Noise in apartment buildings, part 3: Sound insulation of window frames

So, if you don't know where the noise is coming from, can you find out by measuring the vibration and noise levels?

We measure the frequency characteristics of the sound being produced (levels of high and low frequencies), the magnitude of the vibrations, and sound intensity (which can determine the direction from which the sound is coming) to make a judgment, but in reality, the on-site experience of the person conducting the investigation is also necessary. However, there are cases where even veteran consultants and engineers cannot figure it out after on-site measurements and investigations. The "ghost sounds" that have been reported in the media recently are treated as paranormal phenomena because their cause is unknown, but in reality, most of them are caused by natural phenomena, malfunctions in equipment inside the building, or the sounds of doors and sliding screens opening and closing.

What natural phenomena can cause ghost sounds?

Sounds caused by weather include window frames expanding and contracting due to temperature changes from sunlight, creaking and whistling caused by wind, and wind noises on balcony railings.

Speaking of which, on windy days, if there's a small gap in the window, you sometimes hear a whistling sound, right? Is that called a "whistling" sound?

That's right. The whistling and the sound of wind rushing against the railing can be unsettling because they come and go depending on the wind direction and strength, making it difficult to pinpoint the cause. In many cases, even if the sound doesn't completely disappear, the problem of noises in apartments and houses, sometimes called "ghost noises," can be solved once the cause is identified.

Even if you actually hear a sound, it's reassuring to know the cause, like it's because the wind is blowing or because of direct sunlight. But have ghost sounds always existed?

It wasn't much of a problem in the past. Modern houses, including apartments, are highly airtight and well-insulated, meaning the airtightness of the interior is much higher, so outside noise doesn't get in as much. This has likely made sounds from inside buildings, which weren't noticeable before, more audible, which is one reason why noise has become more noticeable.

Now that the outside noise is blocked out, and the sounds from inside are suddenly so noticeable, does that mean we have to take some more measures?

That's right. Even if you use soundproofing technology to block out sounds you don't want to hear, other sounds will just keep popping up. So, even if the noise level is lower, as we discussed earlier, it can actually become more unpleasant. For example, in a room near a main road where road noise is constantly faintly audible, that noise might actually mask unpleasant sounds from the building's equipment and machinery. Road noise includes a range of frequencies, from relatively low to high, and is heard at a fairly consistent level, so it's not necessarily a particularly unpleasant sound. Of course, it depends on the noise level, though.
This phenomenon, where the presence of one type of sound makes it harder to hear another, is called "masking," and I'll explain masking in more detail next time.