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The quitest ambisonic microphone

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Hi everyone,

Searching about amabisonics microphones I found 3 good choices for ambient tracks recordings: Soundfield ST-450, Soundfield SPS200 and Tetramic. For those who experienced this type of mic, the question is:

1) which one has the lowest self noise (considering nature recordings).

2) which one has the best worflow (handling noise, weight, cabling and wind protection)

My recorder is a 788T.

Thanks for your help.

Best,

Paulo Ricardo Nunes

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Hi I bought Mark's SPS200

 

Self noise is 14 dB DIN/IEC (it is 4 x true condenser capsules)

 

I have used the DPA which i made with 5 x electret mike and I guess it would be noisier

 

mike

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All ambisonic mics are inherently noisier than normal mics, because you're combining the noise levels from four capsules. In order of quietness, it's as follows: (based on experience, having owned an SPS200 and currently owning both an ST450 and a TetraMic.)

Quietest - ST450, then SPS200, then TetraMic. (Also order of price!)

The ST450 uses an external control box that requires a 12v supply via a standard Hirose connector and the mic capsules have heaters that help to combat the mic's sensitivity to humidity. It can output B-Format and stereo simultaneously, has headphone monitoring and a switchable gain control. In order to decode in post, you need special software, either one of the free versions from various sources, or the two paid-for versions, Soundfield's own SurroundZone, or the more versatile but a bit less purist Harpex-B. I use Harpex almost exclusively, but it needs a fast computer. There's a free trial of Harpex available and it's worth a listen. Rycote make two versions of a combined windshield and suspension mount and there's a decent range of cables and accessories available. A Rycote USM studio stand-mount and short cable comes with the mic, along with a mains supply for the control box and cables to get from the control box to your recorder in both B-Format and stereo. The 788 has B-Format to stereo decoding built-in, for basic confidence monitoring.

Both the SPS200 and the TetraMic output A-Format only (essentially the four capsule outputs) and unless you have the either a Nagra VI or AETA 4MinX recorder, you won't be able to monitor a decoded signal except through your computer, with the provided software. Both the TetraMic and the SPS200 come with free decoding software (note that you can't use the free Soundfield SPS200 software with the ST450.) The SPS comes with a cable and software and the TetraMic just comes with software download tailored to your mic and links to download Dave McGriffy's excellent and free VVMicVST. All other accessories are paid-for add-ons.

The SPS has balanced outputs, the TetraMic is unbalanced, and you'll need four phantom power adapters, which also balance the signal, to use the mic with standard XLR-3 inputs. The main microphone connector is a Switchcraft TA connector, which is pretty fiddly to repair if you're a bit ham-fisted in disconnecting it and pull the cable out from the connector. There are windshields available from Rycote for both the SPS and the TetraMic, although I had the SPS200SB, which comes custom-installed in a Cinela set-up, which is nice, but adds considerably to the cost.

The TetraMic is very susceptible to handling and cable noise and in my experience, it's almost impossible to hand-hold it without transmitting rumble to the recording. On a stable stand, it's pretty good, but you definitely need a decent windshield for outdoor use. I use mine now mainly for unobtrusive music recording situations, where it's extremely good. I wouldn't commend it for low-level nature recording unless you have an incredibly good low-noise pre-amp available. I used a Metric Halo ULN-8 with good results, but that system doesn't really lend itself to fully portable use.

The TetraMic software is tailored to each microphone and can be tweaked to specific requirements, like a more severe low-end roll-off, which may help with handling noise and wind problems. It's also worth noting that Len Moskowitz will calibrate your SPS200 and provide a custom A-B-Format decoder for a small fee, although this does then negate the use of the Soundfield software and you'll need to use Harpex or VVMicVST to do your subsequent B-Format conversion. Users who've had this done mention extended low-frequency characteristics and better spacialisation as a consequence, so it may well be worth consiring.

Personally, I don't think any of them are totally suitable for recording extremely quiet sounds* and you may well be better off researching a Schoeps double M/S system if you don't need the height information. However, I'm more than happy with my ST450 and it mates well with my 788, although the outputs on the control unit are on the opposite side to the inputs on the 788, which is a bit of a nuisance. I can pack the whole set-up in the Sound Devices bag, along with the Tracer battery pack and a couple of spare batteries for the 788, and with the addition of a short carbon-fibre boom and Manfrotto Nano stand, I can go pretty much anywhere. The quietest material I've recorded was cicadas in Florida and the loudest was a Lancaster Bomber at full engine revs at a distance of about ten feet and the ST450 produced very good results all round.

I highly recommend that if you do go ambisonic, you invest in Harpex-B, which is just a fantastic piece of software. It's not cheap, but the results are outstanding.

If you're rolling in money, you may be able to persuade DPA to make you one of the ambisonic mics which my old mate Anthony Morris had them build for him. Its designation is the DPA-4 and it's A-Format, so you'll need to find someone to sort out decoding software. I think it's about $15,000.00

Let me know if you want any more information.

Regards,

John

*Just a note to say that I believe that Chris Watson (Famed UK-based wildlife recordist) is an enthusiastic ST450 user, so you may want see what he has to say about it as well.)




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Is it absolutely necessary to use the ST450 with the factory control box, or can it be hooked up directly to 4 mic channels like the SPS200, presumably with an additional DC feed for the heaters (I guess)?

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The mic outputs on a multi-pin Lemo, and I think the pin-out is in the manual, so theoretically it should be possible, but why would you want to? You'd lose all the functionality of the control box, including the gain control, power for the capsules, pattern control for stereo work, etc. Part of the appeal of the ST450 is that it can be used as a multi-pattern stereo microphone as well as for surround.

And you'd have to get someone to sort out the A-B conversion for you, as the ST450 uses different capsules from the SPS200.

If you don't need the full surround with height experience, then there are other possibilities aside from the Schoeps double M/S set-up. You might consider the Josephson C700S which is a three capsule design, for example.

Always happy to waffle on about ambisonics, so feel free to chime in with any other questions.

Regards,

John

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As a Nagra VI owner, just curious if there was a way to leverage the monitoring abilities of the VI and more than adequate preamps without having to add the electronic front end to the mix.  For stereo use, would probably use other mic(s), but just curious if I ever enter the world of point source surround arrays.

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Hi Tom,

 

With the V3.10 firmware upgrade, the Nagra VI can do A or B-Format monitoring as standard. It'll just give you a stereo output and you'll still have to use software to do the proper decoding. As far as the mic pre-amps go, I'm not sure how you'd go about interfacing the raw outputs of the ST450 capsules, but the tech spec and full connection details of the 12 pin Lemo are here:

 

http://www.soundfield.co.uk/downloads/st450_manual.pdf

 

How's the Zoom H2n mod coming along, by the way?

 

Regards,

 

John

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Thanks for the info John.  I'm booked solid up until at least the end of September.  As soon as a get a chance to take a breath, I'll start addressing my other side projects, which include finishing the H2n project, recapping a couple of center section boards on an SSL4056 plus fixing a few problems on a G channel strip, recapping my Revox MR8, finish building out a new cart of some sorts...

 

I F'd up some of the design on my H2n case, rotozipped my way out of that, but I'll save the gory details for the right thread when I get back into it.

 

I might have some interesting upcoming music based projects, where something like a Soundfield might be appropriate.

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One thing I forgot to mention, is that the ST450 control unit outputs at line level, whereas the others are mic level devices.

Regards,

John

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Just to throw our hat in, we've just made an ambisonics microphone called the Brahma, please see the details on our kickstarter page. It's at a late development stage, we plan to ship microphones out by February 2014. We are also using electret based capsules, but larger diaphragm capsules than the Tetramic, so we should have a higher output and lower noise in comparison, also RF protection and a wind shield. Currently the capsules we are using are the TSB 140A 's. We have plans on make a large diaphragm version very soon that will be very quiet. Please keep an eye out for ambisonic developments from our company and if you can support us now, please do so.  We're modifying the Zoom H2n to fit an ambisonics head inside one, as well as using a modified Zoom H2n as a 4 channel recorder. Hopefully you'll like what we're doing."
 

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Just to throw our hat in, we've just made an ambisonics microphone called the Brahma, please see the details on our kickstarter page. It's at a late development stage, we plan to ship microphones out by February 2014. We are also using electret based capsules, but larger diaphragm capsules than the Tetramic, so we should have a higher output and lower noise in comparison, also RF protection and a wind shield. Currently the capsules we are using are the TSB 140A 's. We have plans on make a large diaphragm version very soon that will be very quiet. Please keep an eye out for ambisonic developments from our company and if you can support us now, please do so. We're modifying the Zoom H2n to fit an ambisonics head inside one, as well as using a modified Zoom H2n as a 4 channel recorder. Hopefully you'll like what we're doing."

http://www.kickstarter.com/projects/1569945514/brahma-affordable-ambisonics-microphone

Sound quite interesting. Except for the Zoom bit...

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 We are also using electret based capsules, but larger diaphragm capsules than the Tetramic, so we should have a higher output and lower noise in comparison, also RF protection and a wind shield. Currently the capsules we are using are the TSB 140A 's. We have plans on make a large diaphragm version very soon that will be very quiet. 

 

 

Hello Nakul, 

 

Good effort, but no big difference between the TSB 140A and the TSB 120A, 27dBA of equivalent noise both and the same output (+/-1mV). 

 

Good luck with your own capsule.

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The SPS200 are a superb microphone, isn't the quietest, but is very good for a SDC (I prefer a little noise before using an LDC). The SPS200 is very small (Any regular blimp is ok).

 

This is a comparison between the SPS200 against the DPA-4 (4x DPA 4011 capsules)

 

https://soundcloud.com/suso-ramallo/mic-a

 

https://soundcloud.com/suso-ramallo/mic-b 

 

A Soundfield

B DPA-4

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Just to throw our hat in, we've just made an ambisonics microphone called the Brahma, please see the details on our kickstarter page. It's at a late development stage, we plan to ship microphones out by February 2014. We are also using electret based capsules, but larger diaphragm capsules than the Tetramic, so we should have a higher output and lower noise in comparison, also RF protection and a wind shield. Currently the capsules we are using are the TSB 140A 's. We have plans on make a large diaphragm version very soon that will be very quiet. Please keep an eye out for ambisonic developments from our company and if you can support us now, please do so.  We're modifying the Zoom H2n to fit an ambisonics head inside one, as well as using a modified Zoom H2n as a 4 channel recorder. Hopefully you'll like what we're doing."
 

 

 

 

The TSB140A 's mic are omnidirectionnal. 
It seems to me that the A-format's mic are supposed to be sub cardiod ?
 
On your kick starter link,  will it be possible to have more different extracts ?
The ability to download the  A or B format extracts  would be a good way to help us having an opinion on your mic.

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The TSB140A 's mic are omnidirectionnal. 
It seems to me that the A-format's mic are supposed to be sub cardiod ?

 

 

The TSB140 is a cardioid capsule 

 

http://www.transsound.net/electrets/tsb-140a.htm

 

Usually the quad-mic capsules are cardioid, but sub-cardioid would be a good idea

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Ramallo, on the link I give it is written "omnidirectionnel", I cannot open your link. As I don't have any of these capsules I do not know who is right !
 
Do you think that in the ambisonic theory you can change the A-format directivity as easily as that ? 
You can, and that's the goal, when decoding sounds in post, but when recording the raw sounds ?

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Ramallo, on the link I give it is written "omnidirectionnel", I cannot open your link. As I don't have any of these capsules I do not know who is right !
 
Do you think that in the ambisonic theory you can change the A-format directivity as easily as that ? 
You can, and that's the goal, when decoding sounds in post, but when recording the raw sounds ?

 

 

My link is the maker of these capsules, probably your link have a typo.

 

Aeta 4Minx can decode a SPS200 (Type A) on the fly  (Page 59), and is on "to do" list of the Nomad

 

 

A to B: http://pcfarina.eng.unipr.it/Public/B-format/A2B-conversion/A2B.htm

 

Free plugin: http://www.radio.uqam.ca/ambisonic/b2x.html

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Links are working now. They give different directivity ! Yes, the maker's link is probably the good one.

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Hi I bought Mark's SPS200

 

Self noise is 14 dB DIN/IEC (it is 4 x true condenser capsules)

 

I have used the DPA which i made with 5 x electret mike and I guess it would be noisier

 

mike

 

not sure what you mean by "the DPA which i made". can you elaborate? 

 

-emory

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