Hi Len, As we’ve discussed before…
This simply isn’t true. If you add two omnidirectional microphones together you get a 6dB increase in peak audio signal (voltage) but only a 3dB increase in noise because noise is an average power. P=I^2*R and V=IR. The square makes the difference. If you double the number of capsules twice, i.e. adding eight omnis, you get a 9dB increase in noise (3*3) and a 24dB increase in peak signal (3*6). A 15dB increase in signal to noise ratio (SNR, the difference between the peak signal and the noise power, expressed in decibels). Adding eight cardioids together to create a single omni W channel for ambisonic use is not the same thing at all. Cardioids are made up of an omnidirectional, pressure component and a velocity, figure-of-eight component. If you add two cardioids, pointing in opposite directions, the figure of eight components cancel out, leaving just the omnidirectional components. The omni component is only half of the energy of the cardioid microphone, so you only get half the peak signal benefit when adding cardioids arranged in A-Format to produce a B-Format W channel. Adding eight cardioids in A-Format arrangement will give you 9dB more noise, but only a 12dB (24/2) increase in peak level. An increase in signal to noise ratio of 3dB. Not 9dB. So if you are expecting a 9dB increase in SNR and your published 15dBA SNR, which is equivalent to 79dB signal to noise ratio, is based on that assumption, those numbers can’t possibly be accurate. If your mic has eight capsules and you claim you are getting a 9dB SNR benefit from adding the capsules that would imply 70dB SNR per capsule (79-9). I suspect that number should actually be more like 21dBA or 73dB SNR for the W omni channel and 70dB SNR per single capsule, since you only get a 3dB SNR benefit when adding eight. We will confirm these numbers by measuring a single Tetramic capsule on axis with a known SPL white noise signal and subsequently comparing the single capsule numbers to the W channel SNR. I’m sorry to have to point these things out. I just want transparency in our industry and any misleading claims or doubts cast on our mic comparison study must be addressed. Cheers Jack Sent from my iPhone > On 9 Nov 2023, at 01:37, lenmoskow...@optonline.net wrote: > Do Many Small Capsules Mean More Self-Noise Or Less? Less! > > > As we've discussed before, the more capsules an array microphone has, the > lower its self-noise. That's because as you double the number of capsules, > the combined output voltage goes up 6 dB, but the self-noise only goes up 3 > dB. > > The noise increases only 3 dB because it's uncorrelated across capsules. So > each time you double the number of capsules, self-noise drops 3 dB. OctoMic's > combined eight capsules have 9 dB lower self-noise than a single capsule. > > That results in a low self-noise specification. We specify it conservatively > as 15 dBA. That's the same as DPA's wonderful 4003, or only 1 dB more than > Schoeps' Mk 4. > > > > Len Moskowitz (mosko...@core-sound.com) > Core Sound LLC > www.core-sound.com > Home of OctoMic and TetraMic > -------------- next part -------------- > An HTML attachment was scrubbed... > URL: > <https://mail.music.vt.edu/mailman/private/sursound/attachments/20231108/3a4c2ad2/attachment.htm> > _______________________________________________ > Sursound mailing list > Sursound@music.vt.edu > https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit > account or options, view archives and so on. _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
