“This is easily the most complicated instrument humans ever invented,” declared Old South Church associate organist George Sargeant. He gestured to the tall wooden pipes standing at either side of the church’s sanctuary. “If someone wants to disagree, they can take it up with me.”
Sargeant was referring to the pipe organ broadly, but as organs go, the instrument at Old South isn’t what anyone would call simple. From the wood organ console in the nave of the church, the organist can call on any number of over 100 sounds, created by more than 7,000 pipes. The smallest of these are thinner than a pencil, the largest several stories high and wide enough to drop an average-size watermelon in, should one want to make a very expensive mess.
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The keyboard might look like a piano’s, but unlike a piano, the volume entirely depends on which stops are pulled out and therefore how much air is coming through the pipes, so it doesn’t make a difference how hard you press the keys. And that’s not even getting into the pedals — laid out like a piano keyboard, but played with the feet.
The organ is “insanely complicated until you get used to it,” said Mitchell Crawford, minister of music at Old South. But “once you learn it, it’s like riding a bike.”
The holiday season is one of the busiest times of the year for organists like Sargeant and Crawford. “After Thanksgiving, until First Night, it’s just —” Crawford spread his hands out to indicate a full calendar.
However, for curious listeners, this also means it’s one of the easiest times to hear these instruments sounding off live.

And you should hear them live, said organist Louise Mundinger in an interview at a Malden cafe. No two organs, or spaces where the organs live, are the same. It is possible to “get an idea” of an instrument’s sound from a recording, she said. But the spatial aspect is what really makes the experience special.
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“I don’t understand why people don’t like the sound of the organ. A good organ has such a presence,” she said. “It’s like hot fudge without the sin. It just gets your soul.”
When Mundinger moved to Boston from Minnesota in the 1980s to study at New England Conservatory with renowned organ pedagogue Yuko Hayashi, the organs made the city feel ”like a candy store,” she said. “It still is.”
Part of that is because of the city’s history with the instrument, she said. According to the Boston Organ Studio, the city was home to the first church organ in the American colonies, circa 1714. Some of the most well-regarded organ builders in American history have called the Boston area home, including 19th-century titan E. and G.G. Hook & Hastings; Skinner, which later merged to become Aeolian-Skinner; and CB Fisk, still based in Gloucester.
The sheer variety was another factor. During the decades in which Mundinger taught at Milton Academy, she served as a substitute organist in local churches, and played instruments ranging from small mechanical (tracker) organs to massive electro-pneumatic constructions, each with its own character and personality.
“The organs themselves are sentient in many ways,” said Mundinger, now director of music at St. Paul’s Cathedral in Boston. “The one I’m playing right now needs work, but the pipes are 150 years old, and they’re so sweet.”
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Significant amounts of specialized work are necessary to keep the city’s organs in shape. In late October, organ builder and technician Stefan Maier visited Old North Church in the North End to tune the church’s stately tracker organ. It was his 100th service of that organ since 2000, give or take a few.
“Seasonal changes do affect these instruments, and so they will go out of tune as a result of humidity and temperature changes, and that needs to be corrected,” said Maier, who squeezes into a cramped chamber inside the organ to tune it.

The Old North organ perches in the church’s rear balcony and contains between 1,500 and 2,000 pipes, but Maier only tunes the reed pipes, which represent about a tenth of those. Those pipes, which make sound with a brass reed, actually aren’t too sensitive to temperature, Maier explained. The sensitive ones are the flue pipes, which don’t have moving parts and operate much as a whistle does, sounding one pitch when air moves through them.
“What we actually do is we cheat,” he said with a smile. “We adjust the stable ones to the hundreds of others that do move.”
The organ’s wooden case dates to 1759, when it was commissioned from builder Thomas Johnson, but much of the organ has been replaced, restored, and rebuilt to varying degrees over the centuries. In one major overhaul, a new organ built by Vermont-based A. David Moore was placed inside the historic case, with a maker’s plaque announcing “Opus 20 1992″ on the console.
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When an organ does relocate, it’s usually a complicated process. Old South’s 1921 Skinner electro-pneumatic organ, which arrived in the early 1980s, was initially built for the Municipal Auditorium in St. Paul, Minn., which sat thousands. However, along with the building, it fell into disrepair. Weeks before the structure was razed with the organ still inside it, Old South (which seats a comfortable 800) bought the massive instrument and set about restoring it, installing pipework at both the front and rear of the sanctuary.
Now, its surround sound can be heard during worship services, concerts, and Boston’s First Night celebrations on New Year’s Eve, as the church hosts demonstrations of the instrument and pops concerts.
“This is a visceral organ because it’s so large,” Crawford said. “It can be felt tangibly.” When the instrument is in full cry, the floor vibrates and the air seems to shimmer.

In 2008, construction work on the Copley MBTA station caused a large crack on the Dartmouth Street side of the church, directly behind the organ. The building was deemed safe for occupation, said organ technician and Old South church member Sean O’Donnell, but there were concerns about whether playing the organ might cause showers of debris to rain down on the instrument, so it went silent for several months.
“Even after it was safe to play, the middle section was gone for quite a while,” said O’Donnell. “The then-organist Harry Huff was in despair of how he was going to have services with that much organ gone. I reminded him that he had gone from the third-largest organ in Boston to the seventh-largest with those pipes missing, and there was still enough to get by!”
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The largest organ in Boston can be found at the First Church of Christ, Scientist on Massachusetts Avenue, where a 1952 Aeolian-Skinner organ stretches across the front wall of the domed sanctuary. The imposing console, which controls upward of 200 sets of reeds and more than 13,000 pipes, sits in a pit behind a high railing near the front of the church.
“It’s like sitting in the cockpit of an airplane,” said the church’s organist Bryan Ashley.

With the flip of a switch on the console, a motor in a nearby room starts up, and the leviathan audibly stirs to life. Ashley mostly performs French romantic, German baroque, and British music, but every two months, a visiting organist slides onto the bench for the church’s Pipes on the Plaza lunchtime concert series. Guest players come from as close as the local area and as far away as Germany. The next is scheduled for Dec. 12, with organist Katelyn Emerson.
But one need not be an established name to take a seat on the bench, said Ashley. Anytime an interested musician reaches out to him, he tries to arrange a visit. “Sometimes after service, kids will come up and the parents will say, ‘Can we see the organ?’ And I’ll park them on the bench and let them play it,” he said. “I know how much it marked me when people would be like, ‘You can look but can’t touch.’” But when he visited family in Boston as a teenager, then-organist Thomas Richner would “turn him loose” on that same organ.
“It was pretty exciting. I mean, it was terrifying,” he said. “I remember not being able to get through a piece because it was so overwhelming.”

PIPES ON THE PLAZA Dec. 12. Featuring Katelyn Emerson. First Church of Christ, Scientist. www.christianscience.com/find-us/visit-the-mother-church
FIRST NIGHT Dec. 31. Details TBD. Old South Church.
A.Z. Madonna can be reached at az.madonna@globe.com. Follow her @knitandlisten.