Cerwin-Vega SL-12, SL-28, SL-8 User Manual

UNDERSTANDING BASS MANAGEMENT IN PA SYSTEMS

A Guide for Performers

3000 SW 42nd St. • Hollywood, FL 33312 • P 954.316.1501 • F 954.316.1590 • www.cerwin-vega.com

Table Of Content

Forward 3
Introduction 3
Why Would I Need a Subwoofer? 4
What is Bass? 4
The Boom in the Room 5
Some History of Bass Reproduction 5
So How Does This Affect Me? 6
Setting Up Your System with a Non-Powered Subwoofer 7
Time to Choose an Amplifier 7
What if I Want More Than One Subwoofer on an Amp Channel? 8
Cables and Connectors 8
Understanding the Crossover 9
Crossover Point Selection for Subwoofers 10
Subsonic Filters 10
The Active Subwoofer 11
In Conclusion 11
Acknowledgements 11

Forward

Effective low frequency management can be the difference between a performance that has a great, tight low end with
punch, or a disappointing murk. How many times have you been to a gig or have one of your gigs been turned into a sea
of mud by out of control low end? It doesn’t have to be that way and by using some basic techniques and applying them
to any given situation, you can get the most out of your gear and results you may not have thought possible.

Where you put your subs, and how you use them makes all the difference. By learning the basics of how low
frequencies behave and then implementing some basic means with which to deploy them, you’ll be able to clean up your
stage sound and provide clear, crisp sound with a bigger than life thump on the bottom end.

This information is relevant from the smallest coffee house stage to the arenas and theaters of the pros. Once you master
the concepts and grasp the basics of the deployment techniques, no matter what size gig you or your band does, this
information will go a long way to getting you and your band the quality sound you’ve been after.

Dave Stevens

Dave is a 20 year veteran sound mixer, specializing in large scale sound reinforcement, who has been involved in live
mixing for Heart, Pearl Jam, Paul Rodgers, Al Jarreau, Everclear, David Sanborn, Neil Young, Nirvana, Kenny Loggins, Alan
Persons, The Smithereens, Jefferson Starship, and Toad the Wet Sprocket.

Introduction

For many people, the most fun aspect of being a musician or DJ is the live performance. Let’s face it, most people enjoy being
recognized and appreciated. And what can be more enjoyable than performing your craft in front of a live crowd and
hearing the applause of an audience that enjoys the show?

Of course to create a good performance you need a certain level of sound quality as well. It is this aspect of live
performance that is frustrating for many people. From purchasing the correct products, to setting them up to sculpting the
sound of the performance–this can be a daunting task even for experienced musicians.

Many people do not perform in live situations enough to acquire the skills needed for equipment set up and use. Also you
are always under pressure to set up and be ready for show time.

This document is not an all encompassing guide to PA gear. It focuses on one of the toughest aspects of proper PA use and
set up: bass frequencies. Who better to provide this information than Cerwin-Vega!? We are the industry leader in bass since
the introduction of PA gear.

From the incorporation of wheels on bass cabinets to the use of our folded horns for the sound effects in the movie
Earthquake, reliable, bullet proof, earth thumping bass is what we do.

Bass can be overpowering, non-existent, or many degrees in between. From a wide variety of bass cabinets to crossover
settings to the sound space–all can induce variables that can make you sound like a wimpy act, a thumping, earthquake
rumbling phenomenon, or a thick wall of mud that no one wants to listen to.

In this guide, we’ll introduce you to several concepts that will help you get the sound you want—and that means a better
performance for everyone. This is a challenge you will need to address if you want your PA to transfer your ideas accurately
to the audience.

We hope you will find this document useful for your performances. We also hope you will consider Cerwin-Vega! products
for your next PA system.

The Cerwin-Vega Team

3

Why Would I Need a Subwoofer?

You can gain many advantages by adding a subwoofer to your PA setup. A woofer in a full range PA speaker is asked to do
numerous things. It must accurately reproduce the lowest frequencies at high volume, along with the low-mid and mid
range material. By moving the lowest frequencies from your main PA speakers and directing them to a subwoofer, you
eliminate a large amount of the excess work that your main top box was trying to reproduce. As a result, your main cabinets
will run more efficiently and at higher volumes. In the process, you will also be sending those bass frequencies to a speaker
that is specifically designed to handle them.

While the subject of bass management can be quite extensive, the goal of this guide is to provide you with the basics—a
concise look at what you need to get the job done, why you need it, and a look at your available options. By grasping the
concepts of bass management, we’re confident you’ll be headed down the right path to better sound.

What is Bass?

For the purpose of this guide, the bass we’ll be discussing focuses on the low end of the audio spectrum dominated by bass
guitar, kick drum, synthesizers, bass pedals, etc. When we’re talking about bass, we mean low frequency sound waves. Sound
waves? What are they?

Imagine dropping a pebble into a still pool of water. As the pebble hits the surface, it sends
out ripples that have a high crest followed by a dip, or low point, in a familiar circular
pattern of waves. Much like the waves produced by the impact of the pebble, a sound wave
is an alternating pattern of high and low pressure areas that emanate from a sound source.
When the speaker pushes out, it creates a high pressure area. When it pulls in, a low
pressure area is created. Unlike the waves in the pond, however, sound travels much faster—
at roughly 761 miles per hour at sea level.

When we listen, what we hear, in terms of high or low notes, is dependent upon
how close together the successive high and low pressure areas are as they pass our
ear. This is known as the frequency of the sound wave, and it is measured in cycles
per second. A cycle consists of one high pressure zone followed by one low
pressure zone, as indicated in Figure 1.

Another measurement that can help you visualize this concept is wavelength. Wavelength is the actual distance between
cycle peaks. In Figure 1, it is the distance denoted as one complete cycle. The longer the distance between peaks, the lower
the frequency. For example, the high “E” string on a guitar is about 330 cycles per second. At the speed of sound, that would
make the wave crests about 41.1 inches apart. For the low “B” string on a five string bass, the frequency is about 30.87
cycles per second, and the wavelength is 439 inches or 36.6 feet!

We measure frequency in Hertz, abbreviated Hz. A bass PA speaker, often called a subwoofer, is designed to reproduce
frequencies from approximately 120 Hz and below, down to the lower limits of human hearing, which is approximately 20
Hz.

Sound waves do a few confusing things on their way to our ears. For example, their directionality varies with frequency. If
you stand directly in front of a PA speaker and walk off to the side, you’ll notice that the higher notes decrease in level. The
farther you walk away from the front of the speaker, the more noticeable the loss of high frequency (HF) content, or sound,
becomes. Why does this occur? The higher the frequency, the more directional its dispersion pattern—the area over which
the speaker yields acoustic radiation (the sound). Hence, when you walk off to the side, you lose the highs.

Referring back to our description of the high “E” string on the guitar versus the low “B” string on a five string bass, the
difference between wavelengths is not inches, but feet! Hence, low sounds just seem to “spread out” everywhere, while
high sounds seem to easily disappear. This is precisely why people tend to complain about low, muddied sound with a lack
of top end.

Mid/high frequency speakers will often have their dispersion pattern listed on the product’s spec sheet, such as 60x40
degrees or 90x60 degrees. This is a measurement of the horn pattern of the HF drivers and is referred to as pattern control.
A 90x60 degree horn will send the sound 45 degrees out to each side (45x2) and 30 degrees up and down (30x2) from its
center point.

4

Figure 1. A Complete Sound Wave Cycle

Complete Cycle