Audio engineer here. Definitely don’t get a directional mic like a shotgun (fuzzy) mic or a cardioid mic (like singers use on stage). These require at least an audio interface, careful placement and multiple mics. For your situation, something like a Zoom H2n will be the best and perhaps cheapest option. It has 5 built in mics, so you’ll be able to capture sounds from all over the lecture hall. Use the 4 channel surround option, or the X/Y or Mid-Side options, and see what works best. It won’t be perfect, but it will be the easiest option to improve audio and simplify recording. Plus, the batteries last for many hours (ideally use the best rechargeable Eneloop Pro AA batteries).

The professional way to do it would require a mixing desk, an expensive DPA, Shure or Sennheisser lavalier mic on the lecturer, at least 2 room mics and possibly a boom operator with a shotgun mic to capture audience questions. (Although this last option could be replaced with room mics or additional fixed mics pointing at the audience). There are various options for room mics depending on the acoustics of the room, and there are no one size fits all solutions for professional quality audio.

But you don’t need professional quality, just the best you can get. With a Zoom H2n, you can put it on a tripod near the lecturer, and it will pick up sound better than average human ears. It will be better on a tripod, because it won’t pick up floor noise as much. To reduce floor noise further, get a decoupler to reduce handling noise and use a mini tripod sitting on a desk or chair. If the lecturer hall is windy (lots of air conditioning or windows and doors open) use a windshield.

You could use any handheld recorder that does X/Y recording and it might be fine. But 4 channel recording might help pick up more from the audience, and you can still boost the lecturer’s audio by keeping the device close to them and having the “mid” mic pointing at them. The recordings can be fiddly to edit at first (especially if you want to boost part of them, like the “mid” or “sides”, but it doesn’t take long to get the hang of it. Use Audacity to edit the audio or any free audio editor you happen to have access to.

Please feel free to get in touch if you have any questions, and good luck with it!

Don’t get a directional microphone, they’re directional and won’t be very useful in a lecture hall or clasroom setting unless you’re willing to constantly adjust its focus by swiveling the mic around, and still won’t help much with the range.

they’re meant to exclude anything not directly in its line of audio rather than to extend range.

You’re on the right track with a conference style mic If you want to record everybody, although you will lose clarity of your professor’s voice compared to the lavalier, get a Yeti omnidirectional snowball style, or the digital voice recorder someone else suggested will work also.

depending on the size of the room, even the omnidirectional mic won’t work for students and the professor.

no matter what the microphone is, there’s no way to get clear audio of both your professor and a student in the back of the room with one microphone.

The lavalier you’re using is best for recording your professor. with any microphone not right next to them, recording quality is going to lose clarity.

Short of a range of mics with recording equipment and a crew to operate them, nothing is going to handle all these issues.

The best option is a hand-held digital recorder that you can leave at the podium or wherever is the closest spot. There are a large number of devices designed specifically to record lectures for college students. I highly recommend you research those and skip trying to record directly to your computer.

Wireless mics are just adding a range of issues for you when you can spend that money on a more robust recorder. You will find yourself spending more money on a less specialized and poorer performing setup than just buying the right portable recorder.

Sony and Zoom (not the telepresence company) are some notable leading brands for these devices.

Edit: the H1N and UX570 are highly regarded.

My wife got this for recording board meetings and it does a pretty impressive job picking up different people around a room. https://a.co/d/9QiaXvr

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Can you, ehm, involve some psychological tricks?

1. Say beforehand that you are recording and explain how to turn the mic off\on to get their attention to the audio.
2. Test it with each of them to double down on that.
3. If that place is big (even if it’s not), use speakers to send there all the inputs to amplify the volume. They subconsciously get used to hearing themselves from the back and losing that feel makes them a little uncomfortable so they walk back to the mic. Just be careful not to launch a feedback loop of mic-speakers playing a human centipede to the eeeEEEEICK sound deafening everyone.

That is possible with (some splitters? and) a laptop.

But if you want to turn it into something basic but more fun (that your department may later use for more than lectures, so you can even ask for some funding), for a good cheap setup for nice recordings you’d need a laptop, a pair of headphones for yourself, a basic audio mixer you can get second hand with usb, a pair of dynamic mics (condensed are more specialized and too precize, that’s the next level) and a bunch of cords for them and said speakers. Mixer is important to take in multiple inputs and level their volume independently, turn them off at will, all in physical buttons\sliders.

And if you want to go superfrugal, fing a way to grab multiple audio channels with your laptop, use OBS for recording, add each channel and level them here, and use stupid ass webcam-tier mics aimed in a general direction where a group of speakers (teacher, students) appear, then right click at every input audio channel and play with it’s built-in filters for noise cancellation and compression, but be careful, because it can easily cancel out everything spoken (that totally didn’t happen to me a couple of times, lol).