The best way to troubleshoot this scenario is to have someone in the conference room join with an Amazon Chime client - if you are using a different audio source, be sure to choose to join without your Mic & Speakers selected (so you don't cause echo).
If you see the audio indicator in the Amazon Chime roster bouncing up and down associated with another attendees roster - this probably means that your speakers are not connected.
Make sure the speakers on the audio source are not muted and the volume on the source is turned up. When you are using the Amazon Chime client we have built in the capability to un-mute the device and raise the volume, but if you are using an in-room conference system (video or dial in) you may need to adjust the sound.
If you are in a video conference room, make sure you check the volume on the display (often a TV) as well as the volume on the touch pad or video system.
View the Amazon Chime User, Administration Guide and API Reference on the AWS Documentation site.
Find more information about the Amazon Chime solution, pricing, customer references, getting started, and other resources.