dB loss calculator for Fire alarm Speakers

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ron

ron

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I always wished for one, but no luck.

On page 8 of http://www.cooperindustries.com/con...tification/Resources/Brochures/StepsAhead.pdf
they talk about Distance and the 6 dB rule.

Also page 25 of http://www.pottersignal.com/fire/tools/advancedfiretraining.pdf

Start with the output from the speaker from the data sheet. Maybe 90dB at 10'. Every time you double the distance, it drops 6db.By the time you get within range of the next one or a wall, with what is left, you need to be above the minimum established by NFPA 72 above ambient (you need to make a guess at ambient)
 
Smart $

Smart $

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Location
Ohio
That is for open-field, spherical wave propagation... such as outside with no walls or objects to bounce or absorb the sound wave.

Taking actual measurements is the best method. However, you can't measure SPL if it's not yet installed. :p

So using 6dB at the design stage should suffice in most cases.
 
G

GoldDigger

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Shujinko said:
I meant dB loss wiring calculator in reference to f/a wiring.
Click to expand...
I have never seen electrical calculations for sensors use dB instead of actual volts or amps for wiring loss calculations, although it is nice to be able to add losses instead of multiplying loss ratios. :)
For speaker type annunciators, maybe more sensible.
 
hbiss

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
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EC
Right. But what I'm saying is that you can't just subtract the db loss of the wiring from the designed SPL (in db) of the speaker. I think this is what the OP is wanting to do in order to determine the reduction in SPL due to wire length/resistance. It's really going to be negligible anyway if you size the wire properly and the amp sized to have enough reserve capacity to be able to be "turned up" to compensate.

-Hal
 
Smart $

Smart $

Esteemed Member
Location
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hbiss said:
Right. But what I'm saying is that you can't just subtract the db loss of the wiring from the designed SPL (in db) of the speaker. I think this is what the OP is wanting to do in order to determine the reduction in SPL due to wire length/resistance. It's really going to be negligible anyway if you size the wire properly and the amp sized to have enough reserve capacity to be able to be "turned up" to compensate.

-Hal
Click to expand...
And what I'm saying is you can.

A -3dB change in voltage from source to load will correlate to a 3dB loss in output SPL. But I emphasize again, this is a generalization.
 
F

FireAlarmsOnline

Member
Location
San Francisco, CA
I have a dB Line Loss Calculator among others if interested

I have a dB Line Loss Calculator among others if interested

Hello group. I am new hear and stumbled across this thread when trying to perform my own research on this topic. With that being said, I had not luck finding one so I created one. Our Excel file contains a few calculators revolving around the fire alarm industry. These include: NAC Voltage Drop Calculators for System Sensor and Wheelock, dB Line Loss, Sound Pressure loss, Strobe Illumination Calculator for Wall/Ceiling, and Battery Calcs. Feel free to download it here and let me know what you think. Hopefully it helps!! https://www.facebook.com/download/1448693922119836/FireAlarmsOnline.com Multi Tool 7-1-15.xlsx
 
gadfly56

gadfly56

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Location
New Jersey
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Professional Engineer, Fire & Life Safety
Smart $ said:
And what I'm saying is you can.

A -3dB change in voltage from source to load will correlate to a 3dB loss in output SPL. But I emphasize again, this is a generalization.
Click to expand...

Mmmm, no. Horns or speakers are listed to constant output within their operating range, typically 16 - 33 VDC for horns. If the horn is set for 90 db, you'll get 90 db over the entire operating voltage range. Current draw will vary, but all the figures they give you for current draw assume the lowest allowable voltage, hence "max current draw".
 
Smart $

Smart $

Esteemed Member
Location
Ohio
gadfly56 said:
Mmmm, no. Horns or speakers are listed to constant output within their operating range, typically 16 - 33 VDC for horns. If the horn is set for 90 db, you'll get 90 db over the entire operating voltage range. Current draw will vary, but all the figures they give you for current draw assume the lowest allowable voltage, hence "max current draw".
Click to expand...
Not an area I'm well versed in, so I never rely on one source. As such, I'm getting some conflicting info.

From a Cooper Horn Strobes document:
* UL max current rating is the maximum RMS current within the listed voltage range (16-33V dc for 24V dc units). For strobes the UL max current is usually at the minimum listed voltage (16V dc for 24V dc units). For audibles the max current is usually at the maximum listed voltage (33V dc for 24V dc units). For unfiltered ratings, see installation instructions.
Click to expand...
SOURCE: http://www.cooperfire.com/sites/default/files/product/tech-docs/CFS0077-UL-C-WEB_Part15.pdf
 
hbiss

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Ok. I think the confusion is the term "speakers". A speaker to me is a simple voice coil device driven by electronics some distance away. They are capable of providing an alarm tone as well as spoken voice, music, etc. An example is a life safety installation.

I suspect that the OP is really talking about "audible devices". These are not speakers at all but self contained tone generators/transducers that will provide the designed output with no variation over a range of voltages.

-Hal
 
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