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MECHANICAL SIRENS

Mechanical Sirens pump air, compressing and accelerating it to more than 130,000 inches per minute (or 124 miles per hour) where a rotor pulses it on and off on in a square wave form. This spirals at 9,000 revolutions per minute as it expands from the 2 3/4 inch diameter guiding throat.

The Mechanical Siren's spiraling wave is like an ocean’s wave curl projected from a short guiding throat, on off on off, producing the variable sound. The operator controls the volume and the pattern with the foot switch.

ELECTRONIC SIRENS

Electronic Sirens translate a transistor generated signal to an electro magnetic driver which pulses a 3/4 inch diameter diaphragm back and forth rigorously 1/32 inch to move the air in a sine wave form, creating the familiar Whoo Whoo sound
projected from the speaker horn.

Here are some frequently asked questions regarding Mechanical Sirens:

Why the controversy between mechanical and electronic sirens?

Is it just the modern vs. the old fashioned diehard? Well, it is true electronic sirens made their entrance to the emergency warning business in the 1960’s coinciding with the industry wide increase in electrical demand brought on by more lights, radios, computers, and new EMS equipment. Typical mechanical sirens of the era drew 200 to 300 amps compared to only 12 to 17 amps for the new electronic style. Switching sirens was an easy trade off, many cars were not air conditioned and sound insulation was only minimal. Electronic tones from alarms, buzzers, games, and computers were not common. Thus the new sirens enjoyed an acceptance for a season. However, today it’s a different story.

How mechanical sirens work

 

A mechanical siren produces a spiraling square wave, thus offering a very strong and focused pattern.
How electronic sirens work Electronic sirens are notorious for having dead spots and creating noise pollution without direct sound penetration making them less effective.

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Why is it said that mechanical sirens are more effective?

One must look at the physics of the air movement! Electronic Sirens translate a transistor generated signal to an electro magnetic driver which pulses a 3/4 inch diameter diaphragm back and forth rigorously 1/32 inch to move the air in a sine wave form, creating the familiar Whoo Whoo sound projected from the speaker horn. The electronic siren works like an ice cream truck speaker, creating sine waves like ripples on the lake which go and go and go in all directions. Mechanical Sirens pump air, compressing and accelerating it to more than 130,000 inches per minute (or 124 miles per hour) where a rotor pulses it, off on, off on in a square wave form which spirals at 9,000 revolutions per minute as it expands from the 2 3/4 inch diameter guiding throat. The Mechanical Siren’s spiraling wave is like an ocean’s wave curl projected from a short guiding throat, on off on off, making the Whoo sound. The operator controls the volume and the pattern with the foot switch.
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The waves are different, but how do they affect me?

The electronic siren wave pattern is spotty and tends to have dead spots. The electronic siren waves roll and can pass over a vehicle. Did you ever hear someone say, “ I didn’t even hear the siren,” and there was the Fire Truck, or the Ambulance, or the Police Car, next to me!! ?? The Mechanical Siren’s waves are projected in an expanding spiral line to encompass entire vehicles, and to penetrate thru them, causing the air within the car to vibrate, so one can’t ignore the siren, alerting the driver and passengers to the possible approaching danger.
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How does a mechanical siren affect the community?

Because the mechanical siren produces a spiraling square wave, directed by the tuned throat to expand in a narrow pattern, one can not only hear the approaching siren, but can also discern the direction it is traveling. Another advantage is that the waves deaden out, as their spiraling components strike the ground and other porous surfaces. For this reason, one does not hear emergency vehicles with mechanical sirens thru the night from all over the town.
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Does an electronic siren contribute to noise pollution?

Absolutely! The wave of the electronic siren, being essentially two dimensional, widens its path as it travels, further and further, broader and broader. This simple wave expands to create sound over a large expanse, pennetrating and annoying neighboring homes, causing unnecessary noise pollution over a great distance.
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How does speed affect a siren?

Vehicles with electronic sirens tend to out run their sound waves at approximately 55 mph. This phenomena is so common in the industry, they call it sirencide. Vehicles equipped with mechanical sirens do not outrun their sound waves. The air or shock wave is accelerated to more than 120 mph allowing the vehicle’s speed to never be a concern.
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But, what about the new electronic “Q”?

Sounds just like a mechanical siren! Two companies offer these new sirens which digitize the sound of the old standard “Q.” This digitized signal is played from a special large speaker horn. But it still is an Electronic Siren. It only moves air by a 3/4 inch diameter diaphragm, pushed and pulled by electro magnets. Even if it sounds good to the Firefighter, it does not penetrate a car 100 feet away.
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But, I already have a siren and it is the public address and re-broadcast system too!

To this we say no. You do have a public address and rebroadcast speaker which makes sine waves. But no! You do not have a siren engineered to penetrate cars as the TimberWolf siren does.
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What choices does one have for a 123dB Class A mechanical siren?

INDUSTRY COMPARISONS
 

B&M
Super
Chief

Federal
Q2B

TimberWolf
45

Diameter
8 "
10 "
5 "
Weight
23 lbs
48 lbs
14 lbs
Height on Pedestal
9.3 "
10.5 "
6.5 "
Length
14 "
14 "
10.5 "
Sound Directing
Yes
No
Yes
Amps Running
60
125
28
Amps Inrush
175
350
78
Wire (AWG)
6
2
8

Size comparison

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