More opinion to add into the mix. There are really tiny microphones which are also directional. An example of the case in point is the Knowles FG which is available with several different directivities. <http://www.digikey.com/Web%20Export/Supplier%20Content/Knowles_423/PDF/knowles-an-dfg-microphone.pdf?redirected=1>
The DFG is about 2.6x2.6 mm in size, which is small enough to lose under your thumbnail! It's available with 3 different directivities, one of which is approximately a cardioid. The directivity is maintained pretty well over the audio bandwidth. Does the directivity change when it's located next to an object? Yes, and that's one of the main challenges in designing a microphone into a hearing aid. The self noise is fairly low, at least for the omni version which has a self noise of about 25 dBA. The trouble with using these for ordinary audio work is that the bass rolls off below about 7 kHz. That necessitates a substantial amount of equalization to restore flat free-field response. That has a negative effect on the SNR. It's also worth noting that these hearing aid microphones typically can only go to about 105 dB SPL or so when configured as directed by the manufacturer. Smart circuit design can alleviate that problem. Hearing aid microphones illustrate a certain sweet spot in microphone design. Comparing the Knowles FG omni to a modern small diaphragm recording microphone such as the KM83 shows that it has about 12 dB more noise (25 dBA vs. 15 dBA), a bit more low-frequency roll-off (the ones that I've tested are -3 dB at 10 Hz), less high frequency bump (+5 dB at 12 kHz vs. +8 dB at 10 kHz) and a reduced maximum input level (105 dB SPL vs. 140 dB SPL). The main point is that hearing aid microphones are small enough to retain their directional characteristics all the way up to the top of the audio bandwidth, and also small enough to be put in places where other microphones just won't fit. Whether they are good enough for a particular recording or measurement purpose depends on the exact needs of that purpose. Eric ----- Original Message ---- From: Fons Adriaensen <[email protected]> To: [email protected] Sent: Wed, November 7, 2012 2:49:58 PM Subject: Re: [Sursound] Which order (but not extactly high order)? On Mon, Nov 05, 2012 at 03:59:19PM -0800, Eric Carmichel wrote: > I would like to model microphone pickup patterns in conjunction > with HRTFs and Ambisonic recordings that I've made. To give a > specific example, I would like model a miniature supercardiod > mic, pointed forward, that is located proximal (or superior) > to the pinna. A tricky problem, and I don't have an immediate answer to it. But I do have question. Are these miniature mics *really* directional, or do they become directional by being deployed in the way they were designed to be, e.g as you describe ? The reason I ask is because a) making a really small mic directional while preserving other required performance characteristics (e.g. sensitivity or self-noise) is not an easy thing given the physics, and b) when a mic is placed very close to any object having the size of a human head its polar pattern is likely to be modified by the presence of that object, at least at medium and high frequencies. -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound _______________________________________________ Sursound mailing list [email protected] https://mail.music.vt.edu/mailman/listinfo/sursound
