Low Voice
Whisper
noun, の adjective
A small voice is so small that you can hardly hear it. It's a low voice or a whisper.
こごえ
The readings for this word are both kun'yomi readings. You've learned both of these readings by now so you should be able to read this on your own. Just watch out because, like in 大声, the こえ becomes ごえ thanks to our old friend rendaku.
二人とも、どうして小声ではなしているの？
Why are they both whispering?
「ビエトに学ランをきてもらいたいんだ。に合うと思うんだよね。」と、わたしのもうそうの中でコウイチがビエトに小声で言った。
"I want you to try on a school uniform. I think you'll look good in it." Koichi whispered to Viet in my fantasy.
男は、小声で話し始めた。
The man started speaking in a low voice.