In Part 1 of this series we covered Frequency Response, Sensitivity, and SPL. This segment will explain speaker Power Ratings, Crossover Systems, and Coverage Specs.
Full Range Power @ 8ohms: 600w Continuous /1200w Program / 2400w Peak
Output power specs can be confusing at first. Another way to look at it, for example, is if you had some heavy amps to move. It would make a difference how much you could lift at one time comfortably, how much weight on the average you could carry without a break, and knowing the heaviest load you could lift, but not carry very far. Going past this limit might lead to injury or exhaustion. For common use, Continuous Power indicates the power level the system can sustain for long periods of time without overheating and causing thermal damage. Conversely, Peak Power tells you the maximum instantaneous power level the system can handle in short bursts without causing damage.
Note: This is all based on clean, non-clipped output power. Clipping can produce four times the power to the speaker and it becomes more than continuous with its flat top clipped off signals. Be sure you are not clipping your amps.
Have you ever got yelled at by the sound tech for unplugging your guitar at the wrong time, producing a loud pop? That's because it creates a very high instantaneous signal level that can harm the speaker system. Watch out for unscrupulous manufacturers that try to sell speakers by advertising the Peak Power in a way that misleads you into believing the system can sustain such high levels.
The inside designing details: These three power ratings are actually tested by most manufactures. The test is done using a pink noise generator with a crest factor of 6dB. The continuous power is the RMS measured power of the pink noise. The peak power is the 6dB higher peaks from the crest factor. Program Power is the maximum wattage that the speaker can handle in bursts.
Program Power is how much of a typical musical signal the speaker can sustain over time in a more practical application. Notice that all of these specifications are accompanied by the impedance of the system. This is so you can use the correct amplifier output power specification.
Crossover: 2-Way with Speaker Guard™ HF protection
Crossover Frequency: 1.5 k Hz 2-way
Bi-amp LF: 8 ohms 600w /1200w /2400w
Bi-amp HF: 8 ohms 80w /160w /320w
Full-range speaker designs typically utilize a combination of drivers in order to achieve a cleaner signal with wider frequency response and more efficient power distribution. The Crossover specification tells you how many frequency divisions the speaker is designed with and at which frequency the circuit splits the full-range signal. Our sample spec tells us this is a 2-Way crossover that divides the signal at 1.5kHz in order to separate the high and low frequency parts of the musical signal. Most passive speaker systems have a 2-Way crossover that splits a full-range signal at the speaker input into high and low ranges. More sophisticated systems might be 3-Way or even 4-Way designs. Some can have separate inputs for each division requiring separate amplifiers and an outboard active crossover to split the signal before it reaches the speakers. The Bi-amp LF (low frequency) and Bi-amp HF (high frequency) specifications in our sample tell you the power ratings for each separate speaker input. Notice the low frequency rating is much higher than the high frequency rating. This is because low frequencies consume much more power to reproduce than high frequencies. In the case of our example (Carvin Audio's TRx2115) we've also provided a proprietary Speaker Guard circuit to help prevent damage to your high frequency drivers caused by excessive input levels.
Coverage Pattern: 80H x 50V
Coverage pattern is pretty basic, but is important to know when setting up your system or comparing various types of speakers. This simply tells you the width of sound dispersion in degrees both horizontal and vertical. Wider might seem better but depending upon the dimensions and shape of the venue sometimes a narrow dispersion can help you avoid unwanted sound reflections and phase-cancellation that can make your music sound unnatural or change the frequency response of your system. Carvin Audio's TRX3903 Vertical Array System produces a very wide 120H horizontal coverage for an even spread from across the room and a very narrow 10V vertical coverage to prevent excess reflections from the floor and ceiling. The column array effect yields a very even sound pressure level from front to back, so you don't have to overwhelm the front rows of your audience in order to adequately cover the back rows.
Carvin Audio's TRC400 System with TRx3903 Vertical Arrays
Now that you are familiar with the most typical speaker specifications you will be better equipped not only to choose the best speaker system for your application, but also to set-up your system for the best results in a variety of venues. A knowledgeable approach to speaker selection will help you accomplish what you need most from your PA system - your music to the listener - without excessive volume or distortion.