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HOME > Ono Sokki's Patio > Air-borne-sound and structure-borne-sound |
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Ken: I told Jim what you told me about the floor impact sound the other day. He said that in the meeting of home-management-association, the floor impact sound was the main topic as we had thought. But it was not solved so far and to be continued until the next meeting. I also told him about the community. He also said that there were talks about the sound of washing machines and cleaners besides floor impact sound.
Dad: In a condominium, it sometimes happens that the sound
from neighbors is heard much louder than expected, especially such as
sound from washing machines, cleaners, restroom drainage and exhaust
fans. There are roughly two kinds of sound. One is called
“air-borne-sound”, such as talking voice and sound from TV/stereo set,
which travel through air. The other is called “structure-borne sound”,
which travels through concrete mass and water ducts. It is hard to
imagine a sound traveling through concrete mass but will you remind of
an experience at school for instance that you heard loud noise when a
construction is nearby? The vibration(slight fluctuation) when casting
concrete or drilling travels through concrete mass or ground to your
classroom and is felt as a sound mediating walls or ceilings. Though the
word “structure-borne- sound” is very difficult to understand, it is a
resultant of vibration through ceilings and walls which has originally
been a sound. This is called “sound radiation”. The sound travels as
air-borne-sound through air and reach you all in the classroom finally. Ken: Then, the floor impact sound you told me at the last time is the same kind as this, isn’t it? Dad: Yes, you are right. The vibration caused by jumping up and down on the above floor travels through wooden floor or concrete slab as structure-borne sound and can be heard radiating from ceiling. Ken: Are the sound of washing machines or cleaners same as above? Dad: Yes. A washing machine has legs on the floor and when it vibrates loudly in dehydrating, the vibration is provided with the floor and it travels as structure-borne-sound through the floor. But the washing machine or cleaner makes not only vibration but also sound in a room where it is placed. This is conveyed as air-borne-sound. But it becomes a very little when it is blocked by floors or walls. So it does hardly travel to the neighbor’s house as air-borne-sound. The sound of TV set doesn’t come from the neighbor’s unless its sound is so loud. Ken: By the way, Jim said that the sound of drainage in restroom was also a topic in the meeting yesterday. Dad: It is also the problem concerning “structure-borne sound”. When the drainage comes from the upstairs, the watering sound can be heard on the floor below because the duct (pipe for miscellaneous water) penetrates those floors vertically. The watering sound travels through the duct as structure-borne-sound and radiates from walls mediating the support which holds up the duct or concrete with duct buried within. Ken: I see. There are several kinds of structure-borne-sound in a condominium and comparing to air-borne-sound such as TV sound or talking voice, it goes often to be a problem. Dad: Yes, it does. It easily becomes a problem because a condominium is a massive building and the floors, walls and ducts are commonly used among multi rooms and houses. Ken: Are there any solution that you can feel free from the structure-borne sound? Dad: I told you the other day that cushioning such as carpeting partially, or put a cushion on the foot of a chair can erase the floor impact sound. Floor impact sound (heavy impact sources) can be avoided only by not jumping up or down. Talking about the sound of washing machines and cleaners, it is the best way not to make them use early in the morning or late at night. Ken: Is it because it is the time to be quiet around? Dad: Yes, it is. I will tell you another day in future about the relation between noise and quietness because it needs a long time for explanation. At this moment, shortly speaking, there are unexpectedly large amount of level of noise in a room during day time till evening because there are various kinds of noise, such as TVs and vehicles outside etc. Ken: The level of noise? Dad: To make it simple, the sound you hear is classified by a certain level. If a sound comes in a room where there is high level of noise already, you may not hear the sound which comes from outside. When you listen to what you want, you say “Be quiet!” to others. This is it. Ken: I see. You can hear clearly a sound from outside when there is only a low level of noise in a room in the early morning or at night with less cars outside or no TVs. Dad: Yeah. Talking of washing machines, you can take measures by putting a rubber cushion on foot of it to reduce or stop the transmission of the vibration. But make sure that any rubber cushion does not always work and you need to choose appropriated one depending on the weight of the machine. The pipe vibration can be also avoided, but only handled while design stage and it will cost a huge amount after being built. Ken: I understand. But doesn’t it happen that the source of the sound is not to be found? Dad: Such varieties of source of structure-borne sound as elevator, working of automatic doors, kitchen ventilation fan, equipment of machine room, pump room, restroom, parking area, and walking on the steel stairs are those of many examples which have come to be a problem on top of the sources explained so far. It often happens that you can find the source of the noise only after measuring the vibration or the noise. When you live in a condominium, you must presuppose that such a noise exist to an extent. You keep it in your mind that you need to be aware of not making noise considering time as there are a lot of families live in separated only by concrete slabs, walls and sharing pipes with each other.
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