Sound in Collective Housing: Part 1 - Floor Impact Sound

Today, I heard that a management committee meeting will be held at "Kouzou-kun"'s house on the 3rd floor of the apartment building behind us. According to Kouzou-kun, several noise complaints have been brought to the management committee by residents between the upper and lower floors. The noise from the people on the upper floor is said to be very loud for those on the lower floor, and they are arguing about how to resolve this complaint.
Dad works at a company that measures noise and vibration, right? Even though the apartments are separated by thick concrete walls between rooms and between floors, why is such loud noise still transmitted? What can be done to prevent such sounds? Please tell me a little.

The space where I, Oto, and Kouzou-kun, along with many others, live every day can be broadly categorized into homes, schools, workplaces, and the external environments that connect them, such as roads and parks. People always wish to be in a comfortable environment, no matter what space they are in. Especially in homes where one seeks tranquility, it is understandable to desire a quiet environment free from unpleasant noise. This is particularly true for students who want to concentrate on studying; if voices, music, or clattering sounds from outside enter their rooms, it can be distracting and hinder their focus. Even in our house, when my older brother plays the stereo on the second floor, you complain to him about the noise. Our house is a small single-family home, but in a multi-family dwelling like an apartment, where many families live separately, there can be different noise issues due to the shared walls and floors. Recently, a common issue has been floor impact noise, which might also apply to Kouzou-kun's apartment.

Hmm, it's not good because my brother plays the stereo at a really loud volume.
So, what is that sound of impact on the floor??

Floor impact noise refers to the sounds heard on the lower floor when objects are dropped or children run or jump on the upper floor. Sounds like the scraping or moving of chairs, or the high-pitched sounds made when light, hard objects like spoons or coins are dropped from a height, are generally referred to as lightweight floor impact noise. On the other hand, the heavy sounds like thuds or crashes made when children or toddlers jump off chairs or sofas are called heavyweight floor impact noise. Among these two types of impact noise, lightweight floor impact noise tends to be particularly problematic with flooring materials that are increasingly used as finishing materials in apartments. The recent increase in rooms with flooring instead of tatami mats is a significant cause of this issue. It seems that Kouzou's apartment also has many rooms with flooring. In such cases, it is possible to mitigate the noise by partially laying carpets, changing slippers to ones that do not make noise, or attaching cushioning materials to the legs of chairs. However, for heavyweight floor impact noise, the performance is largely determined by the specifications of the concrete floor slab, such as its thickness, the area surrounded by beams, and the type of floor slab. Additionally, a method called raised flooring is used, where supports are placed in the structure to create a space between the finished floor and the slab for utility piping, but this can sometimes reduce sound insulation performance compared to just using the floor slab. It gets a bit complicated, but simply put, heavyweight impact noise is determined by the design plans when constructing a building. Therefore, addressing this issue is difficult. The best solution is for the people on the upper and lower floors to communicate well and be careful not to make loud noises. The ideal situation is to become friends; after all, friends are more likely to listen to each other's requests.

Shall we be friends?
But, isn't there a more specific measure for this?

Impact noise from the floor can clearly be divided between the people on the upper and lower floors, making it difficult to find a compromise since each side feels they are 100% affected. If they are family, one might ask for a little patience, but sound is a sensory experience, and the level of discomfort varies from person to person. Even the same person can be affected by their condition or mood, making it quite troublesome. However, recently, as issues with such noise in apartments have increased, standards regarding sound have been established and are now being displayed. This is referred to as sound insulation ratings, which classify how difficult it is for sound to travel. The impact noise from the floor is also defined by an L+number rating, where a smaller number after L indicates a higher sound insulation rating and a structure that transmits sound less easily. However, this is not a solution. While this numerical rating is useful for those looking to purchase an apartment, it is not helpful once the purchase has been made. Since this apartment where Kozo-kun lives is not newly built, it likely did not have this L value rating displayed. Apartments are communities where many families live, so we must prioritize coexistence, meaning we should all be considerate of each other and make small efforts to accommodate one another.

I'll ask Kouzou-kun what happened tomorrow.
Maybe I'll tell him about today's story too.