Ok say I am going to build some 2 Way pa apeakers of 100 watts, 50 watt
Bass and 50 watt highs. When making the crossover I can figure out everything apart from power rating of conponents. I can find a resistor with the right value but the power rating is 20watt for example, is that enough? I have been looking around and there are so few resistors with wattage ratings even close to loudspeaker power ratings, am I looking for something that doesn't exist?
And on another Note, do I need drivers with matching power ratings? As
Mentioned above? Or can you mix and match? Like a 150 watt
Bass Driver and 50 watt tweeter?
Much thanls
Bass and 50 watt highs. When making the crossover I can figure out everything apart from power rating of conponents. I can find a resistor with the right value but the power rating is 20watt for example, is that enough? I have been looking around and there are so few resistors with wattage ratings even close to loudspeaker power ratings, am I looking for something that doesn't exist?
And on another Note, do I need drivers with matching power ratings? As
Mentioned above? Or can you mix and match? Like a 150 watt
Bass Driver and 50 watt tweeter?
Much thanls
The math for those calculations is not difficult.
You can find design tutorials on crossovers or buy a book such as Vance Dickason's Loudspeaker Design Cookbook, which explains things in great detail.
To get large wattage resistors simply parallel smaller wattage resistors of the correct value.
For example, if you need a 20Ω 20 Watt resistor you could get the same thing by paralleling two 40Ω 10 Watt resistors or four 80Ω 5 Watt resistors.
As for driver power, 50% of musical audio power is at 500 Hz or below. If your tweeter crossover point is high enough your power rating can easily be less than the bass driver.
Again, you can easily calculate your needs by looking at the SPL of your tweeter @ 1 Watt and then calculating how loud it is at its rated power.
A better method would be to determine what your maximum listening volume needs are and the listening distances first, then select drivers that deliver that volume plus some headroom to avoid distortion.
You can find design tutorials on crossovers or buy a book such as Vance Dickason's Loudspeaker Design Cookbook, which explains things in great detail.
To get large wattage resistors simply parallel smaller wattage resistors of the correct value.
For example, if you need a 20Ω 20 Watt resistor you could get the same thing by paralleling two 40Ω 10 Watt resistors or four 80Ω 5 Watt resistors.
As for driver power, 50% of musical audio power is at 500 Hz or below. If your tweeter crossover point is high enough your power rating can easily be less than the bass driver.
Again, you can easily calculate your needs by looking at the SPL of your tweeter @ 1 Watt and then calculating how loud it is at its rated power.
A better method would be to determine what your maximum listening volume needs are and the listening distances first, then select drivers that deliver that volume plus some headroom to avoid distortion.
Cheers for that, iv been reading up on this for ages but never found that info
Anywhere, I will get on with some design work ASAP.
Anywhere, I will get on with some design work ASAP.
The power of a speaker is typically the rated power of the bass diver. However, as Loren42 point out, the bulk of the power is consumed under 500hz. So, it depends on where you crossover.
For full orchestral music the peak power band is in the 250 to 500hz range and centered on about 355zh.
But I wouldn't use this as strict guideline. So, you can use a lower power mid-range with a lower powered tweeter, and still achieve a 100w speaker.
Part of what needs to be determined, especially with tweeters, is how close are they to their low limit. For example if a tweeter has a rated low end of 1500hz, and your cross at 1500hz, then you better have a low powered amp and you better have steep crossover slope. However, if you cross that same tweeter over at 2500hz, the power handling is going to be higher because the excursion is going to be lower.
So, you can't just say, 100w woofer, 50w mid-range, and 25w tweeter, many factors come into play.
As to crossover components in general, capacitors are rated by voltage. You want minimum double the actual voltage, so if you have a 100w amp, that means you have 40v to 50v on the power supply which in turn means 80v to 100v capacitors. Though that's not that bad as most crossover caps are 250v or more.
Coils are rated on current, well actually they are rated on wire gauge and that implies a current capability. 18ga coils are common, but if you want a bit of a safety edge, 16ga or 14ga are better. Unless you have massively powerful amps, 12ga is probably massive overkill.
As to power resistors, you can get power resistor as high as 100w.
Digi-Key.com - 100w Ceramic Wire Wound Resistor 10 ohms
Digi-key.com - 100w Heat Sink Power Resistor 10 ohms
But the only place you are likely to need power resistors is in the tweeter. And as you can see from the diagram above, the power in the high frequency range is pretty low. Plus, you have to consider the voltage across the resistor. If you make a voltage divider L-Pad, neither resistor is going to get full voltage, so ... lower current.
Typically, for L-Pad attenuators 10w and 20w are usually sufficient and much cheaper, and must easier to find.
As pointed out, you can gang resistor either in parallel or series to share the load. In series each resistor only gets a portion of the voltage, so they consume less power. In parallel, they all get the same voltage, but each has a smaller share of the current, hence ... less power.
So, it depends on the where the resistor is being used, and how it is being used, but for most applications 10w or 20w are fine.
Steve/bluewizard
For full orchestral music the peak power band is in the 250 to 500hz range and centered on about 355zh.
But I wouldn't use this as strict guideline. So, you can use a lower power mid-range with a lower powered tweeter, and still achieve a 100w speaker.
Part of what needs to be determined, especially with tweeters, is how close are they to their low limit. For example if a tweeter has a rated low end of 1500hz, and your cross at 1500hz, then you better have a low powered amp and you better have steep crossover slope. However, if you cross that same tweeter over at 2500hz, the power handling is going to be higher because the excursion is going to be lower.
So, you can't just say, 100w woofer, 50w mid-range, and 25w tweeter, many factors come into play.
As to crossover components in general, capacitors are rated by voltage. You want minimum double the actual voltage, so if you have a 100w amp, that means you have 40v to 50v on the power supply which in turn means 80v to 100v capacitors. Though that's not that bad as most crossover caps are 250v or more.
Coils are rated on current, well actually they are rated on wire gauge and that implies a current capability. 18ga coils are common, but if you want a bit of a safety edge, 16ga or 14ga are better. Unless you have massively powerful amps, 12ga is probably massive overkill.
As to power resistors, you can get power resistor as high as 100w.
Digi-Key.com - 100w Ceramic Wire Wound Resistor 10 ohms
Digi-key.com - 100w Heat Sink Power Resistor 10 ohms
But the only place you are likely to need power resistors is in the tweeter. And as you can see from the diagram above, the power in the high frequency range is pretty low. Plus, you have to consider the voltage across the resistor. If you make a voltage divider L-Pad, neither resistor is going to get full voltage, so ... lower current.
Typically, for L-Pad attenuators 10w and 20w are usually sufficient and much cheaper, and must easier to find.
As pointed out, you can gang resistor either in parallel or series to share the load. In series each resistor only gets a portion of the voltage, so they consume less power. In parallel, they all get the same voltage, but each has a smaller share of the current, hence ... less power.
So, it depends on the where the resistor is being used, and how it is being used, but for most applications 10w or 20w are fine.
Steve/bluewizard
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