Please bear with me while I digress into physics for a bit.
There is a category of physical effect known as an "inverse-square law". One occurs when energy starts at a point and radiates outward in all directions. A good example is a candle on a table: The light and heat goes out from the flame in all directions, initially. When an inverse-square law applies, the amount of energy at a point is based on the inverse of the distance to the energy source, squared. This means that doubling the distance between an observer and the energy source divides the amount of energy that reaches the observer by four. The reason for this, for the curious, is that the energy outputted by such a source can be viewed as if it is distributed on the surface of a sphere, with the radius of the sphere being the distance between the source and the observer. As the distance increases, the same energy must cover a larger area, and therefore there is less energy per point, and the surface area of a sphere depends on its radius squared.
By this point you're probably wondering why I'm bringing this up in a blog about handbells. At least, I hope you are; if you already know why then this will be a rather boring paragraph for you. Sound waves, such as those generated by handbells, are governed by an inverse-square law. When one rings a bell, it emits energy, in the form of sound waves, in all directions. Now, imagine that you have a few hundred ringers filling a room. The difference in the distances between one choir and the audience and a different choir and the audience can get quite significant, and ringers must account for this. In other words, a choir farther away from the audience is harder to hear, and therefore should play louder. Given the size of the room we're playing in, the difference can be huge.
Choirs near the back of the room, incidentally, have another disadvantage. In handbell ringing, as in all ensemble music, it is very important to stay synchronized with the other players. In massed ringing, this is even more the case, because not only do you have to stay synchronized with your own choir, but with many other choirs as well. This is why there is a conductor: He or she indicates key points in the music with his or her baton, and if people watch him or her, this allows them to ensure that they are at the same point in the music as everyone else. Music is divided into measures, which are divided into beats; a measure is typically a few seconds, and there are usually three or four beats per measure, though there can be more or sometimes fewer. The beats are what the conductor indicates, so as long as you know what measure you are in you could synchronize yourself about once every two seconds. (Not knowing what measure you are in is called "being lost" and is a bad idea.) The problem, of course, is that choirs at the back have to look over the heads of those in front to see the conductor.
Speaking of conductors, the Japanese girls' choir immediately behind us apparently usually plays without one. Every day, a few choirs give performances to the others by themselves. The choir in question did not have a conductor, but instead relied on each other. At any given point one ringer would probably be playing a repeating pattern for a few measures; the other ringers would look at that ringer and use her notes to stay synchronized. They can do this because they have their music memorized. It's incredibly impressive.
About equally impressive was the solo ringer who played on Tuesday. English handbells only ring if played in a certain direction; playing one sideways or backwards produces no sound. This is used in various ringing techniques, such as "four-in-hand" or the "Shelly grip", which allows one to hold two bells in one hand. The common techniques are to place both bells in different directions, or to place them so that one may be rung with the other rotating instead of moving. Getting four bells in two hands can be difficult, and doing it at high speeds is fairly advanced. This man had four bells in each hand, and the song he performed was not exactly slow. His performance was impressive. Actually, there are just a lot of impressive people here. It's pretty awesome.