A kilowatt sub amp drives a distributed sub array. Two subs are closer to the rear wall than the front wall. Room is 16.5' x 25.5'. Main speakers on the short wall.
For the 2 subs closer to the rear wall, I ran a single conductor "loop" around the room's circumference. Wow, surprised to see the sum total loop length is about 80+ feet. The 2 subs are in series, 4 + 4 = 8 Ohm on this half of the sub amp load (4 subs total).
Wire is equivalent to 6AWG copper, subs crossed 4th order @ 50 Hz.
A brilliant, highly accomplished digital/analog engineer, said the speaker cable loop described above is an antenna which amplifies signals in the loop, such as from even a mobile phone.
Please qualify or quantify the risk of the loop audibly degrading performance compared to 14AWG copper twisted pair, one pair to each sub, 40 feet and 25 feet respectively (in this case each cable pair sees a 4 Ohm load; the above described loop load is 8 Ohm).
For the 2 subs closer to the rear wall, I ran a single conductor "loop" around the room's circumference. Wow, surprised to see the sum total loop length is about 80+ feet. The 2 subs are in series, 4 + 4 = 8 Ohm on this half of the sub amp load (4 subs total).
Wire is equivalent to 6AWG copper, subs crossed 4th order @ 50 Hz.
A brilliant, highly accomplished digital/analog engineer, said the speaker cable loop described above is an antenna which amplifies signals in the loop, such as from even a mobile phone.
Please qualify or quantify the risk of the loop audibly degrading performance compared to 14AWG copper twisted pair, one pair to each sub, 40 feet and 25 feet respectively (in this case each cable pair sees a 4 Ohm load; the above described loop load is 8 Ohm).
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> I ran a single conductor "loop" around the room's circumference.
A very strange thing to do, not what wiremen usually do; for good reasons which are obscure.
My first thought is that milliwatt cellphones can't compete against kilowatt audio. And another reason is that short cell-waves tend to average-out of these long wire runs.
The *resistance* is easily computed (did you?):
#6 ___ 0.016r __ (-0.017dB)
#14 ____0.1r ___ (-0.1dB)
However in AC wiring the *inductance* can matter. On my 500 foot inf-2.4r impedance power line from the street, neglecting inductance gives a small error of voltage-sag (at 60Hz!); including the inductance of my cable-type from the tables makes my math real-close.
While my inductance is a small miss in my math for 60Hz, at 600Hz it would be significant.
Open spaced pair gives some inductance. Twisted-pair (what I have) gives less inductance; we want to minimize the free space between the two conductors.
A loop is going entirely the wrong way for low inductance. And that configuration will not be in any cable-table. You may find a ham-radio loop calculator. Use round numbers to assume a round loop, that will give the order-of-magnitude for consideration.
Wire gauge has little effect on line inductance.
Using this calc: https://www.eeweb.com/tools/parallel-wire-inductance I get these numbers:
#6 loop: 0.000,034 H (X ~ 0.07r @ 600Hz) DCR ~ 0.016r
#6 pair: 0.000,004 H (X ~ 0.014r @ 600Hz) DCR ~ 0.016r
#14 pair: 0.000,004 H (X ~ 0.014r @ 600Hz) DCR ~ 0.1r
These all look plenty-low for the audio. SO low that _I_ would run #18 lamp-cord and call it done.
A very strange thing to do, not what wiremen usually do; for good reasons which are obscure.
My first thought is that milliwatt cellphones can't compete against kilowatt audio. And another reason is that short cell-waves tend to average-out of these long wire runs.
The *resistance* is easily computed (did you?):
#6 ___ 0.016r __ (-0.017dB)
#14 ____0.1r ___ (-0.1dB)
However in AC wiring the *inductance* can matter. On my 500 foot inf-2.4r impedance power line from the street, neglecting inductance gives a small error of voltage-sag (at 60Hz!); including the inductance of my cable-type from the tables makes my math real-close.
While my inductance is a small miss in my math for 60Hz, at 600Hz it would be significant.
Open spaced pair gives some inductance. Twisted-pair (what I have) gives less inductance; we want to minimize the free space between the two conductors.
A loop is going entirely the wrong way for low inductance. And that configuration will not be in any cable-table. You may find a ham-radio loop calculator. Use round numbers to assume a round loop, that will give the order-of-magnitude for consideration.
Wire gauge has little effect on line inductance.
Using this calc: https://www.eeweb.com/tools/parallel-wire-inductance I get these numbers:
#6 loop: 0.000,034 H (X ~ 0.07r @ 600Hz) DCR ~ 0.016r
#6 pair: 0.000,004 H (X ~ 0.014r @ 600Hz) DCR ~ 0.016r
#14 pair: 0.000,004 H (X ~ 0.014r @ 600Hz) DCR ~ 0.1r
These all look plenty-low for the audio. SO low that _I_ would run #18 lamp-cord and call it done.
"A brilliant, highly accomplished digital/analog engineer, said the speaker cable loop described above is an antenna which amplifies signals in the loop, such as from even a mobile phone."
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In a loop, there is no signal amplification whatsoever. Furthermore such a basic loop is definitely not tuned to a microwave frequency band that is used by cellphones so I would not expect an interaction with such equipment. The described loop may be tuned to some shortwave frequency band, at best.
However a loop antenna has some gain. (with respect to RF)
I am not sure if I would want to sit in a large loop with some kW pumped through it and get exposed to such fields. I pass.
If you physically separate forward path from the return path you create a nice basic loop antenna. Whatever signal you have on these separated paths will radiate nicely and may be picked up by other equipment or even the amplifier that drives it. This can and will cause nasty oscillation and misbehavior. Generally such wants to be avoided, unless you do intend to radiate, but then this is the wrong forum, radio amateurs forum would then be suggested.
In particular when using high power it is imperative to keep the forward path physically as close as possible (generally twisted) to the return path such that the magnet fields can cancel each other and so no or very little signal is radiated. So I am with scottjoplin, on that. And again, no excuse.
Same principle is applicable to PCB and layout. This is the main reason why some designers utilize, very successfully, a solid ground plane on they're boards where it is needed and where it is applicable. Solid ground plane is a subject of great controversy, here on this forum and elsewhere, argued mostly by those DC 'experts' who have difficulty understanding basic AC theory.
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In a loop, there is no signal amplification whatsoever. Furthermore such a basic loop is definitely not tuned to a microwave frequency band that is used by cellphones so I would not expect an interaction with such equipment. The described loop may be tuned to some shortwave frequency band, at best.
However a loop antenna has some gain. (with respect to RF)
I am not sure if I would want to sit in a large loop with some kW pumped through it and get exposed to such fields. I pass.
If you physically separate forward path from the return path you create a nice basic loop antenna. Whatever signal you have on these separated paths will radiate nicely and may be picked up by other equipment or even the amplifier that drives it. This can and will cause nasty oscillation and misbehavior. Generally such wants to be avoided,
unless you do intend to radiate, but then this is the wrong forum, radio amateurs forum would then be suggested.In particular when using high power it is imperative to keep the forward path physically as close as possible (generally twisted) to the return path such that the magnet fields can cancel each other and so no or very little signal is radiated. So I am with scottjoplin, on that. And again, no excuse.
Same principle is applicable to PCB and layout. This is the main reason why some designers utilize, very successfully, a solid ground plane on they're boards where it is needed and where it is applicable. Solid ground plane is a subject of great controversy, here on this forum and elsewhere, argued mostly by those DC 'experts' who have difficulty understanding basic AC theory.
On this side of the ocean we often connect wire loops to PA outputs in conference centers to help the hearing impaired. Their hearing aids can then pick up the magnetic field.
Anyway, I think you've connected a nice loop antenna to your amplifier. It is reciprocal, so it will both transmit whatever you're playing as a low-frequency magnetic field and pick up the signals of any nearby transmitters and inject them into your amplifier. Whether that will cause interference depends on what transmitters are nearby, whether your amplifier has an output filter (just a Zobel won't help much), what the input stage looks like and so on. So basically you are asking for trouble, but it is difficult to predict whether you will get what you ask for.
Anyway, I think you've connected a nice loop antenna to your amplifier. It is reciprocal, so it will both transmit whatever you're playing as a low-frequency magnetic field and pick up the signals of any nearby transmitters and inject them into your amplifier. Whether that will cause interference depends on what transmitters are nearby, whether your amplifier has an output filter (just a Zobel won't help much), what the input stage looks like and so on. So basically you are asking for trouble, but it is difficult to predict whether you will get what you ask for.
It seems that it is possible to be both "brilliant" and ignorant. You have installed a nice HF loop antenna, which may be quite good at picking up a range of frequencies from MW to higher HF. Unlikely to be particularly good for UHF and microwaves, as used by mobile phones. Interference from broadcast radio is the most likely problem, but that would depend on exactly how the amplifier works.
As a (probably pedantic) aside, antennas do not amplify signals the way we think of amplification -- all antenna "gain" is a function of directivity (focusing sensitivity in one direction, while rejecting -- of noise -- in other directions). [retired RF engineer with some antenna design experience, here]
There is another thing (different but often confused) called 'reactive coupling', like what happens between two windings of a transformer, or through capacitance between conductors or in those audio frequency inductive-transfer loops for hard of hearing. That can also transfer energy or signals but follows different physics than antenna propagation. There can be of course more or less coupling, though still that's not exactly 'gain'.
All that said, if concern about nearby MHz band transmitters exists, keep the feed and return wires near each other..... like zip cord.
There is another thing (different but often confused) called 'reactive coupling', like what happens between two windings of a transformer, or through capacitance between conductors or in those audio frequency inductive-transfer loops for hard of hearing. That can also transfer energy or signals but follows different physics than antenna propagation. There can be of course more or less coupling, though still that's not exactly 'gain'.
All that said, if concern about nearby MHz band transmitters exists, keep the feed and return wires near each other..... like zip cord.
Are you thinking "Ring Mains"?
The described wiring is not a Ring Main, the purported advantages of a Ring arise mostly for many distributed loads around the ring, and in this over-built case the impedances are negligible.
Ring Mains arose in the UK as an idea to reduce the cost of re-electrification in a copper-poor economy. If the fusebox is in the front of the house and you need lights an electric-fire loads all around the house, a Ring Main may reduce both the total copper and the need for very fat cables.
Look at the OP's description. He did a single-conductor loop. He could pick up the wire on the west wall, sling it over to the east wall to run with the other conductor. The total wire-length will be similar (a few feet longer). The Loop Area will go from huge to small; inductance will fall by an order of magnitude.
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