Is a special instrument/guitar needed for slack key?
No. Slack key can techniquely be played on any stringed instrument. Nylon stringed guitars are beautiful for slack key although steel strings are more convenient for playing in many tunings. This is due to the memory of the nylon string. After retuning, it will try to reshape itself to the original tuning causing the instrument to go quickly out of tune on the next song. Today there are special instruments that are designed just to be played in a slackened tuning. They are called baritone guitars. Their neck is slightly longer and the design allows the soundboard to receive enough tension and vibration even in the slackened tuning to create the most beautiful sounds and frequencies.
