If you use Read&Write for Google Chrome and no voices are available then they are likely being blocked from loading. Click on the dropdown button and go to Options > Speech
You may get the following message:
Read&Write for Google Chrome requires access to our speech engine servers. If you’re not able to hear speech on multiple machines, then it is likely to be an issue with streaming speech being blocked by a network firewall.
You need to ask your system administrator to allow the following URLs through your firewall:
Once these are added speech should work fine.
If you find that speech is still not working, please run our Diagnostic Tool and check that everything is running as it should: