Frequency specific sound meter to control HEPA flow rate

Experimental evidence suggests that humans exhale a larger volume of aerosols when speaking louder, or when yelling and singing. I'm trying to design a device that will increase the speed of a HEPA unit/ventilation system in response to the volume of human voices. I'm thinking this would be useful in houses of worship, schools and restaurants. Briefly, when a sensor detects CO2 above baseline, indicating the presence of people, the microphone starts sampling at ~1250 Hz (based on this is the frequency with a large change in dB as the volume of the voice increases). The difference between normal speech and yelling at this frequency is about 40 dB. I've never used microphones with my arduino projects, and I have no idea if this is even feasible. I think background noise and microphone placement will be tricky variables. Does anyone have a microphone suggestion that I could use for the protype? Any thoughts or similar projects anyone knows about? I have a lot to learn.

Where will this sensor be placed. Have you done a study to determine how much time is needed for human created CO2 to be normalized through out a room?

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Hi,
Welcome to the forum.
Microphones are commonly used in Arduino projects. Many just use one of the modules. Since you want to detect a specific frequency, you may need to do some analysis in code, and I have lined a couple of projects that do this.

You will need to experiment to see if the sensitivity of the microphones is adequate for your needs. But this should help get you going.

Thank you! I came across the lighting bowl project, that looked fun. I'll check out the other reference. I'm seeing a lot of references to FFT, which I recall my engineering friends in college complaining about. I love how I come up with some idea that I think will be easy and it takes me 3 months to figure out.

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I use CO2 sensors a lot, just the basic Aranet4 and Sensirion SCD40. If a room is poorly ventilated, CO2 rises within minutes. There are a lot of variables in how air currents in a room move aerosols around, depending mostly on ventilation/air leakage, but for this project, I just want CO2 to be the trigger that tells the microphone/arduino that people are present. I think the microphones should be located within 1 meter of people. If a room has multiple HEPA filters, each one could be connected to a microphone. If it will be controlling the room ventilation blowers, and there isn't someone using a microphone to amplify their voice, maybe just a few microphones around the room. The more I think about this project the more complicated it gets. Thanks for your questions.

PErhaps not! Is this link wrong?

Carbon dioxide is dispersed in a room, there is not a significant difference between the ceiling and floor. For using CO2 measurements as a marker of human breath aerosols, an accuracy of 50-100 ppm is adequate. Outside air is ~420 ppm, inside ranges from 480 ppm to over 3000 ppm. Cognitive performance declines at ~1200 ppm. There are new standards being proposed by ASHRAE that have increased the room air exchange rates considerably. CO2 can be used as an indicator of the ventilation in a space. A HEPA filter does not alter the CO2 level, but it's output is added to the ventilation rate when determining if a room's air is clean. Ideal CO2 is less than 600 ppm. At 800 ppm, 1% of your breath is rebreathed air.

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