Ceiling mounted Fire Alarm Horns vs Speakers

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Shujinko

Senior Member
In my previous experiences when dealing with fire alarm voice systems I have seen that with the use of FA speakers you need more devices if you use ceiling mounted speakers in-lieu of wall mounted speakers. This is due to the different sound distribution characteristics and placement of the FA speakers.

My question is....would the same thing apply for ceiling mounted FA horns, would the sound distribution be similar concept wise?
 

luckylerado

Senior Member
No. You are not dealing with intelligibility of the voice message only decibel level. More is not always better especially with hard floors, walls and ceilings. Stairwells are a good example of when more horn/strobe devices can cause disorientation for people trying to find their way out of a building.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
If your application is for a high ceiling space, such as a factory or warehouse floor, calculation of the db levels likely to be perceived by an occupant may suggest that for ambient over 80 db or so (not uncommon on a production floor) you'll never meet the +15 db requirement. You then have to rely on the visual component of the device. IIRC this is allowed. Typically we put ceiling mounts at 20 feet AFF on 50 foot spacing at 110 candela. This will get you the correct strobe coverage. As an aside, even though the calculations suggest that the sound pressure level will be inadequate, actual experience says it will be deafening.
 

Shujinko

Senior Member
My application is not a high bay application, in all actuality it's a group study area in a library with 9 foot ceilings.

However, per my experience with ceiling mounted devices the lower the ceiling the sound distribution doesn't travel as far horizontally based on the listener's height. I ran into a problem with this with dB levels on a voice system, now I'm looking to get it right when using ceiling mounted FA horns. I basically use the following calc for ceiling monted speakers in the link below on pages 2-14, 2-15, 2-16. Can I use the same calc for FA ceiling mounted strobes?

https://simplex-fire.com/en/us/DocumentsandMedia/579-769.PDF
 
If it's a study hall/library, it's well insulated, low ceiling, and is a low ambient dB level occupancy...sound won't be an issue.

If you want ceiling mount horn strobes, simply space them for strobe coverage in accordance with the edition of NFPA 72 your jurisdiction has adopted and you'll be fine.
 
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