Round 4 of the “secret” negotiations is over. Round 5 is coming soon — perhaps to a suburban locale near you.

NFL owners and players met for the second straight day in Hull, Mass., 18 miles south of Boston, as they attempt to close in on a collective bargaining agreement.

“The players and owners were here over the last two days,” Commissioner Roger Goodell said Thursday as he stood next to DeMaurice Smith, the head of the players association. “(Smith) and I were here for the entire meetings also. And it’s complicated and it’s complex, but we’re working hard and we understand the fans’ frustration.

“But I think both of us feel strongly that we’re going to continue to work hard at it.”

A league statement said the sides will have more meetings. Those talks are expected next week; in the last four weeks, the owners and players have met outside of Chicago and New York and on the Maryland shore before heading to New England.

Among those at the meetings were owners John Mara of the New York Giants, Jerry Richardson of the Carolina Panthers, Clark Hunt of the Kansas City Chiefs, Robert Kraft of the New England Patriots and Dean Spanos of the San Diego Chargers.

Smith was there along with several players, including Jeff Saturday of the Indianapolis Colts, Tony Richardson of the New York Jets and Domonique Foxworth of the Baltimore Ravens.

“Someone asked me whether I was optimistic,” Smith said. “I think we’re both optimistic when we have the right people in the room.

“We know we’re talking about the right issues and that we’re working hard to get it done.”

The latest talks took place at Nantasket Beach Resort and ended late Thursday afternoon.

The sides have exchanged proposals on a variety of issues. The main topic has been how to divide revenues — $9.3 billion last year — and league owners were briefed this week on a plan that would give the players just under 50 percent of total income. An off-the-top expense credit of about $1 billion that went to the owners would be eliminated.

Also being discussed are a rookie wage scale and a more specific breakdown of benefits for retired players.

A lengthy new CBA — between six and eight years, for example — would enable the league to negotiate more lucrative contracts with its broadcast partners.

“It is extremely complicated, it requires a lot of hard work by a lot of people, but we’re committed to getting something done and we’re going to keep working at it,” Smith said.

One item that has the players’ support is a salary floor keeping teams within 90 percent of the cap. Recently, particularly in 2010 when there was no cap, several teams whose revenue streams don’t match up with the richer clubs did not spend near what those teams did.

The proposal would require the full salary cap spending to be in cash.

“Through our player reps, things sound really good,” Rams wide receiver Mark Clayton said. “From the players’ perspective, we’re kind of set with what we want.

“We pretty much agreed to what our (players association) was fighting for on our behalf. It sounds like a lot of what we asked for, apart from the finances, they’ve been able to agree upon. At that point, we’re just kind of waiting to get the final say-so and just roll it out “