Carter and Klaxon siren questions

[Mister_Penetrator]

My questions about the Carter and Klaxon sirens are:

1. Is the sound output concentrated in front of the rotors through the main openning or the slots around the rotor?

2. Do they have to be placed in a specific position and direction, to alert as many people as possible?

[danwisbey85]

1. The sound is drawn in from the main side openings, and forced out through the slots.

2. Carters+Klaxons, must be on either a high pole or a roof to get maximum sound coverage.
It's not good doing like shown in this pic http://homepage.ntlworld.com/andrew_pol ... mpton1.jpg
Because the sound will only cover the area facing the siren.

Dan.

[SirenSteveUK]

With regards to Carter, Klaxon and Secomak sirens - consideration was never given in the UK to placing these sirens in a certain direction as the claims of the '...manufacturers of the power sirens used for the warning system ... claimed that their sound output was omnidirectional... Anechoic chamber measurements commissioned by the Home Office in 1985, however, showed that the output was far from omnidrectional... Calculations showed that the resulting coverage pattern on the ground was the shape of an "hour glass", covering only 60% of the area of its circumscribed circle...'.

I've covered some of the points regarding positioning of UK sirens in a reply on the post 'More Sirens from Across the Pond'.

Out of interest - the 'polar plot of sound output' of single ended Klaxon sirens is included in this pdf file http://www.klaxonsignals.com/instructio ... s/GP12.pdf

I've noticed though that all my hand sirens seem to be louder where the air intake is and quieter where the air actually comes out of the siren. I don't know why this would be, but it would correspond with the findings of the Home Office that dual-toned UK sirens had an "hour glass" plot of sound output.

In 1989 the police (who had the responsibility of operating, maintaining and identifying new siren emplacements) were insturcted to cease the installation of new sirens. A study group set up by the Home Office in 1991 to investigate UK Warning Arrangements decided that if a siren system should still exist - '(a system) which used powerful modern electronic sirens, computer controlled by radio transmission, was selected as the preferred alternative of the Study Group'. However, Ministers decided to base future warning arrangements exclusively on media broadcasts and the existing siren system was dismantled during late 1992 and early 1993.

[danwisbey85]

I have heard on a website that many UK ministers are dicussing for a new siren network for the UK!
Mainly for terrorist reasons of course.

Dan.

[SirenSteveUK]

Yes - a new siren system was looked into but it looks like the decision was a no. The National Steering Committee - Warning and Informing the Public (NSCWIP) was set up after 'Civil Defence' responsibilities moved from the Home Office Emergency Planning Division to the Civil Contingencies Secretariat of the Cabinet Office. Unfortunately, they 'do not believe that there is a need for a national siren network at present (in the UK), as the current threat status does not warrant the extreme costs involved in installing, maintaining, and managing such a system. However, sirens that are installed as part of local networks could be adopted into a national network in the future, if the threat status warrants it. This will be possible as a result of the national siren standard implementation... setting out minimum specifications, back-up power requirements, testing arrangements, a single UK warning tone, and a single UK all-clear tone'.

Shame - no siren system for now (though I wonder how bad the threat status has to be before they decide on one). Sounds like they are going the French way of legislating as to what tone each siren must sound, etc.

[AndrewPollard]

Just on the sound profile, when filming tests of Castle Castings sirens, I've noticed the sound is quite a bit louder looking at the siren end on. Not what I would have expected at all but it agrees with other observations.