There is no direct connection between the channel spacing, and the allowed TX bandwidth. If the bandwidth is wider than the channel spacing (for AM BC), all th

There is no direct connection between the channel spacing, and the allowed TX bandwidth. If the bandwidth is wider than the channel spacing (for AM BC), all that happens is that adjacent stations hear a little "monkey chatter". And that is minimised because most stations are arranged on a geographic grid which prevents a local station having another local on an adjacent channel. In Australia the local Government ABC stations most definitely do transmit 15KHz wide audio. A quick search turned up this article from September 1980 ETI magazine which discusses stations having 30KHz total bandwidth. https://imgur.com/a/gVpSwoo https://imgur.com/a/gVpSwoo Whatever, just tuning around with a high-end SDR shows many stations at 20KHz bandwidth. The Commercial stations have a problem in that they use aggressive audio processing in order to maximise their coverage, given their licensed power output. So as soon as the commercials decided to concentrate on talk shows, they wound down their bandwidth.