There's a lot that goes into buying a home theater system, knowing the key terms can help you make an informed decision when buying.
Channels
This refers to the number of audio channels. When you’re setting up a surround sound system, you’re going to run across numbers like 2.1, 5.1., 7.1, 7.1.2, 9.2.2, and beyond. As you see them over and over again, you may begin to wonder what they are.
What do the different speaker channels mean?
When it comes to surround sound channels, the first number defines the number of main speakers. The second number defines the number of subwoofers, and the third number defines the number of “height” speakers.
Surround Sound
Surround sound systems have many channels, typically five, seven, nine and more, arranged around the listener to create an immersive experience where you can hear where things are coming from with high precision. You will feel like you’re in the middle of whatever is happening on screen. Of course, the media you're watching must be mastered for surround sound to take full advantage of a setup like this.
Dolby Atmos
Atmos is a surround sound mastering standard that's mainly known for adding height channels, which means having speakers on the ceiling (or upward-firing floor speakers that bounds off the ceiling) that let you hear things going overhead, or coming from above. It supports up to 128 audio channels when mastering, depending on the implementation, and can map virtual sound "objects" to specific positions within 3D space using those height channel speakers. Of course, to take full advantage of Atmos, you need some pretty elaborate gear.
DTS
DTS or Digital Theater System is a competitor to Dolby, and there have been various DTS codecs over the years. If you check the back of a DVD or Blu Ray, you'll usually see which DTS version its mastered for, but as long as your audio system supports DTS you should hear something come out of your speakers. DTS is widely used and supported.
THX Certification
This is a certification from Lucasfilm that means a given piece of gear complies with their strict criteria for audio reproduction. You've probably seen the THX logo and booming, sweeping intro sound before. Gear with a THX sticker carries a premium. However, just because something lacks this certification, doesn't make it worse than THX-certified gear!
Subwoofer
A subwoofer, or "SUB", is a speaker that produces low-frequency sounds, also known as BASS, that are typically below 200 Hz. Subwoofers can enhance the sound of music and movies by making them more immersive and fuller. They can also reproduce sounds like bass-heavy songs, kick drums, and movie sound effects. Subwoofers are not used alone, but are intended to work with main speakers.
Frequency Response
This is the range of audio frequencies a speaker can produce measured in Hz (Hertz). Human hearing typically falls between 20Hz and 20KHz. The wider the frequency response range, the more accurate and truer the sound reproduction is compared to the original recording. So wider is generally better.
Crossover
A crossover is an electronic device (or a software function) that determines at which frequencies sound should be sent to different speakers. For example, if you have a speaker cabinet with a tweeter, midrange speaker, and subwoofer, the crossover will only send frequencies to each speaker that it's best suited for. By giving each speaker the optimum range of frequencies, you'll get better, fuller, and well-separated sound.
Speaker Sensitivity
This is a speaker specification measured in dB (decibels), and is measured one meter away from a speaker receiving one Watt of power. So a sensitivity of 90dB means it produces 90dB of sound pressure using one watt of power from the amplifier. Remember that for every 3dB increase you get double the pressure, since dB is not on a linear scale.
Sensitivity is useful for a number of things, such as figuring out how loud a given speaker can get paired with a specific amp. It's also useful to ensure that if you're connecting multiple speakers to one amp, that some aren't a lot louder at the same amplification levels.
Alternatively, if you have a setup where every speaker isn't the same distance from you, you can compensate for the loss of volume by using speakers that are more sensitive, and then by the time the sound arrives at your ears, the volume levels are the same as the speakers closer to you. As you can see, this is a pretty useful number!
Impedance
This is the amount of electrical resistance a speaker has to the power coming from an amplifier. Impedance is an important, and rather deep subject in audio, so I suggest you check our in-depth impedance explainer.
Amplifier
This is a device that takes a low-power audio signal, and then amplifies it using electrical power so that it can physically move the cone of a large speaker. Amp power is measured in Watts, and the wattage of an amp should not exceed the peak wattage specification of any speaker you connect to.
AV Receiver
This is the central hub of a home theater system that processes audio and video signals, amplifies them, and routes them to the appropriate outputs. Receivers are a big deal in home theater circles, and they are the foundation of enthusiast setups.
Acoustic Treatment
The room that you put your home theater setup in has a huge influence on how it sounds. Acoustic treatment refers to the set of modifications and tricks that can be used to get rid of unwanted effects on audio, such as room reverberation. Typically, this involved adding strategic acoustic panels.
Room Calibration
If acoustic treatment is about adapting your room to your home theater system, room calibration is about changing the settings of your home theater, to optimize it for your room. For example, you may want to boost the volume of faraway rear channels or otherwise tweak spatial audio for the unique shape of your room.
Speaker Placement
Choosing where to put the speakers in your sound system is both an art and a science. Getting speaker placement just right is the difference between magical immersive audio, and a muddy mess.
Equalization (EQ)
The equalizer in an audio system, whether physical or virtual, alters which frequencies in the audio you want to emphasize or de-emphasize. Adjusting an EQ can seem tricky, but it's usually just a matter of using your ears until the music or other content sounds the way you prefer.
Dynamic Range
Dynamic range refers to the difference between the quietest and loudest parts of the audio. In regard to recordings, this is the range of volumes that can be captured, and related to audio systems, it's the range that can be reproduced. Human hearing has a dynamic range of around 120dB in deal conditions, but anything over 90dB can cause hearing damage if sustained. Typically, high quality modern recordings can capture 96dB of dynamic range, but up to 144dB isn't unheard of.
Just because that range can be captures doesn't mean sounds over 90dB are reproduced at that volume. The whole range can be shifted up or down, which is what you do whenever you adjust the volume but the relative size of the range remains the same.
Audio Codec
An audio codec or "coder-decoder" is a compression algorithm that transforms an audio recording so that it takes up less space, but tries to retain as much of the original quality as possible. As codecs and computer processing power have advanced, the quality and compression ratios have improved immensely.
Bitrate
Bitrate is the amount of data transferred per second in a video or audio file. It's measured in bits per second (bps), kilobits per second (kbps), or megabits per second (Mbps).
A higher bitrate usually means better video quality. However, a large file size can cause buffering for viewers. Streaming services offer different bitrate options to accommodate users with different internet speeds. A stable stream with a lower resolution or frame rate is better than a higher bitrate with a delay.
Sampling Rate
Sampling rate is important in digital audio because it determines the quality of the final digital file. A higher sampling rate means more samples are taken, which results in a more accurate representation of the original audio. For example, CDs are usually recorded at 44.1 kHz, which means that 44,100 samples are taken every second.
However, higher sampling rates require more storage capacity and computational power. It's important to balance these factors when working with digital signal processing.
Lossless Audio
Lossless audio is a digital format that preserves all of the original audio information, resulting in a file that is identical to the source. This means that no data is lost during the compression process, resulting in a high-quality audio file that is indistinguishable from the original. Lossless audio is typically more extensive in file size than lossy audio formats, but audiophiles and professionals prefer it for its superior sound quality.
On the other hand, lossy audio refers to a digital format that removes some of the audio information to reduce the file size. The removed audio information is considered to be “inaudible” or “irrelevant” by the encoder and is, therefore, not missed by the listener. Lossy audio formats are typically smaller in file size than lossless audio, making them more convenient for storage and streaming. However, the trade-off is a loss in sound quality, as some of the original audio information is lost during the compression process.