New ASC E-Class

[va_nuke_pe]

Typo - I meant to write 110 dBC at 100 feet at 1000 Hz

[jkvernon]

I have to ask where ASC and ATI are getting their output ratings for their sirens. If they've proven in the field that they're underperforming, can they really market their products as having a 126 to 128db rating? Is this just another pi**ing contest perhaps?

[Civil D Siren]

I have to ask where ASC and ATI are getting their output ratings for their sirens. If they've proven in the field that they're underperforming, can they really market their products as having a 126 to 128db rating? Is this just another pi**ing contest perhaps?

ASC has a room at their headquarters that they do tests on sirens in. How they can measure it at 100 feet in a tiny room is beyond me, but they also have the trailer that they can haul to a field to get ratings on decibel output. Federal has also overated their sirens in the past. For example, I think Federal rated the EWOS 812 at 128dB @ 100ft. and that was proven to be wrong. I think they did the same thing with the ThunderBeam too.

[TboltTX1]

Federal also claimed at one point that their Thunderbolt 1000 was capable of producing 130 decibels @ 100 feet.

[va_nuke_pe]

Sometimes companies take the peak reading as their output. Peak is the highest "fast" measurement (Lpk, 1/4-second) on the meter. Sometimes, they use max - highest "slow" measurement (Lmax, 1-second) on the meter.

For a rotator, the best measurement is with the rotation stopped and take the average (equivalent sound level or Leq) for the measurement period that starts after windup and ends before wind down.

In terms of correction factors, spherical divergence from a point source corresponds to 6 dB per distance doubled. That is how anechoic test chamber distance corrections are supposed to be done.

However, there are a few subtleties that have to be understood so as not to either unintentionally under=rate or over-rate the output.

1) Bucket truck 100 foot measurements are 100 feet from the vertical centerline of the siren mount (e.g, center of the pole they are mounted on). Anechoic chamber test distances are from the end of the horn. So to make the correct distance correction, you have to make sure that you use the same reference point.
2) To make sure that for multiple horn (e.g, stacked Kingstars, WPS-2900 series or Modulator series) you don't hit the "sweet spot" for sound interference patterns (sound from multiple wavefronts can add and subtract depending on precisely where the sound waves intersect), one has to waggle the meter slowly up and down and side to side during measuring - covering roughly a 2 foot X 2 foot area with the 100 foot along the siren horizontal centerline being the centerpoint. In an anechoic test chamber, an array of meters has to be used taking an average of the measurements. The latter is not often done by vendors, based on my observations.
3) As I am sure that all of you aware, siren output is not constant - either for an individual siren or for a group of sirens of the same make and model. Getting average measurements from a single siren that vary by ~2 dB up or down is not uncommon; and getting average measurements that vary by ~4 dB among a group of identical sirens is not uncommon either. And for electronics, the hotter the drivers are (how long they are being run), the lower the sound output.