It seems to make mathematical sense: Get more people through your doors, and you increase the number of purchases made throughout the day. And up to a point, that's true.
Only up to a point.
If a store gets too crowded, people start spending less.
Wouldn't it be great if you could get more customers in, and keep them spending more?
It turns out you can.
They found that fast music mitigates the negative effects of high social density.
Fast music keeps your customers spending, and spending more, even when your store gets crowded to the point where customers would ordinarily start to spend less.
Music has less of an effect in a lower density scenario
As you can see in Fig. 1, at a lower social density, there's not too much of a difference between fast music, slow music, and no music at all (although any kind of music at that density has a marginal positive effect).
But as a store becomes more crowded, slow music can sometimes actually cause customer spending to decrease more than if there was no music at all!
Customer spending while listening to slow music is never higher than with fast music, and it turns out that the increase in spending has more to do with customers buying more products than buying more expensive products.
This implies that combining fast music and a small shop space with a large variety of non-luxury goods may lead to positive business outcomes.
The Key Takeaway
If you are a retailer of non-luxury goods, your in-store music should be at a tempo greater than 107BPM, except when your store is nearly empty. (But then, you'd be having other problems)
What music should you choose? That's a whole different question.
My article on the 2 Things You Should Know About Audio Branding addresses this somewhat.