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Say for instance that you have a speaker that is 400w/8ohms… It would need 56 volts…
Now if i would add another speaker on the same channel that would be 800w/4ohms… Would they also only need 56 volts?
Im just confused on how you can add more speakers and still require the same amount of voltage from your amplifier…. My guess would be double the speakers, double the voltage, but I know that has to be wrong...

Ohm's Law answers this. With (voltage) amplifiers like what we all use, the amperage and impedance fluctuate, in opposite directions. IOW, as the impedance goes down, the amperage goes up, and vice-versa. For the most part, voltage stays constant, but can go up or down, dependent on a number of factors. Watts are used as a reference because it just sounds better (inflated numbers = better sales) and it is widely accepted.

DJPhatman wrote:Ohm's Law answers this. With (voltage) amplifiers like what we all use, the amperage and impedance fluctuate, in opposite directions. IOW, as the impedance goes down, the amperage goes up, and vice-versa. For the most part, voltage stays constant, but can go up or down, dependent on a number of factors. Watts are used as a reference because it just sounds better (inflated numbers = better sales) and it is widely accepted.

Thanks!! one more question, when using horn drivers rated for a certain wattage should you consider this when limiting tops? for example If I have a speaker that has a mid driver that can handle 400w and a Tweeter that can handle 80w, What should I limit the voltage to? 25v for the tweeter or 56v for the mid?

My guess would be double the speakers, double the voltage, but I know that has to be wrong

Your guess isn't totally wrong.

The answer depends on how you wire two speakers (either per channel and even in one cab if you build a dual cab driver) together.

Using your example, yes, wired in parallel, 2 drivers would be 800W/4ohms and the voltage would be 56V.
However, if you were to series wire the 2 drivers, voltage would indeed be double.
The figures in that situation would be 800W/16 ohms 112V.

Without going into it fully, there are situations where someone building a very big PA can use both series and parallel wiring combinations to increase the amount of drivers on a given channel, but still present a load the amplifier can handle.
An example:
I want to run 4 x drivers on my 8 ohm amp. So I build 2 cabs with 2 x 8ohm series wired drivers (16 ohms), and wired the two cabs together in parallel. Now the load for the amp is 8 ohms.

Thanks!! one more question, when using horn drivers rated for a certain wattage should you consider this when limiting tops? for example If I have a speaker that has a mid driver that can handle 400w and a Tweeter that can handle 80w, What should I limit the voltage to? 25v for the tweeter or 56v for the mid

This is different. To start with, most cabs like this are either full range, or mid/high cabs, and (unless you biamp) they will have internal passive crossover/filters. Part of the function of the internal passive crossover/filter is to decrease power to the HF components, ie the tweeter in your example.
So you should limit to the entire cab to the mid driver rating, and the tweeter will be fine.

+1 to what Grant has posted. As an add-on, the higher the frequency is, the less power it takes. Crossovers don't remove power, per say, they just remove the much higher powered, low frequencies that the tweeter section can't handle.

DJPhatman wrote: Crossovers don't remove power, per say, they just remove the much higher powered, low frequencies that the tweeter section can't handle.

This isn't exactly true. Crossovers do reduce power in a frequency limited band. Remember that voltage and power vary with frequency, so power varies with the signal. To remove remove a significant part of the signal, you must power that pushes that signal, which is what a crossover does.

We do talk a lot about voltage around here because voltage is measurable, and voltage is directly correlated to driver excursion. That said, amps and drivers are both rated in watts (power) for a reason. To say that a signal is 60v (for instance) is not enough, you must state the parameters of that voltage for the measurement to be meaningful, for instance, a 60V signal into 8 ohms at 1khz. However, using that same example, that 60v 1khz signal will have less RMS power than a signal of pink noise at 60v into 8 ohms, because there are more frequencies involved. This is why when you measure output from your amp with tones you can get higher voltage than with music, and it's also why you want an amp that has about double the power rating you actually need.

For instance, my IPR3000 amps are rated "440 watts per channel @ 1 kHz at <0.1% T.H.D. both channels driven." so they can put out about 59v. However, with a broadband signal, you never see 59 volts out of them, becasue the power supply can't quite supply that much and the DDT limiters kick in. The QSC RMX2450, on the other hand, is rated for 450w (close enough to the same) but at "8Ω / FTC 20 Hz - 20 kHz / 0.1% THD" which is a pink noise signal, meaning that it can actually put out the full power into a broadband signal. It's also much heavier. The IPRs do quite well, and the 3000 gets well into the 50-55v range with music program, so it's no slouch, but that's the difference between them.

On the other side, passive crossovers work by increasing impedance and therefore decreasing power beyond the crossover point, so the power is effectively burned off. The amp still produces the signal, it just isn't used. The problem is that the amp is still generating the signal, so it's not as clean as an active system.

This is also part of why actively crossed over systems work better than passively crossed over systems, especially in the subwoofer band. By actively crossing between subs and tops, you remove all the sub power from the top boxes so the amps are only dealing with frequencies in the correct pass band, and you remove all the HF from the subs likewise so the power will be focused into the passband, and thus cleaner (less distortion). The result is that the system sounds better than with comparable passive crossovers. A bass hit will not affect mids or highs, etc, where it will in a passive system.

BrentEvans wrote:

DJPhatman wrote: Crossovers don't remove power, per say, they just remove the much higher powered, low frequencies that the tweeter section can't handle.

This isn't exactly true. Crossovers do reduce power in a frequency limited band. Remember that voltage and power vary with frequency, so power varies with the signal. To remove remove a significant part of the signal, you must power that pushes that signal, which is what a crossover does.

We do talk a lot about voltage around here because voltage is measurable, and voltage is directly correlated to driver excursion. That said, amps and drivers are both rated in watts (power) for a reason. To say that a signal is 60v (for instance) is not enough, you must state the parameters of that voltage for the measurement to be meaningful, for instance, a 60V signal into 8 ohms at 1khz. However, using that same example, that 60v 1khz signal will have less RMS power than a signal of pink noise at 60v into 8 ohms, because there are more frequencies involved. This is why when you measure output from your amp with tones you can get higher voltage than with music, and it's also why you want an amp that has about double the power rating you actually need.

For instance, my IPR3000 amps are rated "440 watts per channel @ 1 kHz at <0.1% T.H.D. both channels driven." so they can put out about 59v. However, with a broadband signal, you never see 59 volts out of them, becasue the power supply can't quite supply that much and the DDT limiters kick in. The QSC RMX2450, on the other hand, is rated for 450w (close enough to the same) but at "8Ω / FTC 20 Hz - 20 kHz / 0.1% THD" which is a pink noise signal, meaning that it can actually put out the full power into a broadband signal. It's also much heavier. The IPRs do quite well, and the 3000 gets well into the 50-55v range with music program, so it's no slouch, but that's the difference between them.

On the other side, passive crossovers work by increasing impedance and therefore decreasing power beyond the crossover point, so the power is effectively burned off. The amp still produces the signal, it just isn't used. The problem is that the amp is still generating the signal, so it's not as clean as an active system.

This is also part of why actively crossed over systems work better than passively crossed over systems, especially in the subwoofer band. By actively crossing between subs and tops, you remove all the sub power from the top boxes so the amps are only dealing with frequencies in the correct pass band, and you remove all the HF from the subs likewise so the power will be focused into the passband, and thus cleaner (less distortion). The result is that the system sounds better than with comparable passive crossovers. A bass hit will not affect mids or highs, etc, where it will in a passive system.

Wow !!! This is exactly what i was looking for.I always thought my Peavey PV2000 amp was 400 watts (56.5 volts) @ 8 ohms but thats the 1khz rating.The 20 hz-20 khz rating is 370 watts (54.4 volts) which means i should be getting another amp.I'm leaning towards the Crown XLS 2500,lightweight,59 volts @ 8 ohms,55 volts @ 4 ohms which will be just right for me if im using 4 t-48's,i dont have to push them to the max.Thanks Brent.

The difference between 54.4 volts and 59 volts is insignificant, IMHO, just a few db which would be barely discernible.

Tom Smit wrote:The difference between 54.4 volts and 59 volts is insignificant, IMHO, just a few db which would be barely discernible.

Someone told me that once,but i dont like the idea of DDT compression on every bass note plus the amp is 625 watts (50 volts) @ 4ohms and my T48's will take 60.Also i want alighter amp so i can put my whole rig in a 8-10 space rack.

Aahh, there you go. I see.

crest prolight 5.0 dsp....

biggest plus, post dsp thru outs.