rbrown9940
Member
- Location
- Iowa
Can anyone give me some input on what an intelligibility testing point is for a fire alarm system?
intelligibility testing point for fire alarm system
- Thread starter rbrown9940
- Start date
- Status
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
A fire alarm system that has a voice annunciator and/or a public address system function is of little use if you cannot understand the words.
How well you can make out the words, not just how loud the sound is, is jointly referred to as intellegibility and is specified in the requirements for such an alarm system.
There are standardized tests, but the intellegibility will also vary from point to point within the building. Rather than require testing in every alcove and corner as well as everywhere along a hallway, the standard specifies positions (points) at which the testing must be done.
Sound reflections and hearing sound from multiple speakers at different distances can adversely affect intellegibility, as can poor speaker quality or poor installation of the speakers.
An alarm technician will likely be more familiar with both the terminology and the requirements than a general electrician.
How well you can make out the words, not just how loud the sound is, is jointly referred to as intellegibility and is specified in the requirements for such an alarm system.
There are standardized tests, but the intellegibility will also vary from point to point within the building. Rather than require testing in every alcove and corner as well as everywhere along a hallway, the standard specifies positions (points) at which the testing must be done.
Sound reflections and hearing sound from multiple speakers at different distances can adversely affect intellegibility, as can poor speaker quality or poor installation of the speakers.
An alarm technician will likely be more familiar with both the terminology and the requirements than a general electrician.
Last edited:
peter d
Senior Member
- Location
- New England
Good info. :thumbsup: I'm familiar with basic fire alarm systems but not voice evac and high rise systems.
ron
Senior Member
- Location
- New York, 40.7514,-73.9925
Lots of White Papers if you Google voice evacuation intelligibility test
Here's one https://www.systemsensor.com/en-us/Documents/AV-NFPA-DODintelligibility_WhitePaper_AVWP002.pdf
Here's one https://www.systemsensor.com/en-us/Documents/AV-NFPA-DODintelligibility_WhitePaper_AVWP002.pdf
Sound Sleuth
New member
- Location
- Lewes, East Sussex, UK
Ron
This discussion popped up in my Google Alerts, and thought I might add to it.
Speech Transmission Index - STI (note there is no reference to intelligibility) is now seen as a way to assess sound system intelligibility. STI is essentially about how little the signal changes from beginning to end - how clean it is. Distortion in its purest sense is the measure of how much something changes from the original sound, so STI is an all in one distortion measure.
However, for intelligibility, distortion is not necessarily a bad thing. Voices with bass reduced and highs emphasized can improve intelligibility. There is also not much evidence that distortion caused by over driving amplifiers and or loudspeakers has much negative impact on intelligibility.
The bigger issue for intelligibility is the confusion over who is responsible for the intelligibility of communications through air (public address systems)?
Reverberation and noise in the room do have a large impact on intelligibility neither of which are in the control of the sound system supplier, designer or installer. From my tests using the same sound equipment a quiet non reverberant space produces a high STI number (good news), a quiet reverberant space a lower number and a noisy reverberant space a low STI number (bad news) - all with the same sound kit.
Obviously with careful positioning of loudspeakers and careful choice of loudspeakers you can improve that STI number a little. But if the space is bad (noisy and reverberant) you will struggle to make much improvement. Also if the STI number doesn't correlate well with actual intelligibility then begins the arguing phase of the project:happysad:
The point to all this is first don't allow anyone to confuse intelligibility with an STI reading. Secondly, if the space is quiet and non-reverberant (like most office spaces) almost any sound system will pass an STI and subjective intelligibility test. But as the space deteriorates you will need to be more careful and if it is a very difficult space then the architect needs to do something about it.
In summary as an integrator/contractor be careful taking on responsibility for a sound system's intelligibility. You might end up paying to have the place carpeted:roll:
This discussion popped up in my Google Alerts, and thought I might add to it.
Speech Transmission Index - STI (note there is no reference to intelligibility) is now seen as a way to assess sound system intelligibility. STI is essentially about how little the signal changes from beginning to end - how clean it is. Distortion in its purest sense is the measure of how much something changes from the original sound, so STI is an all in one distortion measure.
However, for intelligibility, distortion is not necessarily a bad thing. Voices with bass reduced and highs emphasized can improve intelligibility. There is also not much evidence that distortion caused by over driving amplifiers and or loudspeakers has much negative impact on intelligibility.
The bigger issue for intelligibility is the confusion over who is responsible for the intelligibility of communications through air (public address systems)?
Reverberation and noise in the room do have a large impact on intelligibility neither of which are in the control of the sound system supplier, designer or installer. From my tests using the same sound equipment a quiet non reverberant space produces a high STI number (good news), a quiet reverberant space a lower number and a noisy reverberant space a low STI number (bad news) - all with the same sound kit.
Obviously with careful positioning of loudspeakers and careful choice of loudspeakers you can improve that STI number a little. But if the space is bad (noisy and reverberant) you will struggle to make much improvement. Also if the STI number doesn't correlate well with actual intelligibility then begins the arguing phase of the project:happysad:
The point to all this is first don't allow anyone to confuse intelligibility with an STI reading. Secondly, if the space is quiet and non-reverberant (like most office spaces) almost any sound system will pass an STI and subjective intelligibility test. But as the space deteriorates you will need to be more careful and if it is a very difficult space then the architect needs to do something about it.
In summary as an integrator/contractor be careful taking on responsibility for a sound system's intelligibility. You might end up paying to have the place carpeted:roll:
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