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Author Topic: Ambient sound & Jecklin disc for quad?  (Read 1231 times)

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Offline Gutbucket

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Re: Ambient sound & Jecklin disc for quad?
« Reply #15 on: February 16, 2021, 04:29:10 PM »
A directional microphone oriented more or less tangentially along the surface of the floor, in your case angled upward toward the lecturer but still close to the floor, may not benefit from significant sensitivity increase, but the arrangement should reduce the effect of the floor bounce interfering with the direct path arrival- addressing the "hollow sound" issue mentioned in the lower red-boxed portion of the Shure literature in DSatz's post above.  Placing the arrangement on a yoga mat probably won't hurt.

You may recall my previous posts about on-stage taping using directional mics positioned very close to the stage floor.  I think the reduction of floor bounce lead to increased clarity in those situations.  Those mics were angled upward at angles of 45 degrees or less toward relatively close drum kit and acoustic bass sources.  Noted and certainly related, although I'm not sure of all the details of the underlying phenomena, was the unusual and exceptional clear projection and pickup across larger distance of the guitar amplifier cabinet placed directly on the hardwood stage floor and projecting tangentially across it toward to the microphones.  Perhaps that was doubling the effect by it's application at both the source and receiving end of things.

On the frequency-selective sensitivity increase of a stereo sphere baffle like the Schoeps KFM6 using flush-mounted omnis in the +/- 90 degree positions, the maximum sensitivity increase should occur at +90 degrees in one channel and -90 degrees in the other.  That is in combination with the sensitivity decreasing shadowing effect toward the opposite direction across the same frequency range.  Because of that I imagine the averaged response across all directions is likely to be flat for each channel or close to it.  And I imagine the response along the median plane (source at 0 or 180 degrees), which is on-axis with respect to the stereo array but 90 degree off axis to either microphone, to be flat as well.  DSatz, please correct me if I'm incorrect about this.  Any additional information you have access to regarding the response of KFM6 would seem quite applicable to these questions.

The first stereo recording array I purpose-built after finding Taperssection 15 years ago was modeled on the KFM6, although modified as a boundary-mounted 7" diameter hemisphere mated to a larger diameter flat disk, intended to be placed on the floor, on a stool or a table rather than a full sphere placed in free space.  It was designed for recording instructor lectures, demonstrations and performances in a classroom setting at an acoustic guitar camp, as well as something I could place in the center of a circle of players, optionally housing the preamp and recorder within the hemisphere to form an easily portable all-in-one device that would fit into a guitar gig bag front pocket.   It worked well, yet was best when the sources were relatively low to it's 'horizon' such as the players seated on the floor itself, or with it placed on a table or high stool.  It lost directional differentiation as the angle to the sources grew higher, similar to how our own directional hearing becomes less differentiated for sources with significant elevation above the horizontal plane.

The original discussion is here - https://taperssection.com/index.php?topic=70134.msg939807#msg939807  I dubbed it Boundrisphere. Unfortunately it looks like the photos were stripped from that thread and I cannot find one of it on this computer, but I still have it at home if you'd like me to dig it up and take a photo. [edit- Hmm, I now see them again and am inserting a few from that thread below]





« Last Edit: February 17, 2021, 10:19:47 AM by Gutbucket »
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Offline Gutbucket

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Re: Ambient sound & Jecklin disc for quad?
« Reply #16 on: February 17, 2021, 10:04:26 AM »
Apologies for getting OT w/r/t the OP, but to follow up on my reply to kuba e-

You may recall my previous posts about on-stage taping using directional mics positioned very close to the stage floor.  I think the reduction of floor bounce lead to increased clarity in those situations.  Those mics were angled upward at angles of 45 degrees or less toward relatively close to the drum kit and acoustic bass.  Noted and certainly related, although I'm not sure of all the details of the underlying phenomena, was the unusual and exceptional clear projection and pickup across a larger distance of the guitar amplifier cabinet placed directly on the hardwood stage floor and projecting tangentially across it toward to the microphones.  Perhaps that was doubling the effect by it's application at both the source and receiving end of things.
^
Below are photos of this from three different evenings recording a jazz trio.  The mics aren't close enough to the floor to achieve boundary effect through the highest audible frequency range, but no high frequency comb-filtering was apparent.  The guitar cabinet mentioned can be seen to the right and was farther away than seems apparent in the photos, partly because it was placed further away from the front of the stage than the drums and bass, and partly because the microphone array was intentionally not centered directly in front of the drum kit but positioned to the right of it (stage left) for increased proximity to the acoustic bass (amplifier-reinforced) and to avoid having the mics directly on-axis with the kick drum.  The 3 large diameter diaphragm ADK TL microphones in the small-format triangular decca tree-like arrangement on the stage were set to a supercardioid pickup pattern.  The room/audience/ambience/surround microphones clamped just below the stage-lip facing out into the room are Microtech Gefell supercardioids.







musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #17 on: February 17, 2021, 12:02:55 PM »
Congratulations, you overcame Schoeps. I like the ears you made to the ball. The musicians certainly liked the ball too.

Yes, that's a good note. Boundary microphone's  advantage is avoiding reflections from the floor. I will experiment with it more. I will try the microphones on the stand and on the ground. I will see how the reflections from the ground affect the recording.

Thank you for nice photos and explanation of onstage recording. It is beautiful setup. Photos are very good for creating an idea. Maybe the recording went also well because the cabinets were placed on the floor, so the microphones were at the same level.

Unfortunately I didn't find much information about sound boundary layer. I only found a mention that the width of the boundary layer depends on the frequency and that the gain of 6db only applies to sounds incident perpendicular to the surface. This is really just a guess, but if I recalculate it by simple relations for ideal flow (without friction), the gain in the boundary layer for sounds at an angle of 30 degrees would be only 1.5db. Anyway, this is not important. It is important to avoid reflections from the floor. I'm looking forward to trying it and being able to compare boundary and classic settings.
« Last Edit: February 17, 2021, 12:14:14 PM by kuba e »

Offline Gutbucket

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Re: Ambient sound & Jecklin disc for quad?
« Reply #18 on: February 17, 2021, 01:08:34 PM »
Don't know about overcame.  A modified emulation inspired by Schoeps, and based upon the same underlying principles, I'd say

Most of the times I've used "standard" boundary mounting involved attaching the miniature omnis directly to the back wall of the room facing the stage, in a spaced A-B arrangement.  That produced a more advantageous direct/reverberant ratio in the resulting recording with better clarity and less low frequency "muddiness" than using directional microphones placed a similar distance away from the stage (perhaps a meter or two in front of the back wall - either way, more distant from the stage than desirable).  As the only option was to record from back there or not at all, the boundary mounted omnis placed on the back wall produced the best result in that situation.  If I could have moved closer and used directional mics in a typical arrangement I would have chosen that.  I tried this same back wall boundary-mounting arrangement in the onstage recording scenarios pictured above.  Ironically it picked up too much direct sound from the stage for the room/audience/ambience/surround channels role.  Moving them to the front wall underneath the stage facing out into the room did work well as an alternate configuration to using the MG supercards.

Also, along with other directional microphone arrangements for the trio above I tried boundary mounted omnis on the stage surface facing upwards, but preferred elevating the omnis a few feet above the stage and ultimately preferred the L/C/R directional microphone arrangement pictured above which I stuck with for the remainder of the series.
musical volition > vibrations > voltages > numeric values > voltages > vibrations> virtual teleportation time-machine experience
Better recording made easy - >>Improved PAS table<< | Made excellent- >>click here to download the Oddball Microphone Technique illustrated PDF booklet<<

Offline kuba e

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Re: Ambient sound & Jecklin disc for quad?
« Reply #19 on: February 18, 2021, 08:00:50 AM »
Don't know about overcame.  A modified emulation inspired by Schoeps, and based upon the same underlying principles, I'd say

I meant it's a very good job and it has style. I understand that Schoeps had to make black ball on the stick, because it's dark at concerts and they don't want it to be seen. But for lectures or workshops, your ball is better, it's happier. It is easier for musicians to accept it.

Also, along with other directional microphone arrangements for the trio above I tried boundary mounted omnis on the stage surface facing upwards, but preferred elevating the omnis a few feet above the stage and ultimately preferred the L/C/R directional microphone arrangement pictured above which I stuck with for the remainder of the series.

This is good information that is worth experimenting with the height of the stand when recording onstage. I like onstage recording, but I haven't tried this yet.

 

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