AUDIO SYSTEMS - PART 2

Basic Principles of a PA System

PART 2 - Three-Way PA Systems

Please follow me on Instagram and subscribe to my Youtube Channel

So far we’ve discussed the following:

1. How a PA System works, and its intended function.
2. Basic Elements on how to connect a PA System and splitting this up as sources, modifiers and destinations.
3. Types of PA Systems,
4. Full Range Point Source PA System
5. Two-Way PA System

This article will cover basic Three-Way PA Systems, and look at the differences and

functionalities between two-way and three-way PA Systems.

First and foremost, let’s look at the fundamental key basic differences between a two-way and
three-way PA Systems.

Again, we make use of basic components such as passive speakers, electronic crossovers and

non-DSP based power amplifiers.

The Basic Differences between two-way and three way PA Systems

Two-Way	Three-Way
Makes use of two types of speakers (Separate Bass and Mid-High speakers)	Makes use of three types of speakers (Separate Bass, Mid and High speakers)
Makes use of one electronic crossover and two separate amplifiers	Makes use of two electronic crossovers and three separate amplifiers
One Crossover Point, to send separate Bass and Mid-High Frequencies to two separate amplifiers	Two Crossover points, to send separate Bass, Mid and High frequencies to three separate amplifiers
Typical Crossover point: 120Hz This means that all frequencies from 120Hz and below will go to the Bass speaker, and frequencies from 120Hz up, will go to the Mid-High speaker	Typical Crossover points: 120Hz, 1kHz.  This means that frequencies from 120Hz and below will go to the Bass speaker, frequencies between 120Hz to 1kHz will go to the Mid speaker, and frequencies from 1kHz and up will go to the High speaker

Three-Way PA System

A Three-Way PA System basically works on the same principle as a Two-Way PA system. 
The difference is that a Three-Way PA System splits frequencies to different speakers in
three ways, instead of two for a Two-Way PA System. 

Typically with a Two-Way PA System, frequencies are split between Bass and Mid-Top
Speakers, where the Mid-Top speakers are typically full range speakers, meaning there’s
two speaker drivers in the same cabinet, that produces Mid and Top frequencies separately,
through an internal speaker crossover, whereas with a Three-Way PA System, frequencies
are split between separate Bass, Mid and Top speakers.

So essentially, there’s a separate speaker to produce the required frequencies when
slit between bass, mid and high frequencies. This allows sound engineers to better control
a PA System with frequencies being split over more speakers in a Three-Way PA System
as compared to a Two-Way PA System.

Three-Way PA Systems tend to have more of a midrange sweet spot when compared to
a two-way system, where the mid and high frequencies are produced with a speaker
enclosure containing a midrange and high speaker drivers.

So, the active crossover still plays a role in managing and splitting frequencies.
With most modern active crossovers, they can be used in either two-way or three-way modes,
but in three-way mode, two active crossover units will be needed.

Most modern Amplifiers nowadays include an onboard DSP (Digital Signal Processing),
which users can choose a crossover point, amongst other available settings.

Passive Internal Speaker Crossovers

So, to explain how a three-way PA system’s speakers work, let’s look at very basic passive

speaker designs to illustrate the differences between two-way and three-way speakers. 

Here are two basic examples as used in Hi-Fi/ bookshelf speaker systems:

Remember that Hi-Fi/ bookshelf speakers will make use of an internal passive crossover
network to distribute frequencies to individual speaker drivers, meaning that the crossover
receives its signal from an Amplifier, instead of an Active Crossover sending a signal to a
dedicated Amplifier, before it is sent to a dedicated speaker driver.

Internal Passive Speaker Crossovers will have specific specifications for the speaker
that it's in and should also stipulate the crossover frequency points, as there are
various crossovers available on the market with specific frequency and power ratings.

So, a professional Three-way PA system makes use of dedicated speaker drivers
within dedicated speaker enclosures, to produce sound within a specific frequency range.
The frequencies are set on the active crossover, then sent to a dedicated amplifier,
before it is sent to the dedicated speaker.

Below is a diagram illustrating a very basic three-way system configuration, consisting of
Bass, Mid and High frequency speakers in separate enclosures, connected to three-way
active crossovers and dedicated Bass, Mid and High frequency amplifiers.

Components of a basic three-way PA system could be as follows:

1 x Mixer/ Sound Console

2 x Active Speaker Crossover units (Each set to three-way Mono)

3 x Power Amplifiers

2 x Bass speakers

2 x Mid speakers

2 x High speakers

Audio interconnect cables

Speaker cables

So, let’s look at how to connect this all together, making use of signal and speaker cables.

Fine tuning frequencies and volume to each speaker is what is key for the best sound delivery

within a specific venue, to get to that “sweet spot”. 

Now, designing a three-way PA system is definitely more challenging than two-way systems,

because there’s a few factors to consider. For instance, speaker driver specifications

(power rating, frequency response and driver size) and amplifier specifications, are key factors

to consider. 

Bass speakers are typically bigger in diameter and power rating, compared to the mid and

high frequency speakers. 

Amplifier power for a high frequency speaker will require less power when compared to a

bass speaker. Amplifier and speaker ratings are also key, so best make sure that amplifier

power ratings match speaker ratings. For instance, a bass speaker will require more

power compared to a high speaker or tweeter.

This is where experience and venue acoustics play a big role in deciding the design of a

system, suited to the venue, intended use and the type of audience. 

Three-way PA systems typically produce a warmer sound quality when compared to a

two-way PA system, meaning there’s better control over the mid frequency range. 

Depending on what equalisation system you use, the mid frequency range is split into

low-mid, mid and high-mid frequencies, hence why setting up and tuning a three-way

PA system takes patience and a good ear to set it up. 

With today’s technology, digital DSP’s (Digital Sound Processor) definitely make it a lot simpler

to set up a three-way PA system, but the basic fundamentals of listening to each speaker and

what it produces, before listening to the overall system, is what makes the difference.

Too much volume on the bass could potentially drown out the mid and high frequencies,

which could drown out a singer’s vocals, so it is very important to fine tune the system so that

all individual parts are set optimally to produce an overall good sound quality.

Also, too much high frequency volume produced by the high speakers/ tweeters,

could cause unnecessary vocal microphone feedback.

Individual three-way speakers that are mounted in separate speaker enclosures typically

do not have internal passive crossovers, but in some cases, could make use of a passive

filter circuit to only produce certain frequencies.

For instance, high frequency driver/ tweeter speakers typically make use of a passive high

pass speaker filter and could make use of a filter circuit, to smooth out frequencies being

sent to the high frequency driver/ tweeter speaker. 

So, What is a High Pass Speaker Filter?

A high-pass filter is an EQ curve that is used to remove low-frequency sounds from an

audio signal. It is called a high-pass filter because it allows high-frequency signals to

pass through, while attenuating (reducing the amplitude of) lower-frequency signals.

Below is an example of the size of speaker drivers and enclosures that a three-way PA system:

Driver Size	Driver Design	Enclosure Design
18”	Bass/ Subwoofer driver	Band Pass, Ported, Horn loaded
12”	Mid speaker driver	Horn Loaded, ported
1”	High frequency compression driver	Bolted to a Horn flair

There are many different types of speaker sizes and enclosure designs available on the market.

Speaker driver manufacturers will typically provide data for the optimal enclosure design

so that the speaker driver works at its best. 

The type of enclosure you want for your speaker drivers will depend on the application,

venue size and intended audience.

This is a simple three-way PA System, with dual sub-bass speakers, mid-range and high frequency/ tweeter cabinets

Quick Recap

So, we’ve learned the following with three-way PA systems:

1. The differences between two-way and three-way PA Systems.
2. Internal passive speaker crossovers are used to split frequencies to speakers
inside an enclosure.
3. Three-way PA system set up requires fine tuning to produce an optimal sound quality
4. The use and design of a three-way PA system will depend on the intended application,

venue size, venue acoustics and the intended audience.

Next Up…

Distributed Sound Systems, their intended use, how to identify a distributed sound system, design and individual components used to make a distributed PA System work.

© Intellectual Property Rights Reserved - Marius van Vuuren, Dubai, UAE

AUDIO SYSTEMS - PART 1

Basic Principles of a PA System

PART 1 - Basic PA System Configurations

Please follow me on Instagram and subscribe to my Youtube channel

PA or Public Address Systems can trace their origins back to the early 1900’s when scientists

first experimented with a dynamic moving coil loudspeaker, a microphone
and an amplifier.

These three basic components are what shaped the future for the
modern day PA system as we know it today.
So, today the basic fundamentals of a PA system consist of these basic elements, but to better
understand how it works, the following is key to understand before setting up a system.

1. Source

The most common source is a microphone, but a sound source can also come from a singer's voice before being captured by a microphone. Other sound sources are pre-recorded music playback devices, such as a Laptop/ MP3 player.

2. Modifier

This is commonly where a sound source is modified or manipulated after it is received from the microphone or music playback device. The common modifier is called a mixer/ sound console. This device is typically between the source before it reaches the destination: speakers. Amplifiers are therefore modifiers.

3. Destination

Speakers connected to the Amplifier, is the final destination, before the amplified sound

reaches our ears. Here is a simple diagram to show the signal flow of a PA system,

illustrating the Source, Modifier and Destination devices.

The final destination after the speakers produce sound is your ears.

So, what is the basic principle of a PA System?

It’s used to amplify a sound source (voice into microphone) by means of a modifier/s

(mixer into amplifier) to reach its destination (speakers to the human ear)This is ultimately to convey a message that is loud enough to be heard by a group of people

that could otherwise not be heard without the use of a PA System.

A PA System is used for sound reinforcement to enable groups of people to hear a

conversation, speech or music within an environment, either indoor or outdoors.

PA System Types

PA systems are used in many different types of configurations and each serve a very different

purpose. Let’s look at the four most common types of PA System configurations:

Full Range Point Source PA Systems

This is the most basic form of PA system, with an amplifier and two full range speakers(a cabinet containing a high frequency and a mid-low frequency speaker driver) as an example. 

Two-Way PA System

This system will have a full range speaker and a separate bass or subwoofer speaker driven

by separate amplifiers and a two-way active crossover.

Three-Way PA System

This system will have separate high frequency, mid frequency and low frequency speakers in

separate cabinets, driven by separate amplifiers and a 3-way active crossover.

Distributed PA System

This system is found in office, boardrooms, restaurants, etc. primarily with downward firing

ceiling speakers, and a high voltage 75 volt/ 100 volt  Amplifier.

This system is most commonly referred to as a100 volt line or high impedance system

Line Array PA System

This type of system is found in either indoor or outdoor venues, and is most commonly used

for larger venues for music concerts, public gatherings and sporting events.

The same principle of source, modifier and destination applies to all PA System types.

Full Range Point Source PA Systems

This type of system is the most basic type of PA System. It would commonly comprise a microphone,

a mixer, an amplifier and two full range speakers or two active speakers, all interconnected to

form a system. If a decent mixer is used with a good number of inputs, multiple microphones,

instruments and music sources, such as a laptop or MP3 player can be connected to the mixer.

A PA System that makes use of a mixer and amplifier to power the speakers, the speakers are referred

to as Passive Speakers. If a PA System consists of a mixer and speakers that have their own

built-in amplifiers, these speakers are referred to as Active Speakers.

There are also mixers available with built-in amplifiers, and connect to Passive Speakers.

Below follow examples of basic PA Systems:

Two-Way PA Systems

A two-way PA System consists of separate bass and mid-high speakers.

These systems will always consist of separate amplifiers for bass and mid-high frequencies,

but the most important part of a two-way PA System is an Active Crossover.

This separates bass and mid-high frequencies before it is sent to the individual bass and mid-high

amplifiers. A two-way system can also make use of either passive or active speakers. 

The difference between a full range point source PA system and a two-way PA system is that a two-way PA System makes use of separate speakers and separate amplifiers for low and mid-high frequencies. An active audio crossover forms an integral part of making a two-way system work, to split frequencies.

So, what is an Active Crossover and what is its purpose?

An active crossover is a device that modifies an audio signal before the amplifier.

It works on line-level or preamp signals only. 

Active crossovers combine op-amps, resistors and capacitors to alter different frequency ranges

of the signal. An active crossover has selectable frequencies for bass and mid-high speakers. 

A crossover point can be manually adjusted on the active crossover, meaning it is at the crossover point where frequencies lower than this point will go to the bass speakers and frequencies higher than the crossover point will go to the mid-high speakers. Most modern active crossovers are either usable as two-way stereo or three-way mono active crossovers, meaning that two active crossovers in three-way mode would be needed for a three-way system.

If the crossover point is too low, the frequencies above the crossover point or high pass frequencies, may not be correctly produced in the mid-high speakers and the same will go for the bass speaker, as it may not be able to produce the low frequencies from the crossover point, if the bass speaker is not designed for low frequencies below its designed specifications. 

For instance, if the crossover point is set to 60Hz, the bass and mid-high speakers that are used, may not be able to effectively produce a good enough quality sound, meaning the mid-high speakers may not be able to produce bass frequencies as low as 60Hz, but the mid-high speakers might be able to work better at a higher crossover point of 120Hz. 

Let’s say we choose a crossover point of 120Hz, this means frequencies from 120Hz and below will be sent to the bass speakers and frequencies from 120Hz above will be sent to the mid-high speakers. 

Below is a diagram illustrating a crossover point of approximately 400Hz

Active Crossover

Front

Rear

Here INPUT levels can be adjusted, as well as the crossover frequency point, and also separate low and high output levels.

Below follows a series of illustrations, demonstrating the wiring interconnectivity between an Active Crossover, Bass and High Amplifiers and Bass and Mid-High Speakers.

Two-Way Active Crossover Inputs and Outputs

Interconnectivity between the Crossover and Amplifiers

Interconnectivity between Amplifiers and Speakers

Quick Recap of what we've learned so far

1. Source, Modifier and Destinations are terms used to describe the basic principle of how

a PA System works, as it needs a sound source, which is then modified and fine tuned before it

reaches its destination.

2. A basic PA System consists of a microphone, mixer, amplifier, two speakers and the required

speaker and signal cables to connect it all together.
3. A two-way PA System consists of an active crossover to send dedicated frequencies to the

correct speaker.
4. Two-way PA Systems also consist of separate amplifiers and separate bass and mid-high speakers.

Next Up...

We discuss Three-Way and Distributed PA Systems. Line Array PA Systems will follow in

the third in an in-depth and separate article.

© Intellectual Property Rights Reserved - Marius van Vuuren, Dubai, UAE