请确保您的设备未触发进入静音模式.

另外，对于简短的系统声音，您可以使用AudioToolbox的系统声音( https://developer.apple.com/library/ios/documentation/AudioToolbox/Reference/SystemSoundServicesReference/):

Make sure that your device is not triggered into silent mode.

Also, for short system sounds you can use System Sounds from AudioToolbox (https://developer.apple.com/library/ios/documentation/AudioToolbox/Reference/SystemSoundServicesReference/):

if let soundURL = NSBundle.mainBundle().URLForResource("Metal_Gong", withExtension: "wav") {
    var mySound: SystemSoundID = 0
    AudioServicesCreateSystemSoundID(soundURL, &mySound)
    AudioServicesPlaySystemSound(mySound);
}