Long cable run for speakers

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Long cable run for speakers

Post by twotoedsloth »

Hello and thanks for taking the time to read and/or respond to this query.

A friend of mine belongs to a church that wants to replace their speaker cables.

She is concerned that the cable run is too long - 140 feet. In the concert hall I work in we have cables running 200 feet with no problems.

Could she use 8 gauge cables instead of 12 gauge cables to mitigate this problem?

Please let me know what you think.

Peter
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Re: Long cable run for speakers

Post by Sam Spoons »

Assuming these are passive speakers then long cable runs will cost some power and maybe cause impedance issues, using larger conductors will mitigate the issue but without more info it's impossible to say exactly what cable cross section would be suitable.
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Re: Long cable run for speakers

Post by twotoedsloth »

Hello and thank you for your response.

Yes, these will be passive speakers. I remember reading somewhere that speaker wire can be 300 meters, can't recall where..

What info would you need to help me out here?

Many thanks
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Re: Long cable run for speakers

Post by Folderol »

It depends on the type of speaker too. Assuming you are talking about ones already in place, seeing as they are in a church (which will have all sorts of acoustic issues anyway) they may be 100V line types, in which case you can have much longer cables for the same cross section. Other than that, for any given speaker power, if you double the impedance the cable current is divided by 4.
Also are the runs daisy chained, or independent back to the amplifier?
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Re: Long cable run for speakers

Post by Wonks »

A lot is down to how much power (and therefore current) you are putting through the cables.

12 gauge is 4mm2 cable and 8 gauge is 10mm2 cable. 12 gauge should be more than OK if you aren't using too much power.

Let's say 500W into 8 ohms. That's a current of 7.9A.

140 feet is a round trip of 280 feet, so let's say it's a bit over 300 feet, or 100m.

Put that into a cable loss calculator for copper cables and you get a 26W loss from the cable, which isn't going to be noticeable. Going to 8 gauge/10mm2 only drops that to a 10W loss, a 15W difference, and you've got much more expensive cable to install and it's a lot stiffer, so won't go round bends so easily.

But 1000W into 8 ohms results in a 100W cable loss for 12 gauge cable, so you'd really want a bigger cable for that.

So it really depends on what sort of power you are putting out and your speaker resistance (as that determines the current, and power loss is based on the square of the current).
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Re: Long cable run for speakers

Post by James Perrett »

The first question I would ask is why do they want to replace their speaker cables? Reasonably modern (i.e. made in the last 50 years) installed cables don't wear out.
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Re: Long cable run for speakers

Post by twotoedsloth »

Hello and thanks again.

From what I have read, aside from stiffer, less manageable cables, there is no downside to used 8 gauge speaker cable. Do I understand this correctly?

The cables will be run under the floor, so a stiffer, recalcitrant cable isn't really an issue.

I don't know the specs on the power amp or speakers, but I will ask her right away.

Best regards
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Re: Long cable run for speakers

Post by Wonks »

Well, there is always the issue of being able to terminate 8 gauge cables at the speakers. Standard Neutrik Speakon connectors will accept up to 6mm2/10 gauge cable for termination and an overall maximum cable diameter of 14.5mm O/D.

If the speakers have Speakon connectors, then 10 gauge will be the largest cable that will fit them.

You can always run the final length at each end in 12 or 10 gauge, and run the main length in 8 gauge, but you then need some connection boxes at either end, and I'd prefer to avoid the risks of loose screws within the connection boxes if possible.

Find out what power you are talking about, the speaker make/type/resistance if possible and the connection details at the amp and the speakers. Then decide on the best speaker cable size.
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Re: Long cable run for speakers

Post by twotoedsloth »

Okay,

Apparently the amp is a Rogers S200B 140 watt amp with 4 ohms outputs to the speakers.

Does that help?
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Re: Long cable run for speakers

Post by Folderol »

Ouch! Bad combination. Oh well, what are the actual speaker impedances.
How may speakers are there?
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Re: Long cable run for speakers

Post by Wonks »

A bit. Not a lot of info out there that I can find on it apart from that it's a valve amp and looks to have hi-fi style banana plug/binding posts for the speaker lead terminations. As it's a valve amp you don't want to risk the speaker cables coming loose so I'd avoid having connection boxes if possible.

140W into 4 ohms gives 5.9 amps and a 14W (10%) loss over 100m for 12 gauge cable. If 140 feet is the actual cable run distance then that's 85m in total, so the cable loss is 12.4 Watts.

But that's at a maximum of 140W and I doubt the amp will be pushed that hard, so speaker cable losses will be significantly less in practice at lower outputs. But if it is running at near maximum output, then 12 gauge is probably a bit too thin and 10 gauge would be better. You could use 8 gauge, but there could be termination issues with this size wire.

8 gauge/10mm2 cable has a diameter of around 3.6mm (without insulation) approx 1/8". I'd have a look at the connections on the amp and the speakers and see of they will accept that size wire. 10 gauge is about 1/10" or 2.5mm in diameter.
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Re: Long cable run for speakers

Post by twotoedsloth »

Thank you all for your help.

I will wait for my friend to get back to me with the speakers to be used, probably Sunday.

Your help is greatly appreciated.

Peter
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