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Ken: Can we find the source of the noise by measuring the vibration or the noise?

Dad: We judge it by measuring the sound with the frequency characteristic (level of high or low-tone sound), amplitude of the vibration or sound intensity which tells direction of noise. In addition, it requires actually experience of people on site who investigate. But cases are that even if a well experienced consultant or engineer measures it on site, they can not identify the source. Undefined sound that mass media reports recently is brought up as a unnatural phenomenon due to its unknown source but it often is caused by natural phenomenon and trouble of equipment inside building or opening and closing of doors or “FUSUMA” (Japanese style sliding doors with wall paper on its surface).

Ken: What kind of natural phenomenon becomes the source of the undefined sound?

Dad: Window sash making a sound by its expansion and contraction caused by direct sunlight, or squeak noise, whistle noise by wind or wind roar around balcony are the source sound caused by atmospheric phenomena.

Ken: Well, if there is gap in a sash in a windy day, you can hear hurtling sound. Do you call it whistle noise?

Dad: You are correct. Those are not heard depending on a wind direction or strength of wind and such an uncertainty make you feel uneasy. Once you find the cause of the noise in a condominium or a house called undefined sound, you can often solve the problem even though it still exists.

Ken: When you hear a noise whose cause is identifiable, such as wind or direct sunlight, you find yourself feel relaxed. Does it used to be a noise called undefined sound in the long ago?

Dad: No, it doesn’t. It was not a problem in the past. One of the reasons is that because of people’s living in a house including a condominium with an air tight and high insulation place recently. The air tightness decreasing sounds from outside makes people hear mere sounds inside which were not remarkable before.

Ken: Does it mean that you need to take another measure for the newly sensible sounds though you have got to be free from noise outside?

Dad: Yeah, even though you try to be away from noise with sound insulation technique blocking unfavorable sounds, you get a new sensible sound one after another. It is possible to be more uncomfortable even if the noise level which I explained before goes lower. For example, there is a case that in an apartment where you always hear traffic noise slightly because of closeness to an arterial highway, you are able to be free from such annoying noise as equipment noise inside. Traffic noise is not so uncomfortable than we consider, because it consists of comparatively well-mixed high-tone noise and low one and you hear it in a uniform level. Of course, it depends on a level of noise, not to mention… A sound becoming unheard because of a different kind of sound is called “masking”, which I will tell you later on.

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