Sony unveils the 7509 HD Headphones, which have a frequency range up to 80 kHz, far above most other headphones. The human ear can actually only hear sounds in the 20 Hz to 20 kHz range, but it has been theorized that frequencies above 20 kHz produce what is called the "hypersonic effect." In essence, even though you can't hear those high-frequency sounds, they do have an effect on your brain and make for a more enjoyable listening experience. If the hypersonic effect doesn't impress you, just think how wicked it'd be to record a dog whistle and play it back for your dog through the 7509 HD.