how do you figure out the amount a watts a speaker can handle?

[Txgrizzly]

i have built the RS150 MT with the Dayton RS28A-4 (rated at 100 watts RMS/150 watts max) and the Dayton RS150S-8 ( 40 watts RMS/65 watts max).
with the "no BSC" crossover attached below what would be the power handling of this speaker in a sealed enclosure? i love the way it sounds i just dont want to overdrive them...

[BobEllis]

In most cases (home use) you are better off having "too much" power than trying to match the power handling of the drivers. Low power means that you might clip and that sends a ton of energy to the tweeter potentially frying it. Most drivers will start to distort noticeably before they reach their power handling limits. If it sounds bad turn it down, and you shouldn't hurt your drivers.

The RS-28's 100W rating is for typical music average power with a filter. The thermal power handling limit is probably closer to 10W RMS into the tweeter. I've got an active system with ~150W available for the RS-150s and the same for the 27TDFCs. They get plenty loud in my bedroom at relatively low average power and I've never damaged a driver.

[brianpowers27]

If I had to hazard a guess... An honest 25 watts RMS would put the woofers at or beyond their x-max (excursion upper bound).

I found that I can abuse speakers and they generally hold up. I have seen others blow speakers but it took a lot. I have an uncle who sets up speakers in the house and cranks them. He works out in the garden about 150 feet behind the house! :E

You notice as the power increases, that there will be a point where the bass output ceases to increase. You are well into overdriving the speakers, at this point.

[bluewizard]

You don't overdrive speakers with available potential power, you overdrive them by applying too much voltage.

Or as I like to say -

It is never overpowered or underpowered amps that blow speakers; it is always the idiot running the volume control.

The bulk of the acoustic power is in the 250hz to 500hz range. Based on some charts I have in a speaker design book, if you are running at 10watt in this band, then you are typically running at 2 watts in the 500hz t0 1000hz band. In the 2000hz to 4000hz band, you are running closer to 1 watt, and above 4000hz, it is closer to a half watt.

This is for full orchestral music, rock'n'roll and hip-hop are probably a little more bass heavy.

Next power and volume are not proportional, small changes in volume equal huge changes in power. Everytime you turn the volume up a small but perceptible amount (+3db), you double the average power. On this low end, you are running at a fraction of a watt, and are increasing by fractions of a watt. When you are up to loud but comfortable listening levels, you are probably averaging a watt or so. When you get up to very loud, but still comfortably listenable, you are at maybe 2 to 3 watts average power.

But remember, every time you nudge the volume control upwards, the power DOUBLES, and this is where you get into trouble. If we start at a loud 2 watts, and start slowly turning the volume up, the power goes from 2 to 4, to 8, to 16, to 32, to 64, to 128, to 256 watts, etc....

You see what is happening here? To our ears each of these changes represents an equal increase in perceived loudness. But near the end, we are making HUGE jumps in power for that small increase in loudness. When you try to nudge that last little bit of extra volume out of your speakers, the power leaps up, and the speakers turn to toast.

So, back to your speaker, you have tons of rated power on the tweeter, it is your woofer that is lacking, but it is still a respectable 40 to 65 watts, so that is the rating of your speaker system.

But again, it gets down to the idiot running the volume control. You could safely use these speakers on a 100watt amp, as long are you kept the volume control at a reasonable level. Don't get me wrong, you can still play them loud...party loud..., but when you push up into the ridiculously loud area, every nudge of the volume control puts the speakers at massively greater risk.

So, again, a fair and safe rating on these speakers would probably be 50 watts, but that doesn't mean you are limited to 50w and smaller amp. It means you can use any reasonably amp as long as you use it reasonably.

So, I would say, it could be used on any amp up to 100 watts, but, again, that has to be tempered with common sense. Anytime you move your volume control over half way, you are into bad sounding and dangerous territory. Clipping become more substantial. Power ramps up dangerously fast. Yet, at half volume, your speakers are going to be painfully loud.

Use them....don't abuse them.

Now, if you are using them on 300w to 500w amps, I would say that is just too volatile. But then why would you have a fortune in high powered amp, only to use them with home-made 50w speakers? Seems slightly out of proportion.

Just a few thoughts.

Steve/bluewizard

[Txgrizzly]

THanks Guys, this was very educational... i will try to keep the idiot off the volume knob...

[Alaric]

I'm going to go with BobEllis. Lack of power has killed more drivers than too much power-and I've cooked some soft-dome tweeters and mids by overpowering them. Bluewizard makes a fair point , as well.

[bluewizard]

While I know there is some valid theory and science behind the idea; the problem with the theory that underpowered amps are dangerous, is that no one ever defines 'underpowered amps'.

Are we talking 10watts, 25watts, 50watts, 100watts? All those are underpowered to someone.

The biggest dangers to a speaker are heat and mechanical abuse. In the most common interpretation of 'blowing a speaker', the culprit is usually heat.

That heat can come from several sources. It can be the excess application of sustained raw power. It can be from low power sustain unrelentingly over a long period of time. Or it can be caused by an offset voltage due to clipping, or perhaps, a fault in the amp.

Underpowered amps are more likely to clip, but remember that power and voltage are not proportional. A 100 watt amps is only ever so slightly louder than a 50 watt amp. The same is true of a 200 watt amp, it is slightly louder than a 100watts, and only slightly more than slightly louder than a 50 watt amp.

Even the available signal voltage doesn't change that much. Here are the rough specs for the necessary voltage to reach the various power ratings (assuming an 8 ohm load) -

50w = 20v
100w = 28.3v
200w = 40v

To understand the danger of clipping, we must look at AC light dimmers. Like a stereo amp, a light dimmer must be a zero power, zero voltage device. That is, if must go PLUS 50 watts followed by Minus 50 watts for a net of zero. The same with voltage, if it goes +20v, then it must go -20v for a net of zero.

To dim a light, you must apply full voltage, but steal some of the cycles (one type of dimmer). But you must be careful to steal FULL cycles. If you block a negative but let the positive half cycle through, you no long have a net of zero, and that will quickly cause problems.

Audio signals, are more complex than simple 60hz line voltage. It is possible for complex audio signals to be asymmetrical, but over time, it averages out to zero power, zero voltage. That is, until the amp goes into clipping.

Two things happen in clipping, one is that when you reach the voltage limit of the amp, the output sustains at the voltage level. For example, if a loud complex signal has substantial peaks, it is going to sustain the max voltage (20v for 50w) for a longer period of time. Just sustaining the voltage is enough to cause heat to build up.

Next, asymmetrical signals gradually build up an non-zereo DC voltage on the output. Again, a sustained DC voltage is a bad thing, and that combined with the amp not being a net zero power and voltage causes problems. One of the problems is the build up of heat in the speaker.

So, it is true that the earlier you clip, the more likely you are to have a problem. But those levels of clipping that are dangerous, are at extreme ridiculous volume levels. No one should ever drive and amp that hard or that high. Plus, driven that hard, with that much clipping and distortion, it will sound like crappola.

So, yes, low powered amps are a danger, but the danger is not in the amp, but in how it is used, which in turn brings us back to the idiot running the volume control

The next application of heat, in the absents of clipping, is the application of raw power. If you put a 10 watt speaker on a 1000 watt amp, don't expect the speaker to last long.

Now, certainly that is an extreme example, but it illustrates what can happen when you put a 75 watt speaker on a 200 watt amp. You can actually do that, and it will work fine. You can even play loud, but when you get too carried away, and start cranking the volume, the shear power is going to overwhelm the speaker. ...too much heat ...blown speaker.

But again, is it the fault of the amp, or the fault of the idiot running the volume control?

As long as you can keep idiots away from your stereo or AV equipment, you will be fine. But let one idiot on the volume control who has nothing to lose, and you are in trouble.

The last scenario for speaker damage is a little odd because it involves neither raw power nor clipping. I have on occasion witnessed a speaker being damaged by a very low level signal that was sustained indefinitely.

As an example, we were testing a new speaker cabinet with a guitar, got bored after a while and decided to take a break. So, my friend set the guitar down and we left. When we returned several hours later, we found the speaker in a very low level feedback that was the equivalent of a sustained low level tone. The speaker was also buzzing and crackling. The voice coil was melted.

A continuous test tone, or sinewave signal is unrelenting. Music is dynamic, it rises and falls, and as such the voice coil has time to heat up and cool down. But a sine wave signal never stops, so heat just keep building and building and building, until it becomes too much.

This last item is very rare, but when I am running test tones through my speakers, especially when I am doing long slow bass sweeps, I pause now and then to give the speaker time to cool down. I've got too much money into them, and not enough money to replace or repair them, so I intend to treat them delicately.

Just a few more thoughts.

Steve/bluewizard

[Txgrizzly]

Steve, very good explanation... Thanks that was very informative.

[cotdt]

A 10W sine wave would fry the tweeter, and at low frequencies can easily drive the woofer to its xmax, but in terms of musical power, you can get away with much, much more. Around 100-150W in my experience.