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What gauge of power and speaker wire?

Rupertrealbear

Mar 31, 2021
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Mar 31, 2021
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I have a Nobosound NS-10G 50W stereo hifi power amp (powered by two 12V 9AH lead acid batteries in series) to which I connected four 8 ohm speakers (Mordaunt Short MS 20s) - each channel connected in series. This way, twice the normal [12V supply] output is shared between the two speakers and the same "inside volume" can be perceived while listening physically outside. This is no "rave" set up and each speaker wire is appropriately 3.5 meters making an approximate 36 square metre listening area. The sound is pleasant and seems less loud than it really is.

My question is does the gauge of the wires in this set up need to be particularly generous for an evening of 30 - 50 Watts of music. I used some "test probe" wires to connect the power (for the crocodile clips) and some pretty flimsy looking speaker wire (with banana connectors) and it all seemed good for twenty minutes.
 

crutschow

May 7, 2021
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Typically you want the wire resistance to be a small percentage of the speaker impedance so it depends upon that and the length of wire.
For example 20ga copper wire has a resistance of about 33mΩ per meter, so 3.5 meters of dual speaker wire would have about 7 * 33mΩ = 0.23Ω resistance, which should be fine for your application.
Often common 18ga zip cord is used for speaker connections, which would give about 0.146Ω resistance (and no it doesn't need be pure, oxygen free, audio super cable:rolleyes:) .

If the two speakers for each channel are connected in series, that will reduce the maximum volume.
Since the amp can tolerate a 4 ohm load you can connect two speakers in parallel.
That also improves the damping for each speaker, as most modern speakers are designed to sound best with a high damping factor from the amp (<1ohm).
Two 8Ω speakers in series means the damping impedance for each speaker is now >8Ω.
 

Rupertrealbear

Mar 31, 2021
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Mar 31, 2021
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Typically you want the wire resistance to be a small percentage of the speaker impedance so it depends upon that and the length of wire.
For example 20ga copper wire has a resistance of about 33mΩ per meter, so 3.5 meters of dual speaker wire would have about 7 * 33mΩ = 0.23Ω resistance, which should be fine for your application.
Often common 18ga zip cord is used for speaker connections, which would give about 0.146Ω resistance (and no it doesn't need be pure, oxygen free, audio super cable:rolleyes:) .

If the two speakers for each channel are connected in series, that will reduce the maximum volume.
Since the amp can tolerate a 4 ohm load you can connect two speakers in parallel.
That also improves the damping for each speaker, as most modern speakers are designed to sound best with a high damping factor from the amp (<1ohm).
Two 8Ω speakers in series means the damping impedance for each speaker is now >8Ω.
Thanks crutschow, I guess it's a stable setup that should continue to produce sound efficiently without strain (I don't like to the speakers under much pressure, they are the opposite of "tight" and reproduce bass inherently in the signal without having to play around)
 

crutschow

May 7, 2021
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I don't like to the speakers under much pressure, they are the opposite of "tight" and reproduce bass inherently in the signal without having to play around
I think we have a language problem here.
Afraid I don't really understand any of that.
What are "speakers under pressure", "opposite of "tight"", and "reproduce bass inherently"?
 

Audioguru

Sep 24, 2016
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The upgraded new version of the Nobosound NS-10G "50W" amplifier uses the Texas instruments TPA3116 IC that produces 50W per channel into 8 ohm speakers with severe distortion using a 24V supply, or 30W per channel with reasonably low distortion. It can drive 4 ohm speakers with nearly double the output power if a heatsink is added but the amplifier is too small for a heatsink. It comes with a 24V/3A (72W) power supply then its output is 30W plus 30W to the speakers and 12W of heating.

Speakers have a low frequency resonance that is damped by the extremely low output impedance of an amplifier. Speakers in series have poor damping then produce one-note-bass at the resonant frequency like a bongo drum. Speakers in series also reduce the maximum output power.

The Mordaunt Short MS 20s speakers are old then I could not find a datasheet. A sales sheet says the woofers are only 6.5" and go down to 60Hz (no deep bass). I use a same size 2-way speaker on my cheap clock radio.
 

Audioguru

Sep 24, 2016
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I guessed the efficiency. The datasheet shows that the heating is only 6W at 30W per channel, not the 12W I guessed.
The actual heating will be much less unless continuous full power tones are played (acid rock?).
 
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