The Submarine pickup is a guitar pickup, invented by singer/songwriter Pete Roe, that can add extra low-end to both electric and acoustic guitars.
Roe came up the event when he performed as a solo opening act for a band and found that his audience was louder than he was. This led him to experiment to create a pickup that could be used to give the first two strings of the guitar an extra boost. The resulting Submarine pickup can add an extra bass punch without in any way interfering with the guitar's natural sound.
The Submarine pickup truly adds greater depth and range to guitars, and gives guitarists -- particularly those performing as solo acts -- a greater voice.
The Submarine Pickup Can Make One Guitar Sound Like Two
Rahul Kalvapalle — June 26, 2015 — Tech
References: submarinepickup & gizmag