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Ac interference


CR Alarms

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Hi all, i am moving my internal alarm speaker in the upstairs landing, one thing that just occurred to me is that the speaker is driven by low voltage ac, what i would like to know is if the small ac voltage to drive the speaker is enough to interfere with other alarm cables on the system? I plan to run alarm cable from the panel to the new speaker location in the landing following the same route the rest of the alarm cables, my concern is one of the alarm cables upstairs supplies a keypad. The cable lengths from the alarm panel up to  the attic are 20-30m long. Am i worrying over nothing? Is this ac voltage enough to interfere with other devices or is it only mains voltage ac that is capable to cause problems if it is run too close to alarm cables? 

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3 minutes ago, CR Alarms said:

Hi all, i am moving my internal alarm speaker in the upstairs landing, one thing that just occurred to me is that the speaker is driven by low voltage ac, what i would like to know is if the small ac voltage to drive the speaker is enough to interfere with other alarm cables on the system? I plan to run alarm cable from the panel to the new speaker location in the landing following the same route the rest of the alarm cables, my concern is one of the alarm cables upstairs supplies a keypad. The cable lengths from the alarm panel up to  the attic are 20-30m long. Am i worrying over nothing? Is this ac voltage enough to interfere with other devices or is it only mains voltage ac that is capable to cause problems if it is run too close to alarm cables? 

Just run the cable and go for it 

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Indeed. I know you shouldn't do it but the number of takeovers / upgrades* where I've had to run speaker connections within existing RKP or PIR lines = Many

Number of genuine real world issues I've ever had = None

 

*actually thinking about it, the most common scenario is builders pre-wires, where they don't put in a sounder line, needing it to be shared if the location of the CCU isn't all that,

not only that but it's often crappy CCA cable too, still no issues.

 

Edited by datadiffusion

So, I've decided to take my work back underground.... to stop it falling into the wrong hands

 

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It's not dc a speaker needs ac. I wouldn't by choice run speakers with anything else. Speakers and drivers can be very electrically noisy. 

You will probably get away with it but still

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5 hours ago, MrHappy said:

all speakers are ac ?

Audio is ac , speakers AC 

 

 

7 hours ago, Logan said:

Its dc thats why theres a diode on the speaker output on panels on the PCB

Mr Logan how many diodes ?

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This all depends on the panel circuit. Where a panel circuit is dedicated to a speaker connection, the design may be AC driven. Where it's a regular transistor based open collector output, with the option of being configured for regular or speaker output (like in the Galaxy G2 or Flex), the output is pulsed DC when in speaker mode. Pulsed DC isn't AC.

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4 minutes ago, GalaxyGuy said:

This all depends on the panel circuit. Where a panel circuit is dedicated to a speaker connection, the design may be AC driven. Where it's a regular transistor based open collector output, with the option of being configured for regular or speaker output (like in the Galaxy G2 or Flex), the output is pulsed DC when in speaker mode. Pulsed DC isn't AC.

But audio is still ac 

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Just now, al-yeti said:

But audio is still ac 

 

What's your definition of audio?   A speaker makes a noise because the diaphragm is driven in and out by the voice coil. An AC signal will drive the speaker coil in both directions rapidly at various changing frequency, thus giving audible sound. By just switching the diaphragm between one direction and rest, at various frequency, as in pulsed DC, you will also generate audible sound.

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2 minutes ago, GalaxyGuy said:

 

What's your definition of audio?   A speaker makes a noise because the diaphragm is driven in and out by the voice coil. An AC signal will drive the speaker coil in both directions rapidly at various changing frequency, thus giving audible sound. By just switching the diaphragm between one direction and rest, at various frequency, as in pulsed DC, you will also generate audible sound.

Audio is ac basically, I am not questioning the DC output drive on a panel , but audio signal itself is ac ?

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18 minutes ago, al-yeti said:

But audio is still ac 

 

What's your definition of audio?   A speaker makes a noise because the diaphragm is driven in and out by the voice coil. An AC signal will drive the speaker coil in both directions rapidly at various changing frequency, thus giving audible sound. By just switching the diaphragm between one direction and rest, at various frequency, as in pulsed DC, you will also generate audible sound.

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1 minute ago, GalaxyGuy said:

 

What's your definition of audio?   A speaker makes a noise because the diaphragm is driven in and out by the voice coil. An AC signal will drive the speaker coil in both directions rapidly at various changing frequency, thus giving audible sound. By just switching the diaphragm between one direction and rest, at various frequency, as in pulsed DC, you will also generate audible sound.

Yes but makes no difference going in circles with this speakers are AC and audio is generally ac 

 

Maybe go through all the theory again instead of looking at an alley no offence .....

 

 

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1 minute ago, al-yeti said:

Yes but makes no difference going in circles with this speakers are AC and audio is generally ac 

 

Maybe go through all the theory again instead of looking at an alley no offence .....

 

 

 

So, how does the current change direction on an output that can only switch from +12v DC to 0v ?   

 

Ah, I see that you've changed to "generally ac" now.

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1 hour ago, al-yeti said:

This is a discussion forum I thought 

 

 

 

Yes, indeed.   In the context of the original question, the point is moot, as both AC and DC can cause interference with the 'circuit' signal. In the case of the differential pair of the RS485 bus, this is less of an issue, as it's the differential that's important and as both wires are impacted by the same external noise, the data signal isn't impacted.  The problem usually comes with mains based signals where heavy currents drawn by mains based appliances can cause huge induced voltages in nearby cables, that can damage the bus drivers and the analog to digital multiplexers that read zone voltages. The actual zone voltages can also be disturbed, causing nasty false alarms that can be really difficult to diagnose.  

 

I'm not sure if there's enough current driving the alarm speaker to cause any issue, but if the manufacturer advises against it, then it's probably based on some measurement or experience of a problem in the past.

 

15 minutes ago, james.wilson said:

If using pulsed dc drive you would only have half throw so less volume than ac drive? 

 

Yes.

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Getting back on topic...

It's not good practice to run speaker circuits within the same cable as other circuits. I don't believe there is a rule for this apart from some manufacturers say you must not do it.

Main concern in the wild is normally the other way, as in getting annoying data noise from bus devices out of your speaker.

 

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