A Wattage Question

[DeanT]

OK all you electrical engineers out there, put on your thinking caps.

If I have a cabinet that's rated at 200 watts, and a head that's capable of pushing at least 200 watts (and all things being equal of course), will a 400 watt cabinet be twice as loud?

Does wattage directly relate to volume? Is a higher wattage cabinet louder than a lower wattage one (with the same ohms and everything else)?

When it comes to how electricity works, I'm ********, so bear with me here.

 

[billfitzmaurice]

If I have a cabinet that's rated at 200 watts, and a head that's capable of pushing at least 200 watts (and all things being equal of course), will a 400 watt cabinet be twice as loud?

No.

Does wattage directly relate to volume?

No.

Is a higher wattage cabinet louder than a lower wattage one (with the same ohms and everything else)?

No. The answers to your questions literally fill books. This is one of the best.
[Invalid or Expired Link Removed]

 

[KJung]

To more directly answer your question... the cabinet power rating is a 'maximum' safe power recommendation, and has very little to do with volume.

However, more power from a head or amp into the same cab will result in somewhat great volume, and a more open, full, clean low end.... depending on the absolute amount of wattage, the speaker SPL, and a million other things

OK... maybe Bill's answer was better now that I think of it

 

[ChurchTechnBass]

You're not ********.

As long as manufacturers continue to sell watts as a key metric of performance people will ask similar questions to yours and be similarly confused.

More watts MAY mean more output, but watts are really a metric of measuring heat dissipation. The majority of the watts in any given system are given off as heat. In the case of our bass rigs, that's straight wasted energy (unless it's a cold outdoor gig and you're sitting on your amp; then bring on the watts baby, my buns are cold )

Good, useful specs to look for in choosing a loudspeaker product (bass cabs included) are sensitivity, impedance, continuous power handling (taken with a grain of salt) and frequency response. If you can get a maximum continuous applied voltage spec that's a lot more useful than a power spec, but that's still not a standard specification on loudspeakers. Heck take them all with a grain of salt; there's a lot of specsmanship out there. But those basic specs will get you to a reasonable understanding of what a loudspeaker may be capable of.

You'll need an amplifier to drive the loudspeaker, so some specs to look for in a good amplifier are frequency response, input sensitivity (how much input voltage do I need to get full output voltage), minimum allowable load impedance, maximum continuous output power and a few others that are useful, but not critical (again a maximum continuous output voltage would be more useful than the power spec, but it's not always easy to come by).

All we want our amplifier to do is take the small signal we put into it and make it big enough to drive the loudspeaker(s) we plug into it. If the amp clips and we can't get it loud enough, then we may need a larger amplifier, but we shouldn't drive it into clipping indefinitely. If the amplifier overpowers the loudspeaker and causes it to make "pop" or "crack" sounds we may need a smaller amplifer or to turn it down. If it's not loud enough we may need another loudspeaker or one big enough to take more voltage input.

If we want to change the tone or contour of our sound, then we will likely need a preamp of some kind. Some active basses are capable of driving a power amplifier directly, but most passive basses simply won't have enough output voltage to drive the input of a power amp directly. Also the input of most power amps would load a passive bass output down too much and ruin the sound of the instrument; much like plugging that passive acoustic guitar into a channel on your sound board - sounds like poop. The preamp gets us some tone control and enough output voltage to drive a power amp to full output voltage - which in turn will drive a loudspeaker to the desired volume.

billfitzmaurice's answer is the short answer; this one has been much longer, but I hope it's helpful to someone...

Jeremy J

 

[DeanT]

You're not ********.
Good, useful specs to look for in choosing a loudspeaker product (bass cabs included) are sensitivity, impedance, continuous power handling (taken with a grain of salt) and frequency response.
Jeremy J

Awsome responses. Thanks guys.

JJ - in terms of impedence, is a larger number "better"? For instance, is an amp with an impedeance output of 10K ohms weaker (or less responsive, whatever the correct term is) than one with 22K ohms. Is the higher number "better" or "worse" in terms of performance?

 

[ChurchTechnBass]

Dean,

The input impedance of an amplifier is a function of circuit design and topology. A common input impedance for a power amp is 6k ohms (6,000 ohms) unbalanced; 12k balanced. That refers to the type of input you connect to it. If you connect a mixing board output to the input of the amplifier, the mixing board will probably have a balanced output and "see" a 12k-ohm impedance looking into the amplifier.

A passive stringed instrument will usually be looking for an input impedance more like 1M-ohms (1,000,000 ohms) or some other very high number. That's the reason many passive instruments don't sound good plugged straight into a sound board or some passive DIs; the input impedance isn't high enough so the instrument output is loaded down and can't deliver the goods.

Higher or lower input impedance isn't necessarily better or worse, but it tells you what you can interface with it. In general, the lower the output impedance of your instrument, the lower the input impedance you can get away with - you usually want to keep a ratio of something more than 10:1. So, a passive guitar may have an output impedance of a couple thousand ohms; then you'd want to plug it into a device (typically a DI or a preamp input) that has an input impedance of something like 10*2,000 or 20,000 ohms or more. In the case of the passive instrument, since it doesn't have much output current capability, then plugging it into a very high input impedance will keep it from being overloaded and give you good sounding results.

For an active instrument with higher output voltage, lower output impedance and generally more current capacity, a lower input impedance is used. You still want to maintain a ratio of something greater than 10:1 (note, 10:1 isn't a hard fast rule - it's more like a guideline )

This works for amplifier to loudspeaker connections too - A power amplifier typically has an output impedance on the order of maybe 100m-ohms (0.1 ohms) and you typically plug it into a loudspeaker that has 4 or 8 ohms "input" impedance. that's a ratio of 40 or 80:1. When you start loading the output of the amplifier down say to 2 ohms or less, now your ratio has gone down and some amplifiers can't deliver enough current to keep up with the demand. They'll clip earlier and they may sound "flubby" or out of control. That change in tone is often associated with Damping Factor. Damping Factor is a ratio of the output impedance of an amplifier to it's load impedance.

I've written another novel up there; sorry...

Jeremy J

 

[DeanT]

Thanks again Jeremy. I realize there are no quick, easy answers to these questions. But I appreciate your comprehensive answers. It's starting to make more sense to me now.

 

[bongomania]

A couple of vague guidelines:
-The higher the wattage of an amp, the more power it can put out without distorting (depending on the speaker connected to it).
-The higher the wattage rating of a speaker cab, the more power it can handle without distorting (depending on the amp).
-The "depending" part has to do with how well-matched the components are, in terms of efficiency, impedance, etc.

But at the most primitive level, taking all the variables people mentioned above into consideration, more power delivered to more speakers = louder.

 

[billfitzmaurice]

But at the most primitive level, taking all the variables people mentioned above into consideration, more power delivered to more speakers = louder.

As far as the drivers are concerned the two most important specs with regards to potential low frequency output are xmax and xlim, and those are two specs that one will not be able to find at least 90% of the time. Drivers with the same xmax and xlim may have a 4:1 spread in wattage ratings. For this reason, amongst others, wattage ratings in and of themselves are almost irrelevent.