Asked to explain why the talent contest's ratings have been dropping, the coach suggested that viewers are unable to get to know the hopefuls well as there are so many of them.
According to the Daily Mail, the Script frontman said: "When it hits the live shows you have 40 people to try and get to know, which is really hard.
"We're still trying to get to know who they are, and I think when it breaks down to about eight, it will start to get really palatable."
He also conceded that the show's gentler approach on its contestants "doesn't make for good TV".
While The Voice UK struggled in the ratings against fellow reality show Britain's Got Talent, it was the most-watched programme on TV last Saturday (May 12).
However, BBC One boss Danny Cohen has said that he isn't concerned by the drop in viewers from a high of 10.7m to around 6.6m.
The Voice UK continues tonight (May 19) on BBC One at 6.30pm.