The convention couldn’t sound less rock-and-roll — the National Association of Music Merchants Show. But when the doors open at the Anaheim Convention Center, people stream in to scour rows of Fenders, Les Pauls and the oddball, custom-built creations such as the 5-foot-4-inch mermaid guitar crafted of 15 kinds of wood.

Standing in the center of the biggest, six-string candy store in the United States, you can almost believe all is well within the guitar world.

Except if, like George Gruhn, you know better. The 71-year-old Nashville dealer has sold guitars to Eric Clapton, Neil Young, Paul McCartney and Taylor Swift. Walking through NAMM with Gruhn is like shadowing Bill Belichick at the NFL Scouting Combine. There is great love for the product and great skepticism. What others might see as a boom — the seemingly endless line of manufacturers showcasing instruments — Gruhn sees as two trains on a collision course.

“There are more makers now than ever before in the history of the instrument, but the market is not growing,” Gruhn says in a voice that flutters between a groan and a grumble. “I’m not all doomsday, but this — this is not sustainable.”

The numbers back him up. In the past decade, electric guitar sales have plummeted, from about 1.5 million sold annually to just over 1 million. The two biggest companies, Gibson and Fender, are in debt, and a third, PRS Guitars, had to cut staff and expand production of cheaper guitars. In April, Moody’s downgraded Guitar Center, the largest chain retailer, as it faces $1.6 billion in debt. And at Sweetwater.com, the online retailer, a brand-new, interest-free Fender can be had for as little as $8 a month.

What worries Gruhn is not simply that profits are down. That happens in business. He’s concerned by the “why” behind the sales decline. When he opened his store 46 years ago, everyone wanted to be a guitar god, inspired by the men who roamed the concert stage, including Clapton, Jeff Beck, Jimi Hendrix, Carlos Santana and Jimmy Page. Now those boomers are retiring, downsizing and adjusting to fixed incomes. They’re looking to shed, not add to, their collections, and the younger generation isn’t stepping in to replace them.

Gruhn knows why.

“What we need is guitar heroes,” he says.

He is asked about Clapton, who himself recently downsized his collection. Gruhn sold 29 of his guitars.

“Eric Clapton is my age,” he says.

How about Creed’s Mark Tremonti, Joe Bonamassa, John Mayer? He shakes his head.

“John Mayer?” he asks. “You don’t see a bunch of kids emulating John Mayer and listening to him and wanting to pick up a guitar because of him.”

Guitar heroes. They arrived with the first wave of rock-and-roll. Chuck Berry duckwalking across the big screen. Scotty Moore’s reverb-soaked Gibson on Elvis’s Sun records. Link Wray, with his biker cool, blasting through “Rumble” in 1958.

That instrumental wasn’t a technical feat. It required just four chords. But four chords were enough for Jimmy Page.

“That was something that had so much profound attitude to it,” Page told Jack White and the Edge in the 2009 documentary “It Might Get Loud.”

The ’60s brought a wave of white blues — Clapton, Jeff Beck, Keith Richards — as well as the theatrics of the guitar-smashing Pete Townshend and the sonic revolutionary Hendrix.

McCartney saw Hendrix play at the Bag O’Nails club in London in 1967. He thinks back on those days fondly and, in his sets today, picks up a left-handed Les Paul to jam through Hendrix’s “Foxy Lady.”

“The electric guitar was new and fascinatingly exciting in a period before Jimi and immediately after,” the former Beatle says wistfully in a recent interview. “So you got loads of great players emulating guys like B.B. King and Buddy Guy, and you had a few generations there.”

He pauses.

“Now, it’s more electronic music and kids listen differently,” McCartney says. “They don’t have guitar heroes like you and I did.”

Nirvana was huge when the Black Keys’ Dan Auerbach, 38, was growing up.

“And everybody wanted a guitar,” he says. “This is not surprising. It has to do with what’s in the Top 20.”

Living Colour’s Vernon Reid agrees but also speaks to a larger shift. He remembers being inspired when he heard Santana on the radio. “There was a culture of guitar playing, and music was central,” adds Reid, 58. “A record would come out and you would hear about that record, and you would make the journey. There was a certain investment in time and resources.”

Lita Ford, also 58, remembers curling up on the couch one night in 1977 to watch Cheap Trick on “Don Kirshner’s Rock Concert.” She was 19 and her band, the Runaways, had played gigs with them.

“It was just a different world,” Ford says. “There was ‘Don Kirshner’s Rock Concert,’ Ed Sullivan, Dick Clark, and they would have one band on and you would wait all week to see who that band was going to be. And you could talk about it all week long with your friends — ‘Saturday night, Deep Purple’s going to be on, what are they going to play?’ — and then everybody’s around the TV like you’re watching a football game.”

By the ’80s, when Ford went solo and cracked the Top 40, she became one of the few female guitar heroes on a playlist packed with men, including Stevie Ray Vaughan, Joe Satriani and Eddie Van Halen.

Guitar culture was pervasive, whether in movie houses (“Karate Kid” Ralph Macchio outdueling Steve Vai in the 1986 movie “Crossroads”; Michael J. Fox playing a blistering solo in “Back to the Future” and co-starring with Joan Jett in 1987’s rock-band drama “Light of Day”) or on MTV and the older, concert films featuring the Who and Led Zeppelin on seemingly endless repeats.

But there were already hints of the change to come, of the evolutions in music technology that would eventually compete with the guitar. In 1979, Tascam’s Portastudio 144 arrived on the market, allowing anybody with a microphone and a patch cord to record with multiple tracks. (Bruce Springsteen used a Portastudio for 1982’s “Nebraska.”) In 1981, Oberheim introduced the DMX drum machine, revolutionizing hip-hop.

So instead of Hendrix or Santana, Linkin Park’s Brad Delson drew his inspiration from Run-DMC’s “Raising Hell,” the crossover smash released in 1986. Delson, whose band recently landed atop the charts with an album notably light on guitar, doesn’t look at the leap from ax men to DJs as a bad thing.

“Music is music,” he says. “These guys are all musical heroes, whatever cool instrument they play. And today, they’re gravitating toward programming beats on an Ableton. I don’t think that’s any less creative as playing bass. I’m open to the evolution as it unfolds. Musical genius is musical genius. It just takes different forms.”

Tell that to Guitar Center, now $1.6 billion in debt and so fearful of publicity that a spokeswoman would only make an executive available for an interview on one condition: “He cannot discuss financials or politics under any circumstances.” (No thanks.)

Richard Ash, the chief executive of Sam Ash, the largest chain of family-owned music stores in the country, isn’t afraid to state the obvious.

“Our customers are getting older, and they’re going to be gone soon,” he says.

Over the past three years, Gibson’s annual revenue has fallen from $2.1 billion to $1.7 billion, according to data gathered by Music Trades magazine. The company’s 2014 purchase of Philips’s audio division for $135 million led to debt — how much, the company won’t say — and a Moody’s downgrading last year. Fender, which had to abandon a public offering in 2012, has fallen from $675 million in revenue to $545 million. It has cut its debt in recent years, but it remains at $100 million.

[How much did this guitar story cost me? $2, 376.99.]

And starting in 2010, the industry witnessed a milestone that would have been unthinkable during the hair-metal era: Acoustic models began to outsell electric.

Still, the leaders of Gibson, Fender and PRS say they have not given up.

“The death of the guitar, to paraphrase Mark Twain, is greatly exaggerated,” says Fender’s chief executive, Andy Mooney.

He says that the company has a strategy designed to reach millennials. The key, Mooney says, is to get more beginners to stick with an instrument they often abandon within a year. To that end, in July the company will launch a subscription-based service it says will change the way new guitarists learn to play through a series of online tools.

Paul Reed Smith, the Maryland-based guitar designer, says the industry is just now recovering from the recession that struck in 2009. He points to PRS’s sustained revenue — the company says they’re between $42 million and $45 million a year — and an increased demand for guitars.

“This is a very complicated mix of economy versus market, demand versus what products are they putting out, versus are their products as good as they used to be, versus what’s going on with the Internet, versus how are the big-box stores dealing with what’s going on,” Smith says. “But I’ll tell you this: You put a magic guitar in a case and ship it to a dealer, it will sell.”

Then there’s Henry Juszkiewicz, the biggest and most controversial of the music instrument moguls. When he and a partner bought Gibson in 1986, for just $5 million, the onetime giant was dying.

[Behind the scenes: how we got paid to set a guitar on fire]

“It was a failed company that had an iconic name, but it really was on its last legs,” Ash says. “[Juszkiewicz] completely revived the Gibson line.”

Juszkiewicz, 64, is known for being temperamental, ultracompetitive and difficult to work for. A former Gibson staffer recalls a company retreat in Las Vegas punctuated by a trip to a shooting range, where executives shot up a Fender Stratocaster. In recent years, Juszkiewicz has made two major pushes, both seemingly aimed at expanding a company when a product itself — the guitar — has shown a limited ability to grow its market.

In 2014, he acquired Philips’s audio division to add headphones, speakers and digital recorders to Gibson’s brand. The idea, Juszkiewicz says, is to recast Gibson from a guitar company to a consumer electronics company.

There’s also the line of self-tuning “robot” guitars that Gibson spent more than a decade and millions of dollars developing. In 2015, Juszkiewicz made the feature standard on most new guitars. Sales dropped so dramatically, as players and collectors questioned the added cost and value, that Gibson told dealers to slash prices. The company then abandoned making self-tuners a standard feature. You can still buy them — they call them “G Force” — but they’re now simply an add-on option.

Journey’s Neal Schon says he battled with Juszkiewicz when he served as a consultant to Gibson.

“I was trying to help Henry and shoo him away from areas that he was spending a whole lot of money in,” Schon says. “All this electronical, robot crap. I told him, point blank, ‘What you’re doing, Roland and other companies are light-years in front of you, you’ve got this whole building you’ve designated to be working on this synth guitar. I’ve played it. And it just doesn’t work.’ And he refused to believe that.”

Juszkiewicz says that one day, the self-tuning guitars will be recognized as a great innovation, comparing them with the advent of the television remote control. He also believes in the Philips purchase. Eventually, he says, the acquisition will be recognized as the right decision.

“Everything we do is about music,” Juszkiewicz says. “It doesn’t matter whether it’s the making of music with instruments or the listening of music with a player. To me, we’re a music company. That’s what I want to be. And I want to be number one. And, you know, nobody else seems to be applying for the job right now.”

If there is a singular question in the guitar industry, it’s no different from what drives Apple. How do you get the product into a teenager’s hands? And once it’s there, how do you get them to fall in love with it?

Fender’s trying through lessons and a slew of online tools (Fender Tune, Fender Tone, Fender Riffstation). The Music Experience, a Florida-based company, has recruited PRS, Fender, Gibson and other companies to set up tents at festivals for people to try out guitars. There is also School of Rock, which has almost 200 branches across the country.

On a Friday night in Watertown, Mass., practice is just getting started.

Joe Pessia runs the board and coaches the band. He’s 47, a guitarist who once played in a band with Extreme’s Nuno Bettencourt and has worked at School of Rock since 2008.

Watching practice, it’s easy to understand why.

With Pessia presiding, the school’s showcase group blasts through three songs released decades before any of them were born.

The Cars’ “Bye Bye Love” blends quirky, new-wave keyboards and barre chords. Journey’s “Stone in Love” is classic ’80s arena rock punctuated by Schon’s melodic guitar line. Matt Martin, a 17-year-old guitarist wearing white sneakers, jeans and a House of Blues T-shirt, takes the lead on this.

The band’s other Stratocaster is played by Mena Lemos, a 15-year-old sophomore. She takes on Rush’s “The Spirit of Radio.”

As they play, the teenagers dance, laugh and work to get the songs right. Their parents are also happy. Arezou Lemos, Mena’s mother, sees a daughter who is confident and has two sets of friends — the kids at School of Rock and her peers at Newton South High School.

“There are a lot of not-easy times that they go through as teenagers,” she says, “and having music in her life, it’s been a savior.”

Julie Martin says her son Matt was a quiet boy who played in Little League but never connected with sports. She and her husband bought him his first guitar when he was 6.

“It was immediate,” she says. “He could play right away. It gave him confidence, in the immediate, and I think long term it helps him in every aspect of his life.”

She remembers her own childhood in working-class Boston.

“I know exactly what he could be out doing,” Martin says. “That enters my mind. We are so lucky to have found School of Rock. He’s there Thursday, Friday and Saturday every week, all year.”

Rush’s prog-metal is not for beginners, with its time shifts and reggae twist.

“They’ve never played this before,” Pessia says, turning to whisper in awe. “The first time.”

So who are these kids? The future? An aberration?

It’s hard to know. But Matt Martin didn’t need to think long about why he wanted to play a Strat as a kid.

“Eric Clapton,” he says. “He’s my number one.”

To Phillip McKnight, a 42-year-old guitarist and former music store owner in Arizona, the spread of School of Rock isn’t surprising.

He carved out space for guitar lessons shortly after opening his music store in a strip mall in 2005. The sideline began to grow, and eventually, he founded the McKnight Music Academy. As it grew, from two rooms to eight, from 25 students to 250, McKnight noticed a curious development.

Around 2012, the gender mix of his student base shifted dramatically. The eight to 12 girls taking lessons jumped to 27 to 59 to 119, eventually outnumbering the boys. Why? He asked them.

Taylor Swift.

Nobody would confuse the pop star’s chops with Bonnie Raitt’s. But she does play a guitar.

Andy Mooney, the Fender CEO, calls Swift “the most influential guitarist of recent years.”

“I don’t think that young girls looked at Taylor and said, ‘I’m really impressed by the way she plays G major arpeggios.’ ” Mooney says. “They liked how she looked, and they wanted to emulate her.”

When McKnight launched a video series on YouTube, he did an episode called “Is Taylor Swift the next Eddie Van Halen?” He wasn’t talking about technique. He was talking about inspiring younger players. The video series, in the end, grew faster than guitar sales or lessons. Earlier this year, McKnight shut down his store.

The videos? He’ll keep doing them. They’re making money.