Plymouth-based Miracle-Ear, which says it sells America’s most popular hearing aid, is turning up the volume for its Italian parent, Amplifon.

Moreover, the Twin Cities hearing aid trade, which boasts several firms, appears to be growing thanks to aging baby boomers who need hearing help, powerful digital products and the willingness of some health insurers to cover at least some of the cost.

“The technology has evolved and become smaller, more powerful and affordable,” said Pablo Hoyos, Miracle-Ear’s regional manager. “Our franchisees determine the retail price, but the average price of many products is between $2,500 and $5,000. We can always find a solution. And we have technology that allows you to stream sound from your TV or cellphone through a small programmer.’’

Hoyos said last week that Miracle-Ear plans to add six stores in the Twin Cities area, bringing the total to 16 stores.

Through Miracle-Ear, formerly known as Amplifon USA, there are about 400 local employees at the Plymouth headquarters and manufacturing complex, and another 2,250 who work at 1,200 corporate and franchise stores around the country.

In the first quarter, Milan-based Amplifon reported operating earnings of about $23 million on revenue of about $246 million, a decline of about 3 percent from 2012 first-quarter revenue, thanks to the economic slowdown in Europe, Amplifon’s biggest market, and flat sales in the Asia-Pacific region.

But the company’s Plymouth-based North American operations saw first-quarter revenue increase 11 percent to about $45 million. Amplifon termed its North American results “brilliant growth.”

Amplifon’s North American revenue grew 14 percent last year while overall revenue grew only 2 percent to about $1.1 billion.

Anne Gowen, Miracle-Ear’s marketing director, said the Plymouth manufacturing operations may expand from two to three shifts daily if demand continues to grow.

Kendra Klemme, a spokeswoman for Eden Prairie-based Starkey Hearing Technologies, said Starkey is the only U.S.-based outfit among the world’s six largest hearing aid manufacturers. Starkey employs about 3,500 employees around the globe. The other five are based in Europe.

Klemme declined to disclose the revenue of privately held ­Starkey, which was founded in 1967.

Switzerland-based Unitron, another hearing aid maker, two years ago completed an expanded headquarters and manufacturing center in Plymouth that cost $3 million and employs more than 200.

Amplifon says it’s the largest retailer of hearing instruments around the globe. Gowen said U.S. growth is challenged a bit because there are not enough salespeople being certified to sell hearing products.

“We’re reaping the benefit of baby boomers starting to age into our demographic,” Gowen said. “Typically, it takes a person five to seven years to have their hearing tested. And with people starting to work longer in their careers, well, they need to be able to hear.”

Amplifon USA sells its products through its Miracle-Ear retail network and also through Elite, a member-based network of independent retailers.

The late Ken Dahlberg, who started Dahlberg Electronics in 1948, was considered the father of Miracle-Ear when his company produced the first electronic hearing aid designed to be worn in the ear in 1955.

The company was acquired for $139 million in 1993 by Bausch & Lomb, which sold it to Amplifon in 1999 for an undisclosed amount after Bausch decided to focus on eye products. Miracle-Ear shrank under Bausch: Revenue fell below $90 million and the parent company wrote down the value of Miracle-Ear.

That’s the same Plymouth-based Miracle-Ear that’s now the growth engine inside Amplifon.