About Cats Ears.
An odd-eyed deaf white cat named Sebastian (Photo credit: Wikipedia)
Cats are born without any hearing, but gradually over the course of two weeks their ears develop. On the third week their ears are fully functional. Cats can pick up a wide range of noises, but especially high pitched noises at which they are better than dogs. That is part of what makes them excellent hunters. Cats can hear five times better than humans, and dogs only have two thirds the ability of cats. Undeniably, cats can also hear ultrasonic sounds such as before an earthquake ect. The cat’s inner ear has many chambers and canals that are filled with hairs that contain fluid and crystals that assist with balance. These hairs can detect the slightest movement and signal the brain to make adjustments which is why cats always land on their feet. No doubt about it, cats have excellent hearing. But you might want to refrain from making very loud noises around any cat. Just like humans, cats can go deaf or become hard of hearing. And the last thing you want is an old grumpy deaf cat.
Vet In Training 
I volunteer to take care of the Grumpy Old Cats for free. If you know what I mean.
Ok, hopefully no Old Grumpy Cats. Tooo Funny.