8 ohm cab question

[agedhorse]

I would, but I regret to inform you that you make way too much sense!

One thing, though:
You actually CAN use the numbers printed on the cabs. At least if you know how.
Firstly, you need to eliminate all the BS numbers. An example would be the Bugera cabs (2x10 with 1600W and 1x15 with 1000W), where obviously someone in the lab fell on the voltmeter and broke the display.
When you're left with brands that seem to have a clue what the numbers they print on their cabs mean, you're still left with the thermal rating of the voicecoil. But since you have no clue whatsoever how much juice you are pumping into the cab, the number does not matter that much.
But let's say you're in the range of one brand and you own two 8 ohm cabs, each ratet at 600W and a head that is rated at 500W at 4 ohms, it is fairly safe to assume that you can turn up your head pretty far, if not all the way without causing harm - as long as you're playing bass and not pumping a square wave at 25Hz in there.
Most numbers from respected brands work well as a rough guideline.
My head says 300 and the cab says 250? better watch out.
My cab says 800 and the head 200? I probably can do what I want.
Your ears should always be the last line of defense before a speaker spills its innards, as you can pretty much hear the farting long before that happens. If you're forced to max out what you got - get more.

I disagree, based on what I see from day to day supporting products and bass players.

There are different metrics used by different manufacturers (and even different models within a brand) that might be used to describe exactly the same power.

For example, on an amplifier that is rated at 500 watts "RMS", it is also going to be capable of delivering 1000 watts peak, because the mathematical definition of the peak voltage of a sine wave (used for ratings) is 1.414x the RMS voltage, and when this 1.414 factor is squared in the power equation, it results in 2x.

The same thing applies to speakers, but with an added twist based on some old colloquial information that you may not be aware of. Speakers tend to be rated in two ways, the first being the same "RMS" (or continuous average) and peak that we discussed above for amplifiers. The second way, which is more common in the pro audio industry, is 'RMS", "program" and "peak... the meanings being different here. "RMS" is the same, program is defined as 2x the RMS value and comes from when speaker manufacturers were very conservative in their ratings and clipped/compressed program is excluded, and peak which is defined as 2x the program power or 4x the peak power. So, a speaker rated at 500 watts "RMS" might also be rated at 1000 watts "program" or "2000 watts peak. Which units that are being used is often left to the imagination (or the marketing departments). Also, most speaker power ratings are based on a "must survive, damage allowed) time period of 2 hours. When you extend this test to say 200 hours it's common to see a 1/3 reduction in power rating. Another factor is that the mechanical part of power handling starts falling rapidly at low frequencies (often below 60Hz), right where the biggest demands are placed on them. At say 30Hz, the power handling might be only 50% of rated speaker power.

The challenge is that you have an amp like the Subway, which is rated at 400 watts RMS into 8 ohms, and somebody buys a "500 watt" cabinet thinking that it will be fine BUT it's 500 watts "program" or only 250 watts "RMS" and maybe not so fine. It's even worse if these numbers are peak units.

Therefore, it's not anywhere near as easy as it seems, and this is one big reason IMO why many cabinets fail through no direct fault of the user.