voice, throat
嗓 centers on the physical source of vocal sound: the throat and the voice that comes from it.
嗓 combines 口 (mouth) with 桑, which likely contributes the sound. The character is used for throat and voice.
The mouth radical 口 beside 桑 (mulberry) suggests the throat as the passage where voice is produced, like a mulberry-shaped resonance chamber.
For ソウ, imagine a singer's voice resonating like a deep 'soul' sound from the throat: soul -> ソウ.