Pharrell William (left) and Enrique Iglesias
Frazer Harrison/Getty; Jordan Strauss/WireImage
10/12/2011 at 11:00 AM EDT
They survived boot camp but can they make it on the home front?
The X Factor
's 32 remaining contestants
are heading to the homes of Simon Cowell
, Paula Abdul
, Nicole Scherzinger and L.A. Reid this week to work closely with the judges ... and their surprise star guests.
Pharrell Williams and Enrique Inglesias are two of music's heavy hitters who will help the hopeful vocalists on Wednesday night's show (FOX, 8 p.m. ET) before they face another round of elimination on the road to The X Factor
's live shows. Rihanna
and Mariah Carey
, who was Cowell's choice for the gig
, will also act as guest judges in the latest round of competition.
"The acts were totally blown away meeting their mentors at these amazing homes – then it was even more nerve-racking performing for a guest judge," a source tells PEOPLE. "Some of the girls especially were delighted when they saw Enrique and Pharrell. The acts who met Rihanna were totally speechless – who knows how they managed to sing!"
The 32 contestants who are divided into four groups – girls, boys, groups and singers over 30 – will be cut down to 16 after visits to the judges' homes, with only four from each category moving on to the live shows. The judges and their star guests will make the decisions together.
"Enrique has sold over 100 million records and there's nothing Pharrell doesn't know how to do in music. He's a solo artist and he's in a group, a writer, producer. That's massive pressure on these acts," the source says. "Pharrell was a tough guest. He knew exactly the uniqueness he was looking for."
With reporting by LIZ MCNEIL