The Siren Board

The3t22sOfUSA wrote:The SPL of a 40V2T is 130dB @ 100ft.

The only powerhouse omni-directional. Pretty epic.

Midnight Drifter wrote:can't think of a single directional unit off the top of my head, either.

I'd bet this is because generally, it's eaiser to build a deadzone-free system without rotational sirens. Which I imagine would also be a little more useful in Europe, where sirens are often on very uneven terrain like mountains.

The3t22sOfUSA wrote:The SPL of a 40V2T is 130dB @ 100ft.

Its actually 127dB. Sentry magically changed it to 130 one day.

Midnight Drifter wrote:European sirens tend to not follow the classic American formula of Build it BIGGER. They all seem to be between 5-15 horsepower, if that, can't think of a single directional unit off the top of my head, either.

First, there are no european sirens.
Every country in Europe has it's own sirens, only a few sirens can be seen in more than one countrys.

One example are german sirens like the sirens from Siemens.
They were mounted in the conquered nations during World War 2 and because of the high quality, they still work today.
After World War 2, germany exported sirens to the whole world, mainly the HLS-System.

The next thing is, many countries don't have a real siren network or had it dismantled after the cold war. There are nearly no other catastrophes than flood in middle europe. Storms do lower damage because the buildings here are much more massiv. The heaviest damages are normaly destroyed roofs.
Sirens are mainly used to alarm the fire brigade.

In countries like Austria , very big sirens are useless since the land is not flat.

Germany is a flat land and has the only mechanical high-power-siren, the HLS.
Now, at least germany has very powerful electronic sirens.
Electronic sirens are the first directed sirens in europe but they don't rotate.

Magically changed! It's interesting how manufacturers can get by with things like this. An SPL of 127 dB at 100 feet is certainly nothing to sneeze at, but it's still only half the acoustical power of its implied dB rating. I don't believe inflated ratings are unique to Sentry, as I have seen lower than advertised ratings on Federal Signal's Thunderbolt and ACA's P-50 as well. Who knows just how many others are somewhat less than advertised?

Even more important than the 100 foot dB rating is the 70 dB radius. Are these based on actual measurements or that archaic and arbitrary rule of estimating a loss of 10 dB/doubling the distance, which has no basis on reality?

Crazywarriorman wrote:

The3t22sOfUSA wrote:The SPL of a 40V2T is 130dB @ 100ft.

Its actually 127dB. Sentry magically changed it to 130 one day.

I would say that they were chamber tested, however I may be wrong. The only way to truly tell is have someone record the decibels with a meter in a field. Example is Dane County WI. They have each of their sirens tested that way after each installation.

From posts to this board within the past year we know this is the case for at least one major manufacturer. Testing in an anechoic chamber can yield accurate results in the near field if the tests are done correctly. Chamber tests should correspond well to dB at 100 feet ratings.

However, long range performance data cannot be based on an estimate, but on actual field tests under ideal conditions (or data based on the inverse square law and frequency dependent atmospheric absorption losses), certainly not from incorrect estimations based on the 10 dB/doubling the distance rule found in FEMA CPG1-17. Recognizing this long running error would then put all warning signals on a fair and equal basis for comparison.

This document was published on March 1, 1980 over 30 years ago and this 10 dB/doubling the distance estimation is strictly arbitrary. It is not based on inverse square law and frequency dependent atmospheric absorption losses that actual sound obeys. It yields low results within the first few hundred feet and optimistically high results in the thousands of feet (and miles) which follow.


[quote="Josh(bearlovesox)"]I would say that they were chamber tested, however I may be wrong. quote]

Josh(bearlovesox) wrote:I would say that they were chamber tested, however I may be wrong. The only way to truly tell is have someone record the decibels with a meter in a field. Example is Dane County WI. They have each of their sirens tested that way after each installation.

Do they measure on-axis? That can make a dramatic difference.

As far as manufactures go they always go for the unit's maximum SPL. That means getting the on axis reading. Any others testing the output of a unit should do the same at 100 feet. By the time you reach the unit's 70 dB radius it doesn't much matter as long as the unit is not on a hill or in a valley.

There should also not be buildings, trees or other obstructions between the unit and the point of measurement. These conditions are variable and can change over time. Bonneville Salt Flats would be an ideal location for far field testing. Since finding an ideal site for far field testing would normally present a problem, you could go by the inverse square law and factor in the atmospheric absorption loss for the frequency plus a correction factor for the harmonic content. This would be much more accurate than simply estimating a loss of 10 dB/doubling the distance as is currently done.

Thunderboltlover wrote:

Josh(bearlovesox) wrote:I would say that they were chamber tested, however I may be wrong. The only way to truly tell is have someone record the decibels with a meter in a field. Example is Dane County WI. They have each of their sirens tested that way after each installation.

Do they measure on-axis? That can make a dramatic difference.