Noise in apartment buildings, Part 1: Impact noise from floors

Today, the residents' association is having a meeting at the apartment of "Kozo-kun," who lives on the 3rd floor of the apartment building behind ours. According to Kozo-kun, there have been several noise complaints brought to the association between residents on the upper and lower floors. The noise from the people on the upper floors is very loud for the people on the lower floors, and they are arguing about how to resolve these complaints.
Dad, you work at a company where you measure noise and vibration, right? In an apartment building, there are thick concrete walls separating the rooms and the floors above and below, so why do such loud noises still get through? What can be done to block out these noises? Please tell me.

Many people, including myself, Oto, and Kozo, live in spaces that can be broadly categorized into homes, schools, workplaces, and external environments such as roads or parks that connect them. And no matter what space we're in, we always want a comfortable environment. Especially in homes where we seek peace and tranquility, it's understandable that we want to live in a quiet environment free from unpleasant noises. This is especially true for students preparing for exams; they want to concentrate on their studies, but if they hear people talking, records playing, or rattling noises from outside coming into their room, and they hear things they don't want to hear, it will be distracting and make it difficult to concentrate. Even in our house, when your older brother puts on the stereo on the second floor, you complain to him that it's too loud, right? We live in a small detached house, but in apartment buildings where many families live separately, the noise can be a different problem than in detached houses because you're only separated from your neighbor by a wall or floor. I've been hearing a lot about impact noise from floors lately, and I think that's probably what's happening in Kozo's apartment.

Hmm, it's because my brother blasts the stereo really loud.
So, what exactly is floor impact noise?

Floor impact noise refers to the sounds heard on the floor below when something is dropped on the floor above, or when children run or jump. Sounds like the rattling and banging of chairs being moved on the floor above, or the high-pitched clanging or banging sound when light, hard objects like spoons or coins are dropped from a certain height, are generally called lightweight floor impact noise. On the other hand, the heavy thuds and crashes that occur when children or toddlers jump off chairs or sofas are called heavy floor impact noise. Of these two types of impact noise, lightweight floor impact noise seems to be a particular problem with flooring materials, which are increasingly used as flooring materials in apartments these days. A major reason for this is that the number of rooms with flooring has been increasing in place of tatami mats. I bet there are a lot of rooms with flooring in Kozo's apartment too. In these cases, you can relatively easily mitigate the noise by partially laying carpet, changing to slippers that don't make a flapping sound, or attaching cushioning material to chair legs. However, in the case of heavy impact noise, the performance is almost entirely determined by the specifications and thickness of the concrete floor slab, the area enclosed by beams, and the type of floor slab. Also, because it is used as a space to house equipment piping, a construction method called a raised floor is used, where posts are erected on the structure, creating a space between them and the finished floor. In this case, the sound-blocking performance may be lower compared to a floor slab alone. It's getting a little complicated, but simply put, heavy impact noise is determined from the beginning by the design drawings when the building is constructed. For this reason, it is difficult to take countermeasures. I think the best thing to do is for the people on the upper floor and lower floor to talk to each other and be careful not to make loud noises. The best thing to do is to become friends with them. Even noise will listen to a friend's request. Besides, it's easier to ask a friend for a favor, isn't it?

Shall we be friends?
But isn't there a better solution?

Floor impact noise is a problem because it's clearly divided between the person on the upper floor and the person on the lower floor who is the source of the noise and the person who receives it, making it difficult to find a compromise where both sides are equally affected. If it were family, you could ask them to be patient for a little while, but that's not the case here. Also, sound is subjective, so the level at which people find it unpleasant varies, and even the same person is affected by their physical condition and mood, making it quite troublesome. However, recently, because these noise problems in condominiums have been increasing, standards for sound have been established and are now being displayed, although this isn't exactly a countermeasure. It's called a sound insulation rating, and it's now being displayed by rating how difficult it is for sound to be transmitted. Floor impact noise is also defined by an L + numerical rating, and the smaller the number after L, the higher the sound insulation rating, meaning the condominium has a structure that makes it difficult for sound to be transmitted. However, this is not a countermeasure. It's a useful numerical rating for people who are going to buy a condominium, but it's not so useful once you've bought it. Kozo and this apartment building weren't built recently, so I doubt they had this L-value rating system back then. An apartment building is a community where many families live, so we have no choice but to prioritize coexistence—living together—and be considerate of each other little by little.

I'll ask Kozo what happened tomorrow.
I think I'll tell you about what happened today too.