mat and got busy. Here’s what I came up with:

Kite Aerial Sound Experiments #1 - Micro Wing

It’s far from ideal for several reasons: The microphone spacing in most binaural arrays are close to that of the human head: 5.5-6″. This is closer to 2″. The microphones in the Olson Wing should be arranged in a forward-pointing direction. These are angled out significantly. (Vicki Powys did some experiments on angled wing arrays that indicate I may not be that far off the mark, though the wings on my array aren’t actually angled; just the mics.) Strictly speaking, the Olson Wing uses the microphones as boundary microphones, and needs them to be in contact with the flat surfaces of the wing. The geometry of the DR-05 doesn’t really let me do that unless I cut pockets into the foam, shaped to the body of the DR-05.

At this point I’m not looking for perfect, though. I’m looking for an indicator that I’m on the right track. So I took it outside to the highway and set it up on a tripod to record car passes – a fair test of stereo separation. I recorded two takes – one with the wing and one without – and tacked them together:

 

Neither of these is processed, except to pull out the two 16-second clips, and to add fades at either end.

Conclusions:

  1. I’m terrible at working with craft foam. This is something I need to rectify if I’m going to continue to use it as a construction material.
  2. This thing flutters hopelessly in the wind. If I go with this kind of construction in the air, I’ll need to make it a good bit more rigid than it currently is. (Maybe wood really is a better material!)
  3. The wing does make a difference, but it’s slight. For now I’m chalking that up to the deficiencies I listed above. I’ll move forward with the full-sized version when the EM-172 mics show up.
  4. I’d rather fly a kite than stand by a highway.

As far as experiments go, I’ll call this a success. It gave me information I can use to plan my next move: building a micro SASS around the DR-05.

– Tom

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