| When one wants to buy or rent a
PA speaker system ,.you have choices to make in
purchasing the speakers, amplifiers, and crossover. These
choices are made based on price- size ratio, availability,
quality and marketing. However, marketing claims can be
confusing, as there are different ways of measuring power
ratings and efficiency, etc. When the system is completed
everything looks good on paper and fits in the racks and
the truck or venue, and your budget. (Confused about
basic sytem components? Click here.) Then, the system is set-up for the first time... Why does it get so harsh when you turn it up loud? In this example, the amplifier driving the high frequency has too much power. This problem is not apparent at low volumes, as the amplifier is adding very little gain to the system, but as the signal increases, the mis-match becomes obvious in the "coloration" of the sound. This is illustrated by the relative blend of blue and red in the graphics below. |
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In order to compensate for the over-powered high frequency, the crossover is adjusted, turning up the lows and down the highs. This is balanced at high volume, but the crossover controls the input signal, not the amplifier strength. This means that as the signal level is reduced, the adjusted crossover now "colors" the sound in the other direction. |
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One can imagine the situation in reverse, with the low frequency amplifier out-performing the highs, or complicated further still by a 3, 4, or 5-way crossover dividing the frequencies into more bands. Even sound characteristics over the dynamic range of the system is called linear dynamics.
| What if the the club is too small to fit the whole PA, so only 3 of 5 speakers per side can be set-up, but the same amp rack is used. The impedance loads on the amplifiers are changed, and different types of amplifiers react differently to this change. | |
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| When it is time to expand the system by buying a few more speakers this would drop the impedance on an amplifier channel below its rated ohm load. SO you have to buy more amps, racks, cable , and connectors. This is problem is referred to as scalability in system design. | |
It is a complicated matter to design linear dynamics in a multi-way, scalable sound system, and it is rarely achieved.
The best option is to have a dedicated amplifier and crossover for each driver, built right into the speaker enclosure. The components could be precisely matched to acheive a smooth and balanced signal response throughout the power range. It would possess true linear dynamics. This system would also be scalable, as any additional speakers would have no bearing on impedance or amp loads. Cabling would also be simplified, and you wouldn't need heavy oversized amp racks.
This is what Duran Audio has done with their line of self-powered speakers making the rigors of being a everyday sound man a little easier, a little simplier,and a lot better..
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