Retailers don't think about why they have music. There are a number of issues. It can be very powerful in the right place, where it is played appropriately.

There's a little bit of protocol in the real world which is quite important. If you speak to me, we understand that we've entered into a social contract. But sound that you haven't given permission to receive is noise, and generally unwelcome.

It's an interesting door opening, this use of sonic signalling - using sound to alert us in a more subtle way than a beep.

Julian Treasure Quotes