Sunday, in their showdown with the Rams at CenturyLink Field, the salutary effect of their home-field advantage will be part of the referendum, along with supremacy in the NFC West.

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The Seahawks have had some of their vaunted mystique picked apart and diminished in recent times.

The Legion of Boom is depleted by injury, and the running game that once oozed the aura of Marshawn Lynch is now a revolving crew of underwhelming choices.

Steadfast through it all, however, has been one last bastion of near-magical mystique: the power of the 12s. The Seahawks have won at home with more frequency than any other team except New England since 2012 (they are tied with the Patriots with a 38-8 record over that span), and make it each season’s mission to secure as many home playoff games as possible.

Yet on Sunday, in their showdown with the Rams at CenturyLink Field, the salutary effect of their home-field advantage will be part of the referendum, along with supremacy in the NFC West.

“I know the place is going to be crazy and wild for it, and we’re going to be the same way,’’ coach Pete Carroll said on Friday.

The Seahawks have already lost two home games this year, to Washington on Nov. 5 and to Atlanta on Nov. 20. A third would tie them for the most home losses since Carroll took over.

The Rams would seem to be a team susceptible to the beneficial aspects of CenturyLink, which is centered around the disruptive effect of 60,000-plus fans screaming their heads off in a stadium engineered acoustically for maximum eardrum penetration.

We all know the history of the 12s in their full-throated glory. At least twice, they have raised a big enough ruckus at Century Link to cause documented seismic activity: during Lynch’s famed “Beast Quake” run in the wild-card round against the Saints in 2011, and this season, on Oct. 29, when Jimmy Graham caught a game-winning touchdown pass against Houston with 21 seconds remaining.

The 161 false-start penalties by opponents in Seattle since 2005 are the most in football, and that doesn’t even take into account the delay-of-game penalties caused by the din (which twice reached decibel levels high enough — 131.9 and 136.6 — to break Guinness World Records in 2013) or plays that get off on time yet are messed up by communication issues.

After the New York Giants committed 11 false-start penalties in a 2005 playoff game at CenturyLink (then called Qwest Field) and Seattle won on a field goal, Seahawks coach Mike Holm­gren dedicated the game ball to the fans. And the Giants asked the league to investigate if the Seahawks were piping in artificial noise, a common suspicion of opponents who have the noise ringing in their ears.

A young quarterback like Los Angeles’ Jared Goff without much big-game experience, and with little experience in Seattle, will have to show he can withstand the sensory overload. It might have gotten to Carson Wentz a few weeks ago in a huge Seattle victory over the rampaging Eagles.

Goff also will be facing a Seahawks team that held him to his lowest completion percentage of the season (46.8) in a 16-10 Rams loss in L.A. in early October, with two interceptions.

The Seahawks have lost Cliff Avril, Richard Sherman, Kam Chancellor and possibly linebackers Bobby Wagner and K.J. Wright to injury since that game. And Goff has shown himself to be one of the rising young quarterback stars in the league, leading the upstart Rams to a 9-4 record that leads the division.

But it will be interesting to see how Goff handles the noise at CenturyLink considering the importance the Rams put on helmet-headset communication between coach Sean McVay and Goff. They like to get the team to the line quickly so McVay can call audibles for Goff at the line of scrimmage during the 25-second window that coaches are allowed to communicate with their QB. With 15 seconds left on the play clock, the headset by rule must go silent, and the quarterback is on his own.

Earlier this year, Goff told reporters that he rarely changed the play after getting the skinny from McVay.

“Not too often, no,’’ he said. “Most of the time, he calls the play and he knows what he’s talking about, so I let him do it. But there’s plenty of times where it gets below 15 and we have to ad-lib a little bit.”

If the CenturyLink crowd can drown out McVay, and force more ad-libbing, that would no doubt complicate things further for the Rams. In his CenturyLink debut last year, Goff had a more traditional complication delivered to him by Sherman in a 24-3 Seattle victory. Sprinting for the corner of the end zone late in the game, Goff was tackled so hard by Sherman he had to go into concussion protocol.

“He looked like he was setting up to take a dive into the end zone for a touchdown,’’ Sherman said after the game, “and we don’t give free meals, so he had to feel it.”

Carroll said earlier this week that Goff was “more in the survival mode” last year, and that he’s advanced far beyond that this season.

The Seahawks hope to make Goff and the Rams feel the heat like they did at CenturyLink last season — and feel the noise as well. The mystique is on the line.