The Siren Board

Adam Pollak wrote:From that photo, the blower on the Chrysler looks like a 2-stage centrifugal blower...essentially a large central vac motor.

Yes, it has conventional rotors, but the rotors sitting behind the plate like that really looks like my concept.

The problem here is the majority of posters in this thread have no concept of the time when these machines were built and rated.

Ambient background noise levels were very much lower in 1950 than they are today. With that in mind it is entirely possible someone 50 miles from a Chrysler specificly listening for the siren could have heard it. There well might have been a little puffery in the advertising as well. I can definitely assure you the Rochester machine could be heard 25 miles away during tests.

Adam Pollak wrote:
The patent for the screw blower was issued in 1895, #536925

From that photo, the blower on the Chrysler looks like a 2-stage centrifugal blower...essentially a large central vac motor.

I'm surprised that someone here hasn't experimented with a stack of vacuum cleaner impellers to make a miniature version of the Chrysler.

holler wrote:50 mile audible range, sounds like a slight overstatement to me.

I read an article a few years ago that said the LA Chryslers could be heard on Catalina Island about 50 miles off the coast. This is best case scenario with no background noise or obstructions, and I'm sure, even at that point, it was extremely faint.

The thing people don't realize is that concentric ported cylindrical rotor/stator combinations aren't the only way to chop air. Exposing ports in the siren face does the same thing, and a mutistage compressor, like a jet, pushes air to it just fine. I think someone who wanted to build a siren from scratch could do this easier than casting and balancing a rotor/stator.

That's a great article! I'd like to find a copy of the original.

On the HP rating, I know they've changed the formula for calculating horsepower over the years. I don't know of any Chrysler flat-head six with over 100 true hp... Must be fuzzy math, or some sort of special engine. I think the pre-World War II Chryslers had 60 or 80 HP., if I recall reading that. I've driven a '47 DeSoto with the big six, which couldn't beat a VW Rabbit Diesel if it's life depended on it.

When the V8 Hemi came out in '52 (and was then used in the siren as well), I know that blew the others away.

Charles

JasonC wrote:

holler wrote:50 mile audible range, sounds like a slight overstatement to me.

I read an article a few years ago that said the LA Chryslers could be heard on Catalina Island about 50 miles off the coast. This is best case scenario with no background noise or obstructions, and I'm sure, even at that point, it was extremely faint.

You got a date on the earthquake that doubled the distance between the coast and SantaCatalina?

Franz? wrote:

JasonC wrote:

holler wrote:50 mile audible range, sounds like a slight overstatement to me.

I read an article a few years ago that said the LA Chryslers could be heard on Catalina Island about 50 miles off the coast. This is best case scenario with no background noise or obstructions, and I'm sure, even at that point, it was extremely faint.

You got a date on the earthquake that doubled the distance between the coast and SantaCatalina?

Whoops, you caught me! Catalina Island is actually 22 miles from LA, I should have reread my sources.

It certainly is. I estimate an audible range of slightly under 20 miles maximum for a pure frequency of 440 Hz and and SPL of 138 dB at 100 feet. This is estimating an atmospheric absorption loss of 1 dB/1000 feet at 500 Hz plus the inverse square law loss of 6 dB/doubling the distance while assuming the most ideal quiet conditions at the point of measurement.

The thing is that the Chrysler siren produced a square wave, which means the pure tone component is around 3 dB less or around 135 dB at 100 feet.

For a pure frequency of 220 Hz with an initial SPL of 138 dB at 100 feet, however, you would get around 34 dB at 100,000 feet (18.94 miles). The Chrysler siren used a common blower/chopper, which lost considerable output as the shaft speed reduced. The output at 220 Hz would have been much less than that at 440 Hz, so the SPL at 100,000 feet would be well below 34 dB. The Big Bertha siren, however, used a separate blower and like a Thunderbolt or Hurricane was capable of high output during wind down. It might have actually achieved an SPL as high as 30 dB at 20 miles.

holler wrote:50 mile audible range, sounds like a slight overstatement to me.

acoustics101 wrote:...The thing is that the Chrysler siren produced a square wave, which means the pure tone component is around 3 dB less or around 135 dB at 100 feet.

What is the pure tone component?
Sine wave because the higher frequency harmonics in the square wave are attenuated?

Thank you.