Power to the People

The power output of your stereo system is vital. In other words, the more watts per channel your stereo receiver delivers, the more distortion your system will produce. To understand why, let’s review the basics: Audio information is taken from your source component such as a CD player, AM/FM tuner, turntable, or DAT player and sent through an amplifier. The amplifier takes this low-level signal and boosts it up with more juice so that the woofers and the tweeters inside your speakers move enough air for your ears to hear the soundwaves. The process of turning the sound from a 1-volt weenie signal to a magnificent mass of air that will make you jump up and dance is often considered to be the most vital and the most difficult task of any stereo system. One of the main issues is the compatibility between one’s receiver and one’s speakers. Most receivers don’t really have gobs and gobs of power, but many types of speakers demand a lot of power because they have a design that makes them relatively inefficient. So it’s a constant fight between receiver and speaker which results in wimpy and distorted sound. Now, this might not happen all of the time. In fact, 85% of the time you might have perfectly fine sound because you listen at low levels. The problems arise when you crank it. Even if you listen at medium levels, you will get some distortion if you underpower your speakers. That’s because music is dynamic. It changes from soft to loud and back again, often rather abruptly. This is especially true in jazz and classical music. The tune could be cruisin’ along at a medium dynamic level and, wham! Elvin Jones could smack the bass drum or Vic Firth could beat a timpani in a fortissimo passage. Your amp will have a difficult time finding the power reserve to produce that whack and your amp will clip. Clipping is an annoying form of distortion that occurs when an amp runs out of power and temporarily shuts down. Not a good thing. And more than any other frequency, bass sounds demand the most power to reproduce.

The Powered Subwoofer

A subwoofer is a speaker that’s dedicated to reproducing low bass sounds. In order to do this properly, the sub must have a large driver, or “woofer,” eight inches or larger. It also must have a relatively powerful built-in amplifier. A few years ago, subwoofers could either be active (a euphemism for a speaker with built-in amplification) or passive (sans amp). Now, virtually all stand-alone subwoofers (not part of a total speaker system) are active. Powered subwoofers don’t resemble normal speakers at all. They are generally small and look like a very compact end table. The woofer fires downward instead of directly into the room. This technique enables the manufacturer to make a subwoofer smaller. It also doesn’t really affect the sound because low bass frequencies-75 Hz and below-cannot be localized by the human ear. This is very convenient because you can place the subwoofer anywhere in the room and it sounds as if the bass is coming out of your regular speakers. Also, low bass is a monaural phenomenon: your ear cannot discern a stereo signal when it’s 150 Hz or below. (The human ear can generally hear 20 Hz/20 kHz.) Powered subwoofers can be hooked up using a variety of different methods because most of them accept a variety of inputs. The optimal hookup happens when your receiver has a dedicated subwoofer output. This is a low-level output (standard RCA jack like a tape deck output for example) that delivers only the part of the signal that’s below about 150 Hz. A dedicated subwoofer output is the cleanest of all hookup methods. But other methods work well too, so if your receiver doesn’t have a subwoofer output, don’t fret.

Another hookup method is to use an unused low-level audio output such as a tape recorder output, or an auxiliary output which hooks directly into the subwoofer’s built-in power amplifier. All subwoofers employ a low-pass filter which cuts out the high frequencies so the subwoofer can concentrate on reproducing just the low ones. The other method is to merely hook-up the regular high-level speaker wires into the subwoofer. There is a “loop” within the subwoofer’s circuitry which pulls the low bass information and sends the signal back out to the main speakers, so you just hook up the speaker wires to the subwoofers and then run additional speaker wires from the subwoofer to the left and right speakers.

There are many brands and models of powered subwoofers from which to choose. Generally speaking, people like to buy the same brand of subwoofer as their main speakers. This is because the subs generally have the same types of driver and overall sound quality as the main speakers and it makes a good match. This is not mandatory, however, because a great many people mix and match brands of speakers and subwoofers. Powered subwoofers range in price primarily because higher-end brands cost more (like anything else). But within a certain brand, you pay more for bigger woofers and more powerful amplifiers. Woofers generally range from eight inches to fifteen inches with the understanding that the larger the woofer, the lower the bass. But producing ultra-low bass is not predicated only upon the size of one’s woofer. The size of the power amplifier is of equal importance. Power amps generally range from outputs of 100 watts to 300 watts or greater. So the least expensive sub would feature an eight inch woofer with a 100-watt amp, and the most expensive subwoofer in the line would employ a fifteen-inch woofer with a 300-watt amp.

Powered Three-Piece Speaker Systems

When Bose introduced the AM-5 over 10 years ago, the three-piece speaker system was brought to mainstream America. There were other three-piece systems prior, but the AM-5 was by far the most popular. Three-piece speaker systems were a solution to many people concerned with getting good sound without compromising their living room’s decor by sticking a couple of giant speakers where their chaise lounge used to be.

The issue is one of bass. In order to get solid bass, the speaker has to support a large woofer, and in order to accommodate a large woofer, the speaker needs to be large itself. But audio engineers discovered that low bass cannot be localized, therefore the low bass driver can be in a different part of the room from the tweeter and midrange drivers yet it still seems as if all of the sounds are coming from one place. This is a very good solution, because the tweeters and midrange drivers can be very small and the woofer can be hidden in the “end table” format described in the subwoofer section of this article.

The end result is a three-piece format: a separate subwoofer to handle the low bass and a pair of “satellite speakers” for the treble and midrange frequencies. Three-piece speakers utilize a very small subwoofer about the size of a milk crate. With the woofer in a separate enclosure, the tweeter/midrange modules can be tiny-about the size of a pint of milk. Many people choose to mount these pint-size modules on the wall and stick the subwoofer behind a sofa. The sound is surprisingly huge and the speakers become practically invisible. The tweeter/midrange modules also come in white to better blend with the color of the wall. The latest incarnation of the three-piece subwoofer/satellite system are ones that feature a powered subwoofer. That’s because low bass needs more power than do the high and middle frequencies handled by the satellite modules. Powered three-piece systems are the best of both worlds because the high and midrange frequencies are clear and precise, while the low bass is powerful and dramatic. One can hook up powered three piece speakers in a number of ways; the most advisable way is to run a line from the dedicated subwoofer output (or another auxiliary line output) of your receiver directly to the powered subwoofer and then run the normal speaker wires to the satellites. Or you can send the speaker wires into the subwoofer and then connect the subwoofer to your satellite speakers.

Powered Tower Speakers

Some folks feel more comfortable with standard tower-type speakers than they do with three-piece speaker systems. Maybe it has to do with force of habit. Or perhaps it has to do with the fact that a few audio sticklers feel that there’s a sonic “hole” between the satellites and the subwoofer that results in the loss of some midrange frequencies. This is obviously subjective because so many thousands of three-piece speaker systems are in the homes of satisfied music lovers. Nevertheless, a few speaker manufacturers are now offering standard tower speakers (all three drivers in one box) but with a twist: they sport a built-in amplifier to handle the low bass. In general, these speakers sound pretty great because your receiver’s power is focused on producing high and middle frequencies and the speakers’ built-in amps worry about the bass.

Generally speaking, a powered tower isn’t a heck of a lot bigger than a passive tower speaker because the amp is located out of sight, attached to the back of the speaker. Each speaker does have to be plugged into an AC outlet however. But after that, you merely attach the speaker wires directly from your receiver as you would with passive speakers.

Powered Auxiliary Speakers

There is a variety of ways to pipe music from your main stereo system into other rooms of your house. The most common (and most expensive) way is to snake wires behind your walls and have speaker outputs with volume controls in other rooms. This method requires a professional custom stereo installer to drill holes in your walls, which can be quite costly.

Recently, other methods have been invented for multi-room music. The most common is a system which utilizes powered radio speakers via the 900 MHz frequency band. 900 MHz was designated by the FCC for the sole purpose of broadcasting consumer electronics products. Products theretofore utilizing the 900 MHz signal are cordless telephones, wireless headphones, and now powered speakers. A 900 MHz transmitter is plugged into an auxiliary output of your receiver and it transmits the music throughout the house (actually within a 250-foot radius). Each pair of speakers is plugged into the wall and receives the music via the airwaves. It’s a pretty simple solution except that there is a limit to the fidelity of this system, and although it doesn’t sound bad by any means-the broadcast is clear without radio interference-the frequency response is limited. So for background music, the 900 MHz system is fine, but it’s not recommended for serious listening.

Originally Published October 1, 1998