Helping blind people see using sound?

I had a brainstorm yesterday about a way that might help blind people see using sound. Someone has probably already thought of this, but I figured I'd post it anyway. Anywho, you may have heard of this boy who has learned to get around by making clicking sounds with his mouth and listening to the echoes that come back to get a feel for his surroundings. Bats, as you know, use ultrasonic clicks to create a picture of their surroundings. Basically they are getting an impulse response. All animals have the ability to process this kind of information - everyone can tell the difference between being in a large room or small room based on the way the sound echoes. There have been attempts to turn images into sound (by converting colors to different frequencies) to help blind people 'see', but it really makes more sense to help them focus on the impulse response of the room they are in since the human brain already has this kind of circuitry - it just needs help to be able to learn how to use it better.

So, here's my idea for how it could work. You'd need a high frequency capable speaker, a high frequency stereo recorder, a pair of headphones, and a computer to process the input and output. The speaker, headphones, and recorder would be part of a hat that the sight impaired person would wear. High frequency clicks are outputted from a speaker (ultrasound clicks would probably be best? I don't know much about ultrasound). A stereo recorder simultaneously records all the sounds. You could Highpass filter out everything except ultrasound. The results should resemble the impulse response for the room. Then you use the impulse response to re-create the reverberations of the room (you could feed it with white noise or some other kind of sound) and play it into headphones for the sightless person. Everything would happen in realtime so as you move your head you could hear how the impulse response is affected. You'd be giving them the ability to focus on the sound of the shape of the room and since it's in stereo, get a 3d picture of it. Since it would use high frequency sound, above the normal hearing range, it would be pretty unobtrusive, though there's a chance it might bother dogs and some other animals. ;) The big challenge would probably be making it portable (it might require a lot of processing power) and finding audio equipment capable of high frequency operation. Consumer cards already purport to being able to handle 192khz, but finding speakers and microphones that can handle that might be difficult..