TOKYO -- In Japan, the social penalties for upsetting the neighbors can be harsh. But there are some people who sing, play music or yell at the top of their lungs day or night without worrying about the people next door or on the floor below.

Why? Because their units are soundproof. These days, demand for sonically insulated rooms is no longer limited to musicians and other noisy professionals. Ordinary folks who don't want to tiptoe around are also snapping up such dwellings as the COVID-19 pandemic encourages people to spend more time at home.

"F---!!!," shouts a 32-year-old company employee in his apartment nearly every night as he streams his gaming exploits on YouTube. "Whenever I get hit by an enemy I yell, even at midnight," he says.

The man lives in a room in a soundproof building called a "musision," a portmanteau of "music" and "mansion" -- a slang term for a large apartment or condominium building in Japan.

Livlan, a Tokyo real estate developer, has been marketing soundproof dwellings to musicians since 2000. The company has a total of 727 units in 30 buildings in the Tokyo metropolitan area, including 14 buildings that went up after 2020.

Livlan has been aggressively constructing such buildings since the outbreak of COVID-19. Although rents are around 30% higher for a soundproof unit than for a conventional dwelling of comparable size and location, Livlan has 2,800 people on the waiting list to move in, it says.

The degree of soundproofing a space has is measured by its "D-value." The higher the number, the better insulated it is against noise leaks. The Architectural Institute of Japan recommends a D value of 50 for an apartment, and designates it as "especially soundproof" if it is 55 or higher. Almost all units in soundproofed buildings have a D values over 70; some go as high as 85.

The 32-year-old gamer moved into his soundproof unit in September 2022, nudged out of his previous residence by complaints from his next door neighbor. He put up noise-muffling curtains at his old place and had his friend shout loudly, trying to determine whether the noise was audible outside. "You know, I didn't dare ask my neighbor for permission to check the noise from my room," he said. Cautiously, he began to stream his gaming activities. But one day he started getting complaints about the noise and eventually decided to change apartments.

Some streamers install a soundproof booth in their rooms, but the man decided to move out because, he says, "I didn't want to stream my game-playing from a small booth. Now I can yell out loud without any hesitation."

Hosomi is a voice teacher who works out of his home. He also posts his own music on YouTube. He is a man devoted to his art, saying, "I keep streaming my favorite music and videos at full blast," even when not at work.

But for people living behind their own blissful wall of sound, a question arises: What to do when the delivery person rings the doorbell?

Yuko Toguchi, a spokesperson for Livlan, answers, "A light shines."

Some soundproof apartments have a switch that turns on an indoor light when the intercom is pushed. This allows residents to focus on their sonic passions without missing visitors.

Where did musicians live before soundproof apartments and condos came along? Hiroko Yamakawa, a saxophonist, said she used to live in a multiunit building where tenants had a tacit understanding: "You may play your instrument, but you should be patient if a neighbor makes noises," she says. Many of the tenants were music college students.

The market for soundproof dwellings was once limited to musicians and a few other sound specialists. But demand has increased among ordinary residents as the pandemic kept people at home. The number of people considering buying homes for reasons of sound insulation has jumped 80% compared with the pre-pandemic era, according to a survey by housing information website Lifull Home's.

Real estate developers, spying an opportunity, want to meet this growing demand. Tokyo-based Ascot completed its first soundproof apartment building in the capital last year. "People are spending time at home in a variety of ways, and that has created such needs as being able to work from home without being disturbed by ambient noise," a representative of the company says. The building's 14 units found takers immediately, and Ascot plans to construct two more soundproof buildings in 2024.

Daiwa House Industry in April began offering soundproof rooms called Oto no Jiyuku ("Free Sound Zone") for single-family homes. So far, it has installed them in more than 20 newly built homes. They can also be installed in existing homes.