Possible Clues:

• It's hard for your voice to carry so much weight
• Pounds this to make it hard
• Seems your voice lends weight to this
• 59-Across, e.g.
• Perhaps your voice carries some weight it's so hard
• Fourteen pounds, to a Brit
• Brit's 14-pound measure
• Fourteen pounds
• The sound of your voice has some weight that's hard