Sure that will act as bait for some and not sure why microphone arrays have perked my interest so much since my introduction to Mycroft, they just have.
I am not a sound engineer, I did a bit of audio late teens but that was a long time ago.
Firstly to pull the bait array microphones without fancy dsp are just an array of microphones.
As libs on a Pi3/4 you can do echo cancellation which is handy but apart summing the array which also sums noise many of the non DSP microphone arrays we have are practically pointless.
On a zero the load is too heavy even for Echo Cancellation (EC) and all you can do is increase sensitivity.
Increasing sensitivity is OK for far field in a silent room but apart from that its also pointless as any louder volume source will just swamp the signal and that sensitivity will count for nothing.
Even many of the DSP often USB mics are not that great but they are getting better, but even then with inbuilt EC they still suffer from other non distributed noise sources.
Meaning if your voice is the predominant noise source they work quite well, but against singular competing noise sources not so and the problem with home TV & HiFi are those types of noise source.
As well as being critical of for many options of array, omni directional without DSP is also pretty poor as without DSP you don’t have any form of control.
If you don’t have DSP then actually uni-directional cheap old electrets plugged into a cheap USB sound card especially on a zero or where your struggling with load for EC can be much better.
Its not high tech but they just have holes in the back so sound waves hit the back of the diaphragm and act as noise cancellation and give directionality.
The directionality actually gives you some form of control but again making your own gets a bit geeky as you have to tune a mic so that you sound waves are tuned to cancel.
But anyway here is a uni-directional electret quite a good one as is 16K as you do lose frequency.
Sensitivity is less than mems but the Kingstate is a bit pricey just for a capsule but -37db isn’t bad.
You will see they just have holes in the back of, Primo do really excellent ones but the prices are a bit crazy.
Uni directional microphones are noise cancelling and have an advantage over software EC that does DSP on the playing audio and subtracts from mic input.
The problem is when audio comes from another source as you don’t have that PCM on your sound card to cancel out its input to your Mic.
A directional Mic does if its facing the right way and often how you place a unit can very much give you a 3rd party noise cancelling solution.
If you stick it on top of your voice AI then it becomes a problem as directionality of that noise can be instantaneous at both back and front.
If you do have a Pi3 or Pi4 though you use software EC to cancel local unit noise and use the natural noise cancelation of a uni-directional microphone in conjunction to get the best of both worlds.
You might only have a single mic on a cheap sound card but in many situations it can be superior to a relatively pointless array that you have no control of.
Sensitivity becomes much less of an issue when you can cancel noise and have a ceiling where you can turn up the gain.
Basically they are uni-directional lapel mics that start really cheap.
You can find one for a couple of $ that will go with a couple of $ sound card but even what looks like it might be quite reasonable isn’t actually earth shattering.
But you can go more pro and you will notice more design on the rear cancelation part of the mic.
Or go all out with a shot gun mic but you Mycroft is going to get very Steampunk.
I can not say how well those work on a cheap usb soundcard as sometimes the gain can be pretty poor, hence why I have been taking a more DIY route with preamps as rather than passive I can make an active circuit with things like AGC and controllable hardware gain.
My fave of the moment is the MAX9814 but grabbing cheap clones and replacing the omni-directional.
The AGC timing cap Adafruit choose is rather low unfortunately but tacking on the top another cap is much easier with SMD than I thought, fiddly little things still drive me mad though.
There is a whole range of quite interesting low cost mic hardware.
Less than $3 and it has a noise gate & compressor built in…
I also can not tell you which cheap USB sound cards have decent gain as its a really mixed bag some are dire and others are great and even more confusing you can seem to buy identical but somehow they don’t seem to be.
Also with the mono USB cards I can’t telly you because I have been concentrating on the more expensive but much rare stereo ones.
Edimax Dreambass which is a VIA VT1620A
Syba SD-AUD20101 which is a Cmedia CM6533
Also the likes of AXAGON ADA-17 or https://www.aliexpress.com/item/4001184939273.html
Hence can not say about sensitivity as with preamps and active the problem is too much gain and often in alsamixer set to 0db to about 9db gain depending on module I am using.
Yeah I know stereo and what I said about arrays but its the arrays generally at the moment we have available that seem to make little sense.
I have been playing with the idea of running one channel and then have an input for another Mic on a wired extension for extra coverage and playing with VAD to control channel mixing.
So a long winded post but for some rather than some $90 USB speakerphone if you can find one wit decent a gain a cheap sound card and Lavalier Lapel in the right situation will definitely give it a run for its money and even be in certain circumstances out perform.
If we get DSP especially advances in current DSP then planar Mems arrays are another story, but without they are a bit rubbish and sort of pointless.