Click the link below for manual pages I mention to make changes:http://www.harmankardon.com/resources/Brands/harmankardon/Products/ProductRelatedDocuments/en-US/OwnersManual/AVR1700_OM_EN.pdf
Most dialog sound comes from the center channel / speaker. If not working correctly, it make become difficult to hear people talking especially if there is a lot of other sound going on in movies and some music, too.
Check and adjust the volume level for the center channel or speaker. Check page 8 of the manual to learn how to use the remote to change the volume level of individual channels or speakers.
If you want, you may find it is a good idea to check page 17 to esablish correct volume levels for each channel by runnijng the set up with the microphone. This will allow the system to be "calibrated" for the room. This is a very important step in "getting the sound right".
If none of these suggestions work, you may have a problem with the center speaker itself - or with the amplifier for the center channel.
I hope this helps & good luck!
Check the speaker connections for the center channel. Page 6 shows the location on the rear of the amplifier - but check the speaker itself first as it is easier to get to and the rear of the amp is less likely to be distrubed and have a poor connection.