Portable loudspeakers are amazing in their versatility, able to serve as mains, fills, delays, stage monitors and much more, providing solutions for hundreds of applications in live sound reinforcement.
These 2-way miracle workers usually include an 8-inch, 12-inch or 15-inch ported woofer and a compression driver on a horn or waveguide, with dispersion (6 dB-down points) commonly at 40 degrees (v) by 90 degrees (h) or 40 degrees (v) by 120 degrees (h).
The primary purpose of this dispersion is to focus sound on the audience while not sending it to reflective ceilings.
Coaxial designs, with the compression driver/horn suspended above the cone woofer, are also a popular option.
Fans of coaxial loudspeakers like that high- and low-frequency sounds originate from the same point in space to provide more of a “point source” coherence. Coaxial models also typically take up less real estate.
Not all portable loudspeakers are created equal.
Frequency response should be able to reproduce the sound source accurately, so for speech-only applications, a response of 100 Hz to 12 kHz is usually sufficient, while an acoustic guitar-singer will be better served by a response of 80 Hz to 15 kHz and a rock band should have a response of 40 Hz - 15 kHz (or higher).
These frequency limits are typically 10 dB down or less from the level at 1 kHz. Of course, the flatter the response over the passband, the more accurate is the reproduction.
Another choice is passive or active. Passive loudspeakers need to be driven by separate power amplification and might also require additional outboard processing, while active designs have the amplifier and processing built into the box.
Many active systems are also bi-amplified, with individual amplifiers for the woofer and compression driver.
Bi-amplification can offer several advantages. Distortion frequencies caused by clipping the woofer’s amplifier will not reach the tweeter, so there is less likelihood of tweeter burn-out. In addition, clipping distortion in the woofer amplifier is made less audible.
Further, intermodulation distortion is reduced, peak power output is greater than that of a single amplifier of equivalent power, direct coupling of amplifiers to transducers improves transient response (especially at low frequencies), and the inductive and capacitive loading of the power amplifier is reduced.
Finally, the full power of the tweeter amp is available regardless of the power required by the woofer amp.