DIY RF Condenser Mics

[Gerard]

Rereading Baxandall's paper again last night, I thought it might be interesting to look at some of the references in his article. I found one that looks interesting in it's own right, though I haven't had time to read it in full. It is the paper by J. J. Zaalberg van Zelst: "Circuit for Condenser Microphones with Low Noise Level". It can be found at https://www.americanradiohistory.com/Archive-Philips-Technical-Review/40s/Philips-Technical-Review-1947.pdf, starting at page 357 (p.359 of the pdf file).

Another paper that is available, but only behind a paywall, is "Noise in Condenser Microphones" by Becking and Rademakers. It's at https://www.ingentaconnect.com/contentone/dav/aaua/1954/00000004/00000001/art00033;jsessionid=2pao1jlta9b09.x-ic-live-02

Has anyone found the article by Arends, either the original Dutch article or the German version (or an English translation)? This is reference 7 in the second part of Baxandall's article.

 

[cyrano]

It's also available at ResearchGate:

https://www.researchgate.net/publication/262854727_Noise_in_Condenser_Microphones

IIRC it only requires a free subscription. I've found articles there before, but I don't know if this is true for all their papers. Anyhow, they're preferable over Ingenta in my mind. Ingenta is only in it for the money and the grab what they can get, just like Elsevier.

 

[Gerard]

Thanks. I'll try ResearchGate; though, as I am not an accredited researcher with a recognised institution, I have had very mixed success with them. I think I have only once or twice succeeded in getting a paper through ResearchGate.

 

[cyrano]

I don't use it that often either. And I DON't remember the success rate, to be honest.

 

[ricardo]

I want to get that "trouser-flapping" effect of the low pedal stops. If the mic works properly, next stop is to check the  recorder LF response.

For 'trouser-flapping', you need to record in STEREO with Fig-8s and have STEREO SUBS.

With omnis and mono, (most recording techniques with omnis are 'mono' below 50Hz) or single subs, you only get the unpleasant 'pressure-in-the head' feeling .. suitable for Arnold S. destroying the universe but not so nice for John Seb.

Alas, there are only a handful of mikes with significant Fig-8 response below 50Hz .. mostly my designs.

There's a secret code in TetraMic that unlocks its subsonic response if your recorder & other stuff is up to it.  But no one has complained about TetraMic's usual 25Hz limit.

I've designed speakers for cathedral organs so have some experience with 32' stops.  The biggest installation used to be the nave organ at Worcester which was only replaced a few years ago.  IIRC, it had 16 subs and 16 'organ' speakers.

It's claim to fame was when the organ grinder was dancing on the pedals at an early  recital, a 1 ton block of stone fell from the ceiling, fortunately in the aisle rather than on the audience. 

 

[Marik]

Alas, there are only a handful of mikes with significant Fig-8 response below 50Hz .. mostly my designs.

Ricardo,

I assume we are talking condenser mics here, because ribbons do much better than that. Our MF65 has -0.2dB at 20Hz and newest AL95 with piston ribbon does even better...

Best, M

 

[ricardo]

I assume we are talking condenser mics here, because ribbons do much better than that. Our MF65 has -0.2dB at 20Hz and newest AL95 with piston ribbon does even better...

What distance are you measuring at?  Is the reference mike an omni?

 

[Gerard]

Has anyone tried the TCS-1 capsules from JLI Electronics - for any microphone, not just for this RF design? (https://www.jlielectronics.com/transound/tsc-1). It appears to be significantly cheaper than the equivalent single-sided RK-67 from, say, WGTCentre; but if it's made by Transsound, it should be of decent and consistent quality.

Just a few points make me ask here before trying a couple of these capsules: JLI's shipping costs to Europe are very high (courier only); the specs on the JLI web page are very limited, but they give the frequency range as 100 Hz to 20 kHz; and they don't include a saddle, as WGTCentre does. That LF end of the range is rather high but they don't say how far below the nominal output it is at 100 Hz or how steeply it cuts off; maybe they use a thicker diaphragm.

Are they worthwhile trying?

 

[rogs]

From the images, the Transsound capsules look pretty much like 'standard' Chinese K67 types.
The published specs of most of these capsules are just  made up by the marketing guys - not to be taken too seriously.

WGCenter are OK, but you have to hope they send the right parts (I have just received a double sided K47 when I ordered a C12 -- too much hassle to send it back though --I'll use it somewhere! )

I still think AliExpress are the cheapest for 34mm K67s..... usually with free shipping.

I've used these before:  https://tinyurl.com/y3oveux3

No saddles, but I find these  from Shapeways work well :    https://www.shapeways.com/product/AX4APE9SV/k87-saddle?optionId=65223254&li=marketplace

I've also had quite good results making my own from bits of 2mm and 4mm Neoprene rubber - and a dab of  super glue .... but only when the budget is really  tight!

EDIT: even cheaper one here:  https://tinyurl.com/y37tq3fm  - and apparently UK stock? ... 

 

[Marik]

What distance are you measuring at?  Is the reference mike an omni?

Cross-spectrum did it for us. It's been awhile, but from memory, measured at 80cm with proximity correction applied. Yes, the reference was an omni.

Best, M

 

[Gerard]

Thanks, Rogs. I bought most of my 34 mm capsules from WGTCentre and, so far, they have sent me the right ones each time. Those AliExpress ones look like some I bought; mine came from Rayking (another company that also makes fairly decent electrets, though their 25 mm electret is reputedly not quite as good as the TSB-2555 from Transsound): https://rayking.en.alibaba.com/product/60573293486-803584280/34mm_capsule_microphone_Rayking_factory_large_diaphragm_condenser_microphone.html.

But I wonder how much these capsules vary from vendor to vendor; do they all come out of the same factory? Even if different Chinese vendors all make their own capsules themselves, is quality control better from some vendors? If so which? Transsound have a generally good reputation for electret capsules and claim ISO 9000 accreditation, but does that extend to the 34 mm capsule they offer? Perhaps someone out there knows or can answer from experience of having bought from different vendors and made a comparison.

I have sometimes wondered at the very much higher prices for capsules charged by, for example, Microphone Parts, Studio Products, ADK, Advanced Audio Microphones and others; most of them do not make their own capsules. Do they select capsules to meet a certain standard? or just charge what the market will bear?

 

[rogs]

.......most of them do not make their own capsules. Do they select capsules to meet a certain standard? or just charge what the market will bear?

I think most of them will claim the former ... in reality, I suspect it's often the latter. 

 

[ricardo]

I have sometimes wondered at the very much higher prices for capsules charged by, for example, Microphone Parts, Studio Products, ADK, Advanced Audio Microphones and others; most of them do not make their own capsules. Do they select capsules to meet a certain standard? or just charge what the market will bear?

Certainly Microphone Parts do a lot of selection for those they sell.

Has anyone in Oz made a variable pattern mike with a Microphone Parts RK12 and would be willing to lend it to me for a couple of weeks?  I can promise at least a detailed report.

I made detailed measurements of Zephyr's CK12 mike from WGT IIRC. The results are in Yahoo MicBuilders Files.  You have to join.  It's not bad but there are a few things which could be better ..  notably the fig-8 response.

There's some evidence that the Microphone Parts RK12 won't have this fault but I need to get my paws on a complete mike to confirm this.

 

[zephyrmic]

I certainly would be interested to find out what Microphone Parts C12 type capsule is like by comparison to the one you tested for me, which I very much appreciated. Would be good if a comparison can be  made. And it would add to the overall knowledge of this type of mic and give others a good basis as they consider what capsule to purchase in days to come.
Kindest regards,
zephyrmic

 

[rogs]

Just a quick note to say that I've tried out the figure of eight version of the idea I suggested in post#253.... (sketch attached) ..
Seems to work quite well.  Only tried out with a dual K.47 capsule so far...( I intend to try out a dual C12 as well) 
I did have to add a small capacitor (4.7pF) across one side of the capsule, to correct an imbalance between the output from each side.....Probably down to the fact that the centre tapped 5u3H winding is not bifilar wound?....

One step close to creating a 34mm condenser 'mid-side' mic suitable for outdoor use -- which I've always fancied trying.....

 

[abbey road d enfer]

I did have to add a small capacitor (4.7pF) across one side of the capsule, to correct an imbalance between the output from each side.....Probably down to the fact that the centre tapped 5u3H winding is not bifilar wound?....

Are you sure about this? Do you not think it's due to capsule imbalance? Then the additional cap could be permanently affixed to the capsule and would not require an additional pole to the switch.

 

[rogs]

Are you sure about this? Do you not think it's due to capsule imbalance? Then the additional cap could be permanently affixed to the capsule and would not require an additional pole to the switch.

Good point -- I can reverse the capsule connections to check....

 

[Martin K]

About the paper "Noise in Condenser Microphones" by Becking and Rademakers"; see this link
https://www.icacommission.org/Proceedings/ICA1953Delft/ICA01%20Proceedings%20Vol1%20OCROPT.pdf.
Page 96.

Martin K

 

[Gerard]

Thanks for that. I'll download it and read it later this afternoon.

 

[Gerard]

Good point -- I can reverse the capsule connections to check....

Rogs, did you have time to try that yet? Any result or comment?