Shahed drones have increased in altitude from ~500m at the beginning of the Ukraine war to 2000-3000m, which is a 4x reduction in noise on the ground. The higher the drones are, the less noise they make at ground level, and the less effective this ground-based microphone system will be. The drones have moved to elevations to make them more difficult to target with ground based weapons. Reductions in ground noise are a secondary effect.
The latest versions of Shahed can reach 5000m in altitude, which would largely be inaudible on the ground.
It's not about "can reach", it's fairly easy to get them to fly even higher. It's about danger of interceptors vs danger of detection. Today's Ukrainian detection network (based on radars) is so dense there is no way to hide from it anywhere, anyway, so high altitude wins.
There are extremely sensitive differential pressure sensors available from Sensirion that aren't overly expensive.
If these Shahed drones have a propeller they should have a brutal signature between 0-250Hz as they are moving a lot of air.
Use one differential side and connect it to a kitchen funnel for directional listening the other one to a plastic bottle with a very very small hole in it. It will pick up everything high frequency that's different to the environmental pressure.
That way I was able to detect washing machines that had a physical link to house walls for many hundred meters (machine spinning -> house wall shaking -> pressure waves).
Add this with some GPS PPS frame timestamping and you should have a nice tracking network that doesn't require a lot of bandwidth. But maybe the setup must switch to analog differential pressure sensors as these Senirion-I2C sensors do not have a Sync ping for super precise timestamping.
I believe Ukrainians had already deployed such a system. This is specifically designed to use old Android phones already sitting in a drawer somewhere without any other use, and most importantly by anyone without technical skills.
The latest versions of Shahed can reach 5000m in altitude, which would largely be inaudible on the ground.