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70 volt distributed audio (PA System) Help
Brian Jojade:
Wait, so is this one amp or 5 amps?? The story seems to change between posts.
As far as the exact rating on the amps, yeah, you should try to have the load be less than the rated power of the amp. BUT, it isn't always end of the world if you do go over a bit. First off, if you are running 20 gauge wire, you're adding 1 ohm of resistance per 50 feet of wire. The math gets a little more complicated as you have taps on the line in different spaces, but with the losses in the line, you get a little more play in the load you can put on the amp.
How amps behave when overloaded depends a lot on the amp. Generally speaking, an overloaded amp would have increased distortion, run hotter, or simply not be able to deliver full power. How that impacts your actual usage may be very important, or not matter much at all.
Increased distortion in a PA may be perfectly acceptable as it generally doesn't reduce intelligibility of the message. In fact, some distortion can make the sound stand out more and appear louder against ambient sound (since average power is greater of the clipped signal). It's weird to think that having a distorted signal might actually be a good thing in a PA system.
Often paging systems have messages of relatively short duration. So short that the overloaded amp has no time to overheat. Yes, if you wanted to run at full clip for a very long speech it may overheat and shut down, but in your case, that hasn't happened in the last 10 years.
As far as getting enough volume, adjusting taps on each speaker to get the needed volume is all that needs to be done. If you put another 70v amp in place of your existing system that's rated at 10X the power, it should not change the output volume at all, since the source voltage is constant. Kind of neat how it's designed that way. (constant voltage does not mean constant 70 volts. It means the maximum volume would be 70 volts. Turning down the volume would mean lower voltage)
So a bigger amp would mean potentially less distortion and potentially the amp not running as hot. Again, neither may matter even a little bit.
Jeff Ford:
--- Quote from: Mike Caldwell on October 26, 2021, 07:49:58 PM ---Sounds like they already have the plant divided up into something like 5 zones.
60db is really quite, is that in the office areas. 80db is actually quite for any manufacturing
type of plant on the floor, if that's what kind of plant this is.
--- End quote ---
Yes, plant is slit up and I am working with the one 120 watt amp which covers the plant floor. It is a manufacturing plant and some areas are very quite but most areas top out around the 80db level.
Jeff Ford:
--- Quote from: Brian Jojade on October 26, 2021, 10:52:24 PM ---Wait, so is this one amp or 5 amps?? The story seems to change between posts.
As far as the exact rating on the amps, yeah, you should try to have the load be less than the rated power of the amp. BUT, it isn't always end of the world if you do go over a bit. First off, if you are running 20 gauge wire, you're adding 1 ohm of resistance per 50 feet of wire. The math gets a little more complicated as you have taps on the line in different spaces, but with the losses in the line, you get a little more play in the load you can put on the amp.
How amps behave when overloaded depends a lot on the amp. Generally speaking, an overloaded amp would have increased distortion, run hotter, or simply not be able to deliver full power. How that impacts your actual usage may be very important, or not matter much at all.
Increased distortion in a PA may be perfectly acceptable as it generally doesn't reduce intelligibility of the message. In fact, some distortion can make the sound stand out more and appear louder against ambient sound (since average power is greater of the clipped signal). It's weird to think that having a distorted signal might actually be a good thing in a PA system.
Often paging systems have messages of relatively short duration. So short that the overloaded amp has no time to overheat. Yes, if you wanted to run at full clip for a very long speech it may overheat and shut down, but in your case, that hasn't happened in the last 10 years.
As far as getting enough volume, adjusting taps on each speaker to get the needed volume is all that needs to be done. If you put another 70v amp in place of your existing system that's rated at 10X the power, it should not change the output volume at all, since the source voltage is constant. Kind of neat how it's designed that way. (constant voltage does not mean constant 70 volts. It means the maximum volume would be 70 volts. Turning down the volume would mean lower voltage)
So a bigger amp would mean potentially less distortion and potentially the amp not running as hot. Again, neither may matter even a little bit.
--- End quote ---
The story change just to give more information to maybe satisfy some concernes, I am working working the one system covering the plant floor. This system probably sees more work on day shift hours then any other times. I work second shift and some nights we won't have any pages at all and others maybe 5 to 10. The most work the system has probably seen is me running the emergency broadcast continuously for an hour while checking DB levels. It did this without any problems and when I have checked voltage levels I haven't seen anything spike over 35 volts but I am only able to capture with a DMM, no logging capabilities. I was thinking that I would split the floor coverage to 2 amps as I would like to add some more horns in a couple areas to get better coverage but I will have to see what the load would be on the split runs i guess.
John Roberts {JR}:
Sounds like you are making a good start.
Best practice is to keep the total speaker load less than the amps rated power. If the pages sound clean the amps are probably not overloaded.
JR
Brian Jojade:
--- Quote from: Jeff Ford on October 27, 2021, 01:35:36 AM --- I was thinking that I would split the floor coverage to 2 amps as I would like to add some more horns in a couple areas to get better coverage but I will have to see what the load would be on the split runs i guess.
--- End quote ---
Using 2 amps vs one larger amp doesn't make much difference if you are sending the same signal to everything. One large amp means less thinking about what load is on which amp, so you have a little more flexibility, but using the existing amp and adding another smaller amp might be a few dollars less. You also have the advantage that if an amp does go down, less speakers are impacted.
As far as measuring the volume in each area, that's certainly a good way to document what's happening. However, only taking measurements off hours means you don't have actual data of how loud the space may be while in use. So you're stuck with 'guessing' if it will be loud enough. It would be good to get measurements of the general ambient noise. A good rule of thumb is that your paging speakers should be about 10dB louder than that.
The speakers that you measured at 60dB seems extremely quiet for a Paging speaker. Maybe in a quiet setting like a doctors office that's enough, but anywhere else you may be left wanting more.
When adding paging horns, you also need to take into account coverage patterns. While adding more speakers may help with coverage, take care that you're not overlapping coverage too much. Overlaps will potentially create delay echos that can reduce the intelligibility of sound pretty dramatically. A good example of what NOT to do would be to put horns on either side of the room facing inward. Dead center of the room would be fine, but as you move towards each speaker you'll start to encounter different delays and it'll become a mess.
Placing the speakers centered in the room and projecting outward would be a better solution. Or, placing speakers all pointing the same direction and creating delay zones is a possible option too, but that's a little more complicated.
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