I will be reviewing network-enabled audio equipment in this blog and may use terms that may be unfamiliar to those of you who haven’t set up audio systems beyond very simple stereo setups. As well, I may make reference to these audio terms when talking about Internet radios and other audio equipment through this blog.

Amplifier Roles

Pre-amplifier This is an amplifier circuit that amplifies audio signals for the benefit of another amplifier.
It commonly describes an amplifier circuit that exists between a turntable’s pickup cartridge and the main amplification circuitry in a hi-fi amplifier.
It is also a term commonly used to describe a control amplifier.
Control Amplifier This is a pre-amplifier that allows the user to adjust the level and tonal quality of the sound and, in most cases select different programme sources.
A public-address or sound reinforcement system has this function provided for by the mixer which blends the sound from different sources together.
Power Amplifier This is the final amplifying stage in an amplifier that makes the sound useable by a connected speaker system. It provides most of the energy needed to reproduce the sound from a programme source.
If this circuit is built in to the same physical box as a speaker system, the speaker system is described as being an active or powered speaker.
Integrated Amplifier This common amplifier type has the control amplifier and power-amplifier circuits integrated in the one physical box and powered by the same power supply.
If a radio broadcast tuner is in the same box, this device ends up being known as a receiver.
If the control-amplifier circuitry is in the form of a mixer for a public-address or sound-reinforcement system, the amplifier is described as a powered mixer.

Audio Connection Types

Hi-Fi Public Address
Line-level This is a low-level connection that is independent of the tone and volume controls.
It is typically used to provide a signal to recording devices but can be used for amplification in other areas.
This is a low-level connection that is only affected by the programme level controls on on the mixer.
It is typically used to provide a signal to recording devices, amplification in other areas or for broadcast.
Preamp-level This is a low-level connection that is affected by the tone and volume controls.
It is typically used to provide a signal to power amplifiers such as active speakers
This is a low-level connection that is affected by the master fader and equalisation controls on the mixer.
It represents the final sound to the speakers in the main area and is fed to power amplifiers or active speakers in the same area.
Speaker Level This high-level signal is provided by power amplifiers to drive the sound system’s speakers. This high-level signal is provided by power amplifiers to drive the sound system’s speakers.

Sound System Types and Audio Mixes

Speaker Setup Programme Sound Mix
Monophonic (1.0) A single speaker system reproduces all of the program content A single-channel programme mix that represents all of the sound in the programme
Regular Stereo (2.0) Two speaker systems that reproduce all of the programme content from a stereo mix A two-channel programme mix with sound directed to either the left channel or the right channel
2.1 stereo A speaker setup with two speaker systems reproducing midrange and treble frequencies of a stereo sound mix and a single bass driver reproducing the bass frequencies of that same mixAn increasing number of these speaker setups use a dedicated power amplifier for the single bass driver. This is to provide extra power to reproduce the bass notes effectively.
Centre-Channel Stereo A speaker setup with three speakers where the centre speaker reproduces monophonic content or dialogue and key vocal content and the left and right speakers reproduce stereo content. A sound mix with dialogue and other key vocal content provided through a centre channel and music and other sounds provided through the left channel and right channels.
Quadraphonic (4.0)
– tried as a music-reproduction setup in the early 1970s
Four speakers located around the listening space able to reproduce all of the content from a quadraphonic or surround mix A four-channel mix with programme material directed to speakers located at each corner of the listening space.
Dolby Surround, also known as Dolby Pro-Logic or Dolby Stereo Three speakers located in front of the listener and one speaker used for effects located at the back of the listening space.
The three front speakers include a stereo pair for music and primary effects and a centre-channel speaker for dialogue and primary vocals.
A four-channel mix that is matrixed down to a two-channel recording or broadcast using the Dolby Stereo / Dolby Surround technique.
This mix has one channel for dialogue and primary vocals, a pair of stereo channels for music and primary effects and another channel for surround effects that is to be played through the back speaker.
5.1 surround (Dolby Digital) Three speakers located in front of the listener and two speakers used for effects located towards the back of the listening space, at the side of the listener. There is also a subwoofer used primarily for bass effects. A six-channel mix with two channels used for music and primary effects, a centre channel for dialogue and primary vocals, two channels to place surround effects through the surround speakers and a separate effects channel for bass effects.
7.1 surround Similar to 5.1 surround but has two extra speakers located at the back of the listening space, behind the listener. An eight-channel mix that is similar to the 5.1 surround mix but has two extra channels for the speakers located behind the listener.

It is worth noting that live-concert recordings or broadcasts that are delivered as surround-sound mixes are usually recorded as a stereo mix and the surround channels are made out of delay and reverb effects used to mimic the concert venue.

Special power-amplifier / speaker setups

Bridge or BTL A setup where two power amplifiers of lower power but in the same chassis and usually amplifying separate channels are “ganged” in order to create a more powerful power amplifier that amplifies one channel.
Bi-amp An arrangement where a speaker system consisting of multiple speakers that reproduce different frequencies is amplified by two or more power amplifiers serving the different speakers.
This arrangement typically allows for a more powerful power amplifier to be used for the bass notes while a less powerful amplifier handles the high note. Such systems may have a crossover that works after the control amplifier or typically will work at speaker level.

The recently-reviewed Marantz Audio Consolette speaker dock implements both of these techniques to yield a powerful high-quality sound and this setup is described as the unit having six power amplifiers. Here, the unit has, for each stereo channel, a separate amplifier for the mid to high frequencies and driving its own midrange-tweeter driver and a pair of amplifies that are BTL-bridged for the bass notes driving a woofer.

Headphones and Earphones

Headphone acoustic-design types

Headphone driver-positioning arrangements

These positioning arrangements determine how the speakers in the headphones are positioned relative to your ears and what kind of extra treatments are used to manage the sound

Intra-aural The speaker drivers are placed within or on the ear canal usually in a similar form to an earplug.
They are typically represented by the classic hearing aid or the earphones supplied with most portable audio equipment
Supra-aural or super-aural The speaker drivers simply sit outside and on the ear itself
A classic application are the headphones that used to come with the Walkmans of the 1980s.
Circum-aural The speaker driver sits outside your ear and the headphone unit rests on your ear using a sound-proof foam ring wrapped in vinyl or leather that surrounds your ear in a similar vein to ear-muffs.
A classic application for this type are the aviation headsets and most headphones sold until the late 1970s.

Headphone enclosure or housing types

Closed-back The speaker housing are as large as the speakers themselves and there are no perforation or venting on the housings.
This design typically allows for tight bass reproduction and focused sound with minimal sound leakage.
Open-back The speakers are either mounted on brackets attached to the headband or are in a housing that is perforated in some form.
This design typically can yield an accurate sound with good drivers but cannot be heard easily in noisy environments and can suffer sound leakage where other can hear the content.

Headphone styles

Earphones There is no headband with this style and they either plug in to your ears or clip on your ears in a similar manner to a pair of spectacles.
Traditional headphones These have the speakers attached to a headband that sits over your head. Some intra-aural variants that were often used for airline entertainment or language laboratories have the transducers attached to a neckband
Street-style headphones These have the speakers attached to a headband that sits around the back of your head and rest on your ears in a similar manner to a pair of spectacles.

Headphone terms

Headset Best used to describe headphones that have an integrated microphone attached to the cord or on a boom attached to one of the drivers.
The microphone primarily exists for communications or recording purposes.
Active Noise Cancelling Describes a pair of headphones that has circuitry that creates an “anti-noise” to combat low-frequency transport noise.
You can still hear the program material through the headphones as well as voices around you such as emergency announcements over the vehicle’s or aircraft’s announcement system.
Single-sided cord The cord between the headphones and the audio device connects to one enclosure with the wiring for the other enclosure connected via the headband.
Detachable cord The cord can be easily disconnected from the headphones unit itself for easy replacement.
Also permits the use of a “headset cord” that has an integrated microphone with the headphones