The Siren Board

carexpertandy wrote:According to Whelen's website, the 2909 is 128 dB at 100', and the 2906 is 125 dB at 100', so you don't really need a 2909 to replace a Cyclone.

Also, the 2903 is 119 dB at 100', and the 2902 is 115 dB at 100', so you don't really need a 2903 to replace a STL-10.

I still have a hard time believing the listed outputs for Whelen's omni-directionals, especially after hearing our 2909s up close and personal on several occasions. They just aren't very potent at all, but they do carry pretty well over long distances. As an example, the 2909 should be just ever-so-slightly noticeably louder than a dual-toned Thunderbolt since it's rated 1dB higher, if you're standing 300ft away from each one, and both are 50ft off the ground. Either the Thunderbolt was severely underrated, or that 2909 is just as much overrated, because that Thunderbolt can blow away a large Whelen omni. Yes I know we're talking about a rotational-directional versus an omni-directional, but you should be able to notice some kind of difference in loudness if the omni is supposedly 1dB higher than the rotational. However, comparing apples to apples, the directional Whelens (Vortex and 4000) definitely sound like they're rated about right, as they have about as much of a bite as a Thunderbolt 1000 does. Who knows, maybe it's just me and my hearing's finally shot...

The Vortexes here in OKC aren't that loud. I stood right under one with no earplugs and it didn't hurt. Stood about 50-100 feet away and still. With the Thunderbolt in Moore, I was about thee same distance and it HURT.

When it comes to omnis a sentry 16v1tb is hard to beat. The phasing caused by the dual motors seems to eliminate all of cancellation that occurs in a traditional single tone, dual rotor siren.

One good reason that a Whelen WPS2909 may not sound that impressive from up close is that large vertically stacked omni arrays have a rather narrow vertical dispersion. They gain output on the horizontal plane at the expense of narrowing the donut shaped pattern surrounding the radiator into a rather thin disk, resembling a horizontally spinning propeller. The more vertical elements in an array, the narrower the vertical dispersion. The problem is that the narrower the vertical dispersion, the greater are the chances of skip and areas of inadequate coverage.

The same is the case with the RF pattern of a vertically stacked antenna array. They boost the gain of the antenna and effective radiated power of the transmitter at the expense of vertical dispersion. This is also true with acoustical energy in that you can get high dB ratings with fairly low actual acoustical power. You are only getting about 1000 watts of acoustical output from a 4000 watt amplified system at best. Some of the mechanical sirens the Whelens are replacing produced several kW of acoustical output over a less directive pattern.



[quote="mr_thunderbolt1003 I still have a hard time believing the listed outputs for Whelen's omni-directionals, especially after hearing our 2909s up close and personal on several occasions. They just aren't very potent at all, but they do carry pretty well over long distances. [/quote]

acoustics101 wrote:The same is the case with the RF pattern of a vertically stacked antenna array. They boost the gain of the antenna and effective radiated power of the transmitter at the expense of vertical dispersion.

Commonly referred to as "the umbrella effect" in the industry. I have seen it several times, especially at shorter wavelengths in an environment where the antenna is very high above average terrain.

I'm glad you said this. There is a good analogy between the behavior of electromagnetic wave radiation and acoustic wave radiation in that whenever the radiating source is large in comparison to the wavelength, the directivity index increases. In the case of acoustic waves the frequencies are much lower for a given wavelength due to the speed of sound being orders of magnitude below the speed of light, but the relationship is the same.

In both cases the bulk of the radiated pattern is well above the terrain, especially near the source.

landmobile wrote: Commonly referred to as "the umbrella effect" in the industry. I have seen it several times, especially at shorter wavelengths in an environment where the antenna is very high above average terrain.

I always thought the whelen omnidirectionals were intended to reach a greater distance anyway.

Most of the vendor ratings are based on peak output - especially for electonic devices. When they first ramp up, the drivers are cold and very efficient, that is usually where a brief "bump" in the output occurs which drops off quickly.
The 2-mile to 70 dB (over flat ground) for a T-135 is accurate. The picture to the left is a T-135 taken at 100 feet in front of it from the bucket truck. We sounded it and took measurements 2 miles away (while I was getting my hair blown back from 100 feet in front of it) and got 73 dB. The measurement was taken on a clear day, around 70 F, low humidity and in the cross-wind direction (2 to 5 mph) - so it wasn't wind aided, and temperature lapse was occurring.
And, no, I am not an employee of ASC.