melissalmurphy said:
...you're saying it's best to have an amp that produces twice the W the speakers handle?
No! I'm saying that it's best to have an amp that can provide about twice the average amount of power you'll actually USE at your loudest gigs - this is because, assuming that you want to have the option of a solid, killer CLEAN tone (just about every bassist should!), then it's pretty much the agreed convention that the secret to an authoritive, 'hi-fi' clean sound is that the whole system preserves periodic short, natural transient excursions from the bass strings, all the way through the amp, to the final sound output to the listeners. If these transients are allowed to fairly accurately reach magnitudes that approach about twice the average power (or better) for the most volume that you'll be using (the 'biggest room' or whatever), then you have a good chance of being able to achieve this solid, authoritive tone at any amp volume you need.
The reason I tied the speakers in with this is because I was going for a more strict 'engineering optimization' based on an important criteria for the 'portable' requirement being small size and light weight.**
**Here's the issue that often gets confusing in conversations on these 'how much power do I need' subjects: You generally can't overdrive an amp past it's power rating with a clean, low-distortion signal - when the amp runs out of juice, it pretty much immediately, wave-for-wave, just clips the power off at max. Whether it turns out to be current limit or a voltage limit has to do with amp design and speaker impedance, but either way it'll fairly abrubtly chop-off (clip; distort) these transients, and effectively pretty-much eliminate them from the 'dynamics' of the sound that emerges - this will be described as a 'compressed' or 'dull' or 'weak' or 'not an open-enough' tone or something like that (there are better terms I think - could one of our amp conesseurs chime-in here? How is the 'no headroom'-sound usually described?).
BUT!!: It's a different story with speakers! Speakers and enclosures generally CAN accurately reproduce transients that are over-rated power, as long as they don't take up too high a percentage of the average signal (else they'll over-heat the voice coil or something). Those transients that give a clean sound this certain fidelity and authority take up a very small part of the whole signal time-wise, and the speaker's coil and cone can safely dissapate this little bit of extra heat and wear - it's built-in to the power specs for speakers.
Because of all this, and making the foundational consideration that the rig is 'portable' - taken to mean small and light - then by definition you want the minimum equipment that would be required for your loudest gigs. Since considerations for speaker ratings are a little different than those for amp ratings, it turns out that a good basic rule-of-thumb is; for clean, hi-fidelity tone, if you want both amp and speaker to safely approach their limits at about the same time (that 'same time' part can be a big part of an
optimization), then if the speaker rating is about half the amp rating, then you'll be just about optimized.
Considerations may be a little different for a case where one never runs a clean hi-fi tone, or a punk bassist who perpetually uses a fuzzbox, or one who always uses lots of hard compression (that's me). These situations won't require as much sheer-peak-magnitude headroom, but will tend to dissipate more average power in the head and the speaker. In cases like this, you may still want your amp to be rated for at least close to twice (or maybe 1.5X) the required maximum average power so you won't be running the thing hot all the time - but I'd think then you may want the speakers to be at least a little over-rated too for maximum reliablilty. Clipped or hard-compressed waveforms tend to make everything run somewhat hotter on-average.
If the size and weight optimization requirement weren't in-force,
then the genral rule would be that the the amp could be
any amount greater than twice the loudest average wattage, and the speakers could be
any amount greater than the loudest average wattage!
See what I mean?
Hey, Passinwind: did I explain it better this time?
Joe
