We use Baidu.com's TTS (text-to-speech) engine to deliver audio for our words and example sentences.
If sound isn't working for you, it is likely that your device is unable to connect to Baidu.com.
To most common solution is to turn on / or turn off any VPN that you are using.
If you are in China and using a VPN, Baidu.com may be blocking you. Try turning off your VPN.
Users in India have reported that the entire country has blocked Baidu.com. If you are in India and sound does not work for you, you should try connecting to a VPN before using Hack Chinese.
You can also try these diagnostic steps: