Topic: Baffles for R-09 built-in mics & 4060 boundrisphere contraption

[Gutbucket]

Check out this little mic baffle/recorder package I whipped up.  It’s a special application not really designed for concert recording, but hopefully someone else can make use of something like this.  Credit: this stuff is heavily inspired by Moke's Jecklin disc threads, with a little SparkE™ fishpole twist and a dash of bitters, served over the rocks of the Schoeps KFM 6/360 mic designed by Gunther Theile.  Big thanks to everyone. [edit: lots of photos here, the photos of the final contaption are down in post #940001, the 11th post in this thread]

A little backgound..

I’ve been waiting for a decent flash recorder to come along and needed something last month to record classes, performances & jam circles at a great acoustic music gathering in NC that brings in some heavy hitters from the acoustic guitar, resonator, and mandolin world as instructors.  Taping classes is encouraged and the R-09 became available just in time for the trip.  I'd been planning on putting together a small decent quality recording rig and a week or so after it arrived I ordered a matched set of 4060's, MMA6000 and a few other pieces from DPA.  Before I got a hold of the mini DPA's figured I could make a little Jeklin-disc like baffle to improve the imaging of the built-in mics on the R-09; something simple I could use while grabbing the class sessions. The R-09 mics seemed to have about the same spacing as the mics on the mini Jecklin-discs people have been building here. 

Small ball baffle for internal mics-
The first thing I tried was cutting up a floating practice golf-ball made from dense Nerf-like yellow foam.  I cut a notch in the ball to fit over the top of the recorder so that the mic capsules were on opposite sides of the ball.  Pretty small baffle, but I figured I'd get a little more directionality on the high frequencies like those add on pressure modification spheres DPA makes for their omnis, hopefully rolling off smoothly as the source moved from one side to the other around the ball.  A poor man's back to back 180 deg. close spaced Neumann M-50 wannabe config.  I did a better job notching a just slightly larger diameter Nerf gun ball ($5 for a pack of 5 dense green foam balls) that I sanded to smooth the cut edges and flatten the opposite sides to still fit flush to the mic capsule vents.  The ball just slips on the recorder, snug enough to stay put.  It made a quite appreciable improvement to the smoothness of the high end, but didn't add much additional separation to the playback image.

[Gutbucket]

Improved folding baffle for internal mics-
The foam ball was encouraging, but not really large enough for the separation I wanted.  I needed a larger baffle.  I'd been placing the recorder on a neoprene mouse pad on the table, with and without the foam ball, and decided I could glue a second mouse pad to a plastic baffle that hinged in the middle to form a   wedge, notched at the back to just fit over the recorder.  The wedge would baffle the mics, but allow the screen & clip light to be monitored from behind and the transport buttons to be used.  Simple to fold flat and stow it with the bottom pad.  I cut a pattern for the folding baffle out of cardboard and did some simple tests monitoring with in-ear Etymotic 'phones while my girlfriend walked around the room.  The simple cardboard baffle really did a great job improving the imaging of the built-in mics.  Way more separation in the midrange, strong center, smooth pan across the sound field and the same seemingly a sweeter high end the small ball produced (from reduced comb filtering up high I suppose).  I Before I found something better than cardboard to make the baffle out of, the DPA stuff arrived and I got all googly-eyed and moved on.. so I haven't finished building that little folding baffle yet, but I still think it would be a great improvement when just throwing the recorder on a table or the floor and using the built-in mics.  Provides a vast improvement in payback image, is simple to put together, easy to use, and would be small and flat when broken down in your bag.

[Gutbucket]

DPA boundary mounts for mini mics-
When I ordered the 4060's I also picked up some extension cables and mini boundary mounts.  The boundary mounts are little 3" diameter rubber disks tapered towards the edges with a slot for the cable and mic body on the bottom side and a little rectangular slot that opens to the mic's grill on top.  You bend the rubber to open up the slot and insert the mic and cable into the bottom of the rubber disc.  I figured you'd position the mic so the capsule element faced up towards the slot opening, but DPA instructs you to orient the capsule perpendicular to the boundary for best results.  In other words, the little circuit board that the capsule element is mounted on is to be seen 'edge on' through the slot. Maybe this just avoids inadvertently placing the element face down by accident, I haven't listened to the difference between both orientations yet.

[Gutbucket]

Large sphere boundary-
I've planned on building a little J-disc, and have also wanted to experiment with spherical baffles, so I bought a couple 7" Nerf-like close-cell [edit- they're actually open cell with an exterior skin] foam balls when I picked up the small green balls.  7" is about the diameter of the Schoeps KFM 360, my head, equals ORTF spacing and is a generally lucky number so that's the ball diameter I went with.  I plan on trying one of the balls with the mics mounted flush on opposite sides, either just pushed into slots cut into the foam ball or by cutting the ball flat on opposite sides the same diameter as the boundary mounts, so that the mounts, when attached, would complete the sphere with the capsule openings pointing out on opposite sides.  Then either hang the ball or mount it on a mic stand.  The surface of the sphere should provide a smooth, curved diffractive surface that acts to baffle high and mid frequencies in a smoothly progressive way across the sound stage.  Could work nicely in the center of a circle of musicians.

[Gutbucket]

Boundrisphere all-in-one contraption-
But my initial use was as an easily portable recording rig I could have all set up and ready to go in my bag that I could place on the floor or a table to capture class instruction and instructor jams, and could throw down in the center of an impromptu circle of musicians without setting up a stand or being too imposing.  Instead of building the simple sphere boundary and using it on a stand, I figured I could make a baffle that was sort of an extension of the cardboard wedge idea that would incorporate the mics, baffle, preamp and recorder all in one unit.  So I cut one of the 7" foam balls in half (see photo above) and tucked the boundary mounts under opposite sides, so the mic vents are positioned at the intersection of the boundary plane and the edge of the sphere. OK. I cut a large slot into the foam hemisphere so that the mic preamp and recorder could be fit partially inside it.  A key feature is that the foam ball is not glued directly to the base.  It is glued with construction adhesive to a circular shelf inside the base of the sphere. The circular shelf is 6" in diameter and is inset into the bottom of the hemisphere, leaving 1/2" of foam around the edge.  The preamp slides in on top of this shelf.  The shelf is glued with construction adhesive to a can lid about 4" in diameter which is glued to the base.  The shelf is inset slightly more than the height of the can lid, so that the edge of the foam ball presses lightly against the 12" diameter base plate.  This allows the mic cables to be wrapped around the base of the sphere, with the cables tucked under the edge of the foam into the circular space around the 4" can lid. Rap until the excess cable is taken up and the boundary mounts are in position to be tucked halfway under two small notches in the sphere's bottom edge.  The notches keep the foam from wrinkling when deformed by the thickness of the mounts.

[Gutbucket]

Wrapping the excess mic cable length around the base of the ball and inserting the boundary mounts shown below.  (Text is getting ahead of the photos). Now the boundary mounted mics, baffle, mic preamp and recorder are all wired in one unit on a 10" circular base which can be placed on a flat surface with the screen in view and the transport and gain controls available.  I kept the foam sections I cut out for the preamp and recorder so I could remove the recorder and preamp to use them at a distance if and have a complete, clean sphere surface.  Painted the foam bits 'expensive German mic grey' with a can of upholstery paint from the auto parts store.  The base and shelf are inexpensive plastic board backed cork circles from Target, $3 and $4 each, unmodified except for sanding the base's edge to taper it a bit more to blend smoothly into the floor or table surface.

[kgreener]

hey mon, i seem to be getting a lot of red X's here ... anyone else?

thanks, and +t for your troubles!

[Gutbucket]

The same 6" diameter plastic backed cork material from Target is used for the base for the MMA6000.  I cut off each ether side of the circle and used the center piece for the base which extends out the front to protect the cable connections and switches when in my pocket.  The edge parts of the circle where trimmed and glued to the top of the base to raise the preamp off the base by the thickness of the material and create a spool-like form to wrap excess mic cable around similar to the cable management on the boundrisphere.  The base is taped to the preamp with gaffers tape, excess cable wraped around the slot and secured at the front/top by a Velcro cable tie that came with a computer UPS.  Provides a convenient way to handle excess cable, protection for cable entry and accidental switch adjustments in my pocket and slides nicely into the boundrisphere baffle.

[Gutbucket]

Here's the whole package ready to go.  The recorder and mic pre are a nice snug fit in the foam. This thing got tossed around quite a bit in my bag and some cracks in the paint around the corners where the recorder fits in are showing, could use a touch up.

[Gutbucket]

Here's the removable sections that can take the place of the recorder, or of both the recorder and preamp to complete the hemisphere when using the extension cables on the mics.

[Gutbucket]

And those sections in use.

[Gutbucket]

Use-
Worked great. I recorded everything at 24bit/44.1khz, dumped the files to a laptop and compressed to FLAC after the morning classes (approx. 2-1/2 hrs.) and again before dinner (another 2-1/2 hrs).  Then I'd record some of the night time jams & concerts (mostly using HTRF or with the boundary mounts on my chest not with the boundrisphere thing). Just cycled 2 sets of AA's in the charger for the R-09, and used two 9v's for MMA6k for the whole week.  Sure, could have run mp3’s for the class sessions and dumped once a day but this was a good shakedown for long festival days, I'm pleased.

Results-
Pretty cool playing back through headphones. The class recordings are very listenable with a nice soundstage & depth, without too much room reverb, of course many feature excellent recordings of the HVAC system cutting in and out along with some geat instructor improvisations and way too much stunent noodling for recreational listening.  I only used the omnisphere contraption twice to record a circle of musicians playing outside in the evenings, and one of those times a microdot connector was loose with an intermittent connection.  Placed the thing on the ground in the center of the circle with guitars, mandolin and a fender bass with a little battery powered can amp all around.  Turned it so the bass was at 6 o’clock and the primary singer close to 12 o’clock.  Soundstage worked out very nicely with instruments and voices panned evenly left to right and the back half of the circle flipped over and superimposed over the front.  Good presence. Very nice on the harmony parts.  Great through the phones and surround info decodes well through Dolby PLII.  I'd like to try more of this with a circle of musicians, and the all-in-one form makes it easy to just set it down and roll.  I think the full sphere ball on a stand could work even better in this type of picking cirlcle by raising the mics up to head/instument level - but that's just speculation at this point.

If I can figure how to chop up some takes, convert into mp3 and post somewhere I’ll share samples if anyone is interested in hearing them.

[Gutbucket]

Thanks,
That's what staying up all night in a panicked frenzy the day before your trip will get you.. sometimes.
That how I often get the best things done unfortunately.

[Gutbucket]

I'm not quite following the entire concept, but, I like it.

Do you intend to mount it vertically at any point? such as, on a mic stand, elevated?

Not this version, though I guess you could.  The boundry mounts are supposed to lie on a large surface for an even +6db increase in sensitivity down to the lowest frequencies.  The sensitivity boost shelves down by 6db if the surface is smaller. What frequency that hapens at is dependant on the size of the surface.  Mounted on a stand, the base edge would only be 1-1/2" from the mic capsule so that shelf effect would be pretty high in frequency and the edge would be pretty sharp.  I think there could be diffraction issues there.  I have thought about mounting this thing up on the back wall though.  Just turn it 90 degrees, the baffle would look the same from the mics perspective.

I was thinking of using a whole ball for mounting on a stand, with the mics flush on opposite sides of the sphere, just like the Schoeps mic pictured earlier.

[rowjimmy]

Wow. Thats pretty cool stuff and nice handiwork. +T indeed.
Thank you for explaining everything as you went and the excellent photo documentation.I hope you are as satisfied with the recorded results as you should be with the actual design.