The output speaker voltage will be either 25 or 70.7 volts. The speaker will have a microphone precedence over other input singles and four output terminals with circuit protection. Speaker installation is an important element whenever you install a P.A. system. No matter how good the amplifier is, if the speaker installation is not done properly, the sound produced will be inadequate. There are a number of factors you must consider when you install speakers. The placement and connection of speakers is the most important step. For indoor systems, two types of placement can be used. The speakers may be placed flat against a wall and the speaker turned so that it will radiate sound at an angle from the wall. The other type of placement is to mount the speakers in the corners of a room; for example, alcoves, balconies, booths, and dividing walls. A variation of these two methods mentioned may be considered for installation. For outdoor systems, the main considerations are the area to be covered and the direction of sound. Highly directive trumpet speakers are normally used for an outdoor area. When connecting speakers together, you must consider impedance matching and phase relations. Mismatching the impedance of a speaker to an amplifier output in either an upward or a downward manner will produce different effects. Mismatching upward (connecting an 8-ohm speaker to the 4-ohm output) will affect the power delivered to the speaker. Power loss will be about proportional to the upward impedance mismatch; in this case, about 50 percent. As a general rule, no serious frequency response deficiency will be noted and cannot damage a well-designed amplifier. Mismatching downward (connecting a 4-ohm speaker to an 8-ohm output) should always be avoided. It will reduce the amplifier power output and cause an overload on the output side with possible damage to the amplifier. Figure 6-2 shows an example of two speakers connected in series. Add the individual speaker impedances together to obtain the total matching impedance. The formula for this where Z = impedance is Zt = Z1 + Z2. For parallel connection (fig. 6-3) add the reciprocal of the individual speaker impedances together to obtain the reciprocal of the total matching impedance. The formula for parallel connections is as follows: For series/parallel connections, combine the two formulas as the speaker connections indicate; for example, see figure 6-4, and apply the series formula for
Figure 6-2. - Two speakers connected in series.
A and B, then for C and D. Take the results of this and apply the parallel formula to obtain the final matching impedance.
Figure 6-3. - Matching two speakers connected in parallel.Continue Reading