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Author Topic: DPA 4098H miniature supercardioid  (Read 6547 times)

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Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #15 on: August 09, 2013, 07:50:40 PM »
I'm not sure I understand why the rear ports wouldn't form a traditional chamber  ???  I suppose the diagphragm orientation is unusual in that respect, but it should work the same as the chamber creates the polar response.  Perhaps it has something to do with the timing of the front edge vs. rear edge of the diaphragm, rather than front vs. back as in a usual directional capsule.  I think that is what you are saying  ???

The capsule itself could be nearly identical although directional capsules usually have a lower resonant tuning.

I'm not sure yet, and it may not be evident from closer inspection tonight, but my current assumption has been that the diaphram is only exposed on it's front face, like all the miniature DPA omnis or any other omni with a small enclosed non-vented space (except for a atmospheric pin-hole vent) on the back side of the diaphram.   Since the rectangular diaphram housing is oriented sideways in the cylindrical capsule housing, it does not necessarily block passage around either side of it inside the tube like a traditional diaphragm.  That would mean the space inside the capsule housing would be open to both the interference tube end and the two small vents at the other, but exposing only the front face of the omni diaphram, which would measure pressure variations between the two ends. If on closer inspection I can see light coming through the capsule housing from the back vents around the rectangular diaphram housing then that should be the case. 

If its basically a traditional cardioid design, only folded up in a a bit, the diaphram should be exposed to the interference tube end on its front face, and the two rear vents on its back face.  If that's the case, I shouldn't see light coming around the housing.  That would make a lot more sense, and the more I think about it, the more I think that's probably the way it works.

That this mic appears to use an identical gold rectangular diaphram unit as the miniature DPA omnis, in what looks like an identical capsule housing expept for the rear vents most likey mislead me.

Anyway I drew up a couple quick sketches to explain what I meant, and drawing them is what help me sort out what I think is going on.  I now expect to see no light tonight!
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Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #16 on: August 09, 2013, 07:55:15 PM »
I have been using these for several years..

Thanks for checking in here Jeff, your positive experience with these is what motivated me to give them a try.  It's just taken me much longer than I expected to get around to actually doing it.
« Last Edit: August 09, 2013, 07:57:11 PM by Gutbucket »
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Offline Church-Audio

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Re: DPA 4098H miniature supercardioid
« Reply #17 on: August 09, 2013, 08:16:27 PM »
I'm not sure I understand why the rear ports wouldn't form a traditional chamber  ???  I suppose the diagphragm orientation is unusual in that respect, but it should work the same as the chamber creates the polar response.  Perhaps it has something to do with the timing of the front edge vs. rear edge of the diaphragm, rather than front vs. back as in a usual directional capsule.  I think that is what you are saying  ???

The capsule itself could be nearly identical although directional capsules usually have a lower resonant tuning.

I'm not sure yet, and it may not be evident from closer inspection tonight, but my current assumption has been that the diaphram is only exposed on it's front face, like all the miniature DPA omnis or any other omni with a small enclosed non-vented space (except for a atmospheric pin-hole vent) on the back side of the diaphram.   Since the rectangular diaphram housing is oriented sideways in the cylindrical capsule housing, it does not necessarily block passage around either side of it inside the tube like a traditional diaphragm.  That would mean the space inside the capsule housing would be open to both the interference tube end and the two small vents at the other, but exposing only the front face of the omni diaphram, which would measure pressure variations between the two ends. If on closer inspection I can see light coming through the capsule housing from the back vents around the rectangular diaphram housing then that should be the case. 

If its basically a traditional cardioid design, only folded up in a a bit, the diaphram should be exposed to the interference tube end on its front face, and the two rear vents on its back face.  If that's the case, I shouldn't see light coming around the housing.  That would make a lot more sense, and the more I think about it, the more I think that's probably the way it works.

That this mic appears to use an identical gold rectangular diaphram unit as the miniature DPA omnis, in what looks like an identical capsule housing expept for the rear vents most likey mislead me.

Anyway I drew up a couple quick sketches to explain what I meant, and drawing them is what help me sort out what I think is going on.  I now expect to see no light tonight!
There is another possibility I just thought of.. if you can redirect some of the pickup pattern from the front to the rear.... it's possible to turn a omni into a card the signal from the rear would be 180 degrees out of phase from the front if you could steer the sound from the back to the front. in theoretical terms atleast :) if anyone could pull this off it would be dpa. No need for a back vent on the capsule it self. the small vent is only that to equalize pressure on the diaphragm making it ok for high elevations would be my guess. this is in all dpa 4060 type capsules. this is my best guess.
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Offline F.O.Bean

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Re: DPA 4098H miniature supercardioid
« Reply #18 on: August 09, 2013, 11:15:35 PM »
These are freakin awesome bro ;D Are they wireless? Sorry, havent read the whole thread yet :) VERY TINY, and look amazing!!!

Bean

P.S.-I MUST hear a recording of a concert or ambients with them :)
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Offline MIQ

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Re: DPA 4098H miniature supercardioid
« Reply #19 on: August 10, 2013, 10:20:32 PM »
Hey Gut,

A little while ago I put together a spreadsheet to show the theoretical polar response of interference tubes.  We talked about it here: http://taperssection.com/index.php?topic=148194.msg1928020#msg1928020 
The response is calculated based only on the length of the tube.  By looking at your pics the tube looks like it's about 29mm long.  Below are plots of a 29mm interference tube's polar responses at different frequencies.  You can see that an interference tube of this length is only effective for frequencies above 4 kHz.  Comparing this graph to the polar plots you posted in your OP, you can see the directivity of this mic below 4k is dominated by the rear vents.

Note my plots are on a linear scale 0 - 1 while the DPA plots are in dB (0 to -25dB), but you get the idea.

-MIQ

Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #20 on: August 12, 2013, 12:09:28 PM »
Thanks MIQ, that's how I would expect it to work from what I know of interference tubes.

I think either design is possible and could work.  I don't think you necessarily need a diaphragm as a barrier in a chamber; that's just a convenient design to measure pressure.

Thanks Jon.  After thinking about this I realize you are correct.  Conceptually, phase reinforcement/cancellation due to differing acoustic path length differences could happen either on one side of the diaphragm or on opposite sides of it with the same end result.  I wonder if I'm missing something in regards to the practical realization of that however.  Are you or is anyone here aware of a manufacturer who uses closed back omni capsules in specially designed acoustic housings to produce directional mics? By that I mean rear vented housings, not simply putting an interference tube in front.  Assuming it can be made to work equivalently, I would think the higher diaphram tension of the omni element would be benefitial in providing reduced handling noise at least.


On closer inspection over the weekend with a bright light and reading glasses, it is apparent that the capsule housing surrounding the gold diaphram unit is filled with epoxy or some other material.   There is no internal acoustic path around the retangular gold eletret diaphragm housing inside the external mic housing.  That doesn't shed light on what is happening inside and/or under the eletret housing, but I'm guessing this thing works as a normal cardioid with repect to the rear vents.

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Offline Church-Audio

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Re: DPA 4098H miniature supercardioid
« Reply #21 on: August 12, 2013, 12:42:53 PM »
Thanks MIQ, that's how I would expect it to work from what I know of interference tubes.

I think either design is possible and could work.  I don't think you necessarily need a diaphragm as a barrier in a chamber; that's just a convenient design to measure pressure.

Thanks Jon.  After thinking about this I realize you are correct.  Conceptually, phase reinforcement/cancellation due to differing acoustic path length differences could happen either on one side of the diaphragm or on opposite sides of it with the same end result.  I wonder if I'm missing something in regards to the practical realization of that however.  Are you or is anyone here aware of a manufacturer who uses closed back omni capsules in specially designed acoustic housings to produce directional mics? By that I mean rear vented housings, not simply putting an interference tube in front.  Assuming it can be made to work equivalently, I would think the higher diaphram tension of the omni element would be benefitial in providing reduced handling noise at least.


On closer inspection over the weekend with a bright light and reading glasses, it is apparent that the capsule housing surrounding the gold diaphram unit is filled with epoxy or some other material.   There is no internal acoustic path around the retangular gold eletret diaphragm housing inside the external mic housing.  That doesn't shed light on what is happening inside and/or under the eletret housing, but I'm guessing this thing works as a normal cardioid with repect to the rear vents.

The other possibility.. Another capsule inside the rear vent.
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Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #22 on: August 12, 2013, 06:52:58 PM »
Chris- Like you mention, a second capsule would be another way to manipulate the pickup pattern, yet in this case I can't see how another capsule could fit into a standard 406x omni housing with a couple vents on the back side of it.


Jon- Actually I do think of a cardioid as a being a modified figure-8, but I'm a 'basic-principles' mechanical design minded guy.   I'm getting off topic here, but an aspect I don't understand is how that modification is physically implemented in real-world microphones to produce directional patterns which are as uniform as possible across a broad frequency range and not just peaking as a bell shaped curve, centered around a single frequency. That's the microphone 'black-art' stuff I guess.  All the basic explanations and simplified conceptual illustrations I've come across just show a single pathlength/wavelength arriving at the front of the diaphragm and another arriving at the back of the diaphragm with a phase relationship that varies between the two with source angle, and that seems to me like it would be very frequency specific.
 
Regardless of how that works in real implementations, I speculate a compelling motivation for a manufacturer to use an omni capsule in a directional microphone design would be manufacturing and production related issues, such as using an already developed and well regarded omni capsule that is in full production, minimizing need for additional capsule fabrication and inventory overhead for a new microphone design.  I understand what you are saying on the need to increase the housing diameter to provide a path around the diaphragm inside the housing for a given diaphragm diameter.

Thanks for the 'ah-hah' moment in realizing that the two possibilities I sketched previously are more or less conceptually the same in regards to the path-length phase cancellation/reinforcement.  Actually, looking at it again and excluding the interference tube, I realize a pathlength based directional design using an omni element would require an inverted signal relationship between the two paths compared to a typical design.  In a design with both sides of the diaphragm exposed to signal, identical path-lengths produce identical pressures on each side of the diaphragm, canceling each other and producing a null.  When that interaction happens on one side of the diaphragm only, identical path-lengths instead reinforce one another and produce a maxima.  A reverse polarity signal is required to cancel pressure if the two paths meet on the same side of the diaphragm.
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Offline DSatz

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Re: DPA 4098H miniature supercardioid
« Reply #23 on: August 15, 2013, 12:18:57 AM »
Just wanted to point out something about the frequency response graphs near the top of this thread: The low-frequency response is nearly flat at 20 cm, while at 100 cm measurement distance, the response is roughly 12 dB down at 50 Hz. This response profile indicates a close-speech microphone, not a general-purpose studio microphone.

There is still some proximity effect at 100 cm (= 1 meter), so the low-frequency response to be expected for sound sources farther away than 1 meter would actually be even a little less than the lowest curve shown.

DPA should be commended for publishing this detailed information, which they haven't generally done in the past. Instead, the published curves for their directional microphones (going all the way back to their earliest cardioids) have generally been corrected for a 30 cm pickup distance--a fact which you could read in the fine print if you chose to look for it.

Meanwhile, however, the other leading microphone manufacturers (Neumann, Schoeps and others) generally correct their frequency response measurements of directional microphones for a 1 meter (= 100 cm) measurement distance. Obviously that makes a rather large difference in the results--in this case, about 8 dB at the bottom of the frequency range--and that should be considered when comparing the response curves for DPA directional microphones against those of most other leading manufacturers.

--best regards

A clarifying P.S., I hope: As far as I'm concerned DPA can print any curves they want, as long as they specify their measurement conditions. Quite possibly their studio microphones are typically used at ~30 cm distances; if so, their published curves would indicate something like the actual performance of their microphones in that application, and I think that's ample justification.

But people who need directional microphones for more distant pickup should realize that they won't be getting anything like the low-frequency response shown in the 30 cm curves. And people certainly shouldn't compare 30 cm curves to 1 meter curves no matter what application they have in mind.
« Last Edit: August 15, 2013, 12:32:31 AM by DSatz »
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Offline Len Moskowitz (Core Sound)

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Re: DPA 4098H miniature supercardioid
« Reply #24 on: August 15, 2013, 07:34:38 AM »
It's probably worth noting this real clearly for the newbies:

At normal recording distances these specific capsules have poor bass response. The second graph shows that clearly: 100cm is only ~39-inches.

So these capsules are not well-suited for recording concerts from the audience unless you plan to add lots of EQ in post-production, or as Gutbucket plans, using them in an array with other mics.
« Last Edit: August 15, 2013, 07:48:42 AM by Len Moskowitz (Core Sound) »
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Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #25 on: August 15, 2013, 11:56:08 AM »
Thanks for the clarifications gentlemen.

None of the DPA miniature directional mics are really designed for recording at a distance.  DPA targets the 4089H for hanging choir microphone applications.  I assume that the typical intended installation would place these microphones somewhat farther than 100cm from the source, probably using a number of these in an A-B spaced line configuration ~3-5 meters from the choir members.  Not being much of a choir recordist I assume it may be common practice to high-pass choir mics for PA reinforcement applications, making the falling low frequency response of these somewhat pre-tailored to the indented application.

Below is the frequency response graph for the DPA 4081 miniature supercardioid, designed for close, on-instrument mic'ing.  The polar is identical to the one I posted earlier for the 4098.  The on and off-axis frequency response graphs appears mostly identical to the 4098 except for a slightly more rolled response above 10kHz.  It appears to be a very similar microphone, except for a different mounting configuration and lower sensitivity (6mV/Pa for the 4081 compared to 20 mV/Pa for the 4098, which is the same sensitivity difference as the 4061 compared to the 4060 omni).  The 4098 is the only DPA miniature with a posted proximity graph, there is no proximity effect graph posted for the 4081 or the 4080.  DPA's other miniature directional is the 4080, which the same sensitivity as the 4081 but a contoured response tailored for lavaliere-mounted speech applications and is probably even less applicable to recording music from a distance.

DPA 4081-




And here’s the 4098H again for comparison-





« Last Edit: August 15, 2013, 11:59:21 AM by Gutbucket »
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Offline WiFiJeff

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Re: DPA 4098H miniature supercardioid
« Reply #26 on: August 15, 2013, 06:53:17 PM »
I actually have the 4099s, which are also lower sensitivity 6V/Pa mics like the 4061 and 4081.  The 4098 came out later.  But I have not had any problems using it (although I am quite partial to the 4060s) on even rather quiet acoustic music.  PM me for a sample on some baroque theorbo and string music.

Jeff

Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #27 on: November 05, 2013, 03:56:51 PM »
Anyone have ideas for finding an appropriate larger foam windscreen for use on these outdoors?

I called Shane at DPA USA yesterday and he had no suggestions, and said he had not heard reports from anyone using them outdoors yet.  I need to find something pretty quickly for use in about a week.

The portion which the screen needs to slip over is ~1-1/2" long X 7/32" in diameter (or just under 1/4").
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Offline Church-Audio

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Re: DPA 4098H miniature supercardioid
« Reply #28 on: November 05, 2013, 04:03:44 PM »
Anyone have ideas for finding an appropriate larger foam windscreen for use on these outdoors?

I called Shane at DPA USA yesterday and he had no suggestions, and said he had not heard reports from anyone using them outdoors yet.  I need to find something pretty quickly for use in about a week.

The portion which the screen needs to slip over is ~1-1/2" long X 7/32" in diameter (or just under 1/4").
My dead rats. BTW did you get my email?
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Offline Gutbucket

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Re: DPA 4098H miniature supercardioid
« Reply #29 on: November 05, 2013, 04:25:55 PM »
I'll need them sooner than your's would get here.  I have the material to whip up a couple rats and likely will do so this weekend, but the foam of the existing screens is very thin, even for only playing the role of under-fur spacing.  It's wall thickness is only like 3/32".  I did one outside test recording of some music about a month ago with just the existing foam screens and just a rather-slight occassional breeze produced audible rumble.   I suspect I'll need some thicker foam for effective use of the rats.

Thanks for the heads up on the email, haven't been on-line that much over the past week.
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