[Erik Raucher]

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[ProtegeManiac]

They won't roll off the bass but they're probably (I can only assume as I don't have actual measurements) going to put a bump on the upper bass response. If the bass sounds rolled-off, it's only because relative to that bump, the latter is easier to hear.

 

Are you basing this on what low-power tube amplifiers sound like with many speakers? In those cases the speakers probably aren't that good of a choice to begin with as they probably are the ones that are rolled off and perhaps chosen primarily for their efficiency (with the system owner preferring the midrange qualities over everything else) or that the speakers have less than ideal efficiency or stable, relatively higher nominal impedance for such an amplifier, getting such amps to reach their distortion levels or requiring more current than they are capable of.

 

[Erik Raucher]

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[ProtegeManiac]

  I don't even have that much to base that suspicion off of - it was more a statement based on my thoughts about tube technology.
Essentially, the train of thought went something like
"Tubes are old technology" --> "Old tracks have deep bass that is very recessed" --> "What if the use of tubes in the recording of those tracks resulted in this?"

 

If you're listening to a relatively newer recording it wouldn't matter, and no I don't think it's just the tubes back then. It could be the mics as well for all we know, not to mention music back then didn't really have that much low bass to begin with save for some orchestra pieces (classical, some jazz). There wasn't even much in the way of classical music designed for epic movies (Zimmerman), much less crunk (Lil Jon).
 

 
Do you suggest using a specific kind/model of tube to prevent the increased mid-bass?

 

That will depend more on the circuit design - rolling tubes has less of an effect than that (and usually tube rolling is more along the lines of finding one that fits the circuit better, or actually is less of an ideal match but is preferred by the listener for its distortion qualities anyway).

 

  Or will a preamp have a nearly-negligible (nothing is negligible on head-fi ) effect on powered speakers' bass extension?

 

A preamp ideally should be transparent - it should be able to control the level of the incoming source signal and get it to the amp on the other end without adding or cutting anything. That's why some use passive preamp designs that just pass through the potentiometer, reducing the coloration an active component may introduce. If anything, the added midbass will contribute to the listener's perception that there is an overall stronger bass output.