Ok, so I was back at the customer's place again. This time, to fix the PA system which I bought for them. We had to get a more expensive amplifier since the original model we have been using was not suitable for the job. (It was a Karaoke amplifier). Because the applications are annoy....er, announce to staff, we had to make sure the amplifier does not fail. Hence, we had to connect the large speakers to a pair of audio transformers before connecting to the amplifier itself. So, after plugging in the amplifier, the feeling of hearing my own sound irrita...er, on the staff and scaring the dogs away as well, was, well, gratifying.