A form of horn loading particularly applicable to low-frequency speakers; the rear radiating surface of the speaker feeds the horn and the front part of the speaker is directly exposed to the room.
"The product arrived in fine shape - thank you so much for restoring the tape - I was surprised it came out as well as it did. The voice was my grandfather's from 48 years ago, 1962. He is long gone now but I remember the Christmas gathering rather well. Many memories came back in a rush."