Siren terminology

General terms

Blower

A blower is a device designed to force high-velocity air into a machine or engine. Supercharged sirens utilize blowers to force pressurized air into the rotor, which greatly improves the siren's performance at the cost of reliability. The Roots blower is the most common type used on sirens, using a pair of belt-driven interlocked spinning lobes to compress and force the air through into a pipe. Centrifugal blowers are much simpler, consisting of a perforated disk spun by an electric motor. Centrifugal blower fans are very similar to mechanical siren rotors.

Housing

The housing is a protective cover placed around a siren's rotor/stator assemblies to protect the siren from debris, bird nests, and weather. The housing may surround the entire siren, or may only be a small part of it. Some sirens lack a housing at all, though this is uncommon. The housing often pulls double duty as a projector, especially on vertical omnidirectional sirens.

Intake

The intake is the part of a siren where air is drawn into the siren's rotor. Some sirens lack any special intake, simply drawing in air from the open side of the rotor, while others have intakes designed to maximize the inflow of air. These intakes can be cone or bell-shaped, or cylindrical tubes. Some sirens have their intakes integrated into the rotor itself. A somewhat significant portion of a siren's output is through the intake, leading to it sometimes pulling double duty as a projector.

Projector

The projector is what focuses and projects the output from a siren. In rotational sirens, these typically take the form of horns or smooth, rounded surfaces, while in omnidirectional sirens, they come in the form of louvers.

Rotator

The rotator is a part of a rotational siren responsible for rotating the siren's projector. Rotation mechanisms are motor-driven, either by the siren's main motor or by a small secondary motor. Rotator types include chain-drive, belt-drive, and direct-drive, typically with the motor input fed through a gear reduction drive to achieve the desired rotation speed. Most sirens rotate between 2 and 4 rpm. The rotator can be a separate, non-rotational part of a siren, or it can be integrated into the rest of the siren. Not to be confused with a rotor, mentioned below this entry.

Rotor

A rotor is a rotating part of a machine. In electromechanical sirens, the rotating part is a perforated (each perforation named a "port" by enthusiasts) disk which is typically spun by an electric motor. The rotor is held inside of a stationary hollow disk, called the stator, with a perforation count typically matching that of the rotor. The stator pushes an air stream against the rotor, and as the rotor spins, the airflow will be alternately interrupted and allowed to pass. The ensuing fluctuation in air pressure produces a series of regular pressure waves that we perceive as sound. The faster the rotation of the rotor, the higher the pitch.

Stator

A stator is a stationary part of a machine. In electromechanical sirens, the stationary part is a perforated (each perforation named a "port" by enthusiasts) hollow disk which houses the rotor, the rotating part, with a perforation count typically matching that of the stator. The stator pushes an air stream against the rotor, and as the rotor spins, the airflow will be alternately interrupted and allowed to pass. The ensuing fluctuation in air pressure produces a series of regular pressure waves that we perceive as sound. The faster the rotation of the rotor, the higher the pitch.

Abbreviations

rpm

Rotations per minute.

v

Volts or voltage.

w

Watts or wattage.

dB

Decibels.

AC

Alternating current.

DC

Direct current.

Hz

Hertz.

ARS

The official Air Raid Sirens Forums, which can be found on airraidsirens.net.

Enthusiast terms

These are typically informal terms generally only used by siren enthusiasts.

Intake sound

When sound output is emitted from an electromechanical siren's intake, it is referred to as intake sound. The concept of intake sound is debated within the siren community but has been proven to exist on several occasions.

Mystery siren

A mystery siren is a siren unit, the make and/or model of which is unknown.

Port

A port is an opening in a mechanical siren's rotor or stator. Term most likely originated from the word "porthole".

Port ratio

A port ratio, also referred to as port count, is the number of perforations that a dual tone electromechanical siren's rotor and stator has. Examples would be 5/6, 8/12, 9/12, and 10/12.

Sick

When a siren is sick, it usually means that the siren is running at a lower pitch than standard. This can be due to a variety of reasons, such as a draining battery or undervoltage. Sirens with worn out brushed motors are also often considered "sick", as worn brushes result in an unsteady, wavering pitch.

Siren Board

A name given to the forum section of airraidsirens.net. The forum is officially named the Air Raid Sirens Forums.

Siren graveyard

A siren graveyard or simply a graveyard is a term referring to a location in which several unused sirens are stored. Such examples would be behind West Shore Services, Inc., in Allendale, MI, or the front lot of Clayton Werden Electric Co., Inc., in Cincinnati, OH. Typically, the sirens within graveyards are available for sale, although this only goes for a very few number of locations. It is important to know that siren graveyards are not always publicly accessible, and are, in most cases, located on private property. Please do not tresspass on their property and do not bother/harass the owners to obtain their sirens. This gives enthusiasts a bad rep.

Siren junkie

A siren junkie is a derogatory term referring to a siren enthusiast, though it is sometimes jokingly used among the community.

Siren kiddie

A siren kiddie is a derogatory term for young siren enthusiasts, particularly ones considered to be annoying or cringy. Not all young enthusiasts are considered siren kiddies.

Wire Spool

Nickname for the Federal Signal SD-10, which have some resemblance to wire spools, as previously mentioned. This term was first introduced sometime in the 2000s to refer to Los Angeles' SD-10s.

WKII siren

Used within the German siren community. A WKII siren is a term referring to sirens used during or before World War II. WKII sirens are notable purely because they weathered the war and avoided the standardization of civil defense sirens in Germany, with most WKII sirens being replaced by the standard E57.