The Siren Board

I found this album of two videos while messing around on youtube, one is a video of the Norfolk flood siren and a video of another flood siren from a different area. Both sound good and they both look good too, he is practically right on top of the Norfolk siren! These videos were done by Mr. Andrew Pollard.... I think he might be a member on the board.

Dave

Wow. One of them was awfully low to the ground. What is the model and manufacturer? Is this the same type of siren like the Essex flood siren?

I've noticed that many extant British installations are in what American engineers would consider odd places, such as on low pole mountings or under the eave of a building. Many WWII installations were on poles shorter than the surrounding buildings, not much taller than a lamppost. American manufacturers of horizontal sirens relied on the refraction of sound off of surrounding structures (though they generally preferred taller poles and rooftops), while modern installations of vertical sirens try to aim the source directly at the hearer. Perhaps the British were following the former example.

Is this the same type of siren like the Essex flood siren?

It sure sounds like it, and it is the same shape and mount. I'd say that the flood sirens are the same as the Essex siren (which is a Carters? I forgot...)

The sirens in all the video's are Cold War era Castle Castings models. They were the replacement model for the WWII Carters, and don't sound any different!
The Canvey Islands siren is also in Essex, but a different part from where I filmed the siren in Gladden Fields.
Again the sirens are all Castle Castings models.
As for the low mountings, I can't ohnestly say why they are low as they are, but hey, if they sound you are certainly aware of it! (I should know!)
Saying that not all the UK's sirens were as low as that, many were on roof tops, buildings etc...
I suppose our sirens were designed to just blare out as much noise as possible in all directions???!!!

Dan.

I've got plenty of pictures as well as the videos. I've put a few on the web here:

http://s92.photobucket.com/albums/l28/A ... type=local

Just to answer the questions about the bank in the Norfolk siren video, it's a flood defence. I've added a picture showing the river just the other side. That particular siren is in a very rural location and there are only a few houses nearby. There are none at all in the immediate area on the far side of the river so presumably being lower than the bank doesn't matter too much. The centre of the village is covered by a second siren, by the bridge in the distance (the siren shown in the first picture). That's on much higher poles (it is taller than the building - the perspective is misleading).

I chose to film the siren by the bank because it was possible to get so close!

is this sirenhttp://s92.photobucket.com/albums/l28/A ... =imgAnch15
have hi-lo capabiltys or is that just a sound sheild since its so low to the ground.

I think that is the lowest siren I've seen or heard of in my life. The only other competitor was an STH10 in Ruidoso, NM. It was only 15' high at the most.

I don't think it has hi-low capability - there was no mechanism to shut off the louvres. I suppose it must be some kind of shield but I'm not really sure.

Could the shield be one of the Home Office's investigations to prevent wildlife (as wildlife could block the rotors - birds, etc.). They experminented with various covers (such as protective Glass-Reinforced Plastic shields) but found that these reduced overall sound levels by between 5 and 8 db, finding these methods unsatisfactory. It was then subsequently realised that 'a simple wire-mesh cover would suffice to prevent ingress by wildlife (such as the Portland, Uk, flood warning sirens). Preliminary trials of such covers showed that they produced an attenuation of only about 1 db, which was considered acceptable'. I believe a similar shield to Andrew Pollard's photo on a siren is featured in the UKWMO booklet published in 1985.

Also, on the subject of:

I've noticed that many extant British installations are in what American engineers would consider odd places, such as on low pole mountings or under the eave of a building. Many WWII installations were on poles shorter than the surrounding buildings, not much taller than a lamppost. American manufacturers of horizontal sirens relied on the refraction of sound off of surrounding structures (though they generally preferred taller poles and rooftops), while modern installations of vertical sirens try to aim the source directly at the hearer. Perhaps the British were following the former example.

.. British manufacturers of sirens appeared to suggest lower mountings- but nearby to large open spaces etc. (such as on the corner of parks), as can be seen by this 'Secomak' publicity quote "sirens should not be mounted too high above gound level; 4.5 to 6m is usually recommended. Putting sirens on top of high buildings often has the effect of deflecting the sound waves upwards because of negative temperature gradients. Sirens should not be located close to tall buildings. Ideally there should be at least a clear 50 m radius around each instrument."

Though, this appears to contradict the Home Office's Study Group into sirens (1992) which quotes the FEMA guidance of '...recommends a minimum mounting height of 15 m in low-rise areas, partially to assist the sound propagation, and also to reduce the risk of startle and possibly even ear damage to people near a siren when it was activated. In high-rise areas, it is essential to mount the sirens above the rooftops of the surrounding buildings, and when they are mounted on a parapet roof, they should be at least 3m above the parapet. If these criteria are not satisfied, the coverage is drastically reduced. It was found that for the majority of the (UK) sirens, these criteria were not satisfied'.

However, by 1992 (sorry UK siren manufacturers), the Home Office recognised that 'The design of the exisng power siren system was based on unrealistic claims by the siren manufacturers for the effective ranges of their equipment'.