Hello! We are hoping to trial various external ultrasonic microphones with the new AudioMoth this field season and were wondering what people have for recommendations for microphones? We will be using the devices to record bats in California. Thank you for any input!
I don't have the audiomoth to test it, but a Knowles SPU0410LR5H-QB wired like this works fine on my PC soundcard. Maybe this is something you could try. I think the SPU0410LR5H-QB is the same element as on the PCB of your 1.2.0 version board. Kind regards, Edwin
AudioMoth should work well with the Primo microphones - https://micbooster.com/primo-microphone-capsules/97-primo-em258-mono-module-with-35mm-plug-10m.html
@Alex Rogers The main issue with the EM258 is the max. freq being a bit too low for surveying european bats, for which you need to get up to 120kHz at least. But of course depending on the specific purpose of it might be enough.
I'll be trying the external Knowles micro soon.
Robert
I heard people that were not that enthusiastic about the Primo element. Unfortunately like the good old WM61, where you probably only find clones slold todat, you might also run into a fake Primo. If you want to try the SPU0410RL05-QB you could consider this model. ELV sells these with good documentation, adding just one resistor (about 5 kilo ohms) seems to work fine on my computer. I don't know the hardware of the 1.2.0. version board but what is described here in the link below, lets me think this will work. The attached picture shows a similar microphone to ELV Bausatz Mikrofon MEMS1. I will sent out one to a friend soon to test but maybe someone else has the chance to test this as well, specially a comparison beween the Knowles SPU and the Primo element would be nice. Micbooster also sells the SPU element but seems to need more external components.
I would really like to try and Audiomoth with an external microphone for bat recording. One of the main barriers for me is the attenuation of weaker bat calls at higher frequency, which makes it difficult to use the Audiomoth for the sound identification of Myotis species in particular. I know that several commercial bat detectors use FG microphones produced by Knowles (e.g. the FG-23629), where the main downside seems to be the increased cost, but they are insensitive to water and dust, and they have a much latter frequency response compared with the MEMS microphone at the higher frequencies. Does anyone know if there would there be any particular difficulty in using an FG microphone with the Audiomoth?
Connecting the Knowles SPU and FG seems possible by using the circuit I described earlier. The FG element however is very much less sensitive than the SPU so the FG might need like 20-30db more amplification. (I don't know any exact numbers) A recording will be a whole lot softer when you use an FG element. I have no idea of the gain setting in the audiomoth can compensate for that, maybe running on the higest gain setting will be good enough. The FG has a huge price compared to the SPU, I think the FG is around half the price of an audiomoth. It is also difficult to mount and you would probably double the price of the audiomoth. The knowles SPU element seems to be doing quite a good job on the ultrasound range.
Many thanks Edwin. That's really helpful. I know that colleagues in Belgium have been planning on testing the Knowles SPU0410LR05-QB in an external microphone. I would be really interested if you get any feedback on the performance of this microphone as an external microphone. As I say for me, the main barrier for me is the attenuation of weaker ends of calls at higher frequency, which is a particular problem for Myotis.
I sent some of my elements to David in Belgium, he tested the microphone and compared to the internal (which is te same element) It seems to be working about just as well. I don't know if he has compared the recordings to something that uses an FG element. I wish I had the 1.2.0 version so I could do some test.
I just tried to mod my 1.1.0 so it might look more like te 1.2.0. I recorded a sweep from 150-20Khz which I played with a homebrew speaker, so we can only compare the two (maybe the mics work on higher frequency that te speaker). The SPU was used recording on middel gain setting, the FG on the highest setting.
Unfortunately connecting the FG did not work on my modded 1.1.0 board, so I attached V+ of the microphone to 3v3.