Steve Cotterill and Town have thus far added only midfielder Jordan Shipley to their ranks during the close season – though Caldwell has highlighted a lack of incoming movement across League One generally.
Some supporters have raised the current size of the Town squad with players returning to Sundorne for pre-season training on Monday, but the CEO revealed the daily hard work from Cotterill and head of recruitment Keith Burt has seen a couple of deals speed up over the last 24 hours.
Caldwell said: "There's a lot going on behind the scenes. The League One transfer window has been really slow for some reason.
"I did an analysis and there were roughly 30 players signed, an average of 1.3 per club, which was remarkably slow, when 140 had left clubs since last season.
"I think there's going to be a lot of business done between now and the start of the season on July 30, there's a lot of things going on.
"Steve and Keith are never off the phone, to each other, targets, agents, truing to make sure we build the squad.
"There's a couple of things on the go which have moved quite far forward in the last 24 hours but it's an ever-changing market and we need to make sure we get these over the line to get the squad and players Steve wants."
Caldwell highlighted the academy progress that has seen several youngsters sign professional deals in recent weeks, including goalkeeper duo Jaden Bevan and Xander Parke, as well as defender Kade Craig and midfielder Josh Barlow.
He also referenced the development of Tom Bloxham, who aged just 18 is still 'just a kid'.
The Town chief added: "It's massively important, the work David Longwell and all his staff are putting into the academy is starting to bear fruit.
"We're starting to say players coming through, getting professional contracts, it's so important for a club like Shrewsbury. We've seen for example Tom Bloxham doing well last season. He's still just a kid really at 18 but he's burst on to the first-team scene.
"It's so important we augment our team with as many players from the academy as possible."