Tracy Hart, 25, and her friend Claire Gibbons, 21, shouted the word "quiet," reaching 120.1 decibels at Earls Court - setting the new world record for the loudest duet.
The previous Guinness world record for the loudest duet was 119.6 decibels.
Guinness World Records also recognized the world record for the loudest burp by a female: 107.0 db, achieved by Elisa Cagnoni (Italy).
According to Guinness World Records, the loudest burp by a male is 109.9 db, achieved by Paul Hunn (UK) at Butlins, Bognor Regis, UK.
Tracy, from South Woodham Ferrers, attended the Events and Party Hire Exhibition to promote her prop company, Bespoke Props, in Burnham, when people from the Guinness World Records were stopping passers-by to try and break the record.
Tracy said: "I was not going to go in for it at first because I thought there was no way I could beat some of the men who were taking part.
"When we won I thought it was a joke, but then they said it was going to be written into the newest edition of the book, and we were so excited."
She brought along her adult cheer leading troupe, set up in 2010, where Claire from Greenwich is a member and who have already won three trophies at national level.
When asking when Tracy finds the time, her m said: "I think when you are passionate about other what you do work just doesn't seem like a chore at all.
"My mum has made me really driven as she is amazing with what she does, which probably makes me want to succeed that little bit more."