best headphones maximum range for the lowest buck

[Feuerfalke]

Originally Posted by raaaid

so would be posible cheap headphones with range 5-30000 hz?

Simple answer why a larger frequency range makes more sense?

Because those frequency-ranges mark the maximum range they can possibly represent. If you have a headset starting from 20 Hz, at medium volume it probably has a low frequency of 50, maybe even 200 Hz, depending on the quality.
Same is for high tones. You won't hear 30.000 Hz, but you can be sure these headphones won't ring and crackle at 20.000 Hz, because it's well within their technical ability.

Just the same as a car. If it can go 180 kph it means it will reach this velociy in free fall and with wind from the back. A car that can go 320 kph is much more likely to reach 180 kph without falling apart.