How do you match the power ratings?

[J M Fahey]

Dear Wilder, if you see it that way, I won't try to convince you.
You are entitled to your opinion and I respect it.
For all others, I suggest to be conservative in the PA system design, as to avoid *very* bad experiences .
Peace.

[martin manning]

So many of these "discussions" remind me of the parable of the three blind men and the elephant...

This JBL tech note (different from the link referenced above) seems to cover the basics pretty well:

http://www.jblpro.com/catalog/suppor...=290&doctype=3

The bottom line is captured in this excerpt:

A. For carefully monitored applications where peak transient capability must be maintained, a system should be powered with an amplifier capable of delivering twice its IEC rating. For example, a studio monitor system rated at 300 watts can be safely driven by an amplifier capable of 600 watts output.

Discussion: Careful monitoring is the key here. High quality music production today demands high peak factors in the recorded signal. Such peak signals are normally of such short duration that they hardly stress the system's components. Thus, the extra 3-dB margin (times two) of power will result in cleaner overall operation of the system, with less listening fatigue.

B. For routine application where high continuous, but non-distorted, output is likely to be encountered, a system should be powered with an amplifier capable of delivering the IEC rating of the system.

Discussion: This case describes the bulk of sound reinforcement activities. Such systems can often be inadvertently overdriven, or can go into feedback. When powered with an amplifier equal to their IEC rating, the user is guaranteed of safe operation.

C. For musical instrument application, where distorted (overdriven) output may be a musical requirement, the system should be powered with an amplifier capable of delivering only one-half of the IEC rating for the system.

Discussion: Much rock music is produced at full output with the amplifier well into clipping, and this is a matter of musical choice. When an amplifier capable of, say, 300 watts of undistorted sinewave output is driven well into clipping, its output power can approach 600 watts! So, Berating (sic) the system to one-half its IEC power will result in safe operation of the loudspeaker.

[Wilder Amplification]

A. For carefully monitored applications where peak transient capability must be maintained, a system should be powered with an amplifier capable of delivering twice its IEC rating. For example, a studio monitor system rated at 300 watts can be safely driven by an amplifier capable of 600 watts output.

And there's the key phrase right there...CAPABLE OF DELIVERING. That doesn't mean that your speakers will see twice their program power rating. Matter of fact if the amp is capable of delivering twice the speaker rating, you'll only have to use 1/2 of the amp's available power, and that means "headroom".

Headroom is power that you are not using. If you're using an amp that is only capable of delivering the speaker's required power, you're using up all of the amp's available power to power your system and you have no headroom.

In regards to the "Careful monitoring"...again most people make the mistake of running the amp's input sensitivity knobs maxed out. This will result in high transient spikes to the speaker. By setting the sensitivity knobs to the point at which the amp will not reach clip until the mixer reaches clip, this will pad a lot of the transient spikes that come down the pipe. For everything else, we have limiters.

Now another thing to consider is how these power amp companies derive the specs of their amplifiers and how valid they are. Some amps are rated for power outputs that more than exceed what the amp can possibly draw. Moreover, how much of that power is actually making it to the speakers, and how much of that power is actually getting converted into acoustic power, etc etc.

[martin manning]

John, you seem to be stuck on "A" above. The answer to the OP's question depends upon the context in which the amp and speaker(s) will be used, and that is still unknown at this time.

[Wilder Amplification]

That is very correct. I guess A is my preferred method. Even though I'm a hard rock/metal player I like things to be clean, tight and punchy and over spec'ing the amps for lots of clean power headroom ensures that. Allows you to get that big, full concert sound with lots of punch on the drums (think "baseball bat to the chest" kick drum from a pair of Cerwin Vega Earthquake folded horns).

But you do have to admit...when people look at power specs most of them don't realize that when they say an amp puts out "X" amount of power, they think it puts that out all the time and don't realize that that is actually the "maximum it is capable of delivering". My way of thinking is that if you need that amount of power why would you use an amp that has to run maxed out to put out that amount of power? To me it's like having to drive with your foot to the floor just to do 40mph.

Then there are those who think "Why would you use an amp with more power than you can use?". Well...power you're not using is what headroom is. And headroom is a good thing.

[Wilder Amplification]

Bottom line...if headroom is what you're after, using amplifiers that are spec'ed with a maximum clean power rating that is equal to what the speaker wants to see in program power is not the way to do it.

Again...headroom is power that you're not using. If the amp is rated to source exactly the amount of clean power the speaker needs to perform efficiently, you're gonna have to run the amp at maximum output to get the volume you seek and will have no clean power left, which means no headroom.

However, if you use an amp that is CAPABLE OF SOURCING more clean power than what the speaker calls for, you will only have to use a portion of that available clean power. Since you are only having to use a portion of the available clean power, this means you will end up with power you're not using, and that means...yep you guessed it! "HEADROOM"!

[Chuck H]

Forgive me if I'm way off. I haven't studied the actual meanings of all the power rating scales used by manufacturers. But on a more basic subject:

How does underrating the speakers maximize the volume, or even the dynamics of the system? Do underrated speakers have the ability to accurately produce the dynamics of the amplifier at that point? Wouldn't a speaker rated equivalent to the performance of the amplifier be better for this? Why not?

I wrote above that if your amp is rated above your speakers then the amp can never reach it's potential and this surely wastes headroom. Amplifier headroom above the useful wattage of the speaker system is can't be heard, ever.

Do speakers rated at or above the potential of the amplifier produce less volume or accuracy than those rated below the amplifiers wattage with the same power applied? This seems like a paramount question to this argument.

It seems to me that an amplifier playing into a speaker system of equal capabilities may indeed reach clipping, but not at a lower output than it would with underrated speakers if you could turn it up without blowing the speakers. So where excactly is the advantage to using underrated speakers? I don't follow the logic at all.

Chuck

[Jazz P Bass]

I agree Chuck.
This is turning into a "Silly Thread"
The speakers have to be able to handle the amps power capabilities.
END>

[tedmich]

I agree Chuck.
This is turning into a "Silly Thread"
The speakers have to be able to handle the amps power capabilities.
END>

along those lines, this seems a good time to reintroduce...THE MATTERHORN!


Military grade woofer, 40kw, 40 speakers in a 1280 cubic foot steel shipping container:
http://danleysoundlabs.com/pdf/old/matterhorn%20pdf.pdf

methinks the GIs might have used this to torture Noriega..

[Wilder Amplification]

Think about it...

When we drive our cars at highway speed, are we having to drive them with the gas pedal floored to get to that speed?

When you build a computer, do you use a power supply that is rated for the exact amount of power that the computer will consume from it?

When you design a circuit, do you design the power supply to source EXACTLY the amount of current your circuit will draw?

PA systems with LOTS of reserve power sound cleaner, tighter and punchier as well as ensures that you don't end up with DC on the speaker since you'll never hit clip.

[Chuck H]

Think about it...

When we drive our cars at highway speed, are we having to drive them with the gas pedal floored to get to that speed

Nope. But it's nice to know there's more pedal in case we need to get out of the way. I'm having trouble associating this analogy, but I have one.

Why aren't cars designed so that the power plant (engine) can exceed the capabilities of the chassis and drive train??? Keep in mind that the power supplied by the engine is user adjustable.

When you build a computer, do you use a power supply that is rated for the exact amount of power that the computer will consume from it?

Having trouble equating this analogy too. But I have another one.

Why don't we have user adjustable controls on power supplies with no circuit protection that functions at the power output level that can damage the device it powers???

When you design a circuit, do you design the power supply to source EXACTLY the amount of current your circuit will draw?

Better analogy. But speakers do not draw current. Power is applied to them and they react. This principle is very different from a power supply feeding a hungry circuit.

PA systems with LOTS of reserve power sound cleaner, tighter and punchier as well as ensures that you don't end up with DC on the speaker since you'll never hit clip.

OK, working with your statement lets assume the amplifier never hits clip. Do you think a speaker of lower wattage than the amplifier is any safer when the speakers begin to clip?

We run clipping amps into speakers all the time without any problems. If you're worried about those little tweeters I can tell you that I've seen many blow up because they were under rated for the amp. Not because the amp was clipping.

I have a third analogy. When bottling milk is it better to use a half gallon container for each gallon of milk because it ensures that there will be no wasted space in the container?

[Wilder Amplification]

But speakers do not draw current. Power is applied to them and they react.

And power is...what?

I'll give ya a hint. The MOSFETs in a power amplifier are a metering device. They meter the amount of CURRENT that the amp's +/- rails can draw through the speaker based on how much input signal is applied to the MOSFET gates. The speaker's impedance governs how much VOLTAGE is dropped across the speaker when X amount of current is drawn through the speaker voice coil by the +/- power supply rails in the amp, which again the MOSFETs directly meter based upon how much input signal is applied to their gates.

When you apply an input signal to an amp, you're essentially opening a "current valve". The more input signal you allow to pass through via the main fader, the more the "current valves" in the amplifier open and more current is allowed to be drawn through the speaker by the rails. The more current is pulled through the load by the rails, the more voltage that is dropped across the load and the closer the speaker's terminals are pulled up/down to the rails.

Power is the product of CURRENT and VOLTAGE. By adjusting the amount of applied input signal to the amp, you are directly adjusting the amp's output current/voltage just like on an adjustable power supply.

Speakers typically will not have sufficient volume/punch unless they're being driven right at their program power rating. When you use amplifiers that are rated to max out right at the program power rating of the speaker and driving them at the program power rating of the speaker, you're essentially bouncing the speaker off the +/- rails of the amplifier's power supply, which is where your "clipping" comes in.

However, if you use an amplifier that is capable of delivering more than the program power rating, the rail voltage in the amplifier's power supply will be higher. This means that when you're driving the speakers at program power, the speaker will not be anywhere near the rails. The result is no clipping, plenty of volume and nice clean, tight and punchy sound.

[J M Fahey]

you don't end up with DC on the speaker since you'll never hit clip.

Please don't mix absolutely unrelated things.
1) DC is something which you'll never have on the speaker unless some transistor has shorted, the fuse doesn't blow, the DC protection fails, etc. which is not what we are talking about here.
2) Clipping is something you will *always* have on a PA system at concert levels , *unless* you use limiters, which you already have discarded.
Dynamic range of regular audio signals makes that happen for sure, unless you use the system at Walmart-background-music levels.
This means using systems 20dB below maximum possible output.
Headroom? No problem, just use a 100W amplifier at 1W average power and you instantly have 20dB headroom.
3) We are talking PA Systems or Guitar/Bass systems here, always from a very practical use viewpoint.
Phylosophical discussions about how things "should" or "could" be are often interesting, but shouldn't be confused with what's actually used live.

[Wilder Amplification]

Please don't mix absolutely unrelated things.
1) DC is something which you'll never have on the speaker unless some transistor has shorted, the fuse doesn't blow, the DC protection fails, etc. which is not what we are talking about here.
2) Clipping is something you will *always* have on a PA system at concert levels , *unless* you use limiters, which you already have discarded.
Dynamic range of regular audio signals makes that happen for sure, unless you use the system at Walmart-background-music levels.
This means using systems 20dB below maximum possible output.
Headroom? No problem, just use a 100W amplifier at 1W average power and you instantly have 20dB headroom.
3) We are talking PA Systems or Guitar/Bass systems here, always from a very practical use viewpoint.
Phylosophical discussions about how things "should" or "could" be are often interesting, but shouldn't be confused with what's actually used live.

What do you think clipping is!? Where the speaker is literally being "bounced off the rails"! That's what causes the flat line on top of a clipped wave form (that flat line is DC).

When an output transistor saturates, it pulls the speaker literally up/down to the +/- rails during the duration of the clip. There's your DC on the speaker.

During the duration of the clip, the speaker literally stops moving, which will reduce cooling to the voice coil. On top of that, DC current will overheat a voice coil yet cooling has been reduced during the time when the coil actually would need MORE cooling. This is what overheats these things.

You're acting as if I've never done this before. I've ran live sound...I used to own my own PA system. 9,000 watts of FOH power on 2 x Cerwin Vega Earthquake subs and 2xJBL SRX725s. That system was loud, clean tight and punchy...yet never hit clip and never took out speakers.

Engineering data as well as Ohm's and Watt's Law still apply to this stuff. I understand we don't live in a perfect world blah blah blah. But it really isn't that far off from the laws and theories at all. You speak as if "practical application" is the complete opposite of what the laws and theories dictate and this is far from the case.

[Mark Black]

Good sound system design starts with the speakers. Optimum is to have more power handling than you will ever need to use to achieve required clean SPL. and beyond that are issues of frequency response & coverage as well as physical installation. After the speakers are sorted the amplifiers can be specified accordingly, and the norm is to use amps with higher power capacity than the speaker ratings for best clean/clear sound. The trick is to avoid not only exceeding the long-term-power-handling of the speakers but to also avoid exceeding the xmax (excursion) limitations of the individual drivers under normal use. Frequency-dependent limiting is one tool to go along with the idea of responsible & knowledgeable system operation by trained personnel. Matching speakers to amplifiers such that the amp is operating into an 8 ohm load gets you better damping factor and makes for a tighter-sounding system but at the expense of more and higher-powered amps.

All that being said budgetary concerns usually force all kinds of compromises in the real world for most installations.

And judging by the amount of 18" speakers I've reconed (and the descriptions of what led to their failures) a heavy-handed guest DJ can kill the best-designed system since they seem to largely believe nothing sounds right unless it is "in the red". Yeah - I know there are exceptions and there are some really tech-savvy DJ's out there, somewhere, I just apparently don't get to meet many of them.

Now guitar amps, on the other hand, are a whole different animal where speaker/amp design rules are commonly ignored or intentionally violated to achieve tonal bliss. Pretty much whatever works for ya...

Oh yeah and to the OP: For a bass amp I would choose a speaker system that is rated for at least the amplifier rated output power (but preferably more) for best longevity and clearest sound. If speaker cone distortion is part of your desired resulting sound well, I'm afraid you're on your own there.