The Sterndale Singers are beginning rehearsals for their concert performance on Saturday, July 8 at St Mark's Church in Broomhill.
The centrepiece of the concert will be the singers' performance of Spem in Alium by Elizabethan era composer Thomas Tallis.
It's a long and complex piece of music. It's hard for the singers to even hold the sheet music.
"The copy itself is about 70cm high," musical director Robert Webb said.
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The seven-and-a-half minute piece will sound stunning on the night.
"It's designed so that, if the choir stands in a circle, the music starts on one side and moves to the other," Mr Webb said.
The number 40 is synonymous with the event, and the song.
It's a 40-part motet and the choir will be 40 years old.
"The last time I conducted it was on my 40th birthday," Mr Webb said.
The singers' numbers will expand from 36 to about 90 on the night, to tackle all the parts of the piece.
Some former members will return to sing with the choir.
The singers will also perform I Was Glad, Five Spirituals and Four Shakespeare Songs on the night.
Mr Webb said the approaching milestone was 'quite exciting' for the singers.
The choir, formed in 1977, and has grown significantly over the years.
"It used to be quite a lot smaller," Mr Webb said.
He described it as 'a group of people getting together to sing for fun'.
They perform regular concerts every year, and members also travel to France to sing.
The choir is named after Sheffield born 19th century composer Sir William Sterndale Bennett.
He was one of 'few' English-born composers, Mr Webb said.
William went on to become Professor of Music at Cambridge University. The singers celebrated the 200th anniversary of their namesake's birth, April 13, 1816, last year.
Mr Webb is the sixth musical director of the choir. He has been involved since 2004.
Arthur Robson and Vivien Fisher served in the role from 1977-1982.
They were followed by James Wild (1982-1992), Jill Wild (1992-1998) and Richard Roddis (1999-2004).
Tickets for the upcoming concert are £10 in advance or £12 on the door.
To buy one, visit the website at www.sterndalesingers.co.uk and follow the links.