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omnis and pressure sphere attachements
Old 17th February 2015
  #1
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Bruce Watson's Avatar
 
🎧 10 years
omnis and pressure sphere attachements

I've been reading this thread and it got me thinking about the reasons to use a pressure sphere on an omni. Anyone answer some questions for me?

Schoeps says: "It creates the illusion of closer placement so that greater miking distances can be used while maintaining good ”focus” in the sound. This in turn improves the blend and balance when recording orchestras or choruses, for example. The effect is due partly to an increase in directivity, but mainly to the elevated midrange response (see frequency response curves). The low-frequency response remains undiminished."

This is interesting to me. If I look at the graphs, I can see that the sphere creates a midrange frequency bump in addition to increasing the directionality at higher frequencies. So it's somewhat of a presence boost, which would indeed give the audio effect of being somewhat closer to the source. I can kinda-sorta understand that, but I've got some questions.

Q1: For this presence boost, is there any audible difference between using pressure spheres, and making a broad but low boost in EQ in post? One would think you could replicate the presence boost almost exactly with EQ, but do you get the same effect? IOW, are the spheres doing something else besides this boost (phase shifts, etc.)?

Q2: The HF directionality would seem to be considerably more difficult to handle in post -- is that even possible?

Q3: To increase the directionality of HF on an omni.... makes it less omni, doesn't it? Why is this more desirable than using, for example, a wide cardioid? For example, a Schoeps MK21 vs. a MK2 with a KA40 sphere?

I'm asking these questions because these spheres were invented and used long before we had tools like digital parametric EQ available, and even before we had tools like the MK21 capsule. I guess I'm trying to figure out how useful these spheres are in this "modern era" that we're in.
Old 17th February 2015
  #2
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king2070lplaya's Avatar
You don't get that "omni" bass response with a MK21.

And the zoom factor is a combination of the presence boost and the increased directionality.

While it may seem messy on paper, it's huge success and popularity as a recording tool should assuage any doubts about whether the sphere is worth it.
Old 17th February 2015
  #3
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🎧 15 years
Quote:
Originally Posted by Bruce Watson ➡️
I've been reading this thread and it got me thinking about the reasons to use a pressure sphere on an omni. Anyone answer some questions for me?

Schoeps says: "It creates the illusion of closer placement so that greater miking distances can be used while maintaining good ”focus” in the sound. This in turn improves the blend and balance when recording orchestras or choruses, for example. The effect is due partly to an increase in directivity, but mainly to the elevated midrange response (see frequency response curves). The low-frequency response remains undiminished."

This is interesting to me. If I look at the graphs, I can see that the sphere creates a midrange frequency bump in addition to increasing the directionality at higher frequencies. So it's somewhat of a presence boost, which would indeed give the audio effect of being somewhat closer to the source. I can kinda-sorta understand that, but I've got some questions.

Q1: For this presence boost, is there any audible difference between using pressure spheres, and making a broad but low boost in EQ in post? One would think you could replicate the presence boost almost exactly with EQ, but do you get the same effect? IOW, are the spheres doing something else besides this boost (phase shifts, etc.)?
Yes, it's more than a presence boost- it's the result of changing the polar pattern. You aren't so much increasing low or high, you're cutting the pickup of certain frequencies.


Quote:
Q2: The HF directionality would seem to be considerably more difficult to handle in post -- is that even possible?
Nope

Quote:
Q3: To increase the directionality of HF on an omni.... makes it less omni, doesn't it? Why is this more desirable than using, for example, a wide cardioid? For example, a Schoeps MK21 vs. a MK2 with a KA40 sphere?

I'm asking these questions because these spheres were invented and used long before we had tools like digital parametric EQ available, and even before we had tools like the MK21 capsule. I guess I'm trying to figure out how useful these spheres are in this "modern era" that we're in.
A Wide cardiod is a completely different pattern. An omni with a ball is a different pickup than a wide cardiod. An MK21 is a great capsule, but an MK2 (or 2S or 2H) with a ball is different. The big difference is that you'll find most subcards have similar directionality across the full frequency spectrum whereas the omni with a ball will increase directionality at higher frequencies.

--Ben
Old 17th February 2015
  #4
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boojum's Avatar
 
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Bruce, additionally you can angle the mics away from the source to get an attenuation. These are versatile devices. Check this DPA link: DPA Microphones :: Products
Old 17th February 2015
  #5
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I've taken to using the spheres almost exclusively now on my C617's when miking a large ensemble. It is a more sparkly, brilliant, and focused sound. The bass response does not suffer like a wide cardioid mic, and the brightness is tamed by increased hf directivity. It is important to "aim" them at the appropriate source rather than straight ahead like you might with standard omnis. I tend to point them at the first chair violins and cellos so the sparkle is sourced from the better players. It lets that random violin solo shine through as well.

It is important to note that the increased direction only occurs at frequencies with wavelengths shorter than the actual ball. Low frequencies and most of the mid-range are not affected. So it is a very different thing than a wide-cardioid microphone.
Old 17th February 2015 | Show parent
  #6
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John Willett's Avatar
 
🎧 10 years
Thumbs up

Quote:
Originally Posted by rumleymusic ➡️
I've taken to using the spheres almost exclusively now on my C617's when miking a large ensemble. It is a more sparkly, brilliant, and focused sound. The bass response does not suffer like a wide cardioid mic, and the brightness is tamed by increased hf directivity. It is important to "aim" them at the appropriate source rather than straight ahead like you might with standard omnis. I tend to point them at the first chair violins and cellos so the sparkle is sourced from the better players. It lets that random violin solo shine through as well.

It is important to note that the increased direction only occurs at frequencies with wavelengths shorter than the actual ball. Low frequencies and most of the mid-range are not affected. So it is a very different thing than a wide-cardioid microphone.
The Josephson C617 uses exactly the same capsule as the Gefell M221.

The attached graph shows the frequency response curves with and without a 3cm and 4cm frequency ball of the M221.

.
Attached Thumbnails
omnis and pressure sphere attachements-m221-20frequency-20response-20english-20for-20website.jpg  
Old 17th February 2015
  #7
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🎧 10 years
Quote:
Originally Posted by Bruce Watson ➡️
Q2: The HF directionality would seem to be considerably more difficult to handle in post -- is that even possible?
No, but it can be done - and with powerful flexibility - if you use each omni in tandem with a (coincident) Fig8, then use the Schoeps Polarflex plug-in in post.

Polarflex - SCHOEPS.de
Old 17th February 2015
  #8
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Here is a thread about DIY API balls: https://gearspace.com/board/remote-p...?highlight=api

I explain the method I used to make wooden APIs from post #14 down.

Total cost about $5/working pair and some black matte paint on hands.

And yes, it is a combination of slight HF lift and added directionality also in HF. It is a nice (and if DIY, also cheap) tool to have instead of buying all possible capsules. And even then.
Old 17th February 2015
  #9
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Plush's Avatar
 
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Use of the ball with omni mics all comes from the Neumann M50 design book.

The directional response of the mic with the ball offers a "beaming" effect that focuses violins and cellos.

M50 was used as outriggers picking up a lot of hall sound and it was felt that the desirable string sound must be preserved while the mic was being used at the critical distance. The ball, whether in the design of the mic like in the M50 or as an add on, offered a way to get detail on the vln+vlncello.

The goal was to have the directional pattern be more cardioid at string frequencies. There is also an improvement in reach while using the omni mic.
Old 17th February 2015 | Show parent
  #10
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Quote:
Originally Posted by Plush ➡️
Use of the ball with omni mics all comes from the Neumann M50 design book.
One word: Decca Tree...
Old 17th February 2015
  #11
RPC
Gear Addict
 
1 Review written
🎧 5 years
Imitating a Sphere

Quote:
Originally Posted by Bruce Watson ➡️
Q2: The HF directionality would seem to be considerably more difficult to handle in post -- is that even possible?
This could be done with mikes like the Sennheiser MKH800 Twin or Pearl TL44; a shelf filter on the rear-facing cardioid would do the trick. Actually, thinking just a bit more, a shelf filter on the front cardioid, raising its level, might provide both the increased directivity and high-end boost. If I can get the time, I might haul a spaced MKH800 Twin recording out of the archive and give this a try.
Old 17th February 2015
  #12
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Bruce Watson's Avatar
 
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I apologize in advance if I'm not making much sense. Words just aren't my forte; I'm an engineer. If you could just see the 3D virtual reality with the false colors that's swirling around in my head... but you can't. So I'll try with words.

It's hard to make an omni that's actually an omni at all frequencies. Nearly all of them become more directional as frequency rises. You can see it in the polar diagrams, like this one for the Schoeps MK2. At 16 kHz, it's down more than 10dB at 90 degrees. So at high frequencies, it's not really an omni any more.

The pressure balls would seem to cause a disturbance related to the diameter of the ball. So a 40mm ball -> a frequency of 8.5 kHz, I would guess it's effects would start to be significant at half or even a quarter of that, say 2-4 kHz. And in post #6 above, Mr. Willett's diagram show the onset of boost at around 1.0 kHz which is even lower, but not out of line with expectations.

What I'm getting at, in my less-than-articulate way, is that the existing omnis used widely for orchestral work, are already somewhat directional at HF. And, there are existing omnis, like the Schoeps MK2s that already have an existing bump in their response curves starting above 5 kHz. So it seems as if all that is missing is extending that bump down to 1 kHz, which you could do with a simple application of parametric EQ. Oh, and a tail in that bump, coming back down to the 0 dB response axis again around 15 kHz. So where the MK2s has a rising HF, more a shelf than a bump, if you put a sphere on it, you turn that shelf back into a bump that ends around 15 kHz.

But what I'm hearing from the group, unanimously, is that it's not the same as using the spheres. I'm not doubting this, y'all know way more about it than I do, and I trust your expertise completely.

I'm just having trouble wrapping my head around what the difference(s) are.

Perhaps the spheres make the mics more directional in the mid frequencies? I can see that they probably would. Hmmm.....
Old 17th February 2015
  #13
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pkautzsch's Avatar
 
🎧 15 years
Quote:
Originally Posted by Petrus ➡️
One word: Decca Tree...
That's actually two words

Quote:
Originally Posted by RPC ➡️
This could be done with mikes like the Sennheiser MKH800 Twin or Pearl TL44; a shelf filter on the rear-facing cardioid would do the trick. Actually, thinking just a bit more, a shelf filter on the front cardioid, raising its level, might provide both the increased directivity and high-end boost. If I can get the time, I might haul a spaced MKH800 Twin recording out of the archive and give this a try.
You'd lose, however, the pressure transducer's inherent bass response when using two directional mics back to back.
The pressure omni's bass response is preserved when using APEs.

Quote:
Originally Posted by Bruce Watson ➡️
It's hard to make an omni that's actually an omni at all frequencies. Nearly all of them become more directional as frequency rises. You can see it in the polar diagrams, like this one for the Schoeps MK2. At 16 kHz, it's down more than 10dB at 90 degrees. So at high frequencies, it's not really an omni any more.
Exactly. And why is that so? Because the mic's body disturbs the sound field.
Same as pressure balls, just smaller diameter and therefore higher frequency.

Quote:
The pressure balls would seem to cause a disturbance related to the diameter of the ball. So a 40mm ball -> a frequency of 8.5 kHz, I would guess it's effects would start to be significant at half or even a quarter of that, say 2-4 kHz. And in post #6 above, Mr. Willett's diagram show the onset of boost at around 1.0 kHz which is even lower, but not out of line with expectations.
Right again, so far.
Quote:
What I'm getting at, in my less-than-articulate way, is that the existing omnis used widely for orchestral work, are already somewhat directional at HF. And, there are existing omnis, like the Schoeps MK2s that already have an existing bump in their response curves starting above 5 kHz. So it seems as if all that is missing is extending that bump down to 1 kHz, which you could do with a simple application of parametric EQ.
Here's where you go wrong. APEs don't just extend the bump, but also change the pattern in the bump's frequency range. And you can't do that with an EQ.
Quote:
Perhaps the spheres make the mics more directional in the mid frequencies? I can see that they probably would. Hmmm.....
Yes. That's the way they work. See also my post in that other thread where I linked to the animation on the Neumann website.
Old 17th February 2015 | Show parent
  #14
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Quote:
Originally Posted by Bruce Watson ➡️
Perhaps the spheres make the mics more directional in the mid frequencies? I can see that they probably would. Hmmm.....
ExcActly!

Consider DPA 406x series omnis. They are the size of a match head (almost), and are most omni of them all. While maybe not quite as flat and definitely not as quiet as the best bigger omni microphones, their imaging is superb in AB.

The bigger the omni, the more the body shadows the rear, and that starts from the higher frequencies first. APIs are just a controlled way of making the mic bigger, causing more HF directionality and lift. It does not affect bass response or noise. Like already written a few times, lift can be EQed in post, but not the change in HF directionality.
Old 18th February 2015 | Show parent
  #15
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🎧 10 years
Quote:
Originally Posted by pkautzsch ➡️
Quote:
What I'm getting at, in my less-than-articulate way, is that the existing omnis used widely for orchestral work, are already somewhat directional at HF. And, there are existing omnis, like the Schoeps MK2s that already have an existing bump in their response curves starting above 5 kHz. So it seems as if all that is missing is extending that bump down to 1 kHz, which you could do with a simple application of parametric EQ.
Here's where you go wrong. APEs don't just extend the bump, but also change the pattern in the bump's frequency range. And you can't do that with an EQ.
Yes, that's the key point that Bruce overlooks. No equalization is smart enough to identify and operate on only those signals that arrive from a particular off-axis direction.
Old 18th February 2015 | Show parent
  #16
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Bruce Watson's Avatar
 
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Quote:
Originally Posted by pkautzsch ➡️
Here's where you go wrong. APEs don't just extend the bump, but also change the pattern in the bump's frequency range. And you can't do that with an EQ.
So a MK2 with sphere is an omni below around 1 kHz, then tapers upwards to being something like a cardioid at 16 kHz.

Whereas a MK21 is a wide cardioid below around 8 kHz, then tapers upwards to something like a cardioid at 16 kHz.

So these pressure spheres are actually mostly about the bottom and middle frequencies, yes?

BTW, can anyone tell me what the heck APE stands for? I can't pull that from a search engine for some reason.
Old 18th February 2015 | Show parent
  #17
Gear Maniac
 
🎧 10 years
APE stands for acoustic pressure equalizer.

Microphones like DPA 4060s that have near perfect omni directional response. As a main pair, this depends only on the time difference to create the stereo images.

Using the APE converts your omni to a wide cardioid-like pattern with preserved bass response. The stereo image is more discrete when placing the main pair in near coincident techniques.

Quote:
Originally Posted by Bruce Watson ➡️
So a MK2 with sphere is an omni below around 1 kHz, then tapers upwards to being something like a cardioid at 16 kHz.

Whereas a MK21 is a wide cardioid below around 8 kHz, then tapers upwards to something like a cardioid at 16 kHz.

So these pressure spheres are actually mostly about the bottom and middle frequencies, yes?

BTW, can anyone tell me what the heck APE stands for? I can't pull that from a search engine for some reason.

Last edited by claying; 18th February 2015 at 02:26 AM..
Old 18th February 2015 | Show parent
  #18
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🎧 15 years
Quote:
Originally Posted by claying ➡️
APE stands for acoustic pressure equalizer.

Microphones like DPA 4060s that have near perfect omni directional response will depend only on the time difference to create the stereo image.
Although it would seem so, in practice the 4060 stereo image changes
a lot by angling the omnis outwards.
Old 18th February 2015
  #19
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Quote:
Originally Posted by Bruce Watson ➡️
I'm asking these questions because these spheres were invented and used long before we had tools like digital parametric EQ available, and even before we had tools like the MK21 capsule. I guess I'm trying to figure out how useful these spheres are in this "modern era" that we're in.
Another way of going about it is to use omnis with removable grids and to
use grids which create a similar frequency response as an APE.

Does not add weight to the mic/ mic stand.
Old 18th February 2015 | Show parent
  #20
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Quote:
Originally Posted by Petrus ➡️
ExcActly!

Consider DPA 406x series omnis. They are the size of a match head (almost), and are most omni of them all. While maybe not quite as flat and definitely not as quiet as the best bigger omni microphones, their imaging is superb in AB.

The bigger the omni, the more the body shadows the rear, and that starts from the higher frequencies first. APIs are just a controlled way of making the mic bigger, causing more HF directionality and lift. It does not affect bass response or noise. Like already written a few times, lift can be EQed in post, but not the change in HF directionality.
what about fig 8 mikes. do they suffer from shadowing at their backside?
Old 18th February 2015 | Show parent
  #21
RPC
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1 Review written
🎧 5 years
Quote:
Originally Posted by pkautzsch ➡️

You'd lose, however, the pressure transducer's inherent bass response when using two directional mics back to back.
The pressure omni's bass response is preserved when using APEs.
True! So how about a Josephson C700A?
Old 18th February 2015 | Show parent
  #22
RPC
Gear Addict
 
1 Review written
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Quote:
Originally Posted by monitor ➡️
what about fig 8 mikes. do they suffer from shadowing at their backside?
Figure 8 mikes are almost invariably side address, so any shadowing should be symmetric unless a deliberate design decision is made to vary front and back. (I can't recall ANY figure 8 where the main axis is in line with the body - anyone?)
Old 18th February 2015
  #23
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rumleymusic's Avatar
 
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Quote:
Although it would seem so, in practice the 4060 stereo image changes
a lot by angling the omnis outwards.
I haven't noticed that. Especially when miking at a distance. If you are working with a boundary, however, such as close to a soundboard on with the PZM adapter, you do need to be careful about direction.
Old 18th February 2015 | Show parent
  #24
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Quote:
Originally Posted by monitor ➡️
what about fig 8 mikes. do they suffer from shadowing at their backside?
Symmetrical fig-8 does not have a backside as such. Both lobes are identical, just polarity reversed.
Old 18th February 2015
  #25
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The original m50 omni with sphere had a freq. response of 40 - 16,000 Hz, very different
from a modern omni.

I suppose in those days the wide cardioid had not been invented yet.
Old 18th February 2015 | Show parent
  #26
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Plush's Avatar
 
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Quote:
Originally Posted by aracu ➡️
The original m50 omni with sphere had a freq. response of 40 - 16,000 Hz, very different
from a modern omni.

I suppose in those days the wide cardioid had not been invented yet.
Sorry, but this information about freq. response is not correct. M50 bass response is very extended in low end. In fact there is no microphone that currently (or ever) can offer as extended a bass sound (to the center of the earth) as the M50. This is one of the reasons they are so highly prized and cost now $20,000 each.
Old 18th February 2015
  #27
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The 40-16,000 number is the published spec on the Neumann documentation. Though that was more likely the accurate measurement capability, or standard, of 1960's analog technology. The frequency chart certainly shows not much of a drop-off at 40hz and extends well beyond >0db at 16000kHz.

The bass response anyway is probably not a measure of how low the frequency goes but rather how well the capsule articulates the bass. Only metal diaphragm capsules can match the bass articulation of an M50 IMO, and none with quite the musical flair of the tube electronics.
Old 18th February 2015 | Show parent
  #28
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John Willett's Avatar
 
🎧 10 years
Talking

Quote:
Originally Posted by Plush ➡️
In fact there is no microphone that currently (or ever) can offer as extended a bass sound (to the center of the earth) as the M50.
The Sennheiser MKH 110-1 had a frequency response that was flat down to 0.1Hz
Old 18th February 2015
  #29
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Plush's Avatar
 
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Oh my word.
Old 19th February 2015 | Show parent
  #30
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Bruce Watson's Avatar
 
🎧 10 years
Quote:
Originally Posted by John Willett ➡️
The Sennheiser MKH 110-1 had a frequency response that was flat down to 0.1Hz
Completely off topic, but 1) how would they even measure that? 2) what would be the point of it? And 3) what microphone preamps did they run that into, and how did those preamps react to what is nearly a DC voltage, albeit one that wanders slowly?
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