All TV’s are different and have varying levels of speaker systems. Most of the time you can hear just fine by simply turning your TV up than your normal listening volume if it's quiet.
However, our full enclosures (The TV Shield, The Display Shield, The TV Shield PRO, The TV Shield PRO Portrait blocks around 50-80% of the sound) and our TV Shield Pro Lite blocks around 20% of it (open back design).
The TV Shield’s polycarbonate cover can be raised on its hinge and propped open with its standard prop arms to make more effective use of the TV’s speakers. When The TV Shield® is used in the closed position, TV sound volume is reduced. Some people want to improve sound overall in any case with their TV, especially in outdoor or loud environments so the use of Outdoor Speakers is recommended, if you plan to watch in the closed position or want overall improved sound.
The Display Shield® has been designed with a semi permanently affixed front panel so in some cases external speaker systems are recommended. Again it all depends on the quality of your TV or Displays internal speaker system, the environment and intended use.