AVSpeechSynthesizer扬声器上

Question

我可以听到连接时通过耳机读取的文字。但是，如果我断开耳机，它根本不会播放。如何为此演讲开启演讲者？ 这是我的代码：

[syn stopSpeakingAtBoundary:AVSpeechBoundaryImmediate];
syn = [[AVSpeechSynthesizer alloc] init];
syn.delegate = self;
utt = [AVSpeechUtterance  speechUtteranceWithString:rtext];
float speechSpeed = 0.3;
NSLog(@"Read***** text%@",rtext);
[utt setRate:speechSpeed];
utt.volume = 1;
[syn speakUtterance:utt];