Yamaha P-2200 Owner's Manual - Page 41
Criteria for Selection of a Crossover Dividing Network - drivers
View all Yamaha P-2200 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 41 highlights
8-ohm load, it must be rated at 366 watts (power is proportional to voltage squared). Since the P-2200 is only capable of 230 watts, this waveform is clipped, especially the high-frequency component. If the same two waveforms in Figure 65A and Figure 65B were reproduced by two separate amplifiers, the total amplifier power capacity needed would only be 246 watts (the sum of the two powers), not 366 watts. This power could be provided by one P-2200 and one smaller amplifier. Thus, using two power amplifiers to produce these two waveforms reduces needed amplifier power capacity. Or, if you use two P-2200 amplifiers, there is a substantial increase in headroom. Efficiency A passive crossover is made up of resistors, capacitors, and inductors. The resistors in the crossover "use up" some power as do the losses in the capacitors and inductors. By removing the passive crossover, these losses are also removed. Damping Damping was discussed on Page FOUR 7. With refer- ence to that discussion, any impedance inserted between an amplifier's output terminals and a speaker's input terminals reduces the damping factor; a passive crossover is such an impedance. Thus, biamplification, by removing the passive crossover, improves the effective damping factor. Distortion It is conceivable that a passive crossover could introduce some distortion which could be avoided by removing the crossover. However, the greatest reduction of distortion comes with the increased headroom in biamplified systems, which means less peak clipping in the amplifiers. Dynamic Frequency Response Shift (also Page FOUR 6) When the peaks of a complex waveform are clipped off by inadequate headroom, two things happen. First, since these peaks are usually high frequency information (see Headroom discussion), the high frequencies are lost, or reduced severely. At the same time, the clipping creates new harmonics of the input frequencies. These two factors can be considered to be changing the frequency response of the system on a dynamic (changing) basis, depending on the amount of clipping present. When to Use a Traditional, Passive Crossover In small sound systems, where high sound levels are not needed and economy is a major consideration, a speaker system with a traditional, passive crossover network may be the best choice. For example, Yamaha's S4115H and S0112T are excellent as stage monitors, or as main speaker systems for small to medium sized clubs. For larger installations, a biamplified or triamplified system will not only perform better than a system with passive crossovers, but will probably cost less too; the increased efficiency and headroom allows fewer amplifiers and speakers to produce the same sound level, and fewer crossovers are required. Realizing the Advantages To realize the advantages of a biamplified or tri- amplified system, the electronic crossover must be able to work well with a variety of different power amplifiers and speaker systems. In addition, because it plays a critical role in the sound system, the electronic crossover must be highly reliable, and its performance must be as good, or better than any other component in the system. Yamaha's F1030 electronic frequency dividing network (electronic crossover) meets these needs. It is an excellent choice for any biamplified or triamplified system. Criteria for Biamped Systems Crossover Frequency and Slope: There is a freedom of choice available to the designer of the biamplified (or triamplified) system that is not available to the designer of a non-biamplified system. The added advantage of being able to choose crossover frequency and slope means that the system can be carefully optimized for a specific application, or it can be made highly versatile for use in a wide variety of applications. Most manufacturers of quality speaker components carefully specify both power capacity and frequency range. The choice of crossover frequency can be based on this information. For example, if a high frequency driver's power capacity is rated at 20 watts of pink noise from 2kHz to 20kHz, a crossover frequency of 2kHz or higher is a good choice. A lower crossover frequency might allow over-excursion of the driver's diaphragm, leading to premature failure. If the system is biamplified, the woofer will be chosen to complement the high frequency driver's response. If the system is triamplified, both a woofer and a midrange driver or a super tweeter must be selected so that the frequency ranges of all the components complement each other. Preferably, there should be some overlap in the frequency range of each successive driver. The choice of crossover slope involves a tradeoff between speaker protection and phase shift. A low slope rate of 6dB/octave will produce a smooth system response with minimum phase shift, but it may not adequately protect high frequency drivers from excessive low frequency energy or low frequency drivers from excessive high frequency energy. A high slope rate of 24dB/octave or higher will protect the drivers better, but can introduce more phase shift than a crossover with a lower slope rate. 12dB/octave and 18dB/octave are widely used, and are good com- promises. 12dB/octave is the most common choice, but 18dB/octave can provide a little "extra protection" for sensitive components, especially high frequency drivers. Again, decisions should be based on a careful study of the abilities of the individual components, and of the system requirements. One common method of designing a three way system (with woofers, midrange, and high frequency drivers) is to biamp the system between the woofers and midrange, and to then use a passive, high level crossover between the mid and high frequency drivers. Since there is generally less energy in the high frequency range, the extra headroom and efficiency that would be obtained by triamping may not be needed. This compromise will usually save money without adversely affecting performance or reliability. Criteria for Selection of a Crossover (Dividing Network) There are only a few passive, high level crossovers on the market that are suitable for professional sound systems. Those that are built into a finished speaker system, such as Yamaha's S 4 1 1 5 H and S0112T, are exceptions. Because of the limited selection, a custom designed system with passive high level crossovers usually has to be designed around the crossover instead of around the drivers. Still, the crossover should meet certain criteria. It should have an impedance equal to the desired speaker system impedance (the impedance of the