Satellite Radio growth less starry.

The Stern effect may be wearing off.

Satellite radio subscribership is leveling off, at least among fans of rock radio, according to a new study by Jacobs Media.

About 12% of rockers now subscribe to XM, Sirius or both services, which is the same number as in 2006.

Intent to buy is actually down. Only 9% of those who have not subscribed to either service say that they are very likely to in the next 12 months, down from 12% in the 2006 study.

Men and 30-to-39-year-olds are most apt to be satellite radio customers.

These numbers indicate that rock-format radio listeners are less likely to be satellite’s best customers going forward. That makes sense since they have been strong adopters so far; those inclined to buy have largely already done so. This is especially true of Howard Stern fans, who signed on to Sirius in droves, and say that the show is the main reason they still subscribe.

Satellite radio growth is leveling off among the general population, although about five million new listeners are signing on every year, according to Oppenheimer & Co. The level growth is a sign of a maturing market, but it’s a bad atmosphere for XM and Sirius in which to compete for subscribers.

Other results of the Jacobs study indicated that most satellite radio is closely tied to cars. Three-fourths of subscribing respondents listen to satellite radio in a vehicle, while 44% listen at home. One-fourth tune in during at-work hours, while 12% listen on a portable device.

Satellite radio listeners are generally very happy with their service, with 71% rating their satisfaction as a four or five on a five-point scale. This is down slightly from prior years, but is still at a level most companies would relish.

As for the proposed merger between XM and Sirius, about a third feel it will make no difference, while an additional third say they don’t know enough about the details to say. About one-fourth think it will be a good thing, while one in 10 have concerns.

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