同声[tóng shēng]
词典speak at the same time：同声。
词典danci.911cha.com
词典speak simultaneously：同声。
911chaxun查询·英语单词大全
speak at the same time; speak simultaneously
1. Voci eguali：Mixed [英]混声 | Voci eguali 同声 | Boy's voice [英]童声