http://www.bristolwatch.com/ - Student-Hobbyist Electronics Projects Tutorials

1. http://www.bristolwatch.com/debian/beep.htm- Beep a PC Speaker Add Beeper to Raspberry Pi

https://computers.tutsplus.com/articles/creating-a-speaker-for-your-raspberry-pi-using-a-piezo-element--mac-59336 - Creating a Speaker for Your Raspberry Pi Using a Piezo Element