voice
声 centers on sound produced by a person or living thing: a voice, vocal sound, or utterance.
声 is the modern simplified form of 聲. The older form combines 殸 (a stone chime) with 耳 (ear), representing sound heard by the ear. The modern form retains the top 士 and a simplified lower part.
The top 士 looks like a samurai standing tall, and the lower part resembles a simplified body with an open mouth. Picture a samurai shouting with a loud voice.
For セイ, imagine a samurai's voice saying 'say!' as a command: 'say' -> セイ, and his voice rings out clearly.
voice
voice; speech; sound of a voice
declaration; statement; proclamation
loud voice
singing voice; (sound of) singing
cry (of an animal); call; chirp; song; caw; roar; bark; yelp; meow
low voice; whisper
fame; reputation; renown
cheer; shout of joy
(sound of) laughter; laughing voice
utterance; speaking; vocalization; vocalisation
(shout of) encouragement; cheering; rooting; support
shout (of encouragement, etc.); yell (used to time or encourage activity, e.g. "Heave ho!")
shout; yell; scream; cry
sound of a gunshot; report of a gun
vocal music
loud (of a voice)
cry (e.g. of a baby); sob; whine
call; hail; yell
tone of voice
first words said (e.g. when meeting someone); first thing out of one's mouth
speaking voice; talking voice
natural voice (without a microphone)
tearful voice