Alpine Guy's advice is dead-on accurate as usual. But, danwood, what you and your friend are discussing here (according to the wording in your post) are two different matters entirely. First you wondered which is louder, then the argument went the way of sound quality. Two different things.
First, find your priorities. Wanting a louder sub indicates competition, whether you're competing against friends for the loudest setup or competing for real in db drag. Your post sounds like, on the other hand, that the argument is really about what sounds better for the different music types. There are a few matters that you should bear in mind about this:
- An good subwoofer setup will accurately reproduce the music source. It is inherent in the different music types that the bass sounds different (electronic synthesized vs. kick drum etc.), so no matter whether the sub is sealed or vented these different bass sounds should be reproduced accurately. They should sound the way they were intended to be heard.
- The relatively small confines of an automobile creates an added reponse to the sub frequency range and it's known as "cabin gain". While a sealed sub has a gradual slope that looks to be quieter in the low end than a vented sub's slope (when modeled on paper), the cabin gain increases the low end of the freq spectrum. A good sealed setup usually exhibits very strong lows if the right box size is used and the sub is positioned well. Pushing for an emphasized low end in a vented box can result in too much low end when combined with cabin gain.
- The electrical and physical characteristics of any given subwoofer indicate what type of enclosure is best for their use. Here is a small sample list of some sub manufacturers who make subwoofers that have characteristics that put them in different enclosure categories:
Best in sealed:
Alpine E type (SWE1242)
Alpine S type (SWS1243D)JL 12W3v2JL 12W7RE Audio SE seriesImage Dynamics ID12D4v3Best in vented:
Alpine R type (SWR1241)
JL 8W0RE Audio SX seriesImage Dynamics IDQ12D4v2These box-types are distinguished by the characteristics of the particular sub in question. Key parameters are Fs and Qes when making the determination. Seasoned installers know what's best through first hand experience. So what you need to do is listen to as many sub setups as you possibly can. The sub you choose will perform perfectly for rock music whether it's sealed or vented, as long as you've chosen the proper enclosure and set it up with great attention to the details.
Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.