Related Clues:

• Grouper, e.g.
• Voice below baritone
• Maui instrument
• Hawaiian guitar
• Bigmouth, for one
• Clef below middle C
• He hits low pitches
• Barbershop necessity?
• Source of low pitches?
• Wide-mouthed fish
• Barry White, notably
• It's deep
• Tiny Tim's strings
• Deep end?
• Instrument