Topic: Monheim omnis?

[levoui]

Has anyone here tried these new Monheim Omnis?

http://www.monheimmicrophones.com

[voltronic]

Looking at the FR plot, it appears to have pretty significant bass rolloff for an omni.  That looks more like a chart for a cardioid or even a ribbon fig-8, with the rolloff starting at 50 Hz.  The polar plot is blank, also.  I wonder if this manufacturer has the means to measure his mic properly, or if that's the true response.  Listening to the piano samples made at various distances does make it sound like proximity effect is very much in play and that the chart may be correct.

[SacredMetal]

The sample recordings from Firehouse Studio's were great!

I liked that they posted recordings at different distances & heights so you could get a real feel of what the mike is capable of.

[voltronic]

The polar plot is not blank, it's 0dB at all angles of incidence.  Given that it would be stated for 1kHz, there is no reason to suspect it is incorrect.  And while -6dB at 20Hz is maybe not what you'd want, it is certainly much much better than a fig-8 ribbon would perform at 1m.  Keep in mind that a lot of stated FR charts for cardioids are either not plotted at 1m or are just extremely optimistic.

OK, my ribbon mic comment may have been a bit off base.  Maybe a fig-8 condenser is more closely what it looks like, and I get how it's hard to read these things critically when you don't know what the measurement distance is or how they are smoothing the diagram.

Regarding the polar plot or lack thereof: I never considered that this was an actual polar plot showing just one frequency, especially since it's not labeled.  I figured it was being used to illustrate what "omni" means for those who don't know, and not bothering to include an actual polar plot.  All of the other ones I've seen show a variety of frequencies.

If you go to the sales page for the mic and click the measurement picture, hovering over will allow you to zoom in.  It really is blank; there's nothing plotted there.  Though I understand what you're saying, that for 1 kHz it should be a nearly perfect circle anyway.

[DSatz]

Voltronic, pressure transducers don't have proximity effect; their diaphragms are exposed to the sound field only on one side, while proximity effect results from the continuing expansion of wavefronts as the sound from a point source moves forward in air. The path length to the back of the diaphragm in a pressure gradient transducer is longer and therefore, the nearer the sound source is to the microphone, the greater the relative "flattening out" (synchrony in their time of arrival at a flat surface) of the wavefronts as compared to the sound arriving at the front of the diaphragm. With pressure-gradient transducers it's always the difference between front and back that matters.

So the indicated rolloff is either electronic, or is due to built-in venting in the capsule gone awry. Pressure transducers are nominally sealed like barometers, but they always have some amount of very slow venting designed in, so that they can accommodate changes in ambient air pressure, and not risk bursting during air shipment where they might be in an unpressurized cargo hold.

--best regards

[voltronic]

DSatz,

Thank you for that.  I was aware of the difference between pressure and gradient mics and that omnis don't operate this way (or at least they shouldn't).  What I was saying is that when you listen to the piano samples posted on the site, to my ears these mics don't sound like I expect omnis to sound on piano as distance increases.  In other words, they sound like directional mics exhibiting proximity effect, with the closer distance counteracting the bass roll off as shown in the FR plot.  This is why I would be interested to see a real polar plot, as I'm curious if the roll off is on purpose, or if these mics do have a venting issue as you suggest.

[BonoBeats]

Looks like and specs out similarly to the Avenson STO-2, but with a mild low end cut and high end boost.

The self noise is pretty evident on the first and last samples, though of course concert taping won't require nearly as much preamp gain...

[aaronji]

In other words, they sound like directional mics exhibiting proximity effect, with the closer distance counteracting the bass roll off as shown in the FR plot.  This is why I would be interested to see a real polar plot, as I'm curious if the roll off is on purpose, or if these mics do have a venting issue as you suggest.

Perhaps a stupid question, but how can these things be inferred from a polar plot?

[voltronic]

In other words, they sound like directional mics exhibiting proximity effect, with the closer distance counteracting the bass roll off as shown in the FR plot.  This is why I would be interested to see a real polar plot, as I'm curious if the roll off is on purpose, or if these mics do have a venting issue as you suggest.

Perhaps a stupid question, but how can these things be inferred from a polar plot?

I may be stretching a bit on this, and I'm sure DSatz and/or Jon will set me straight.  My thinking was that if the diaphragm venting was not done properly, then you could wind up with sound leaking into the rear of the capsule and the phase cancellations would cause it to act more like a directional mic.

Again, what got me started on this is what I heard in the piano samples posted on the website; it's not just the frequency response plot.  When you listen to the different distances, the closer placements have very strong bass; the more distant do not.  To my ears, it sounds like proximity effect.  If you listen, disregard the last two tracks as they are not playing anything in the bass range on those. 

With omnis I'd expect only a treble drop-off at increasing distance, which is why mics like Schoeps MK 2H with the gentle HF bump to compensate for distance are so useful for piano recording.

[aaronji]

^ Ah, I see.  I thought you were referring to the proximity effect itself and not directionality at a fixed distance...

[DSatz]

Jon, I'm not sure I follow how this discussion got onto the polar patterns of directional microphones at low frequencies. But concerning the cardioid pattern, a strong distinction should be made between single- and dual-diaphragm capsules. Dual-diaphragm cardioids typically lose directivity starting in the lower midrange, but a single-diaphragm cardioid can still be a real cardioid even at 50 Hz, where a U 47 or U 87 is effectively a "wide cardioid".

A 20 Hz tone has a wavelength in air of 55 feet. Traditional polar response measurements become less and less reliable at such low frequencies because even anechoic chambers have some reflections from the floor, walls and ceiling; a measurement chamber would have to be enormous to avoid significant interference from such reflections at 50 Hz, let alone 20. So it can be tricky to interpret a conventional off-axis response graph for any microphone.