Sirius XM Radio (NASDAQ:SIRI) announced the results of a favorable Arbitron study of satellite-radio subscribers this morning, and the results suggest that the platform may be more popular than you think.

The study found that 35 million adult listeners tune in to Sirius or XM, with 32 million of them checking in at least weekly. This figure is nearly double the service's 18.5 million subscribers.

The news shouldn't be surprising, though. No one assumed that Sirius XM's user base consisted of 18.5 million lone drivers. Folks carpool, couples date, and home-based receivers aren't necessarily shackled to headphones. Just as entire households benefit from a single cable subscription, the same logic follows for satellite radio.

Satellite radio's dissemination is a mixed blessing for Sirius XM. If 18.5 million subscriptions are enough to reach 35 million listeners, maybe the ceiling is closer than Sirius XM bulls think.

I prefer to take a more optimistic view. If 18.5 million subscribers are reaching the eardrums of 16.5 million non-subscribers -- 13.5 million on at least a weekly basis -- it will be a motivating factor for the non-subscribers to come aboard when they have a chance to sign up. There is no more learning curve. They have experienced -- and ideally value -- the product.

If anything, terrestrial radio has to be hating this study. I have long argued that satellite radio removes the most rabid AM/FM listeners, especially those with the disposable income to pay for premium subscriptions. It has to influence advertisers, too, who are now down to marketing to terrestrial freeloaders. Arbitron's study bears that out, in claiming that 24% of its listeners have household incomes of at least $150,000. That figure compares with just 9% of AM/FM listeners who fall within that group.

None of this news means that Sirius and XM subscribers have completely sworn off rival platforms. The Arbitron study provides an interesting breakdown of how Sirius XM subscribers consume their audio.

  • Sirius XM -- 62%
  • AM/FM -- 16%
  • Online streaming -- 4%
  • Mobile devices -- 10%

In other words, subscribing to Sirius XM doesn't mean an end to hearing local sports talk radio, firing up Pandora, or listening to podcasts or iTunes music collections on Apple (NASDAQ:AAPL) iPhones.

I'm not sure whether the "mobile devices" category includes portable media players like the iPod, Microsoft's (NASDAQ:MSFT) Zune, or SanDisk's (NASDAQ:SNDK) Sansa, but the breakdown indicates that even Sirius XM subscribers are spending more than a third of their time consuming audio through other sources.

In the end, it's easy to see why Sirius XM is issuing a press release touting the study's findings. Speculators on the bullish and bearish sides may volley arguments back and forth about the stock's valuation, but it's clear that satellite radio is a popular audio platform.

What do you see as the challenges and opportunities of satellite radio? Share your thoughts in the comments box below.

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Longtime Fool contributor Rick Munarriz is a subscriber to both Sirius and XM. He owns no shares in any of the companies in this story and is also a member of the Rule Breakers analytical team, seeking out the next great growth stock early in its defiance. The Fool has a disclosure policy.