Topic: recording acoustic musicians sitting in a circle

[Gutbucket]

Following up on that-

If you had no spacing between those four IRT-cross cardioids, matrixed them the second way and flipped polarity of the two on one side of the circle, you'd essentially have a Blumlien arrangement.

If you think about the Stereo Zoom implications and consider the spacing between the four cardioid microphones in an IRT configuration, it may be apparent why I suggested a coincident arrangement if using only using two cardioids facing 180 degrees apart. 

[cybergaloot]

I guess I need to make myself a Jecklin disk sometime. I don't if or when I'll ever make it over to the pickin' party I'm thinking about but those boys can play! If you know who Guthrie Trapp is, he is basically a former protege of theirs.

You can make due pretty well by just setting up two omnis at shoulder height, spaced about a foot apart or so on a mic bar, then draping a jacket or sweater or something over the bar between the mics.  Might help to mount the mics upside-down on the bar so they hang beneath it, so the draped jacket or whatever is high enough to properly baffle them.  As long as whatever you put between the mics effectively blocks the sound from arriving from the opposite side, yet both mics can still 'see' the performers to the front and back of the plane between the mics it's good.   It's also somewhat casual and less imposing than a fancy disk, which might make the performers more relaxed.  I like shoulder or chest height because it is about equidistant to both the voices and instruments, so both are clear and close and neither is over represented, and it's low enough that the performers can easily see each other over the top.  That's far less imposing than something at head height blocking the view and potentially killing the vibe, or even up high looking down on things.

Then I'd worry that people would think it was the coat rack!    I don't have a disk and have never played with one so it might be fun to make one. I've got some plywood, foam and dead rat fabric so it wouldn't cost me anything. I think I even have all the mounting hardware I'd need.

I have thought about not wanting the setup to be a distraction for either the musicians or the other listeners. It's not about me, its all about them!

[Gutbucket]

I have thought about not wanting the setup to be a distraction for either the musicians or the other listeners. It's not about me, its all about them!

You know it.  And unfortunately that's the potential issue with any baffle, they can be an imposing distraction.

I once used a small pizza box as a makeshift baffle, stuffed with a couple old dirty t-shirts inside.  Might have made a more tempting target than a coat rack, but would have been an surprise to anyone searching for a bite!

[capnhook]

OK I will ask the dumb question...... ......why not blumlein in the center?  You got a LSD2............

[cybergaloot]

OK I will ask the dumb question...... ......why not blumlein in the center?  You got a LSD2............

That was actually one of the original considerations. You need to come visit sometime Kevin!

[capnhook]

OK I will ask the dumb question...... ......why not blumlein in the center?  You got a LSD2............

That was actually one of the original considerations. You need to come visit sometime Kevin!

Ok, then we can really cover some ground...........lets put 2 LDS2's in the center!

Those pickers are really good, Walter..

[Gutbucket]

Blumlein might work nicely, but the two side quadrants are out of polarity so performers in those sections of the circle may image oddly and suffer from weak bass response.  Would be best to arrange things so players of importance, including the bass player, are within the front and rear quadrants if possible, and the sing-along egg-shaking hangers on and second-liner's are in those side quadrants.

If you play that back through a home theater setup and turn on the Dolby/DTS/Logic7/THX matrix surround mode in the receiver, the sources in those side quadrants will be what gets wrapped around to the surround channels in back half of the room.  The sources in the quadrants directly in front and behind the microphone will image between the front speakers.

[cybergaloot]

Those pickers are really good, Walter..

The guy singing and playing mandolin was a roommate for a while back in the middle 70's and the guy playing bass (also a killer guitar player) is a friend from high school. They just aren't much interested in having a touring band.

[Gutbucket]

I'll have to check out that Youtube link when i get home.

You guys may remember this thing from my oddball thread.. One of the first things I built when I started hanging out around here at TS years ago-  A two omni boundary-mounted hemispherical baffle contraption designed to be set on the ground in the middle of a circle of pickers.  It worked pretty well, but would have worked even better if it was higher up off the ground and provided a bit more baffling between the two channels.  In a few recordings it seemed to really emphasize circadias up in the trees directly above the circle.

I made it before going to a week-long guitar camp.  The baffle housed an R-09 recorder and MMA6000 preamp to form a quick portable an all-in-one recording thingamajobber.  Or take out the recorder and preamp to operate them remotely and insert the foam blocks for a full half-sphere baffle (I never actually used it that way).

[voltronic]

I guess I need to make myself a Jecklin disk sometime. I don't if or when I'll ever make it over to the pickin' party I'm thinking about but those boys can play! If you know who Guthrie Trapp is, he is basically a former protege of theirs.

You can make due pretty well by just setting up two omnis at shoulder height, spaced about a foot apart or so on a mic bar, then draping a jacket or sweater or something over the bar between the mics.  Might help to mount the mics upside-down on the bar so they hang beneath it, so the draped jacket or whatever is high enough to properly baffle them.  As long as whatever you put between the mics effectively blocks the sound from arriving from the opposite side, yet both mics can still 'see' the performers to the front and back of the plane between the mics it's good.   It's also somewhat casual and less imposing than a fancy disk, which might make the performers more relaxed.  I like shoulder or chest height because it is about equidistant to both the voices and instruments, so both are clear and close and neither is over represented, and it's low enough that the performers can easily see each other over the top.  That's far less imposing than something at head height blocking the view and potentially killing the vibe, or even up high looking down on things.

I've also used a towel draped over a vertical music stand, same idea.

[cybergaloot]

You've always come up with some interesting rigs. I remember when I met you that you had a painter's pole stuck in your folding chair with, I think, antennas sticking out with the DPAs at the end. I love it when I'm at the SOSMP and see that curent rig of yours pop up in the middle of the crowd. AAA+++ for inventiveness!

[Tom McCreadie]

I'd go with a Jecklin Disk. You could cobble up a quick 'n dirty JD by glueing a stack of old LP's - I urge you to use up any Barry Manilow's, for optimum sound  :-) - and covering that stack with some rubber carpet underlay or maybe a few old pc mouse mats.

With performers evenly around a circle, the Blumlein array does have two disadvantages:
1. Sounds from the two extreme L and R sectors fall in the "ambiophonic" region. That is, they deliver opposite polarity voltages to the two coincident mics (one mic getting a +ve signal while the other mic gets a -ve value). This results in a woozy, vague imaging of those sound sources.

2. Sounds from the rear sector will - besides generating signals of a polarity inverse to those from the front - also give a 'laterally-inverted' imaging, e.g. sources  located at, say, "4-o'clock" and "5-o'clock" will image as if they had been located at 8- and 7-o'clock, respectively. 

To illustrate this further, a consequence would be that, for a perfectly-centred array and 6 performers A...F stationed at direction angles of  A 10-30, B 11-30, C 12-30, D 1-30, E 5- and F 7-o'clock, the resultant imaging from a two-speaker playback would likely be in the following sequence:
- from Jecklin Disk:        L  ->     A - F - B - C - E - D     ->   R
- but from Blumlein:      L ->      A - E - B - C - F - D     ->   R

[cybergaloot]

I figured the stereo imaging would be weird but I didn't take into account the inversion of the rear sources. And I definitely didn't consider the "ambiophonic" region. That sounds like a game killer to me. Time to make a disk and try testing it some. I think there is a pickers group that meets periodically here in Tallahassee. I'll have to figure out where they meet.

[voltronic]

I'd go with a Jecklin Disk. You could cobble up a quick 'n dirty JD by glueing a stack of old LP's - I urge you to use up any Barry Manilow's, for optimum sound  :-) - and covering that stack with some rubber carpet underlay or maybe a few old pc mouse mats.

With performers evenly around a circle, the Blumlein array does have two disadvantages:
1. Sounds from the two extreme L and R sectors fall in the "ambiophonic" region. That is, they deliver opposite polarity voltages to the two coincident mics (one mic getting a +ve signal while the other mic gets a -ve value). This results in a woozy, vague imaging of those sound sources.

2. Sounds from the rear sector will - besides generating signals of a polarity inverse to those from the front - also give a 'laterally-inverted' imaging, e.g. sources  located at, say, "4-o'clock" and "5-o'clock" will image as if they had been located at 8- and 7-o'clock, respectively. 

To illustrate this further, a consequence would be that, for a perfectly-centred array and 6 performers A...F stationed at direction angles of  A 10-30, B 11-30, C 12-30, D 1-30, E 5- and F 7-o'clock, the resultant imaging from a two-speaker playback would likely be in the following sequence:
- from Jecklin Disk:        L  ->     A - F - B - C - E - D     ->   R
- but from Blumlein:      L ->      A - E - B - C - F - D     ->   R

Every time I've heard a Blumlein recording of singers in an arc around the array, I've always thought it sounded very unrealistic compared to ORTF cards or spaced omnis in the same space.  I wonder if the effect you're describing partially accounts for this.  Maybe this is not a mic setup that is good to use close up when you have sound coming from multiple directions.

[Gutbucket]

Blumlien works best when you only have ambient room sound stuff (reflections, reverb, applause, maybe ambient wash stuff, and whatever) in the side quadrants.  That stuff really works well when located there and is part of what makes Blumlein so magical sounding. The inverse polarity (of both channels equally) and mirror flipped imaging in the back quadrant is really no big deal at all for this IME.  Is anyone really going to remember or care which side everyone was on? Doubtful.   The biggest constraint with Blumlien is that the forward and backward facing main quadrants are so relatively narrow, it's sort of hard to fit all the important direct imaging sources in there.  One little known trick is to narrow the angle between microphones slightly, which widens the front and back recording angle quadrants a bit. Helps solidify the center too.

Not definite yet, but I'm hoping to make it up to Mag next month.  If so I'll be looking forward to seeing you at the porch stage Walter.

'Ambiophonics' is a playback arrangement using narrowly spaced speakers, electronic interchannel cross-cancellation techniques, and optional convolution reverberance.  It is ideally recorded using a front/back baffled and pinna-less dummy head.  But it often works for playing back standard stereo recordings too.  'Ambiophonics' doesn't really apply to coincident crossed figure-8 'Blumlien' stereo in anyway that I'm aware of.