Speakers are the windows to our sonic landscapes. Choosing speakers is the most personal decision that you’ll have to make when putting together a stereo or a multi-channel home theatre system. Every speaker has different sound characteristics and most people have strong opinions whether they like a particular speaker’s sound or not. Home theatre enthusiasts typically look for speakers that produce a clean sound and pack enough punch to reproduce today’s Hollywood soundtracks. Audiophiles search for speakers that reproduce the original sound as accurately as possible. The visual appearance also plays an important part when choosing speakers since speakers are often the most visually dominating component of a system.

Depending on your space, listening preferences and budget, you should begin by choosing the type of speakers that will work best for you. Speakers can be divided into five basic categories: conventional “full-size” speakers, satellite/subwoofer packages, on-wall and in-wall speakers as well as panel speakers.

Recently, some speaker makers have introduced designs that incorporate multiple channels in a single enclosure. These types of speakers use a room’s side and rear wall reflections to imitate separate speakers placed in the room. A single enclosure with a left, a centre and a right channel is typically referred to as an LCR speaker.

Let’s examine how speakers produce sound and what key specifications you should look at when shopping for speakers. I’ll also talk about how you can judge a speaker’s performance.

How Speakers Produce Sound

Every sound that we hear is made of a series of vibrations or pressure waves in the air. In an audio system, a source such as a CD player sends an electrical signal to an amplifier which then sends the signal to the speaker. This signal causes the cone drivers and dome tweeters (used in conventional speaker designs) to vibrate back and forth, reproducing the sound recorded on a CD.

The human ear can hear sound from approximately 20 Hz to 20,000 Hz. Most speaker designs use a tweeter with one or more woofers to produce sound. A crossover inside the speaker is responsible for splitting the incoming audio signal between all of the drivers of a speaker. More drivers in a speaker may look attractive but do not necessarily translate into better sound because crossover design is a tricky business.

A speaker capable of reproducing frequencies from 20 Hz to 20,000 Hz is referred to as a full frequency response speaker. These are usually large, floor-standing speakers that produce clean, realistic sound. They also tend to be expensive.

Most speakers, however, do not reproduce the entire range that is audible to us. The majority of floor-standing speakers will play from about 35 Hz to 20,000 Hz. Bookshelf speakers usually handle frequencies from about 50 Hz to 20,000 Hz.

Many modern speaker systems, especially in the home theatre, use a subwoofer to produce the bass notes ranging from about 150 Hz all the way down to 20 Hz. Most modern subwoofers are powered, meaning that they have a built-in amplifier. They usually also have an adjustable crossover that allows the user to set the subwoofer’s upper frequency response to blend in more effectively with the main speakers.

Speaker Specifications

If you want to hear every sound in the recorded material, your speaker system should have a frequency response from 20 Hz to 20,000 Hz, whether composed of just two large speakers or smaller speakers paired with a subwoofer. Some subwoofers can play even lower than 20 Hz and some speakers can play higher than 20,000 Hz. The frequency response rating of a speaker is always followed by its variation from “flat”, expressed in decibels (dB). The smaller the variation, the more flat or accurate the speaker’s response. Variances usually range from +/- 5 dB to +/- 3 dB.

The sensitivity or efficiency of a speaker, measured in dB, will tell you how loud a speaker will play for a given power input (standardized at 2.83 volts or 1 watt into 8 ohms). This specification is important because it will give you an idea of how powerful an amplifier you will need to drive the speakers. Most speakers have a sensitivity rating between 85 dB and 98 dB. Keep in mind that sensitivity is measured on a logarithmic scale. A 3 dB difference of sensitivity translates into a 2 to 1 power requirement difference. For example, a speaker with a sensitivity of 92 dB needs only half as much power as a speaker with a sensitivity of 89 dB, to play at the same volume.

Impedance is also an important specification to consider. Impedance is measured in ohms and refers to the resistance that an amplifier will encounter when driving the speaker. The impedance of a speaker does not stay constant – it varies with the speaker’s frequency. An amplifier can deliver more power into 4 ohms than it can into 8 ohms. However, the increased power will result in more heat being produced inside the amplifier. Generally, a quality amplifier will be able to drive 8, 6 or 4 ohm speakers with ease. A budget amplifier may shut down or fail if asked to drive speakers rated at 6 ohm or less.

Conventional Speakers

In general, conventional speakers that combine cone woofers and dome tweeters in a properly designed cabinet produce the best sound. Some higher-end speakers may use horn or ribbon tweeters. As a result, conventional speakers are the speakers of choice for audio enthusiasts and serious audiophiles.

The cabinet or enclosure plays an important role in a speaker’s design because it has a major effect on a speaker’s overall sound. A good-quality cabinet should be rigid, well braced and internally dampened to reduce resonances that can colour the speaker’s sound. A simple knock on the cabinet can give you a good idea of how dampened the cabinet is. Good quality cabinets tend to be solid and heavy.

Most floor-standing, bookshelf and centre channel speakers are made of medium density fiberboard (MDF). Some high-end speaker cabinets are made of wood or other premium materials. The size of the cabinet is also important, especially when it comes to reproducing the lower frequencies.

A speaker enclosure can be either ported (bass-reflex design) or sealed (acoustic-suspension design). In a bass-flex design, the port in the back of the speaker is tuned to a frequency that allows some of the sound from the back of the woofer to reinforce the bass frequencies from the front of the woofer. In an acoustic-suspension design, the sound from the back of the woofers is dissipated inside the speaker enclosure.

Centre and Surround Speakers

The centre channel speaker is responsible for the majority of a movie’s dialogue as well as sound effects and the movie soundtrack. Two important factors should be considered about a centre channel speaker, namely timbre matching and off-axis performance. Timbre matching is the centre channel’s ability to match the sound characteristics of the main left and right channels. When a sound pans side to side across the front, it should not change its characteristics as it passes through the centre channel. Off-axis performance refers to the sound of the speaker when you are not sitting directly in front of it. All the seats in your room, no matter how far to the left of right of the centre channel, should hear the same performance.

The surround left and right speakers can be either direct-radiating bookshelves (monopole design) or diffuse-radiating dipole or bipole designs. Monopole speakers are great at precisely positioning sound effects but not the greatest at creating a sense of envelopment. Both dipole and bipole speakers have tweeters located on both sides of the woofer. In a dipole design, the woofer and the tweeters are wired out-of-phase which produces enveloping sound but not very good for precise sound positioning. In a bipole speaker design, the woofer and the tweeters radiate in-phase. Bipole speakers combine the best of direct-radiating and diffuse-radiating designs. They produce an enveloping sound and have the ability to position sounds around the room.

Satellite and Subwoofer Packages

It is almost impossible for us to determine the direction of sound below 100 Hz. Satellite and subwoofer package designers use this knowledge to their advantage. The satellite speakers reproduce the middle and high frequencies, while the subwoofer takes care of the bass.

What makes satellite speaker and subwoofer sets attractive is that they are much more compact than conventional speakers. This allows them to be placed in virtually any room, no matter how small.

Most satellite speaker enclosures are not made out of MDF. Instead plastic, metal or composite materials are used for enclosures allowing them to take attractive, unique styling and finishes. Some subwoofer enclosures are also constructed out of materials other than MDF.

These speaker systems work well in creating small to medium home theatre sound but generally cannot compete with conventional full-range speakers especially when it comes to music playback.

A package that includes satellite speakers, a subwoofer and an A/V receiver is called a Home-Theatre-in-a-Box (HTIB). These systems are great for people looking for a simple home theatre solution with a smaller budget. HTIBs are usually much easier and quicker to set up than individual component systems. The downside of an HTIB is that they are usually not upgradeable.

On-wall and In-wall Speakers

If you enjoy sound but don’t want to see speakers all around the room, look to in-wall speakers. Many in-wall speakers mount between the studs in the drywall and use the space between the two studs as their enclosure. New generation in-wall speakers come with their own enclosures that completely hide inside the wall. This gives them a much more predicable behavior and reduces the amount of sound escaping to adjacent rooms. The mesh or metal grill of most in-wall speakers can be painted to match your room.

Two styles of in-wall speakers are available: square and round. Square in-walls commonly combine a tweeter and one or more woofers, in a typical bookshelf arrangement. Round in-wall speakers are usually mounted in the ceiling. Round models typically combine a tweeter and a woofer in a coaxial arrangement (with the tweeter placed in front of the woofer).

On-wall speakers are a recent and growing speaker category. With on-wall speakers you don’t have to worry about cutting holes in your drywall and anything that may be behind the drywall because they mount directly on the wall. On-wall speakers are a great match for today’s flat panel television sets and are available in MDF as well as other enclosures.

Evaluating Sound Quality

The performance of a speaker system is very subjective. A set of speakers that sounds great to you, may not be the best choice for someone else. This is why, the best thing you can do when shopping around is to listen to the speakers for yourself. Bring a few CDs and DVDs that you are familiar with to the stores and ask the staff to play them for you.

During your listening tests, make sure to evaluate the speaker’s performance throughout the entire frequency range: the highs, the mids and the lows. Even though most of the sound reproduction will happen in the midrange, the sound should be natural and clear at all frequencies.

Midrange and high frequencies should have a tonal neutrality. A human voice should sound like a real life voice. Most rock, pop, electronic and hip-hop music is not good for evaluating speakers. Instead, use jazz, symphony or other easy listening CDs since they generally have clean and clear voices and use instruments that our ears are familiar with hearing.

Some speakers emphasize certain bass frequencies to increase the perceived bass output. If you’re looking for a natural sounding speaker set, it should not be emphasizing any frequencies. The easiest way to tell if a speaker is altering certain bass frequencies is to listen for bass notes that stick out. Is the bass boomy and muddy, or is it nice and tight? Can you distinguish individual bass notes or are they blurred together into one note?

How is the stereo imaging of the speakers? When listening to a well recorded album in stereo, you should be able to approximate the location of various instruments on the soundstage in front of you. Typically, the vocals should be perfectly centred within this soundstage. Acoustic or live recordings are great for determining stereo imaging. Does the soundstage have adequate width, depth and height? Or does it sound compressed, like it’s all coming from right in front of you?

In a multi-channel speaker system, does the system immerse you in sound? Does it create a realistic ambiance in your room? When action takes place on a busy street in a DVD does your room sound like you’re on the street? Does a rainfall during a movie sound real? A multi-channel system should image well. Do sound effects flow smoothly from channel to channel? When an airplane flies overhead, does it sound realistic or slightly disjoint between the channels?

Shopping for speakers should be a fun experience. Take your time and listen to as many speaker systems as you need before making your final decision. In the end, you should buy speakers because you like the way they sound, not based on any other factors.

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