First, how do you know "all the shops" use Tannoy speakers? Lets assume they do, and assume there is (very unlikely) only one model for ceiling installation. Further lets assume (not necessarily the case) that they are infinite baffle (open backed) and have exactly the same amount of free space (also apocryphal) behind them. Further,that each speaker in every instance drew from an adequate 30 watts of source energy. (Probably not.). Lets say the ceilings behind those speakers were un-damped Plaster, and professionally (correctly) installed. Suppose they were all 12 feet overhead. Suppose there were the proper amount of them for the space.covered in the shops. I would then expect that the manager turned down the bass and volume so as not to distract the store patrons ( A choice.) There are other considerations, if the above is not the case, such things as improper installation, too small an amplifier, too big a space for the speakers, will do it too.