One of the reasons why people are so scared of science these days is that technology has become more inexplicable, and somehow more “black box”. Fifty years ago, with a bit of practise and a good grounding in school science, you could fix your car and understand how your radio works. You wouldn’t stand a chance these days, but it was not ever thus: Japanese War Tubas, only a few decades ago, were the very pinnacle of modern technology, and your best bet for locating an enemy in the distance, or in the dark (that’s Hirohito on the right).
At first these devices just look like hearing trumpets, with a pretty obvious mechanism of action.
But there’s actually much more to them than that. Like other pre-radar acoustic location devices, they cunningly exploit and hack the acoustic location hardware you already have in your own ears and brain.
We can locate objects with our ears, using the difference in volume between our left and right ear, but more important is the time delay between the sound hitting one ear and then hitting the other. This is possible because sound travels so incredibly slowly, only 330 metres (or 1000 feet) per second. Thinking out loud, that means sound travels one foot in one millisecond, so if your ears are about six inches apart, the sound coming from your right will hit your right ear about half a millisecond before it hits your left ear. A millisecond is quite a long time: in a piece of music, for example, you can spot notes that are only a few milliseconds out as being in the wrong place.
So these devices amplify the incoming sounds, but also, because the collection horns are placed much wider apart than your ears are (on either side of your head) they also increase the difference in arrival time between each ear. This, as well as the amplified volume, would help you to become more accurate in locating far off objects.
My guess is it would probably take a while for your auditory cortex to re-callibrate and get used to the wider gap, and the greater difference in arrival times, so you’d need plenty of practise.
Consequently, the designers had to make their apparatus as stylish as possible.
Nicely spotted by the excellent Athanasius Kircher Society. I have Grade 5 Tuba and I still put it on my CV.