The Dolan family, which founded Cablevision Systems, raised its offer to take the company private to $30 a share from the $27 a share they originally bid in October.

Cablevision stock fell 73 cents to $28.87 Friday morning after the new offer was announced as some analysts and investors questioned whether the price was high enough.

In a letter to a special committee set up by the Cablevision board of directors to evaluate the offer, the Dolans, led by company chairman Charles F. Dolan and CEO James l. Dolan, called the new proposal its “best and final offer” and in order to expedite a decision, said the offer would expire at the close of business on Jan. 17. “The ongoing uncertainty created by this process is potentially harmful to the company,” the letter said.

Cablevision had no comment on the new offer.

“The Dolan family’s revised ‘best and final’ take-private offer of $30 per share remains no better than market multiples for cable,” said Craig Moffett of Bernstein Research in a report Friday morning. “It is unclear whether the offer will be deemed sufficient.”

(In a release, the Dolans said that their original offer in October was 25.4 percent above the share price.)

Richard Greenfield, an analyst at Pali Capital, said “We believe the special committee will reject the Dolan offer.” In his report Friday morning, entitled “Do not let Chuck and Jim Dolan steal CVC,” Mr. Greenfield said he valued the company at $33.50 a share, adding that “We continue to believe that CVC deserves a valuation premium to its industry peers” partly because of the likelihood of a Time Warner Cable takeover attempt within the next 12 to 18 months.