When Xiaohua was repairing the table in the kitchen at home, there was a constant sound of knocking on objects. In order to avoid being disturbed when Xiao Ming is studying next door, Xiaohua takes

(2) The doors and windows of rooms and kitchens are closed and weakened in the process of communication;

(3) tell Xiao Ming to plug his ears with headphones temporarily to reduce the noise at the receiving place;

(2) When there is a strong sound in the loudspeaker, you can see the candle flame beating;

The beating of candle flame is due to the vibration of air caused by the sound of horn, which shows that air can transmit sound and sound can transmit energy.

(3) Because the morphological structure of different tissues in the workpiece is different, the propagation speed of ultrasonic wave in different media is different, so the degree of reflection, refraction and absorption of ultrasonic wave is different, and the position of workpiece scar can be judged accordingly.

So the answer is: sound source; In the process of communication; Human ear; Energy; The speed of sound is different.