Choosing PA for my 3-way active Cross over circuit

[Shahriar]

Hi

I want to build this Active 3-way cross-over circuit.
But I do Not kow how to choose Power amplifiers. Here the problems:

1- If I choose a 15W subwoofer and a 15W STK power Amplier (STK4121) for it then what kind of Midrange and tweeter will be needed?
Does it mean I have to choose a 15w Midrange and a 15W tweeter?

2- Should the gain of all PA be the same? i.e. if the Midranges are

8Ohm and Subwoofers are 4Ohm, how to choose the gain of PA?

ThanX in advance
Shahriar

[audioguru]

I want to build this Active 3-way cross-over circuit.
But I do Not kow how to choose Power amplifiers. Here the problems:

1- If I choose a 15W subwoofer and a 15W STK power Amplier (STK4121) for it then what kind of Midrange and tweeter will be needed?
Does it mean I have to choose a 15w Midrange and a 15W tweeter?

Hi Shahriar,
Look at the sensitivity spec's and power ratings for the speakers. A sub-woofer has very low sensistivity so needs a very high power, a woofer has low sensistivity and needs high power, a mid-range has medium sensitivity and needs medium power and a tweeter also needs a medium power amplifier.

A difference in sensitivity of only 3dB is half or double the power. A difference of 10dB is 1/10th or 10 times the power.

2- Should the gain of all PA be the same? i.e. if the Midranges are
8Ohm and Subwoofers are 4Ohm, how to choose the gain of PA?

The STK4121 amplifiers are designed for 8 ohm speakers.
The crossover circuit has volume controls for you to adjust the gain to match the different sensitivities of the speakers.
Be careful when you adjust the level for the tweeters because if the amplifiers clip then the distortion will instantly blow the tweeters.