Elk M1kp2 speaker wire

[mikefamig]

I plan to add a M1kp2 keypad to my house and will be putting a speaker in the box behind it. When I installed my first keypad I pulled a separate speaker wire in addition to the cat5e for the data. Now it occurs to me that I should have just used the extra wires in teh cat5e for the speaker.
 
Is this a bad idea? Is the 24 gauge wire ok for a speaker and will the audio signal bother the data on the other pairs of wire?
 
Mike.

 

[RAL]

The audio signal shouldn't bother the other signals on the cable due to the twisted pairs.
 
24 gauge wire is pretty small.  100' would add about 5 ohms resistance to the speaker's impedance.   Not a killer with a 32 ohm speaker, but there will be some reduction in output.
 
I ran a separate 16 gauge wire for all my speakers.  It's overkill for the keypad speaker, but I had the wire on hand.

 

[mikefamig]

How would you measure the ampacity of an analog audio signal? I have a 30 watt elk sp30 speaker. The Elk manual calls for a minimum 20 watt speaker on out1 and out2. What does that say about amperage? I know that wattage is approx volts x amps but I don't know how to determine maximum voltage on an audio signal.
 
Mike.

 

[mikefamig]

Not only am I confused about voltage of an audio signal but I just learned that the resistance of copper wire changes as the frequency of the signal changes.
 
This from bluejeanscable is interesting:
 
One of the most common misconceptions we run into, on the subject of resistance, is that resistance is somehow irrelevant to audio and video signals because those signals are alternating current (AC), and a wire's resistance is expressed as "DC resistance," which refers, of course, to direct current, not alternating current. So, we are often asked, if resistance is DC but the signal is AC, what could resistance have to do with anything?
Resistance acts upon both alternating current and direct current. The reason resistance is expressed as "DC resistance" on spec sheets is not that resistance is not applicable to alternating current. Rather, it's because of something called "skin effect." As the frequency of a signal increases, the current flow in a wire concentrates toward the outside, or "skin," of the conductor. This means that for any given wire, if we measure resistance at different frequencies, we'll find that the resistance increases with frequency. Resistance is expressed in spec sheets as "DC resistance" because the resistance value of one wire at DC can be meaningfully compared to the resistance of any other wire at DC. In theory, if one wanted to do so, one could specify the resistance of wires at any frequency; we could make up tables of "1 MHz resistance" instead of DC resistance. This isn't done because (1) there isn't any handy "reference" frequency which is broadly applicable to all uses of wire, and (2) it's harder to measure resistance properly at higher frequencies because it is difficult to separate out losses to other factors which become relevant as frequency increases, like capacitance, inductance, and return loss. But make no mistake: resistance converts electricity to heat in a wire regardless of whether the electricity is DC or AC. And, by the way: in the case of a stranded wire, the "skin" in question is still the outside of the bundle; it is not, as people often assume, the skin of each individual strand.

 

[RAL]

Skin effect for audio frequencies is not worth worrying about.  The resistance increase is on the order of 3% or so.  A lot of audio cable companies will be happy to sell you some very expensive speaker cables if you want to believe it matters.
 
To calculate the current in the speaker wire, you need to know the output characteristics of the final stage of the amplifier circuit. 
 
You can get a rough estimate using Ohm's Law, if you know the power output of the amp and the impedance of the speaker.  Here's a handy calculator if you don't want to grind through it by hand.
 
Since Elk says you need a minimum of a 20W speaker, let's assume that is the maximum power the amp can put out.  If we assume the speaker is 8 Ohms and purely resistive (it's not, but let's pretend it is), then the current would be about 1.6A and the voltage would need to be 12.6V.   Given the Elk's 12V power supply, these numbers seem possible.   In reality, both are probably both a bit lower than that.

 

[mikefamig]

I ask for academic reasons, I never gave any thought to current on an audio circuit in the past. I wouldn't ordinarily consider using a 24 gauge wire for audio if it wasn't for the fact that the cat cable is already there and it would be so easy to use it for the speaker and this is what got me on the topic.
 
You are assuming a dc current as an example to estimate the current and that I can understand.
 
Mike.

 

[Del91574]

You have to consider the AWG when deciding whether or not the audio circuit is going to be series or parallel or a combination.
 
Will it work, sure. Would I choose to do it, no. I'd rather use those conductors to bring the zone and open collector back to the panel and install the speaker elsewhere.