STH-10

Federal Signal STH-10
Company	Federal Sign & Signal Company Federal Signal Corporation
Produced	1955-2005 (STH-10A) 1955-1995 (STH-10B)
Type	Omnidirectional Electromechanical
Sound output	115 dB @ 100 ft
Frequency	50/60 Hz
Horsepower	7.5 hp 10 hp
Voltage	240 V AC 1 ph (STH-10B) 208-240/480 (STH-10A) V AC 3 ph
Preceded by	Federal Electric Fedelcode Federal Signal STL-10
Succeeded by	Federal Signal Model ECLIPSE
Documentation	Manual Product sheet

The STH-10 (Single Tone High, 10 Horsepower) is an omnidirectional electromechanical siren that was produced by Federal Signal over a span of 50 years. A step up from the general purpose Model 5 lineup, the STH-10 proved to be one of the most popular of Federal Signal's omnidirectional sirens and gained a reputation as a reliable, effective multipurpose siren. It is still a commonly found siren today despite having been discontinued decades ago thanks to its durability and high performance.

History and design

The STH-10 was introduced in 1955 as a higher-pitched option to supplement Federal's existing STL-10 siren. The STH-10 was designed as a general purpose siren intended mainly for use at fire departments, as it had superior range and volume compared to Federal's Model 5 lineup. While it was mainly used as a fire siren, it easily doubled as a standard civil defense and weather siren when necessary. The STH-10 became a popular choice for many fire departments and municipalities, outselling the STL-10 by a significant margin. The STH-10's very simple design resulted in a siren that was very reliable and easy to keep maintained.

The STH-10 is furnished with a bare 7.5 or 10 horsepower electric motor located on top of the siren. The STH-10 was available in either single and three phase power, designated the STH-10B and STH-10A respectively. The STH-10A used a 10 horsepower General Electric (early), Valley or Marathon motor, while the STH-10B used a brushed 7.5 horsepower Northern Electric motor. Due to its large, heavy rotor and high quality ball bearings, the STH-10 is known for having long spool-down times, with the rotor often coasting for well over five minutes after the siren shuts off.

The STH-10 sports a 20.5-inch, 12-port aluminum rotor facing downwards, a few inches smaller than the 24-inch 7-port rotor in the STL-10. The STH-10's rotor has full length vanes for every port, resulting in a smoother sound than the Model 5. The rotor is also bidirectional, allowing three-phase units to operate well regardless of which way they are wired. The STH-10 is able to reach 115 dB at 100 feet, 1 dB more than its lower-pitched counterpart. The STH-10's rotor and stator were reused by the hybrid-rotational RSH-10 Thunderbeam as well as early 500-SH units until the latter switched to using the C3 1/2 Model 5's rotor in the 1960s.

12 conical sheet metal horns are individually attached to each stator port to efficiently project the output from each port. The STH-10 has a cylindrical, tubular intake located below the siren, in between the siren's three included mounting legs. These legs can be bolted to a pole or attached to a rooftop making it versatile and easy to install.

The STH-10's simple and rugged design makes it suitable for a wide variety of applications and often found itself used in places where other sirens were inadequate or unsuitable, such as large industrial facilities and remote communities. One STH-10 has the distinction of being the northernmost siren in North America, located in Grise Fiord, Nunavut, one of the coldest inhabited settlements in the world. Many STH-10 units can be found in the remote northern territories of Canada, and is the most common siren found in the Arctic.

In 1995, the STH-10 and STL-10 were discontinued as part of restructuring though the STH-10A would be reintroduced shortly after due to popular demand. The STH-10B was not reintroduced, leaving the three-phase STH-10A as the only option. Unfortunately, STH-10s produced after 1995 had poor quality control and tend to be more unreliable with motor issues. The STH-10 was fully discontinued a decade later in 2005, being directly replaced by ECLIPSE-8 which matches the STH-10's performance while allowing for battery backup and solar capabilities by using a DC motor. The STH-10 remains a common sight throughout the US and Canada, often in use at volunteer fire stations and smaller towns as a fire and/or severe weather siren.

While discontinued by Federal Signal, the STH-10 is currently sold under license in South America by the Brazilian-based siren manufacturer Engesig, under the EG-109 TITAN name. In addition, a unique dual-rotor variant is sold under the EG-109 TITAN 2 name.

Variants

Darley Type 10 (Darley STH-10)

W.S. Darley & Co. produced their own rebadged variant of the STH-10, designated the Type 10. Often dubbed the "Darley STH-10" by enthusiasts, the Type 10 consists of an inverted STH-10 core placed inside of Darley's custom cylindrical housing. Being inverted, the Darley Type 10's motor is placed underneath the rotor and stator and held up by short legs. The rotor draws in air from above, with a short tubular intake bolted to the top of the stator. The housing is held up by an A-frame with an eyebolt on top. The Type 10's housing has 8 short round horns and a flat rounded rainshield placed on top. Unlike the standard STH-10, the Type 10's horns do not line up with the stator ports. The housing provides much better protection from the elements than a standard STH-10. The Darley Type 10 would be produced until Darley's partnership with Federal Signal ended in the 1960s.

STH-10C

A three-signal variant of the STH-10 was produced for an unknown length of time, using a solenoid-driven damper inside of the intake to allow the siren to produce pulsed signals. These units are designated as the STH-10C by enthusiasts, as its official name is unknown. Likely only having been available as a special order siren, very few STH-10Cs are known to exist though at least one is in private possession.