Electret behavior with low input-Z preamp
Dear mic experts,
I'm trying to design a discrete amplifier for an electret capsule and have quite a technical question that is puzzling me. The device is a PUI AOM-5024L.
I encountered the possibility of driving the capsule with a (common-emitter) preamp that has an input impedance much lower than the capsule itself. Say the electret has 2.2k out-Z, while the preamp would have 850 in-Z. I know this will result in huge attenuation, but this is not a problem for me but rather an advantage. It means lower resistance (noise) on the preamp's first stage bias and the possibility of bypassing later stages for capturing loud environments¨Cwhich is problematic with this very sensitive capsule. However, I don't know if loading the electret with a much lower impedance will affect ie. the capsule's frequency response (flatness) or its maximum headroom. Since there is a JFET buffer in between inside the cartridge, I tend to think that the JFET would absorb the load or separate and only attenuation would be affected, but I'm not sure about it.
Has anyone for instance seen or done frequency and/or headroom measurements on (JFET) electrets at different loading impedances? Or have any theoretical clues about this? I've read opinions that overloaded mics tend to sound bassy, lack highs or sound 'obscure' whatever that means, but might be that those comments refer to passive mics.
All opinions are more than welcome.
Best regards,
Domingo
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Re: Cheap, Makeshift Parabolic Dishes?
https://theelectronicgoldmine.com/products/g20898c?mc_cid=95eb77a4eb&mc_eid=6b88d3e52c
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Re: OPA-Based Binaural Head
No, not like the AKG D99. I used the ITU-T P.58 standard "HEAD AND TORSO SIMULATOR FOR TELEPHONOMETRY" as a design specification and took their drawing and made 3/4 inch slices through it. I cut them on a bandsaw and then shaped it with an angle grinder like the original poster. Thus my dummy head looks very much like the Bruel and Kjaer dummy head, except that mine is painted light gray.
Am So., 19. Nov. 2023 um 06:26?Uhr schrieb eric benjamin < ericmbenj@...>: That is a really lovely piece of work. I made a dummy head out of slices of wood about twenty years ago but it's not nearly as attractive. My slices were horizontal.
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Re: OPA-Based Binaural Head
Am So., 19. Nov. 2023 um 06:26?Uhr schrieb eric benjamin < ericmbenj@...>:
That is a really lovely piece of work. I made a dummy head out of slices of wood about twenty years ago but it's not nearly as attractive. My slices were horizontal.
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Re: OPA-Based Binaural Head
That is a really lovely piece of work. I made a dummy head out of slices of wood about twenty years ago but it's not nearly as attractive. My slices were horizontal.
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Re: OPA-Based Binaural Head
There is FLAC compression. Lossless. It reduced the size substantially.
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Re: Cheap, Makeshift Parabolic Dishes?
Yes, the size matters. Making a bigger head will improve bass separation but will not reproduce acoustic panorama faithfully.
The whole point of the dummy head is to reproduce acoustic character of the real head so that replay matches the resembling spacial phase shifts.
Not only the size matter there but density distribution, resonance cavities, impedance of the materials, etc.?
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Cheap USB powered condenser microphone. Need advice on design.
Hello, I've drafted up a DIY design that I think could work to drive an electret capsule like the TSB-2555B through the use of a DC-DC converter () to derive a stepped up voltage from the 5V supply rail of a .? The generated voltage of the microphone is fed into an amplification circuit from the? Presented below is the proposed amplification scheme:  Similar to the aforementioned OPA-Alice circuit, the amplifier to be used is planned to be the OPA1642. The USB soundcard to be integrated to the design utilizes a CM108 IC with an input range of 2.88 V pk-to-pk and a default input signal gain stage of 20dB (gain of 10). I am relatively new to the design of microphone circuitry and this design is heavily inspired the by videos and instructables from DIY Perkz and DJJules.? I would like to ask for advice regarding the design choices made and the validity/viability of the proposed design.
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Re: electrets with lobar patterns?
Microphones with "lobar" patterns use specific acoustic additions
to achieve them. Typically multiple tubes or multiple tapped
tubes. Capsules by themselves are 1st-order, ranging from omni to
fig-8 via all sorts of cardio.
Higher order directivity can also be achieved using multiple
capsules and signal processing.
Le 16/11/2023 ¨¤ 22:35, cx b a ¨¦crit?:
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Hi there -
i was wondering if there are electret elements with lobar
patterns. i'm not seeing any on a simple google search - and
i'm curious about why that might be.?
Thanks!
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Re: Cheap, Makeshift Parabolic Dishes?
Just about any curved "dish" shape will provide some focusing and gain.
for common items that would serve as reflectors.
Lots of hits if you google "DIY parabolic mic".
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Re: Cheap, Makeshift Parabolic Dishes?
Yes it will effect sound quality. But portability might be something to consider.
---- On Thu,16 Nov 2023 23:00:41 -0500 clistburnham@... wrote ----
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Do the dimensions matter? i'm seeing a lot of shapes and sizes... are there simple rules-of-thumb that people use?
I made one from my neighbor's discarded parabolic heater that he bought at Costco. The rest was easy.?
Hey all -
I'm curious if people here have any recommendations for cheap, makeshift parabolic reflectors? I'd like to experiment a bit with the idea, but I'm hesitant to spend $80 on some meticulously curved glass. Are there any interesting alternatives?
Thanks!
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Re: electrets with lobar patterns?
I suspect the lobar pattern comes more from the interference tube, not the capsule itself.
(I¡¯m definitely not an expert on shotgun mic design¡ but if it were possible to create a lobar pattern within the capsule, then all those shotgun mics wouldn¡¯t need to be 6-20 inches long.)
¡ª
matt.
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On November 16, 2023 at 1:35:17 PM, cx b (clistburnham@...) wrote: Hi there -
i was wondering if there are electret elements with lobar patterns. i'm not
seeing any on a simple google search - and i'm curious about why that might
be.
Thanks!
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electrets with lobar patterns?
Hi there -
i was wondering if there are electret elements with lobar patterns. i'm not seeing any on a simple google search - and i'm curious about why that might be.?
Thanks!
|
Re: Cheap, Makeshift Parabolic Dishes?
Size matters. The larger, the better the bass respons will be. This is in direct relationship of the wavelength. E.g. the disc is 68cm diameter: frequencies above 500Hz will have a boost and high directivity
Do the dimensions matter? i'm seeing a lot of shapes and sizes... are there simple rules-of-thumb that people use?
I made one from my neighbor's discarded parabolic heater that he bought at Costco. The rest was easy.?
Hey all -
I'm curious if people here have any recommendations for cheap, makeshift parabolic reflectors? I'd like to experiment a bit with the idea, but I'm hesitant to spend $80 on some meticulously curved glass. Are there any interesting alternatives?
Thanks!
|
Re: Cheap, Makeshift Parabolic Dishes?
Do the dimensions matter? i'm seeing a lot of shapes and sizes... are there simple rules-of-thumb that people use?
I made one from my neighbor's discarded parabolic heater that he bought at Costco. The rest was easy.?
Hey all -
I'm curious if people here have any recommendations for cheap, makeshift parabolic reflectors? I'd like to experiment a bit with the idea, but I'm hesitant to spend $80 on some meticulously curved glass. Are there any interesting alternatives?
Thanks!
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Re: OPA-Based Binaural Head
My apologies for the huge file size, I¡¯ll keep that in mind for any future posts.
I do plan on adding ears to it so hopefully that will aid in ?generating something approaching an HRTF.?
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Re: OPA-Based Binaural Head
Am 16.11.23 um 16:33 schrieb Dibutil Ftalat: This sounds like a decent, dry stereo recording, did not feel any
"binaurality" which you get if recording live in your own head with
Roland CS-10EM. This "earless head" is more reminiscent of Joerg Wuttke's hapless Spherical Surface Microphone, some sort of dummy head sans HRTF. Basically, yet another variation of the Jecklin disc. Ralf -- Ralf R. Radermacher - K?ln/Cologne, Germany Blog : Audio : Fotos :
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Re: OPA-Based Binaural Head
This sounds like a decent, dry stereo recording, did not feel any "binaurality" which you get if recording live in your own head with Roland CS-10EM.
Much better results I get from a piece PVC tube filled with hard PU foam and plugged from the ends with silicone ear molds used for demonstration of jewelry.?
In oder to reduce reflections off the tube surface I also wrap it in self-sticking neoprene about 4mm thick.
I plug my Roland mics into those ears and record.
The difference witht the real head (mine) is negligible (I guess, the content is similar ?), and the piece of pipe with ears mounted with the camera has much less intimidating effect on the public spectators: I used to record theatrical performances with it.?
In the initial experiment I also used a foam disk of 600mm diameter, 40mm thick put between silicone ears, but the addition of low-end separation was inaudible in the result, so I dissmissed the bulk.
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Re: Cheap, Makeshift Parabolic Dishes?
I made one from my neighbor's discarded parabolic heater that he bought at Costco. The rest was easy.?
Hey all -
I'm curious if people here have any recommendations for cheap, makeshift parabolic reflectors? I'd like to experiment a bit with the idea, but I'm hesitant to spend $80 on some meticulously curved glass. Are there any interesting alternatives?
Thanks!
|
Re: OPA-Based Binaural Head
Very cool!
If you could please, though - please avoid sending huge .wav files to the group.
Thanks,
-Scott
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On 11/15/23 18:05, Jwaters18 via groups.io wrote: Hello,
Been lurking this group for a while and finally got around to actually building something! About 2 years ago I had some extra MDF lying around so I decided it would be fun to make my very own Binaural Head. I based the shape off of the Neumann KU-100 and used a projector to draft some stencils approximating the size of my own head (it ended up being a tad over-sized). After rough cutting/routing the 9 layers I needed to make up the width of the head I ended up with this monstrosity
After some diligent work with an angle grinder, sanding flap disk, and an old can of urethane clear coat the head was looking pretty good.
I then entered the final semester of my EE degree and became very busy with my senior design project so I put the head project on hold. Months turned into years and the head got kicked around my house as my attention turned to more pressing matters. All the while I could feel the hollow, blank stare of the binaural head-to-be piercing into my core.
Well, free time finally made itself available to me once again and I decided to turn this 10 lb mannequin head into a proper microphone. The original plan was to base the impedance converter on a Calrec schematic given to me by a friend. After a few failed attempts I decided instead to modify the popular OPA design that originates from this forum. Since I had already purchased the transformers I opted for a paralleled amplifier configuration. Douglas Self covers this technique in Small Signal Audio Design and details its improved load driving capabilities and reduced self-noise compared to a single opamp. Now, I am not sure whether the noise performance is actually improved when the source impedance is so high. Someone here may have a better idea but I would think that this configuration would reduce the input Z of the amplifier and cancel out any reduction in noise you typically get from a parallel amp combo (corrections welcome).
The capsules I am using are the Omni caps that came with my pair of Lauten LA-120's (good mics btw). They happened to be about the same diameter as a 7/8" Ryobi forstner bit I had so I simply marked their location and drilled holes on both sides of the head. I carefully disassembled the caps and soldered the shield of some mic cable I had to the threaded brass ring that holds in the back plate. After re-assembling the caps I soldered the twisted pair to the back plate connection. I cut this lead to be as short as possible and pressure fit the capsules into the head.
After laying out the circuit in Kicad I etched and drilled a pair of boards. I used some metal 1-gang outlet boxes from HD and some scrap metal from an old receiver as shielding. I drilled a pair of holes in the back of the neck (using the same 7/8" bit) and wired up some Neutrik XLR bulkheads I had laying around.
Overall I'm pretty satisfied with the result, I included a short recording of myself on drums as an initial test. I plan on dusting off my 3D printer and printing out a pair of human ears to help achieve that HRTF stereo image goodness. Update to follow.
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---- Scott Helmke ---- scott@... ---- (734) 604-9340 ----
"I have ceased distinguishing between the religious and the secular,
for everything is holy" - Joe Henry
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underwood
Dibutil Ftalat
Timothy Aguana