集合住宅の音 その2 空気音と固体音
Oto-kun
I told Kouzou about the 'floor impact noise' story that I learned from my dad. It turns out that this floor impact noise was indeed the main topic at Kouzou's condominium management meeting. However, they didn't reach a conclusion, so it will be carried over to the next meeting. I also talked to Kouzou about community matters, and it seems that in the meeting, they discussed not only the floor impact noise but also the sounds from washing machines and vacuum cleaners.
father
In an apartment, sounds from other units can surprisingly be heard from outside. Sounds from washing machines, vacuum cleaners, toilet drainage, and ventilation fans, for example. Sounds can be broadly categorized into two types: one is sound that travels through the air, like voices, television sounds, and stereo sounds, which is called "airborne sound." The other type is sound (vibration) that travels through solid materials like concrete and plumbing, which is referred to as "structure-borne sound." It can be hard to imagine sound traveling through concrete, but for instance, when there is construction work nearby at a school, have you ever experienced hearing loud noises like "giri giri" or "gaa"? This is because the vibrations (small tremors) from machines pouring concrete or drilling holes travel through the concrete and ground, reaching the classroom, and are heard as "sound" from the walls and ceiling.
Structure-borne sound is a complex term, but it essentially means that the original sound travels as vibrations, and ultimately, the classroom's ceiling and walls vibrate, resulting in the sound we hear. Such sounds are called "radiated sound." That "radiated sound" then travels through the air as "airborne sound" and finally reaches everyone's ears in the classroom.
Structure-borne sound is a complex term, but it essentially means that the original sound travels as vibrations, and ultimately, the classroom's ceiling and walls vibrate, resulting in the sound we hear. Such sounds are called "radiated sound." That "radiated sound" then travels through the air as "airborne sound" and finally reaches everyone's ears in the classroom.
Oto-kun
So, the 'floor impact noise' you mentioned the other day is the same as what we're talking about now, right?
father
Exactly. The "vibration" from jumping heavily on the upper floor is transmitted through the flooring (wooden floor finishing material) and concrete (floor slab) as "solid sound," and is radiated from the ceiling, which is what is being heard.
Oto-kun
So, are the sounds of the washing machine and the vacuum cleaner the same?
father
That's right. Since the washing machine's feet are on the floor, when it vibrates significantly during the spin cycle, it adds vibrations to the floor (excitation), which can be transmitted through the floor as 'solid sound.' However, both the washing machine and the vacuum cleaner not only generate vibrations but also produce sound within the room they are used in. This is transmitted as 'air sound.' But 'air sound' diminishes considerably when blocked by walls or floors, so I think it's quite rare for it to be transmitted to the neighboring unit as 'air sound.' The sound from the television, unless it is very loud, is also unlikely to be heard from the neighboring unit.
Oto-kun
Oh, right, it seems that the sound of the toilet drainage was also an issue in yesterday's meeting.
father
This is also a problem of 'solid sound.' The sound of toilet drainage can sometimes be heard as a 'splash' on the lower floor when the drainage sound from the upper floor flows through the pipes (wastewater vertical pipes) that penetrate the floors of different levels. The sound of flowing water inside the pipes is transmitted as 'solid sound' to the supports that hold the pipes and to the concrete that encases the pipes, which then radiates from walls and other surfaces in a similar manner.
Oto-kun
I see, there are various types of 'solid sound' within the apartment, and compared to 'air sound' like television or conversation, they often become problematic.
father
That's right. An apartment building is a large structure where the floors, walls, and plumbing are connected to other units, so solid sound, in particular, tends to be a problem.
Oto-kun
Is there no way to prevent solid sounds from being heard?
father
We talked about how to deal with floor impact noise by attaching soft materials like felt to the legs of chairs or partially laying carpets, right? For heavy floor impact noise, there's nothing we can do but avoid jumping around.
Also, for washing machines and vacuum cleaners, the first thing is to avoid using them during late night or early morning hours.
Also, for washing machines and vacuum cleaners, the first thing is to avoid using them during late night or early morning hours.
Oto-kun
Is it because that time is quiet?
father
That's right. Talking about the relationship between noise and quietness would take a long time, so I'll explain it in detail another time, but during the day and evening, there are quite a few sounds from outside, like car noises and television sounds, which make the noise level inside the room surprisingly high.
Oto-kun
Noise level?
father
In simple terms, it represents the loudness of sounds that humans can hear in levels. In a place with a high noise level, other sounds may not be heard. When you try to listen properly, you would say, 'Shh, be quiet!' It's the same thing.
Oto-kun
I see, during late night or early morning hours, there are fewer cars and the television is off, so the noise level is low and sounds coming from outside can be heard well.
father
Well, regarding the washing machine, you can use anti-vibration rubber under its feet to prevent vibrations from being transmitted. However, not all anti-vibration rubber is effective, and it's necessary to choose the appropriate type based on the weight of the washing machine. Plumbing vibrations can also be addressed with anti-vibration measures. This is a design issue, and once the building is completed, it can be very costly to carry out renovation work.
Oto-kun
I see, I understand well. But, isn't there a time when you don't know where the sound is coming from?
father
Solid noise, apart from what we've just talked about, has many causes that have become noise problems, such as elevators, automatic doors opening and closing, kitchen exhaust fans, equipment in machine rooms, pump rooms, toilet usage sounds, parking lots, and walking on steel stairs. Therefore, in many cases, it is difficult to understand where the sound is coming from and what is causing the noise without measuring vibrations or noise from the rooms where noise is a problem.
First of all, living in an apartment means that we have to assume that such noise exists to some extent. And since apartments are shared by many families who live with concrete floors, walls, and plumbing, we need to be careful about the time of day and make efforts not to create noise for each other.
First of all, living in an apartment means that we have to assume that such noise exists to some extent. And since apartments are shared by many families who live with concrete floors, walls, and plumbing, we need to be careful about the time of day and make efforts not to create noise for each other.