Low Frequency
Emergency Signaling Handbook
A practical guide to compliance and its history
Low Frequency Emergency Signaling Handbook
A practical guide to compliance and its history
© 2015 United Technologies Corporation
All rights reserved. Specifications are subject to change without notice.
EDWARDS is part of UTC Building & Industrial Systems.
1016 Corporate Park Drive, Mebane, NC 27302
85000-0394
This handbook is for information only, does not provide legal or compliance advice and is not
intended as a substitute for verbatim legislated requirements. For authoritative
specifications regarding the application of life safety and incident management systems,
consult current editions of applicable codes and standards. For authoritative interpretation
of those codes and standards, consult your local authority having jurisdiction.
While every effort has been made to ensure the accuracy and completeness of this
handbook, the authors and publishers assume no responsibility for errors, inaccuracies,
omissions, or any inconsistencies herein.
EDWARDS and Genesis Series are trademarks of United Technologies Corporation.
Low Frequency
Emergency Signaling Handbook
A practical guide to compliance and its history
Contents
Introduction .................................................................................................................................................. 1
Compliance only part of the picture ......................................................................................................... 1
Background: History of Horns ....................................................................................................................... 3
Waveforms: The Ups and Downs of Sound .................................................................................................. 5
The 520 Hz Wave ...................................................................................................................................... 6
Wakeup Calls: Codes and Mandates............................................................................................................. 8
Audible devices ........................................................................................................................................... 10
Horns ....................................................................................................................................................... 11
Horn-strobes ........................................................................................................................................... 12
Sounder Bases ......................................................................................................................................... 14
Audio devices .............................................................................................................................................. 14
End-to-end-compliance .......................................................................................................................... 14
Speakers and speaker-strobes ................................................................................................................ 15
Compatibility Lists: Check Them Twice ....................................................................................................... 18
Application Checklist ................................................................................................................................... 19
Retrofits: When and Where ........................................................................................................................ 21
Non-sleeping Areas: Is 520 Hz necessary? .................................................................................................. 22
Better Life Safety: Making the Right Calls ................................................................................................... 23
Introduction
In 2010, NFPA 72 – the National Fire Alarm and Signaling Code – was amended to generally require low
frequency 520 Hz warning tones in newly constructed commercial sleeping areas where audible
appliances are provided. The change went into effect on January 1, 2014. Many jurisdictions across the
U.S. have adopted the 2010 and 2013 NFPA 72, either directly or through codes such as the
International Fire Code and the International Building Code. However, as noted in the National Fire
Protection Association (NFPA) January/February 2015 blog, many U.S. contractors were surprised by the
requirement’s compliance date1. Additionally, the proposed 2016 version of NFPA 72 includes revisions
that will provide more specifications on testing and listing appliances that produce the low-frequency
tone2.
The implementation of changing to low frequency signals isn’t as complex for commercial fire systems
as previous revisions. For example, the adoption of synchronized strobes required modifications to
circuitry that precipitated external modules and to timed synchronizing pulses to eliminate random
flashes of light in the same line of sight. By comparison, devices and functionality for low frequency
signaling are already in place for many commercial systems. Also, since the provisions only apply to new
construction or significant renovations, there is no need to retrofit existing installations.
Some life safety systems may need special design consideration to accommodate low frequency
notification. Power supplies, amplifiers, audio source units, horns, sounders, and speakers all play a part
in achieving code-compliant 520 Hz signaling. The ease or difficulty with which the new requirements
are deployed depends on the system and the manufacturer. Even if it’s as simple as specifying different
horns or speakers for sleeping areas, there remains the challenge among life safety designers and
building owners of using these signals with the greatest life-saving effect and in compliance with local,
state, and national codes.
Compliance only part of the picture
Like all life safety changes, low frequency signaling has raised its share of questions about compliance
and application, best practice, commercial viability, customer considerations and even compatibility.
These concerns make an uncomplicated and straightforward implementation an elusive objective.
Compliance with codes and standards is only part of the picture. As minimum requirements, they don’t
take into account the nuances of good system design. Even the local authority having jurisdiction (AHJ)
may be concerned with what’s right for a particular setting from a compliance point of view.
1
NFPA.org, http://www.nfpa.org/newsandpublications/nfpa-journal/2015/january-february-2015/incompliance/nfpa-72
2
http://www.nfpa.org/newsandpublications/nfpa-journal/2015/may-june-2015/features/nfpa-72
Low Frequency Signaling Handbook | Introduction
1
The primary objective of a life safety system is to keep building occupants safe to the extent feasible.
The trick for a system designer is distinguishing what can be done from what should be done; separating
what is possible from what is practical. Optimal solutions arise where training and experience meet
good information. Even with life safety there are trade-offs between cost and effectiveness, and the cost
doesn’t have to be monetary. For example, cranking up the effective decibel (dB) of a horn will
eventually awaken even the soundest sleeper, but it could also result in hearing loss, ruptured eardrums
or even organ damage. Similarly, system effectiveness needs to be balanced with system overhead. A
good designer will know how to prevent a good plan from becoming cost prohibitive.
Understanding this issue means understanding the reasoning behind it and the circumstances that lead
to its adoption. Only then can decisions be made that act in the best interests of building owners,
designers, and occupants.
Low Frequency Signaling Handbook | Introduction
2
Background: History of Horns
The road to low frequency signals begins approximately 40 years ago, after the transition from using
electro-mechanical buzzers and mechanical bells to electronic horns. This innovation simplified fire
alarm system signaling and increased the number of signals a typical system could handle.
These new devices produced audible output at a much higher auditory frequency than their
predecessors: about 3,000 Hz. Evidence soon emerged that this pitch may not be as effective at waking
the hearing impaired. According to a National Center for Health Statistics report, 37.5 million Americans
suffer from some hearing loss.3 Fueled by the Americans with Disabilities Act (ADA), and mandated by
the widespread adoption of UL 1971 (Signaling Devices for the Hearing Impaired), the fire alarm strobe
became the primary ADA compliant signaling throughout the 1990s, and remains the de facto standard.
The next evolution came following a series of studies testing the various ways of awakening at-risk
populations, including children, older adults and hearing impaired. Conducted by Dorothy Bruck and Ian
Thomas at the Centre for Environmental Safety and Risk Engineering at Victoria University in Melbourne,
Australia, the research projects compared the effectiveness of notification appliances ranging from
recorded messages to strobes to bed shakers to horns of different auditory and temporal frequencies,
including the standard 3,000 Hz pure tone, as well as a 400 Hz and 520 Hz square wave tones.4 In each
case, researchers measured the length of time needed to awaken test subjects.
Why focus so much on sleep? Because studies show that is when people are most vulnerable to the
danger of fire. The U.S. Fire Administration reports 46 percent of fatal residential fires start between 10
p.m. and 6 a.m., and fatal incidents peak between 3 a.m. and 4 a.m., when most people are in deep
sleep.5
Their initial findings prompted the NFPA’s research wing, The Fire Protection Research Foundation, to
commission further study. Funded by the U.S. Fire Administration, the final report was published in 2007
and culminated nearly ten years of work.6 The results found that a 520 Hz square wave tone may be
more effective at awakening the hearing impaired, older adults and adults who had elevated bloodalcohol levels or who were sleep-deprived. It also was the second most effective way to wake young
children – following a voice warning.
3
Blackwell DL, Lucas JW, Clarke TC. Summary health statistics for U.S. adults: National Health Interview
Survey, 2012. National Center for Health Statistics. Vital Health Stat 10(260). 2014, p. 40.
4
Thomas, Ian and Bruck, Dorothy (2008) Awakening of Sleeping People: A Decade of Research.
5
U.S. Fire Administration (2008), “Residential Structure and Building Fires,” p. 20.
6
Bruck, Dorothy; Ian, Thomas (June 2007), "Optimizing Fire Alarm Notification for High Risk Groups)",
Fire Protection Research Foundation, Research Project.
Low Frequency Signaling Handbook | Background: History of Horns
3
Based on these findings, the Fire Protection Research Foundation study stated categorically that “any
recommendations for the use of strobe lights, presented alone, as an emergency alarm to awaken
sleepers who are hard of hearing or of normal hearing should be withdrawn as soon as possible.”
Instead, it clarified that that strobes continue to have value for people who are awake, particularly in
areas of high ambient noise, and as an emergency alert for people who are deaf.7 The NFPA 72 code was
also amended to require 520 Hz signaling in newly constructed and some renovated commercial
sleeping areas that contain fire alarm systems.
The research findings also demonstrated that voice messaging intelligibility is an important factor, even
when asleep. The study found that non-English speakers did not awaken as readily as English speakers
when presented with high dB voice audio in English. This result debunks the theory that, a message may
still be carried with sufficient sound pressure to awaken an individual regardless of whether they
understand the warning. It seems instead, that words and meaning do break through even a deep
sleep.
7
Bruck, Dorothy; Ian, Thomas (June 2007), Optimizing Fire Alarm Notification for High Risk Groups, Fire
Protection Research Foundation, Research Project, p. 11.
Low Frequency Signaling Handbook | Background: History of Horns
4
Waveforms: The Ups and Downs of Sound
Sounds of particular frequencies travel differently than others. Robert Foulis, the inventor of the fog
horn, struck upon the idea for his new long-range warning apparatus when he heard his daughter
playing the piano from a distance. He could only hear some of the notes — the lower frequency ones.
Similarly, the common dog whistle shows that not all hearing is the same. The dog whistle emits a tone
at a frequency that is above the threshold of human hearing — but which canines can hear.
The way an individual perceives sound depends on physiological factors such as the condition of the ear
and its components including the eardrum, the cochlea, and the tiny hairs that convert sound energy to
electrical signals. The individual’s age, an injury, atmospheric conditions, or congenital impairment all
can have an effect. Neurological factors also affect how the brain processes electrical impulses
generated by the inner ear. An individual’s sleep state, drug use, alcohol impairment, and even their
mental state can impact how sound is perceived, or if it is heard at all.
The combinations of factors that can cause people to hear the same sound differently are virtually
limitless, and, along with energy considerations, facility layout, cost considerations and other factors,
creates a challenge for an alarm system to reach and be understood by as many people as possible.
Making a signal louder eliminates some of the disparity, but there are practical and physical limits to
how loud a signal can and should be, as well as practical and commercial limits on the types of devices
available and potential combination of technologies. There are also more subtle ways to improve
audibility in exchange for less energy.
Low Frequency Signaling Handbook | Waveforms: The Ups and Downs of Sound
5
The 520 Hz Wave
Sound takes the form of waves that travel through the atmosphere from their source. Auditory
frequency represents the distance in time between two of these waves. It is related to what we perceive
as pitch. The height of the waves, referred to as amplitude, is related to what we perceive as sound
pressure, or loudness. Sound level is to auditory frequency what voltage is to current, or volume is to
pressure.
Sound frequency is expressed as Hertz (Hz), a unit of measure that represents one wave per second. A
tone of 1 Hz isn’t really a tone because the frequency needs to be much higher to register as a
perceptible note. The standard fire alarm signal, which does have some advantages, is generated at a
3,000 Hz frequency with a sound level output at 75 to 90 dB (decibels).
A 520 Hz tone is a waveform that repeats 520 times per second. Its discovery as a potential tonal sweet
spot came when researchers began to look not only at the sound wave’s frequency but at the shape as
well.
Waveform shapes are split into four broad categories
that describe its path from one occurrence to the next.
The shape affects how the tone sounds. The sine wave
is most commonly regarded as a typical wave; it
describes a sweeping line from the peak of one wave to
the peak of the next in a smooth symmetrical arc. The
standard 3,000 Hz alarm signal employs a sine wave
referred to as a pure tone.
The square wave describes a wave with right angles and
straight lines across the horizontal and vertical axis only.
It resembles a castle rampart. Other waveform shapes
include triangle and sawtooth.
Changing a tone’s waveform shape changes the
character of its sound without altering its pitch. Listen to
the differences below:
Figure 1 The shape of sound waves determine their pitch
and sound characteristics.
Frequency, waveform
3,000 Hz Sine Wave (Pure Tone)
8
Sample8
3000.wav
Files are for demonstration purposes only. Not for use as life safety signals.
Low Frequency Signaling Handbook | Waveforms: The Ups and Downs of Sound
6
520 Hz Sine Wave (Pure Tone)
520 Hz Square Wave
520 Sine.wav
520 Square.wav
The 520 Hz square wave isn’t really square; it has blips and bounces, known as harmonics. In order for
the tone to meet their standards, listings agencies such as Underwriters Laboratories (UL) require that
these harmonics appear at prescribed frequencies and reach predetermined amplitudes relative to each
other and relative to the primary 520 Hz band.
Figure 2 Tones that meet UL requirements include a primary waveform at the 520 Hz mark (seen at the left of this chart), as
well as a series of harmonics at predetermined frequencies.
The chart above shows the primary 520 Hz band at the left followed by three harmonics. In order for a
life safety system to pass UL’s low frequency testing, it must faithfully reproduce the benchmark tone
and its output must exhibit the same acoustic properties, including harmonics.
Low Frequency Signaling Handbook | Waveforms: The Ups and Downs of Sound
7
Wakeup Calls: Codes and Mandates
The study concluded that the 520 Hz square wave tone was the best overall tone for awakening sleeping
individuals, especially those with hearing impairment. The Fire Protection Research Foundation also
recommended to “replace the current high frequency smoke alarm T3 signal with a low frequency
square wave T3 signal”9.
This research kicked off a series of NFPA technical committee meetings and reports that resulted in
changes to the 2010 Edition of NFPA 72: National Fire Code. The revisions require 520 Hz signals in
newly constructed commercial sleeping areas such as dormitory rooms, hotel rooms, sleeping rooms in
retirement and assisted living facilities where audible appliances are provided, and in some jurisdictions,
bedrooms in multi-unit residential buildings such as apartments and condominiums. The NFPA did not
require modification of the signals for residential smoke alarms.
In NFPA 72, chapters 18, 24, and 29 of the code were affected:
NFPA 72, Chapter 18 requires the installation of low frequency audible fire alarm signals in all
applicable sleeping areas to provide the widest possible
benefit. Surveys show many hearing impaired adults
18.4.5.3 Effective January 1, 2014, where
audible appliances are provided to produce
don’t identify themselves as such often because they are
signals for sleeping areas, they shall
not aware of the impairment, or do not believe it is
produce a low frequency alarm signal that
severe enough to warrant special accommodation. Also,
complies with the following:
the studies allege that the 520 Hz signaling benefits
(1) The alarm signal shall be a square
children, older adults, and those impaired by alcohol or
wave or provide equivalent awakening
medication. NFPA 72, Chapter 24 requires the
ability.
(2) The wave shall have a fundamental
integration of a 520 Hz signal into the messaging
frequency of 520 Hz ± 10 percent.
platform for voice audio and mass notification systems.
It calls for two cycles of a Temporal 3 (T3) 520 Hz tone to
be broadcast to sleeping areas at the beginning of every voice message. This revision aligns with
established requirements found in NFPA 72 and UL 864.
Excluded from the provisions of NFPA 72 Chapter 18
and
Chapter
24
are
healthcare
facilities,
correctional/detention facilities and other occupancies
where private mode signaling is employed and where
staff are trained to alert and evacuate occupants
according to established protocols.
24.4.2.4.3 In areas where sleeping
accommodation are provided, but the voice
communication system is used to
communicate to occupants who are awake,
the low-frequency tone shall not be
required.
NFPA 72, Chapter 29 requires 520 Hz signals in all sleeping areas where standalone smoke
alarms or household fire alarm systems are installed and used to awaken people with mild to
9
Bruck, Dorothy; Ian, Thomas (June 2007), Optimizing Fire Alarm Notification for High Risk Groups, Fire Protection
Research Foundation, Research Project, p. 10.
Low Frequency Signaling Handbook | Wakeup Calls: Codes and Mandates
8
severe hearing loss. This provision differs from Chapters 18 and 24 as those refer to protected
premises systems typically installed in commercial facilities and multi-unit residential buildings.
Chapter 29 refers to residential fire alarm systems or standalone devices that cover a single
household or portion. What this means is that households subject to NFPA 72 only require 520
Hz signals if it will be used to awaken someone known to have hearing loss. This is consistent
with rules governing notification systems for people with disabilities, i.e.: the Accessibility
Guidelines under the Americans with Disabilities Act (ADA).
The NFPA 72 provisions apply to new commercial construction only and certain renovations. Single
family residences are not affected. The compliance deadline was January 1, 2014.
The 2015 Edition of NFPA 720: Standard for the Installation of Carbon Monoxide (CO) Detection and
Warning Equipment was also updated to include low frequency signaling. This code applies to the
installation of carbon monoxide detectors, which are required to initiate audible signals that can be
differentiated from those of smoke and heat detectors.
In NFPA 720, Chapter 6 was affected:
NFPA 720, Chapter 6 requires 520 Hz signals in sleeping
areas. Carbon monoxide events are typically signaled by
T4 tones, which are repeating patterns of four tones
followed by a pause. Fire alarm events are signaled by
T3 patterns, which are three tones followed by a pause.
NFPA 720 requires that those T4 signals be 520 Hz
square wave tones in sleeping areas.
Like NFPA 72, the 520 Hz provisions of NFPA 720 apply to new
commercial construction only. The compliance deadline was
January 1, 2015.
6.4.4.3 Effective January 1, 2015, where
audible appliances are provided to produce
signals for sleeping areas, they shall
produce a low frequency alarm signal that
complies with the following:
(1) The alarm signal shall be a square
wave or provide equivalent awakening
ability.
(2) The wave shall have a fundamental
frequency of 520 Hz ± 10 percent.
Low Frequency Signaling Handbook | Wakeup Calls: Codes and Mandates
9
The 520 Hz Solution
Audible devices
For systems that do not include voice audio, designing a new 520 Hz application is a matter of selecting
horns that meet UL 464 (Audible Signaling Appliances) low frequency requirements. The control system
also needs to be listed as one that will support 520 Hz signaling.
Notification appliances that meet UL 464
are labeled on the device’s nameplate.
These appliances are listed and approved
for sleeping areas that require the 520 Hz
tone in accordance with NFPA 72.
Edwards brand UL 464 listed audible
devices include horns and horn-strobes, as
well as sounder bases for smoke and CO
detectors. For sleeping rooms, most codes Figure 3 Nameplate labels found on notification appliances that have been
and standards require a sound pressure UL listed for 520 Hz signaling in sleeping areas state that the device is for
low frequency applications, and show the UL listed mark.
level of at least 75 dB- at the pillow.
Low Frequency Signaling Handbook | Audible devices
10
Horns
The Edwards 520 Hz horn solution is provided by the G4LF Series of notification
appliances. These low-profile devices offer the benefits of Genesis Series life
safety signals with output suitable for sleeping areas requiring UL 464 listed
low frequency tones.
G4LF horns generate the 520 Hz tone in the standard T3 temporal pattern. An
optional setting configures the appliance for continuous audible output, which
is a critical feature for notification appliance circuits controlled by a coder
module such as the CDR-3.
When connected to compatible Edwards control equipment, G4LF Series
audible 520 Hz output remains synchronized with all Genesis Series audible
signals on the same notification appliance circuit. 520 Hz and standard 3,000
Hz Genesis audible signals can be mixed on the same circuit and still
synchronize together per NFPA 72.
Figure 4 Low frequency horns
are clearly marked 520 Hz on
the front of the device. This is
to distinguish it at a glance
from standard horns.
These devices are also field-configurable for high or low dB output; a jumper cut will reduce the audible
output by about five dB. This allows each device to be tuned to the specific sound requirements of the
room in which it is installed, increasing opportunities to reduce system overhead and installation costs.
Horn-only models may be ceiling- or wall-mounted, providing more positioning options for delivering
the required dB output level.
Low Frequency Signaling Handbook | Audible devices
11
Horn-strobes
Combination horn-strobes deliver UL listed 520 Hz alarms with a strobe signal.
The single housing requires only one wall opening and electrical box.
In addition to meeting UL 464, these devices also must meet UL 1971
(Signaling Devices for the Hearing Impaired) requirements, which include light
output intensity levels and limiting flashes within the same field of view in
order to avoid the risk of seizures for people with photosensitive epilepsy
(PSE).
The UL 464 and UL 1971 performance standards must be met in accordance
with NFPA 72, which sets audible and visible requirements for specific Figure 5 Horn-strobes must
meet the UL 464 standard for
applications such as sleeping areas.
audible devices, as well as UL
1971 standards for visible
When installed with a signal master module or other compatible control signals.
source, Genesis Series horn-strobes allow independent horn control over a
single pair of wires. Two control methods are available: traditional NAC signal silence or normally-closed
contact. Both may be used to silence horns without turning off strobes on the same circuit. This valueadded feature saves the expense of running separate wires where independent horn control is required.
Commercial sleeping areas covered by NFPA 72 require a strobe light within 16 feet of the pillow. If the
device is wall-mounted and located 24 inches or further from the ceiling, it should have a light output
intensity of 110 cd or greater. If the strobe light is ceiling or wall-mounted closer than 24 inches to the
ceiling, it must be 177 cd or greater. It also must provide 75 dB sound pressure level at the pillow.
Figure 6 Where horn-strobes are used in sleeping areas, the device must meet UL 1971 placement criteria for strobe lights, as
well as minimum sound levels at the pillow for the device's audible function.
The placement of a combination horn-strobe in a sleeping area can be a challenge. Thankfully, Edwards
has many options available. G4LF horn-strobes may be field configured for high or standard 520 Hz
audible output (dB) and there are four different light intensity settings. Housings come in either red or
white, and with or without FIRE markings.
Low Frequency Signaling Handbook | Audible devices
12
Combined, these options offer a range of solutions that meet most audible and visible sleeping room
requirements for emergency signals. The following 520 Hz horns and horn-strobes are available from
your Edwards equipment supplier. Consult the data sheet for product details and specifications.
Horns and Horn-strobes, Data Sheet 85001-0639
Model
G4LFWN-HVM
G4LFWF-HVM
G4LFRN-HVM
G4LFRF-HVM
G4LFWN-H
G4LFWF-H
G4LFRN-H
G4LFRF-H
Housing
Color
White
Red
White
Red
Text
Marking
Horn Output
Strobe
Output
None
FIRE
Low Frequency
Selectable
None
(520 Hz)
15, 30, 75, or 110 cd
FIRE
with
None
selectable
FIRE
High/Low
None
dB output
Horn-only models
FIRE
Low Frequency Signaling Handbook | Audible devices
13
Sounder Bases
Edwards 520 Hz sounder bases add UL 464 listed low
frequency audible tones to the entire Edwards line of
intelligent smoke, heat, and CO detectors. When
mounted with a matching detector, these bases provide
an unobtrusive alternative to separately installed horns
and detectors. The combination also reduces cost by
only using one electrical box and one wiring run.
Like wall horns, these sounder bases produce a
distinctive 520 Hz signal. Audible signals may be
configured for either coded or non-coded signal circuits.
Figure 7 Sounder bases provide a clean, integrated
look and reduce installation costs by requiring only
one electrical box and wiring run for both the detector
and the sounder.
Sounder bases are subject to the same dB output
requirements for sleeping areas as wall and ceiling
mounted horns — 75 dB at the pillow. They are audible
devices only and do not have a visible, i.e. strobe, component.
Sounder bases on the same circuit may be activated as a group or zone, which sometimes requires the
use of a polarity reversal module. The group or zone may be set for synchronized audible output with
the use of a signal master module or other compatible control source.
Some sounder bases are compatible with carbon monoxide (CO) detectors. NFPA 720 (Standard for the
Installation of Carbon Monoxide Detection and Warning Equipment) requires a distinctive temporal
pattern to warn of CO in order to differentiate it from fire. CO events are signaled by a T4 pattern,
which consists of four beeps followed by a pause. Smoke alarm events are signaled by a T3 pattern,
which consists of three beeps followed by a pause.
Sounder bases that support both CO and fire detection require a temporal pattern generator installed
on the same data loop to synchronize the T3 and T4 patterns. Fire/CO sounder bases have two operating
modes: fire output only, which emits the T3 pattern and Fire-plus-CO, which emits both patterns. .
Audio devices
End-to-end-compliance
The distinction between audio and audible devices represents a wide gulf in function. Audible devices
refer to horns. They produce the 520 Hz tone by virtue of their electronic properties, i.e.: if the
operating voltage is applied to the device, then the sound is produced. Audio devices are part of a larger
system that includes amplifiers, microphones, and source units that produce sound from audio signals.
They are used in voice evacuation systems to play live or recorded messages. (Voice evacuation systems
are usually required in buildings more than six levels or 75 feet high; refer to local codes for specifics.)
Low Frequency Signaling Handbook | Audio devices
14
Where voice evacuation systems are present, NFPA 72 requires that the system produce a preannounce
tone immediately prior to the live or recorded message. Since this tone must be a 520 Hz square wave
generated by a UL 464 listed audio evacuation system in sleeping areas, a system needs end-to-end
compliance.
End-to-end compliance requires that all relevant audio components contributing to the production of
the warning signal be tested and certified to ensure that the UL-defined 520 Hz square wave tone is
produced accurately and consistently. That includes the control system, audio source unit, amplifier,
speaker, and even the 520 Hz .wav file. Once evaluated together as a working system under controlled
conditions, it is then approved and listed to UL 864 and UL 464.
Any audio system may be able to play a 520 Hz .wav audio file, and it may sound to the untrained ear
just like any other 520 Hz square wave tone. But for listing purposes, if it isn’t UL approved, it does not
comply with NFPA low frequency emergency signaling requirements.
For new installations that include sleeping areas, the system designer needs to ensure end-to-end
compliance. Refer to the current system compatibility list, which specifies the arrangement of hardware
components and software necessary to qualify. Some manufacturers may require special amplifiers and
control equipment to gain the UL 464 listing.
Edwards audio systems have achieved, without any modification or upgrade, UL 464 listings for all
currently supported amplifiers and control equipment. These components may be specified without
special consideration for 520 Hz sleeping areas. Only the speakers installed in sleeping areas need to be
specially selected.
Speakers and speaker-strobes
Edwards has a wide variety of 520 Hz ready speakers and speaker-strobes
available. These include wall and ceiling models, as well as speaker-only units
and combination speaker-strobes.
Optional amber lens tints, ALERT or FIRE markings, and red or white housings
ensure there is a 520 Hz-ready speaker for every application, including mass
notification.
Edwards speakers feature selectable wattage taps, while speaker-strobes
allow for both wattage and light output levels to be configured in the field.
This makes it easier to order, stock, stage, track and inventory because the
same unit can be used for a range of room sizes and layouts.
Figure 8 Versatile speakers
and speaker-strobes may be
used for fire alarm, CO alarm,
and mass notification
purposes.
Wattage tap and light output settings remain clearly visible, even after final installation, allowing devices
to be fine-tuned to achieve its maximum benefit in exchange for the lowest possible system overhead.
Models for both 25 and 70 VRMS audio circuits are available.
Low Frequency Signaling Handbook | Audio devices
15
Edwards 520 Hz ready speakers derive the added benefit of high fidelity performance from their ability
to produce the UL-approved low frequency tone. This means they produce crisper, clearer voice audio
output that is highly intelligible over large areas. These speakers also offer potential cost benefits. For
example, when used in non-sleeping areas, it may be possible to place fewer Edwards high fidelity
speakers over the same area compared to standard speakers and still achieve the same audibility.
The following 520 Hz High Fidelity speakers are available and part of a UL listed end-to-end audio system
solution. Consult the data sheet for product details and specifications, and consult the appropriate
system compatibility list for application suitability.
Wall Speakers and Speaker-Strobes, see Data Sheet 85001-0642.
Model
Housing
Color
Text
Marking
Lens
Color
Strobe
Output
Speaker
Voltage
Life Safety 520 Hz High Fidelity Appliances
G4HFWN-S2
White
G4HFRN-S2
Red
G4HFWF-S2
White
G4HFRF-S2
Red
G4HFWN-S2VMC
White
G4HFRN-S2VMC
Red
G4HFWF-S2VMC
White
G4HFRF-S2VMC
Red
G4HFWN-S7
White
G4HFRN-S7
Red
G4HFWF-S7
White
G4HFRF-S7
Red
G4HFWN-S7VMC
White
G4HFRN-S7VMC
Red
G4HFWF-S7VMC
White
G4HFRF-S7VMC
Red
None
Speaker only models
FIRE
25 Volt
(Selectable ¼, ½, 1, or 2 watt)
None
Clear
FIRE
Selectable
15, 30, 75, or 110 cd
None
None
Speaker only models
FIRE
70 Volt
(Selectable ¼, ½, 1, or 2 watt)
None
Clear
FIRE
Selectable
15, 30, 75, or 110 cd
Mass Notification 520 Hz High Fidelity Appliances
G4HFWA-S2VMA
G4HFWA-S2VMC
G4HFWN-S2VMA
ALERT
White
G4HFWA-S2
G4HFWN-S7VMA
G4HFWA-S7
Selectable 13, 26, 65, or 95 cd
Clear
Selectable 15, 30, 75, or 110 cd
25 Volt
Selectable 13, 26, 65, or 95 cd
(Selectable ¼, ½, 1, or 2 watt)
Amber
ALERT
G4HFWA-S7VMA
G4HFWA-S7VMC
None
Amber
ALERT
White
None
ALERT
Speaker Only Model
Amber
Selectable 13, 26, 65, or 95 cd
Clear
Selectable 15, 30, 75, or 110 cd
70 Volt
Selectable 13, 26, 65, or 95 cd
(Selectable ¼, ½, 1, or 2 watt)
Amber
Speaker Only Model
Low Frequency Signaling Handbook | Audio devices
16
Ceiling Speakers and Speaker-strobes, see Data Sheet 85001-0641.
Model
Housing
Color
Text
Marking
Lens
Color
Strobe
Output
Speaker
Voltage
Life Safety 520 Hz High Fidelity Appliances
GCHFRF-S2VMC
Red
GCHFWF-S2VMC
White
GCHFRN-S2VMC
Red
GCHFWN-S2VMC
White
GCHFRF-S2VMCH
Red
GCHFWF-S2VMCH
White
GCHFRN-S2VMCH
Red
GCHFWN-S2VMCH
White
GCHFRF-S2
Red
GCHFWF-S2
White
GCHFRN-S2
Red
GCHFWN-S2
White
GCHFRF-S7VMC
Red
GCHFWF-S7VMC
White
GCHFRN-S7VMC
Red
GCHFWN-S7VMC
White
GCHFRF-S7VMCH
Red
GCHFWF-S7VMCH
White
GCHFRN-S7VMCH
Red
GCHFWN-S7VMCH
White
GCHFRF-S7
Red
GCHFWF-S7
White
GCHFRN-S7
Red
GCHFWN-S7
White
FIRE
Clear
None
FIRE
Clear
None
Selectable
15, 30, 75, or 110 cd
Selectable
25 Volt
95, 115, 150, or 177 cd
(Selectable ¼, ½, 1, or 2 watt)
FIRE
Speaker only models
None
FIRE
Clear
None
FIRE
Clear
None
Selectable
15, 30, 75, or 110 cd
Selectable
70 Volt
95, 115, 150, or 177 cd
(Selectable ¼, ½, 1, or 2 watt)
FIRE
Speaker only models
None
Mass Notification 520 Hz High Fidelity Appliances
GCHFWA-S2VMA
ALERT
Amber
GCHFWN-S2VMA
None
Amber
GCHFWA-S2VMC
GCHFWA-S2VMAH
White
GCHFWN-S2VMAH
ALERT
None
GCHFWA-S2VMCH
ALERT
GCHFWA-S2
Clear
Amber
Amber
Clear
ALERT
Amber
GCHFWN-S7VMA
None
Amber
GCHFWA-S7VMAH
GCHFWN-S7VMAH
GCHFWA-S7VMCH
GCHFWA-S7
White
ALERT
None
ALERT
Selectable 15, 30, 75, or 95 cd
Selectable 82, 100, 130, or 155 cd
25 Volt
(Selectable ¼, ½, 1, or 2
watt)
Selectable 95, 115, 150, or 177 cd
Speaker only model
GCHFWA-S7VMA
GCHFWA-S7VMC
Selectable 13, 26, 65, or 82 cd
Clear
Amber
Amber
Clear
Selectable 13, 26, 65, or 82 cd
Selectable 15, 30, 75, or 95 cd
Selectable 82, 100, 130, or 155 cd
70 Volt
(Selectable ¼, ½, 1, or 2
watt)
Selectable 95, 115, 150, 177
Speaker only model
Low Frequency Signaling Handbook | Audio devices
17
520 Hz Application
Compatibility Lists: Check Them Twice
System design for UL 464 listed low frequency signaling in required sleeping areas begins with the right
equipment. A horn is a simple on-off device with a fixed audible output at operating current. The
nameplate label on the device will state that it is UL listed for 520 Hz signaling applications. When placed
in a bedroom and generating at least 75 dB at the pillow, these devices will meet the basic requirements
under UL 1971 for sleeping areas.
Audio voice systems are more complex. Even though a system may be capable of playing a 520 Hz
square wave pre-announce .wav file, it may not generate a true representation of the tone as defined by
UL. Off-spec harmonics, acoustic interference, audio distortion, and amplifier or speaker limits can cause
an impact. Only listed equipment will demonstrate to the local AHJ that the installation meets UL 464 in
accordance with referenced building codes.
There is no consistent means of labeling the equipment. Horns and speakers will have a label on the
back. Sometimes there is also 520 Hz indication on the front. Amplifiers and other equipment may or
may not be labelled as being UL 464 Listed explicitly for 520 Hz signaling.
To ensure the entire audio system supports 520 Hz signaling, life safety designers need to closely
consult the compatibility list issued by the manufacturer for the control system that will manage the
audio. This list will document all equipment, including amplifiers, speakers, and the sound file that
have been approved and listed. Be sure to obtain the latest list. Earlier documents may not include
low frequency-compatible products.
Also, avoid the frequency response trap. Frequency response is a technical specification for speakers
commonly found on data sheets and installation instructions. A typical value is 400 — 4,000 Hz, which
refers to the speaker’s ability to reproduce sound. Because 520 Hz falls within this range does not mean
the speaker is suitable for sleeping areas. Look for a statement that the device is UL 464 listed, or check
its nameplate label, or consult the appropriate compatibility list. If doubt remains, speak with the AHJ.
Low Frequency Signaling Handbook | Compatibility Lists: Check Them Twice
18
Application Checklist
If subject to the new NFPA 72 520 Hz requirement:
Horns and Sounder Bases
 75 dB- at the pillow
 520 Hz square wave tone output
 UL 464 listed for 520 Hz signaling per nameplate label
Speakers
 Preannounce tones, 520 Hz square wave
 75 dB- at the pillow
 UL 464 and UL 864 listed for 520 Hz signaling per nameplate label
 Documented in the system compatibility list as part of an end-to-end audio chain that is
listed to UL 464 and UL 864
Combination Horn-strobes
Combination horn-strobes are placed in accordance with the requirements for visible notification
appliances.
 75 dB- at the pillow
 520 Hz square wave tone output
 Placed no more than 16 feet from the pillow
 UL 464 listed for 520 Hz signaling per nameplate
 UL 1971 listed as a visible signaling appliance for the visually impaired per nameplate
 Synchronized visible output if more than one device within the same line of sight
 Minimum 110 cd light intensity when wall mounted more than 24 inches from the
ceiling
 Minimum 177 cd light intensity when ceiling mounted or wall mounted less than 24
inches from the ceiling
Low Frequency Signaling Handbook | Application Checklist
19
Combination Speaker-strobes
Combination speaker-strobes are placed in accordance with the requirements for visible notification
appliances.
 Pre-announce tones, 520 Hz square wave
 75 dB- at the pillow
 UL 464 and UL 864 listed for 520 Hz signaling per nameplate
 UL 1971 listed as a visible signaling appliance for the visually impaired per nameplate
 Synchronized visible output if more than one device within the same line of sight
 Placed no more than 16 feet from the pillow
 Minimum 110 cd light intensity when wall mounted more than 24 inches from the
ceiling
 Minimum 177 cd light intensity when ceiling mounted or wall mounted less than 24
inches from the ceiling
 Documented in the system compatibility list as part of an end-to-end audio chain that is
listed to UL 464 and UL 864
Control equipment, amplifiers
 Documented in the system compatibility list as part of an end-to-end audio chain that is
listed to UL 464 and UL 864
 Employs a factory supplied 520 Hz square wave audio file
Low Frequency Signaling Handbook | Application Checklist
20
Retrofits: When and Where
520 Hz signaling requirements apply generally to new construction in specific sleeping areas. However, if
a retrofit requires extensive building renovations, the local AHJ or building standard may qualify the
project as new construction for life safety system purposes. Frequently, a life safety system overhaul,
such as the replacement of the main control panel, will also trigger new construction requirements.
Even if otherwise within the new requirement, low frequency signaling is considered optional for
installations begun prior to January 1, 2014. If desired, the switch can be achieved for non-voice audio
systems by simply adding or replacing standard horns with the low frequency variety. Low frequency
horns have a tendency towards higher current draw, so make sure to also reassess the system battery
and wiring capacities.
Voice audio retrofits require close consultation with the system compatibility list to ensure end-to-end
compliance with UL 464 and UL 864. Some manufacturers require the replacement of amplifiers and
other control equipment, as well as room side speakers. Others, such as Edwards, only need upgraded
speakers.
Low Frequency Signaling Handbook | Retrofits: When and Where
21
Non-sleeping Areas: Is 520 Hz necessary?
The fire alarm code does not specify that the standard 3,000 Hz tone must be used outside of sleeping
areas. If desired, a 520 Hz signal could be used throughout a facility, as long as it meets sound pressure
level requirements.
One example for such use is in hallways outside sleeping rooms. While low frequency signals are not
required in these locations, installing two distinct tones (520 Hz and 3,000 Hz) in close proximity — even
when separated by a door — could compromise the signal’s efficacy. Installing low frequency horns in
the hallway would mitigate this risk.
For voice audio systems nothing precludes the playing of the same 520 Hz pre- and post- announcement
tone in the hallway over standard speakers as long as the sound pressure level is adequate, and the
speakers used in the adjacent sleeping areas are part of an end-to-end audio chain listed to UL 464.
Would building occupants be better served by 520 Hz signals everywhere? Should they become the de
facto standard for all emergency signaling applications? The answer, not surprisingly, is yes and no.
Installing UL listed 520 Hz signals can be more expensive. For horns and horn-strobes, there is a
significant jump in current draw requirements, which could increase system overhead. Battery
calculations and wire capacity also need to be taken into account. Battery life is one of the primary
reasons why 520 Hz is not currently required for residential smoke alarms.
Non-voice audio systems tend to be small applications such as a restaurant, small or medium-sized retail
space, or a small office. If the system is near a point where a supplementary power supply would be
required, then it probably wouldn’t be feasible to go with 520 Hz horns. But if there is room in the
system, and calculating the additional costs shows an insignificant overall increase, 520 Hz horns may
bring potentially better audibility to the application.
Low Frequency Signaling Handbook | Non-sleeping Areas: Is 520 Hz necessary?
22
Better Life Safety: Making the Right Calls
An experienced life safety system designer knows that a large part of each project process is the costbenefit analysis. Even in a code-driven business there remains leeway to enable the system designer to
put his or her personal mark on the project. What they leave behind is a final product that’s built on a
mix of experience, technical knowhow and product knowledge.
The trick is making the right call for the project based on the needs of the building owner and the safety
requirements of its occupants. It’s not an easy task. With technology available today, there is virtually no
limit to the communications measures that can be put in place to save lives. But are all these measures
feasible? Are they practical? Will the builder owner accept the aesthetic look? Do they pass the costbenefit test?
When it comes to 520 Hz implementation, the only easy answers are the ones provided by the life safety
code. Strict compliance with all applicable requirements is, of course, required. However, an
experienced life safety system designer works not merely to comply with the code but to provide the
best possible protection for building occupants given the situation.
Whether 520 Hz finds application beyond sleeping areas will depend on your local AHJ, your client, and
your ability to think beyond the code. This is what distinguishes a good system designer from one that
really excels.
Low Frequency Signaling Handbook | Better Life Safety: Making the Right Calls
23
Low Frequency
Emergency Signaling Handbook
P/N 85000-0394, Issue 1
Contact us...
Email: edwards.fire@fs.utc.com
Web: www.est-fire.com
Edwards Detection and Alarm
1016 Corporate Park Drive
Mebane, NC 27302
In Canada, contact Chubb Edwards...
Email: inquiries@chubbedwards.com
Web: www.chubbedwards.com
© 2015 United Technologies
Corporation, Inc. All rights reserved.
Specifications subject to change without
notice. Edwards is part of UTC Building &
Industrial Systems, a division of United
Technologies Corporation.