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Omni spot mics with foam "baffle" ?
Old 1 week ago
  #1
Gear Head
 
Wavefront's Avatar
 
Omni spot mics with foam "baffle" ?

To avoid confusion, let me preface this by saying that the question is specifically regarding the use of some sort of baffle/absorption on omni microphones when used as spots. Also not about APE spheres, baffled omnis for main pickup, or other tangential topics.

I saw a picture some time ago (which I foolishly did not save) from a (classical) recording session, in a church as I recall, where several SDC omni spots had been outfitted with foam "collars" similar to what I have tried to depict in the attached photoshopped image.

I can easily understand the theoretical rationale behind doing this, but it's a technique I have only seen a handful of times, and I can equally easily believe that in practice it is less helpful than it might seem, etc. so I have been meaning to ask about it.

Curious to hear any anecdotes, particularly from those who have tried such a technique, whether successfully or not.
Attached Thumbnails
Omni spot mics with foam "baffle" ?-omni-foam.jpg  
Old 1 week ago
  #2
Gear Guru
 
1 Review written
🎧 5 years
i haven't tried this 'method' but i doubt that a small foam baffle would be more effective than say using a rug or carpet - actually, i wouldn't expect it to be beneficial at anything, besides potentially messing with the pattern (in the hf range)...
Old 1 week ago
  #3
Lives for gear
 
🎧 10 years
If the baffle (as shown in pic) were both thick/dense enough and also of sufficient area, with an omni mic you might expect some crude attenuation of rear pickup.

Why not just use a sub-cardioid or cardioid mic instead, for the same or better result, and more elegantly/professional-looking at the same time ?
Old 1 week ago | Show parent
  #4
Gear Head
 
Wavefront's Avatar
 
Quote:
Originally Posted by deedeeyeah ➡️
actually, i wouldn't expect it to be beneficial at anything, besides potentially messing with the pattern (in the hf range)...
Yes, although I have not heard the recordings which correspond to the session photo I mentioned, my assumption was that the objective is to somewhat reduce the higher rear-incident frequencies, making it behave perhaps somewhat more like a larger-diaphragm omni (DPA 4041, Sonodore LDM-54, Gefell M102, etc.) which is rather directional at the highest frequencies.

Certainly not advocating this approach either, I am somewhat skeptical, but realized I don't think I've ever seen it discussed on this forum, so thought I'd bring up the question. . .
Old 1 week ago
  #5
Gear Nut
 
This could really be thought of as half-a-Jecklin. With careful selection of materials, it shouldn't be any more colored than a well-made Jecklin disc, and the resulting polar pattern should be quite similar. Advantage over a card would be less off-axis coloration (at the expense of a bit of on-axis coloration), and being fully omni at frequencies below those related to the size of the baffle used. Could be very useful in the right circumstances.

Though a well-absorptive material wouldn't be expected to produce significant edge diffraction effects, if I did this myself, to be on the safe side I'd cut the material in the shape of the Neumann GFM 132 (triangle with each side having carefully determined different lengths), and place the hole in the same position on the baffle.

It would interesting to compare the sound and effectiveness of this to a sphere on the mic - Both give an omni a directional pattern above a certain frequency, the difference being that the sphere boosts the higher frequencies from in front, and the baffle attenuates higher frequencies from the rear. The baffle would much more useful up close, and the sphere from a distance.

One application that comes immediately to mind would be on a Decca tail pair of omnis, where one might want less bleed at high frequencies from nearby sources, but retain the full low end of the omins.
Old 1 week ago | Show parent
  #6
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Quote:
Originally Posted by k brown ➡️
This could really be thought of as half-a-Jecklin. With careful selection of materials, it shouldn't be any more colored than a well-made Jecklin disc, and the resulting polar pattern should be quite similar.
not really - for three reasons:

- it does make a difference whether one 'disturbs' the pattern - even of omnis - from behind or from the sides of the capsule, at least when using typical sdc's; maybe (but only maybe) effects would be less noticeable when using minature mics...

- in order to become effective, a disk needs to be larger (and heavier) than a small, ightweight piece of foam.

- a 'design' as pictured can only aim at damping of hf; oss pursues other goals.
Old 1 week ago
  #7
Gear Nut
 
That's why I said 'careful selection of materials' - it would need to be as absorptive and as acoustically opaque as that used on a Jecklin.

It's size only determines what frequency it operates at, not whether it's effective at all or not.

The 'goals' of OSS have nothing to do with this.
Old 1 week ago | Show parent
  #8
Gear Guru
 
1 Review written
🎧 5 years
Quote:
Originally Posted by k brown ➡️
It's size only determines what frequency it operates at, not whether it's effective at all or not.
nope: of course does the size of a baffle decide on how effective it can become - different story on 'spheres' (which the op clearly isn't talking about).

Quote:
The 'goals' of OSS have nothing to do with this.
wrong again: jürg was aiming at vastly different things/had differnt 'goals' in mind than what this thingy can do...
Old 1 week ago
  #9
Gear Nut
 
It's not a different story on spheres - the size of the sphere is exactly what determine the frequency at which it becomes effective!

OSS/Jecklin is exactly two omnis with a baffle between; this is one omni with a baffle. If this were done with a baffle the same size as a Jecklin, and with material that was as surface-absorptive and acoustically opaque as the disc of a Jecklin, it would be 1/2 a Jecklin, with exactly the same frequency-dependent directionality as each mic on a Jecklin has. Why do you think that would not be the case? The only difference would be, if the baffle were as small as that shown, the directionality would begin a higher frequency.

The directionality of both spheres and baffles is all about their physical size in relation to the physical size of sound wavelengths.
Old 1 week ago | Show parent
  #10
Gear Guru
 
1 Review written
🎧 5 years
Quote:
Originally Posted by k brown ➡️
It's not a different story on spheres - the size of the sphere is exactly what determine the frequency at which it becomes effective!

OSS/Jecklin is exactly two omnis with a baffle between; this is one omni with a baffle. If this were done with a baffle the same size as a Jecklin, and with material that was as surface-absorptive and acoustically opaque as the disc of a Jecklin, it would be 1/2 a Jecklin, with exactly the same frequency-dependent directionality as each mic on a Jecklin has. Why do you think that would not be the case? The only difference would be, if the baffle were as small as that shown, the directionality would begin a higher frequency.

The directionality of both spheres and baffles is all about their physical size in relation to the physical size of sound wavelengths.
you seem to carefully neglect what i wrote in my previous posts, an attitude not unlike to the erratic behaviour in one of the threads you started...

again: oss is NOT about directivity and the size and materials used to build a disk affect the results far beyond directivity - go to the studio design/acoustics forum for basic information on absorption and reflections.

there are fundamental differences between a (reflective) sphere and a (absorptive) disk, the position/distance of a microphone from it, the axis of the mic in relation to the disk; frequency, time, angle and level dependencies of the incident sound need to be taken into account in case of a disk while the size of a sphere does affect exactly one criteria...

...so equating a hard, round sphere with a disk (or even a piece of foam behind a mic) and reducing the comparison to each object's effects on the directivity alone is a completely inadequate simplification and the reason why your equation is entirely flawed!

___


for the record: i assisted jürg for ca. 15 years, from the late 70's onwards, and we used then top-notch gear to measure the effects of dozens of different disk designs; way more important than to measure any effects of the baffle (if that was possible at all...) was though the critical evaluation of results specifically in the context of fm radio:
jürg first and foremost was a radio engineer and was dissatisfied with the results of many conventional stereo main mic techniques when listening to fm radio -THIS (the typical effects of frequency modulation) led him to look around if there might be another technique which would help to overcome some of the limitations - a quest which by chance or sheer luck turned into another tool in our arsenal of stereo mic systems (yet didn't help to overcome issues of fm radio).

you are welcome to calculate the height of fall of your remarks yoursef!
Old 1 week ago
  #11
Gear Nut
 
I recognized the effects of the baffle beyond it's directionality when I said "...at the expense of a bit of on-axis coloration", which is produced by some degree of reflection from the baffle, depending on the material used. Most who've used the Jecklin don't find them serious or objectionable - Simon Eadon uses it quite often as his main pair.

I'm quite familiar with the history and development of OSS/Jecklin; I've studied it for years and used it many, many times.

I didn't 'equate' a sphere and a baffle, I merely said they both produce frequency-dependent directionality, which they do. I already explained quite clearly the differences between the two; each has different additional effects. You've taken my remarks far too literally - they were intended to provide others reasons why someone might want to try this and when it might be useful. You've chosen to dismiss it as a useless 'thingy' - I see no theoretical reason one wouldn't try it and see how effective it is; I hope people do and come to their own conclusions. I see it as a potentially useful tool in the toolbox, that could do useful things that no omni or card could.

My apologies to the OP for dragging in APEs and baffled omnis, but it seemed useful as a way to describe why these things, properly made, might be worth trying.
Old 6 days ago | Show parent
  #12
Gear Guru
 
1 Review written
🎧 5 years
i did not say that this thingy needs to be completely useless: under laboratory conditions, it will be possible to determine that it affects the pickup of reflections, the frequency range and the pattern behaviour towards the hf range.

however, it cannot achieve any of these things very efficiently nor can these microscopic changes be verified without time-consuming comparisons - time that i would not want any musician to waste and which is why i strongly advise not to rely on the equivalent of homeopathy but on more robust procedures which can produce similar results more easily and effectively.

of course anyone who's still got enough time to kill during the pandemic can go ahead - pls keep me posted on your findings!

(i would ask however that the anecdotal findings be accompanied by a note that they are the results of a rather obsessive way of looking at processes which quite rightly do not receive any attention in everyday practice and thus under real-world conditions)
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