Sound output problem

We have set up in a website, Jitsi in an Iframe. We have noticed that during a videoconference on the phone (without going through the Jitisi meet application), the first participant obtains the sound as if he was telephoning. The loudspeaker is not activated. The following participants do not have the problem.
Is there a way to control, or allow the user to control the sound output device?
Thanks for your help