What siren can be heard the furthest away?

[OfficialSquished]

So, I been thinking about this question for the longest now. It really confuses me a lot when every time I think about it, and I need help someone explain it to me. I know the loudest one is P-50 but I wonder what any another siren can be heard the further away?

[Eclipse DDS]

The Penetrator-50 is the second loudest siren I believe, the loudest being Chrysler's V8-powered siren. It has a supposed range of 25 miles, which I think is a tough amount to beat.

[Greenrid]

Sorry to be impolite, but what exactly are you asking? If you're wondering what the loudest siren is after the P-50, Eclipse DDS answered that one above. If you're wondering about how not-as-loud sirens (like how the Thunderbolt isn't as loud as the P-50) can be heard from farther away than the P-50, however, that would all depend on the environment around the siren.

Depending on where the siren is located, different obstacles like buildings, trees, and the terrain can affect the range of the siren. Most P-50s are in urban/suburban areas where there's lots of houses and buildings, which absorb or reflect the sound coming from the siren. Like in some YouTube videos where people can hear a STH-10 from 10 miles away, it's because it's located high enough so it doesn't have as much things shortening it's range. To put very it simply, the higher the siren, the father it can be heard away from!

[Unit of Civil Defense]

It also depends on the atmospheric conditions...night time the air is denser due to higher humidity and sound travels farther than during the day when the air is less denser. A good example would be take any siren you like, sounding either day or night...in Seattle, Washington the sound would travel farther due to its wetter atmosphere than it would in Phoenix, Arizona where there is relatively low humidity.

[singlestrobe]

I’m gonna guess the Chrysler bell cause it’s the loudest siren in the world but let me do some research

[SirenMadness]

Advertised readings claimed at the hundred-foot mark don't necessarily hold much weight at considerable distances where the siren's fundamental pitch is at the mercy of atmospheric and ground absorption. I suppose with the majority of offerings nowadays virtually all being single-tone and within a pretty marginal frequency spread, one could accurately ascertain a siren with a higher standard rating to carry longer than a similar-sounding competitor with a lower number... such wasn't the case back when a contingent of varying port counts and ratios flooded the market, not to mention that emphasis hadn't yet been placed on a siren's 70-dB radius being the better indicator of its overall performance. A two-tone siren may scream louder on site, but over a fair distance the interaction between its two tones may just serve to hamper it.

There are some interesting old threads buried here that delve more into the physics of environments and perceived loudness; and even into lawsuits over inflated or outright bogus ratings or claims. I remember a few installers chiming in on the performance of the T135-DC, claiming that it in fact had superior coverage to that of the P50, which itself allegedly sold with a slightly exaggerated number.

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[ThatGuy2020]

I mean, loud doesn’t mean distance. It certainly helps with the distance, but it has a lot to do with the geography of the location, and frequency of the sound.

2001s at a distance are extremely loud indoors because of their high frequency

[AcousticTheory]

From an engineering perspective, first we have to define what is 'audible'.

Sirens produce a single or dual continuous tone that may be detectable down to the threshold of the ambient noise. Because it's a steady tone, and has a narrow bandwidth, it may not need to be much louder than the background noise in order to be noticed.

In a small town environment, background noise may be between 50 and 65 dBA. In a city, it's closer to 75 dBA. (The A-weighting doesn't have a super significant impact here, even though sirens are rated using C weighting (e.g. dBC), because the weighting curve is mostly effective at lower frequencies than sirens use, although the C-weighting curve is the 'flatter' curve). So to be audible above broadband background noise, the sound level produced by the siren needs to be 65dBA or above, and in a downtown area it should be 70dBA or above.

For a point source, sound level decays with distance at a rate of -6dB per doubling of distance. However, obstacles and the environment obstruct sound propagation. The guideline used by FEMA in CPG 1-17 (the Outdoor Warning Systems Guide) is a rate of -10dB per distance doubled. This accounts for wind, terrain, foliage, and obstructions.

For any siren, you can determine the distance for audibility roughly based on the siren's rated 100' output, then at 200' the output is -10dB from that number, at 400' the output is -20dB down, at 800' it is -30dB down, etc., and this is what a FEMA CPG 1-17 application of a siren will be designed to satisfy. In the real world, the propagation loss will be somewhere between -6dB and -10dB per doubling of distance, so there is some extra margin built into the numerical calculation of siren range.

Where things get more murky is the difference between an ideal -6dB propagation loss and the FEMA -10dB guideline. Lower frequencies naturally penetrate foliage and wrap around obstacles more easily, because wavelengths at lower frequencies are larger. All else being equal, the siren with the lower tone (down to about 300-400 Hz) will produce a louder tone at the distance, but you also have to balance this against the sensitivity of the ear. This is where the A weighting curve comes in to play, and the difference between the A-weighting curve and the C-weighting curve can become significant. The A-weighting curve crosses the C-weighting curve at 1000 Hz; below this, at 200 Hz the A-weighting curve is about -12dB lower. So there is a need to balance the gained distance from longer wavelengths with the naturally decreasing sensitivity of the ear. At ~500Hz, the A-weighting curve is about -3dB from the C-weighted curve. So the ideal siren warning frequencies are in the neighborhood of 400-800 Hz, which is where many sirens operate, and if you could propagate a tone simultaneously at the lower and higher fundamental frequencies, you can produce a 'beat frequency' or 'difference tone' that is lower in frequency while being fringed by higher frequency harmonics (this is the source of the 'buzz' character of sirens like the Thunderbolt).

Download this: https://www.dhs.gov/sites/default/files ... 15-508.pdf for some interesting reading.

Also, A-weighting curve vs C-weighting curve (vs "Z"-weighting curve which is the same as 'unweighted'): https://www.nti-audio.com/en/support/kn ... asurements