If there were a "Saturday Night Live" skit that sums up Kevin Roberts' life, it would have to be The Loud Family.
"My family is full of loud talkers," says the 42-year-old author and educational consultant from Detroit. He jokes, "My mother sneezes so loudly that children in the neighborhood congregate around the house waiting for one.
"I do a lot of public speaking and don't use a microphone, even if I'm talking to 400 people. And whenever I get together with my brother, we're out of hand. Everybody shushes us. We just have booming voices."
Roberts' sister, on the other hand, has her volume set to low.
"My older sister compensates," he says. "She has a first grade subdued teacher voice. She's more of a soft talker."
While loud talkers and soft talkers may seem like the stuff of "Seinfeld," researchers have actually pinpointed why some of us are constantly shushed while others struggle to be heard.
"There are four different factors," says Dr. Amee Shah, director of the speech acoustics and perception laboratory at Cleveland State University. "There's a biological component, a pathological component, a personality component and a cultural component."
Sometimes, loud or soft voices are simply based on the way we're built, Shah explains.
"It can be mechanical," she says. "Everybody is born with a different size larynx and vocal cords within that. Also, some may have smaller lungs and can't generate enough airflow to have a louder voice."
Pathologically speaking, the volume of a person's voice can be due to changes in the tissue or vibration rate of the vocal cords.
"As we age, our tissue atrophies," says Shah. "The vocal cords don't vibrate as fast. Or there could be other things, such as the person is a lifelong smoker or they have vocal nodules or polyps. All those things can contribute to a softer voice."
Personality can play a part in the loud voice-soft voice smackdown, as well (just check out the difference between the "Super Bass" singing cousins Sophia Grace and Rosie in this viral video).
"Some people may be shy and withdrawn and inhibited," says Shah. "They may not be comfortable in a social situation, they may not be a good speaker. This is where some of the examples from 'Seinfeld' come in -- the low talkers or the people who like to mumble. Psychologically, they're not able to project their voices loud enough."
Even culture can affect how loudly (or softly) we talk, says Shah.
"Certain cultures prevent or inhibit loud talking, especially if you're a woman," she says. "There are pragmatic reasons why someone may not make direct eye contact and not project their voice loud enough."
As to whether loud talking is genetic, Shah says it's more about environment.
"At the family level, it's more of a mental influence," she says. "If it's a large family, everybody learns that to be heard, you have to speak up. It's more sociological."
But growing up around a bunch of loud talkers can have the opposite effect, she says, as with Roberts' soft-talking sister.
"Sometimes, if a father or older brother is louder, a sibling might tend to be more withdrawn," she says.
There is good news for soft talkers longing to be heard, though, says Shah.
"You can definitely train yourself to talk louder," she says, pointing to various methods such as using the respiratory control more efficiently, learning to work your optimal pitch so you're not wasting air flow, taking deeper breaths, hydrating yourself more often, and doing yoga.
"All of these give you more projection," she says.
As for talking softer, Shah says that's much more difficult.
"Most of the time, people aren't aware they're doing it," she says. "They may not think they're loud unless somebody tells them. A lot of the time, people focus on content and don't think about delivery."
Are you naturally quiet -- or does your voice seem to be permanently set at the highest possible volume? Got any theories why you're that way?