The selection of loudspeakers available for sound reinforcement applications borders on mind-numbing, and while your friends here at FRONT of HOUSE can’t guide you through every possible option, we can help you identify the plusses and minuses of two distinct loudspeaker varieties: powered and unpowered. Let’s have a look.
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Here’s a quick overview of powered versus unpowered loudspeakers:
- Unpowered, or passive, loudspeakers require external power amplifiers. Most modern multi-way passive loudspeakers have built-in crossovers, but there are a few exceptions.
- The input to a passive speaker requires a speaker cable between the amp and speaker.
- Powered (active) loudspeakers incorporate the power amps inside the loudspeaker cabinet. The crossover in an active speaker usually happens at line level.
- The input to an active speaker is almost always line level. The exception here is products equipped with line/mic input switching, where you might want to connect a mic directly into the speaker for grab-and-go jobs.
Passive Loudspeakers: Pros and Cons
One of the advantages of using passive speakers is that if a speaker fails, you can swap out the speaker and still use the same power amplifier. If the amp fails, you have the option of either replacing the amplifier, or temporarily daisy-chaining the speaker to another speaker that’s being powered from a different amp (let’s say for a wedge mix) to get through the gig.
Purchasing a passive speaker and an external amplifier provides you with the opportunity to upgrade the power amp at a later date. When flying a passive speaker, you only need to worry about running speaker cable from the amp to the speaker — you won’t need to run electrical service to the speakers. Most modern power amps have no trouble driving 100 feet or more of cable, so signal loss through heavy-duty speaker cable (such as 12-gauge) should be minimal.
One of the biggest challenges of using passive speakers and external powering is matching the amp to the speaker. Too much power, and you could blow up the speaker. Too little power, and you could damage a transducer by driving the amp into clipping. Impedance matching between the amp and the speaker is less critical than it was in the old days (power amps are pretty robust these days), but if you intend to daisy-chain multiple speakers from a single amp channel, make sure that the amplifier can handle the load.
One disadvantage of passive speakers is that the crossovers operate at speaker level and will be fed from a power amp. As a result, crossover components receive the full output of the power amp before transferring power to the drivers — and that makes them more subject to damage from high power levels and heat. You may need to spend more time dialing in the crossover settings on a system processor to get the transition right between (for example) a full-range box and a subwoofer.
The power amplifiers for a large P.A. system will probably live in a heavy amp rack, which may require connection to a power distro, whereas many active speakers have a relatively low current draw and can be plugged into standard local power receptacles.
The Ups and Downs of Being Active
When using an active speaker, you’ll never worry about whether or not the power amps match the drivers. Notice I said “amps” plural. Many active speakers are multi-way and have separate amps for the LF, mid and HF drivers. The manufacturer will do the grunt work for you, matching the amps to the speakers, and setting crossover points so that you won’t have to deal with it. That’s a huge relief. It also allows the designer to put the power where it’s most needed.
Let’s suppose you connect a 100-watt power amp to a two-way, passive speaker. As a rule, the LF driver requires more power to produce a given SPL than the smaller HF driver. The crossover absorbs a considerable amount of the power directed to the HF driver to (a) keep it from blowing up and (b) balance the output level of the HF driver to that of the LF driver. That power is dissipated as heat, so it’s basically wasted. For example, using a 500-watt amp for the LF driver and a 100-watt amp for the HF driver is a far more efficient arrangement.
Active speakers typically use active crossovers operating at line level, which increases reliability because the crossover components aren’t stressed from high power levels and heat. An added benefit of placing the crossover at line level is reduced intermodulation distortion. Most powered speakers have onboard DSP with preset (as well as user-adjustable) processing so you can easily modify the crossover and filter response. For example, a full-range active box might have different settings for use with and without a subwoofer, eliminating the guesswork and simplifying the setup process.
When an active speaker fails, you lose the whole box, so tours will need to carry spare boxes and/or power amp modules. If you lose the amp in an active array you’ll have to drop the array to repair or replace the box — and that’s not going to happen during an event. Active speakers will need a power supply, so instead of carrying a lot of heavy speaker cable, you can carry a lot of heavy AC cable. Good grief.
Active speakers are easier to daisy-chain in a hang, but it’s possible that you may experience a loss of high frequencies if the cable capacitance creeps up too high. Bad news: active speakers are heavier than passive speakers. Good news: you won’t have to carry an amp rack, and that saves space on a truck.
There’s one thing that you may be able to do with an active speaker that you definitely can’t do with a passive speaker: leave the mixer home. If you have a coffee house gig, an active speaker with two mic/line inputs would provide sufficient mixing capabilities to do the gig without the hassle of dragging around extra gear. My back feels better already.
Steve “Woody” La Cerra is the tour manager and front of house engineer for Blue Öyster Cult.
