Hi zerolagtime, thanks for replying to my question! Thanks for letting me know also that such a low frequency occurs in a big room like that. I was indeed interested in whether such a low frequency feedback could actually occur in a real setting or whether it was only something that you could accomplish with an artificial pitch shift. It sounded realistic, so I had a feeling that such a thing could be true, but now I know :)
I used audacity to modify the original sound in case someone such as yourself found a lower pitch more effective for their project. I have experienced feedback in real settings at a variety of pitches. The shape of the room, microphone, amplifier, and speakers change the oscillating frequency of any particular setup. My rig that I used to create this sound forced it to have a high pitch, which usually only happens with loud rock bands. Feedback during speaking in a big room with nice microphones usually sounds like the pitch above.
Not everyone can imagine the variation when listening to it here since they might not know that Audacity's built-in "Change Pitch" setting under "Effects" makes this easy.
Hopefully you'll play around in there and find other interesting effects that can help you tweak a sound to your purpose. Two of my favorites are "Noise Removal" and "Change Tempo," but moving over to Spectrogram view of a channel, combined with an equalizer (or a plugin effect called Notch Filter) are pretty handy too for constant tone hums or rings.
I've got a question for you: When you say "low pitch shifted down," do you mean that you shifted the pitch down in an audio editor? Or was this the pitch of the original recording? Thanks :) and thanks for uploading these recordings - I'm finding them very useful for my purposes!
Yes. This work is licensed under the Creative Commons "Attribution License" which says: You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. No additional restrictions — You may not apply legal terms or technological measures that legally restrict others from doing anything the license permits.
I typically would refer to this sound effect in a list of credits for my project and call it '"A Harpsicord Dream" by zerolagtime [freesound.org - CC Attribution 3.0]' and use a URL on the license name if the medium permits. If this is printed or part of a video, I would stick with the quote above.
Good luck with your project and thanks for using freesound!