Hello Audphile1,
Mead Killion at Eytomic Research has various solutions that are a possible good fit for your fathers situation. He has several noise attenuating devices that will most likely address the problem that your father is asking you to research. The Eytomic devices that would appropriately address his problem will be passive solutions not electronic. Mead is a great guy and also a musician, feel free to call his company (888-389-6684) to find the appropriate referral in your area for his products. I am a fan and a user of his solutions. Good luck.
Mead Killion at Eytomic Research has various solutions that are a possible good fit for your fathers situation. He has several noise attenuating devices that will most likely address the problem that your father is asking you to research. The Eytomic devices that would appropriately address his problem will be passive solutions not electronic. Mead is a great guy and also a musician, feel free to call his company (888-389-6684) to find the appropriate referral in your area for his products. I am a fan and a user of his solutions. Good luck.