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Computer speaker systems have brought a new element to the computing experience. Though they may be a form of analog technology, they are not yet archaic or outdated. Instead, speakers serve to merge the digital world to the sensory world that we live in. Ultimately, they have served as a catalyst for multimedia computing—what good would an MP3 or webcast be with just subtitles?

Our society has been bred on television as a medium. Integrated video and audio is a standard set in our childhood that is now fueling a bandwidth hunger via the Internet. As a result, computer speakers are as important as the monitor in our computing environment. The growth of computer audio has also resulted in more choices in size, styling, and format of speaker systems. The challenge is to find a high quality speaker system that will heighten the computer experience through quality and power, instead of an ill chosen system that holds back the entire computer

Speaker Specifications: How to read between the lines

Before listening to any speaker system, the manufacturer’s specifications provide a basis for comparison. Through a variety of tests to determine the sonic quality and electrical characteristics of the speakers, manufacturers determine the numbers intended to reveal the performance of their systems. However, results can, and often are, presented in an ambiguous manner that appears to enhance the specs of a system. In order to reveal these possibilities, careful examination of each specification is necessary.

· Drivers: The actual speakers used in the cabinet. The physical components of a speaker are fairly simple. The cabinet, or enclosure, is the wood or plastic box that contains the drivers, or speakers, and the electronics involved in making the sound, such as an amplifier and crossover networks. This specification indicates the size and type of transducers (speakers) used.

The number of drivers is very revealing as to the nature of the speaker system. When there are more speakers, they can be tailored to fit particular sound spectrums as each component handles just part of the frequency range. In a two way system, low and mid frequencies are reproduced by the woofer while a tweeter reproduces the highs. A three way system is when a subwoofer reproduces the lowest frequencies, a mid range woofer powers the intermediate frequencies, and the tweeter provides the high frequencies. When a transducer handles a smaller frequency band, it can handle higher levels of power; sound is energy and if they are reproducing a more limited range of energy, they can handle higher levels.

In these multi speaker units, a crossover network is used to split the sound spectrum and route the parts to the appropriate speaker. The crossover can also control the relative output levels for the speakers, actually balancing the sound across the frequency spectrum. Most importantly, they are set so as not to overwork the speakers and shorten their life spans by sending high energy frequencies to speakers not designed to handle them.

Here is a breakdown on the components often used in speaker systems. Through a combination of these components, a speaker is able to reproduce the full (or almost full) spectrum of sound.

o Tweeters are used for high frequency sound, usually sounds over 1.5 kHz. A smaller transducer can reproduce high frequency sound. Compression drivers and piezoelectric transducers can also serve as tweeters in a speaker system.

o Woofers are used for low frequency sound reproduction up to around 1.5 kHz. Because low frequencies have a longer wavelength, woofers must be larger in order to move the air volume necessary to reproduce these lower frequencies. As a result, the larger a woofer, the more power it can carry, and the louder the bass will be. In addition, for all the rumbling low frequency noise, the body senses the energy as much as feels it. When used for both low and mid frequency sound, woofer will produce sounds up to around 1.5 kHz

o Sub woofers are use to reproduce the lowest frequencies, usually up to 500 Hz. These provide the rumble element to the sound system as they move the most air and shake the body as much as the eardrums. The larger the sub woofer driver, the more energy it can handle, and the more impressive it can

Frequency Response: How much and how accurately the speakers can reproduce the sound spectrum. The response is measured using an analyzer that reads the speaker’s reproduction of a standard audio test signal.

Human hearing spans the frequency response of 20 Hz to 20 kHz, and in an ideal world, a speaker would reproduce all of these frequencies. Unfortunately, when indicating the frequency response of speakers, manufacturers often fail to tell the whole truth. If they do not indicate how accurate the speaker response is, specs can often look far better than the speaker actually sounds.

The simple description of frequency response of 20 Hz to 20 kHz would seem ideal; however, this is a true statement even if the sound at 20 Hz is 40 dB SPL lower than the sound at 1.2 kHz. This means that the lowest bass frequency is a hundred times less powerful than an average midrange frequency— i.e. the speaker may reproduce all of those frequencies but nowhere near at the same level.

A much more clear method of specifying frequency response involves giving a tolerance, the range within which the speaker produces all of the frequencies within its frequency response range. For example, a frequency response of 20 Hz to 20 kHz +/- 3 dB indicates a much superior speaker to the one mentioned earlier with a bass roll off of 40 dB. Basically, the latter speaker maintains its level all the way into its lowest frequency, while the former just goes away (rolls off) in its lower frequencies. The lowest bass frequency is at most only half of what a typical mid range frequency is reproduced at. Without indicating the tolerance on the specifications, companies can create extremely misleading specifications.

Impedance: Technically, impedance is the opposition to current flow in an alternating current circuit. Its significance in audio is a way to ensure that components work together correctly; the audio input needs to use up the current from an output circuit.

Typically, input impedances are higher than the output impedance of the circuit they are connected to. So, a powered speaker system is taking in a line level input and should have high impedance.

· S/N Ratio: The difference between the nominal program level, or speaker volume, and the noise floor, or underlying hiss and static in an electronic circuit. The larger the S/N ratio, the better.

Higher S/N will be very noticeable. The sound will be cleaner with less noise during playback, and when the speakers are turned on but not in use, quieter with less residual hiss. For critical listeners, this specification should carry some weight. If your music, or games, have a broad dynamic range (the difference between the loudest and quietest portions of the program), it is very important to insure that the S/N ratio is larger than this dynamic range. If is not, then either the quietest portion will be lost beneath the hiss of the noise floor, or the loudest portions will overload the speakers and cause clipping and distortion. Either way, the listening environment will not be satisfactory and deduct from your overall computing experience.

· Output Power: How much power the amplifier provides to the speaker system. The amplifier is often integrated into one or all of the speakers in a configuration known as “powered speakers,” as opposed to having an independent amplifier like in a home stereo system. A larger output power will directly lead to a louder speaker system. Also, in a multichannel system, the principal stereo speakers should be more powerful than the surround speakers, which are just used for spatial effects. Finally, in a sub woofer, higher powers will lead to a punchier system with more presence. When examining speaker’s handling of power, sometimes the speaker’s efficiency is presented. As a speaker is a transducer, its job is to convert forms of energy, from electrical to physical movement of the air. The efficiency measure how much energy is actually transformed instead of lost to heat. Given two equal speakers, one with a higher efficiency will attain higher volume levels at lower power and will perform better than the less efficient speaker.

The trick with output power is how it is measured. When not indicating the standard used in measuring, any specification talking about output power can be deceitful. The most common, and fairly honest, standard is to use the RMS (root mean square) testing method. This technique takes the average of an alternating current signal, such as the power sent to speakers, and gives a specification that would be equivalent to the power dissipated in a comparable direct current circuit. If a company chooses to instead list peak power, this doesn’t always reveal the full truth of the speaker. Sound is produced by alternating current with ever-changing levels, and the RMS value gives a much better idea of what the system can really do, instead of the instantaneous peaks in power. Some other methods, such as describing “music power” or “program power” will vary based on the signal used to create the specification and can prove to be more deceptive, yielding higher ratings than the actual performance in normal listening conditions.

Another specification bundled into output power is the Total Harmonic Distortion, or THD. This is a measurement of the purity of the audio signal. Like digital artifacts in imaging, electronic equipment can introduce distortion in the form of harmonics, or frequencies not present in the source, but reproduced as integer multiples of the source frequency (i.e. a 100Hz source produces an output with 100, 200, 200 Hz and so on). Besides the loss of quality, the human ear is bothered by these imperfections. The distortion can be presented in either of two ways—by presenting the difference in signal between source and harmonics in dB, or by giving a percentage to indicate the ratio between the harmonics and the original source. Therefore, the lower of either two numbers, the higher quality of the audio. Given a typical reading of so and so watts at 0.1% THD, this means that the artifacts are going to be 1/1000^th of the program level, or 30 dB lower. Translated into speaker pressure, that’s 1/64^th of the program source in perceived loudness. What does this all mean? If the program’s dynamic range is greater than 30 dB, then the harmonics are going to be evident in the program as they fall within the dynamic range. However, the dynamics would be present within the range only under the loudest portions, which would drown them out. This makes 0.1% THD reasonable, but a lower value would mean a better speaker.

When these specifications are tested, there is a quick way and there is a thorough way; the two don’t go together. When checking distortion, it is possible to examine just one frequency and how the system reacts to it, or to look at the full spectrum and present the system’s overall distortion. THD across the entire spectrum will indicate a more accurate picture of the speaker’s quality. And seeing as sound is much more than just a test tone, this gives a more accurate picture of how well the speakers will actually sound. Also, computer manufacturers aren’t subjected to the requirement to present all of their specifications from stereo mode, like on home receivers. So their measuring environment may not resemble an actual listening environment; instead it may be optimized for good specs.