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Author Topic: Best option for long speaker cable runs  (Read 15564 times)

David Allred

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Best option for long speaker cable runs
« on: September 12, 2013, 09:48:44 AM »

12 awg cable
1) RMX2450 amp
2) 8 ohm cabs per channel

Amp and speaker locations cannot be moved.  Distances from amp to each speaker in a 100' x 100' room are (as cable would be run)...
30 ft.
130 ft
130 ft
230 ft

Option 1:
Channel A - 2 cables run individually to 30' and 130'.  4 ohm load.
Channel B - 2 cables run individually to 130' and 230'.  4 ohm load.

Option 2:
Channel A - 1 cable run to 30', jump to 130' (100').  4 ohm load.
Channel B - 1 cable run to 130', jump to 230' (100').  4 ohm load.

The Yorkville cabs are rated 131db (1m) continuous.  The amp at 4 ohms can easily deliver enough power to get to 126db each.  I expect each speaker to never get above 115-118db (1m), and in normal situations will cruise around 100db or less.

What is my best option?  Should the 30' run be lengthened?

Thanks
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TJ (Tom) Cornish

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Re: Best option for long speaker cable runs
« Reply #1 on: September 12, 2013, 11:57:53 AM »

12 awg cable
1) RMX2450 amp
2) 8 ohm cabs per channel

Amp and speaker locations cannot be moved.  Distances from amp to each speaker in a 100' x 100' room are (as cable would be run)...
30 ft.
130 ft
130 ft
230 ft

Option 1:
Channel A - 2 cables run individually to 30' and 130'.  4 ohm load.
Channel B - 2 cables run individually to 130' and 230'.  4 ohm load.

Option 2:
Channel A - 1 cable run to 30', jump to 130' (100').  4 ohm load.
Channel B - 1 cable run to 130', jump to 230' (100').  4 ohm load.

The Yorkville cabs are rated 131db (1m) continuous.  The amp at 4 ohms can easily deliver enough power to get to 126db each.  I expect each speaker to never get above 115-118db (1m), and in normal situations will cruise around 100db or less.

What is my best option?  Should the 30' run be lengthened?

Thanks
Why would you lengthen?

Option 1 has more wire - two runs of 12 ga into 8 ohm loads each paralleled at the amplifier is better than option 2, which means the 4 ohm load shares one 12ga run.

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David Allred

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Re: Best option for long speaker cable runs
« Reply #2 on: September 12, 2013, 01:47:18 PM »

Why would you lengthen?


Didn't want it to feel left out.  ;D

Let me throw in a 3rd option then.
Individual runs on the one channel to the 130' & 230' pair, but a jumped run on the other channel's 30' & 130' pair, with the 30' first in line.  Does that make any sense, or would you stick with your first selection?
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Greg_Cameron

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Re: Best option for long speaker cable runs
« Reply #3 on: September 12, 2013, 01:58:15 PM »

Long wire runs suck for both loss of output due to voltage drop and loss of low frequency damping for woofers. 130' & 230' wire runs at 4 ohms sound like a bad deal. My vote would be to figure out a way to co-locate amps closer to the speakers for the really long runs. Longer signal cables work better than longer speaker cables. Use power local to the co-located amps and use high quality signal isolation transformers if you run into ground loop issues.
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TJ (Tom) Cornish

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Re: Best option for long speaker cable runs
« Reply #4 on: September 12, 2013, 05:08:24 PM »

Other choices would be:

- Get another amp so you can bridge each amp into 16 ohms (speakers in series rather than parallel).  Check ratings of amp to see max. voltage swing and if that's enough power for your application

- Use a constant voltage system - 70v, 100v, etc.  Your amp may be big enough to drive this directly, so all you would need would be output transformers at your remote speakers.  If all you really need is 100dB/1m, then each speaker is only using a few watts.
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David Allred

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Re: Best option for long speaker cable runs
« Reply #5 on: September 13, 2013, 10:15:00 AM »

Long wire runs suck for both loss of output due to voltage drop and loss of low frequency damping for woofers. 130' & 230' wire runs at 4 ohms sound like a bad deal. My vote would be to figure out a way to co-locate amps closer to the speakers for the really long runs. Longer signal cables work better than longer speaker cables. Use power local to the co-located amps and use high quality signal isolation transformers if you run into ground loop issues.
Unfortunately, even if I added another amp it could not be moved from the "system closet", and a 70v system was rejected due to cost.
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Scott Wagner

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Re: Best option for long speaker cable runs
« Reply #6 on: September 13, 2013, 11:08:10 AM »

Unfortunately, even if I added another amp it could not be moved from the "system closet", and a 70v system was rejected due to cost.
That cost savings is about to be eaten by the big copper you're about to purchase.  For runs this long, the larger the cable, the better.  You'll be wanting 10 ga or even 8.
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Scott Wagner
Big Nickel Audio

Tim McCulloch

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Re: Best option for long speaker cable runs
« Reply #7 on: September 13, 2013, 11:30:21 AM »

Unfortunately, even if I added another amp it could not be moved from the "system closet", and a 70v system was rejected due to cost.

This is for an install?  What is the program material and what are the client's expectations for SPL/sound quality/etc?

Unless this is for a high-end, audiophool account I think you should run#12 and call it a day.  The client doesn't seem sufficiently interested in quality to pay for it.
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TJ (Tom) Cornish

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Re: Best option for long speaker cable runs
« Reply #8 on: September 13, 2013, 12:09:49 PM »

Unfortunately, even if I added another amp it could not be moved from the "system closet", and a 70v system was rejected due to cost.
70v transformers are not particularly expensive for moderate wattages: http://www.mcmelectronics.com/product/GALAXY-AUDIO-THSPM100-/555-7127

I agree with Tim though - if they have so many hard requirements, 12ga it is.
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Jeff Bankston

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Re: Best option for long speaker cable runs
« Reply #9 on: September 13, 2013, 08:04:00 PM »

use 8 gauge for the 130' and longer runs.
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ProSoundWeb Community

Re: Best option for long speaker cable runs
« Reply #9 on: September 13, 2013, 08:04:00 PM »


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