Conclusion: The approach of "sealing door gaps with tape" is a great choice—it’s highly cost-effective and provides immediate results. However, it’s difficult to "halve" sound leakage with 100-yen items alone; a combination with professional items is necessary.
Late-night Discord or game streaming. For those who are worried because “my parents told me my voice is too loud,” the easiest soundproofing measure you can take is “door gap tape.”
It is actually much more effective to “seal the gaps in the door” than to stick felt all over the walls or buy soundproof curtains.
From a pro’s perspective, we will explain the effect of this “gap sealing” and the hacks to make it even more powerful.
1. Why is “Sealing Gaps” the Right Move?#
Sound Leaks Like “Water”#
Sound (air vibration) has properties similar to water. Even if you are inside a solid concrete wall (a thick cup), if there is a tiny hole (gap) at the bottom, water will leak out vigorously.
In modern Japanese housing (24-hour ventilation systems), a gap of about 1cm called an “undercut” is always provided under the door to circulate air. Furthermore, there are gaps of several millimeters on the hinge side of the door frame and the latch side of the lock.
In other words, no matter how quietly you try to speak in the center of the room, your voice is leaking out to the living room through the “door gap” passage.
2. Effect of 100-Yen Gap Tape (The -7dB Wall)#
Let’s try sticking “gap filling tape (sponge material)” that you can buy at 100-yen shops (Daiso, Seria, etc.) all around the door frame and in the gap at the bottom.
Actual Measurement Data#
According to actual measurement data using a sound level meter, the effect of sticking sponge tape from a 100-yen shop on a door that has nothing done to it is only a reduction of about -7dB (decibels).
- The feel of -7dB: You feel like “Oh? Maybe the sound got a little smaller?”
The human ear only feels that the sound has been “reduced by about half (halved)” when the sound decreases by -10dB. In other words, 100-yen sponge tape alone is slightly insufficient to “halve” sound leakage.
3. Hacks (Secrets) to “Halve or More” Sound Leakage#
The weakness of 100-yen sponge tape is that it is “light and easy for air to pass through (low density).” If you seriously want to halve sound leakage (-10dB or more), you need to combine the following three items (or use professional products).
[Hack 1] Use Professional Gap Tape Like “Tokyo Bouon”#
The most reliable way is not to use 100-yen sponge tape, but to invest several hundred to a thousand yen to use professional high-density gap tape (made of EPDM rubber, etc.) such as “Tokyo Bouon” or “Nitoms.”
Since it completely seals the gap with the “elasticity of rubber” rather than sponge, the sound insulation is significantly improved.
[Hack 2] Double Up with a “Draft Stopper” Under the Door#
For the undercut under the door, where sound leakage is the most intense, sound insulation effect will double by using a “plug-in type draft stopper (twin draft guard)” that you insert under the door, in addition to sticking sponge on one side.
[Hack 3] Make the Door “Heavy” (Sandwich Method)#
The ultimate hack to further increase the soundproofing effect after completely sealing the gaps is to stick “heavy soundproof sheets” and “sound-absorbing materials” on the door panel itself.
By turning the thin board of a door into a “thick soundproof wall,” complaints from your family will drastically decrease.