The Voice Amplification Modulator can make even the quietest voice be heard. Just don't put two of them close together or the feedback will be horrible.
The voice amplification modulator is a human invention. The human tinker mage Allavan was well-known for his use of technological devices to aid his arcane casting abilities. He found, through much experimentation, that many of the disadvantages arcane casters suffered could be countered through the appropriate use of science. One problem in particular was that if he found himself silenced, he couldn't cast spell with verbal components—that is to say, most of his spells. To deal with this eventuality, he developed the voice amplification modulator, a technological device that replicated sound as a series of vibrations. Although he never perfected the item, he did find that it worked well enough to suit his purposes.
The modulator is a blocky piece of metal that fastens around the neck with a leather strap. The device's inventor claims that the voice modulator transforms the user's voice into a series of vibrations that approximate sound.