Meeting the 75db requirement

I have to retrofit an existing bldg adding speakers in sleeping rooms that do not have them.

will it work if I adjust the existing speakers and just add the new ones to existing circuits staying under the wattage of the amplifier of course.

Has anyone done this? is the audibility still clean?

Thank you

*Disclaimer: This answer assumes you are qualified to do the work (trained and licensed in your area).
That depends on the local codes where you live. If the retrofit is significant, the AHJ may require you to bring either just the sleeping rooms or potentially the entire system up to code. I believe (anyone can correct me if I’m wrong) the most recent NFPA codes recommend low-frequency sounders and/or speakers capable of producing low-frequency tones to be used for designated sleeping areas, so check with your local AHJ to see if they have adopted any of these requirements. Most modern speakers/speaker strobes are capable of this, but check the documentation to confirm.

Adding speakers to an evac NAC will not distort the quality of the sound from an electrical standpoint, however if you place the speakers too near to eachother or in rooms with significant echo then the sound can get distorted. The amplifier provides a 25 or 70 volt audio signal and the speakers just play it, the amp doesn’t care how many speakers are connected (so long as the power limit is not exceeded).

Adding speakers (or horns/strobes) to an existing NAC is where it gets tricky. It’s considered good design/installation practice to plan each NAC with a 20% current draw tolerance specifically to allow adding additional signals during the system’s lifetime without exceeding current limits or performing major re-wiring. However, not all facilities have been engineered this way. Your best bet is to check the As-Built plans (if possible) and verify each device is where it’s supposed to be, add up their rated power consumption, and check the rating of the NAC to see how many more speakers you can add. Make sure you note on building plans where you’ve added signals and to which NACs you’ve added them, just in case you or someone else finds themselves needing to add devices later on down the line.

Depends on what wattage the speakers on the system are. But, I think it would be easier to just install a speaker or two in each unit, thats how we do all our upgrades. But you would most likely have to add an amp/booster panel or two, depending on how big the building is.

Adding notification appliances to existing circuits can get hairy fast. Especially in a situation like yours where you are probably more than doubling the number of appliances on each circuit. When the original calculations are not available, we almost always create a new circuit with NAC panels, or in your case, new amplifiers. That way, you can make load calculations with some clue about what you are dealing with.

Thanks All for the replies. We did end up adding a speaker in every sleep dwelling that did not have one. Had to add 2 new amplifiers for the new speakers. It now meets the new code.