Model M

	Sterling Model M
	; A post-1928 Sterling Model M in Mantua, OH.
Company	Inter-state Machine Products Company (1920-1925) Sterling Siren Fire Alarm Co. (1925-1973) Sentry Siren, Inc. (1973-1986)
Produced	1920-1986
Type	Omnidirectional Electromechanical
Sound output	- Figure not available, Estimated 113dB@100ft
Horsepower	1.5-10HP
Succeeded by	Sentry 10V2T

The Model M is a horizontally oriented electric siren manufactured by The Sterling Siren Fire Alarm Company, of Rochester, New York and later produced by Sentry Siren, Inc. These sirens were primarily marketed for fire alarm and general alarm use, intended to serve as a more distinct and efficient alternative to fire bells and steam whistles. The Model M is believed to have started its production in 1920, intended to compete with the Type Mach. B, but was quickly and widely successful, so much so that it knocked the sales of the Mach. B out of the water. Due to the popularity of this siren, it is believed almost every volunteer fire department in the New England area had one at some point.

Model M's were offered in a single and double head configurations, Single and dual tone configurations were also offered, with the Sterling Model M being among the first double toned sirens manufactured. It was sold alongside the industrial Type F and F-2, as well as the Vertical Siren and Little Giant.

While the community often calls these sirens "M-10", "M-5" and "Y-10", these are misnomers. Sterling never used the siren horsepower in the model name, or any letter other than "M". These sirens are simply the Model M, or Sterling Code Sirens for coded Ms. The only exception are units built by Sentry Siren post-1973, which are called the M-10. "N-5" and "M-3" are also misnomers and not real model names.

History and Design

The Model M was designed in 1919 by Merton C. Armstrong, superintendent and lead designer of the Sterling Siren Fire Alarm Company, with the goal of creating a new and distinct fire alarm signal to replace antiquated methods such as the use of air/steam whistles and bells. The Model M does this by employing the same principles used on Sterling Siren's smaller vehicular models, but at a substantially larger scale.

The design of the Model M centers around a modular unit construction, consisting of an electric motor on a cast iron base, and two "Heads", consisting of a 14-inch aluminum impeller that rests in front of a cast iron backplate and within a cast iron fan housing. A sheet metal hood shields the motor from the elements, while a semi-circular hood known as a "sounder" serves to both keep the head assembly safe from the weather and guide sound down to the ground. Most models feature spun aluminum projectors on each end of the siren, intended to tighten intake airflow and better project intake sound, which makes up about half of the Model M's overall sound output.

The cast parts of the Model M were designed very carefully, such that many of them fit tightly within each other, making the siren nigh-immune to damage through misalignment. This resulted in the Model M being among the most robust and reliable siren designs to ever be produced, easily beating its primary competitors in this field.

Variations

Sterling Model M sirens have four distinct variations that were produced over the span of their production:

Pre-1928

Pre-1928 models encompass all variants of the Model M produced before 1928, which use a distinct, perfectly cylindrical head design, giving the siren an overall narrower profile. While all of them share distinct characteristics, there are various known inconsistencies and differences between pre-1928 models. Pre-1928 models, like all variants of the Model M, were offered in single and double head configurations. Single heads are commonly 1.5HP and 3HP, while double heads are usually 3HP or 5HP. While most commonly being 16 port, 8 port and 8/16 port pre-1928 units are known to exist, though pre-1928 Model Ms with 8 port heads are extremely rare.

Post-1928

A few years after the introduction of the Sterling Code Siren, the original Pre-1928 pattern Model M sirens were dropped in favor of what Sterling Siren referred to as the "Improved Model M" siren, made distinct by their larger backplates, stouter form factor and prolific use of distinct, vented weatherproof horns. The "Improved" Post-1928 Model M sirens were designed to simplify production by allowing the Sterling Code Siren and Model M sirens to share parts with each other. Post-1928 Model Ms are most commonly 3HP in the single head configuration, and 5HP or occasionally 7.5HP in the double head configuration. Post-1928 Model Ms are commonly found in 8/16 port dual tone and 16 port single tone configurations, with earlier models using slimmer Howell Red Band electric motors and being more commonly 16 port. The vast majority of Post-1928 Model Ms use Peerless electric motors, and were offered in 115/230V Single Phase and 220/440V Three phase configurations.

Aluminum Heads

To be added...

Trivia