Shielded speakers cables

[sbronf]

Hi, I have a question about shielding speaker cables. Out of curiosity I opened a shielded cable of a well-known brand, to see what the shield was connected to and to my surprise I saw that the shield (aluminium foil) is not connected to anything, neither on the amplifier side nor on the speaker side. I wanted to ask if this configuration makes sense or if it can lead to problems. thank you all.

 

[MaxwellsEq]

Hi, I have a question about shielding speaker cables. Out of curiosity I opened a shielded cable of a well-known brand, to see what the shield was connected to and to my surprise I saw that the shield (aluminium foil) is not connected to anything, neither on the amplifier side nor on the speaker side. I wanted to ask if this configuration makes sense or if it can lead to problems. thank you all.

I've never been convinced that speaker cables in domestic installations and normal run lengths need to be shielded. The signal voltages are relatively high and the impedances are low, so pickup should be low with a well designed amplifier.

 

[solderdude]

A not connected shield does not shield much also depending on the used material for the shield and the frequency band.
It will likely increase capacitance a tiny bit (depending how close it is to the wires).
Twisted wires in a cable would make more sense when it comes to immunity and radiation.

 

[dedobot]

Grounding the shield both ends can be double edged sword. Anyway speakers are passive device so both ends grounding isnt a option . Grounding at at one end makes the shield picky to RF emissions.

 

[Speedskater]

a] it is possible for a speaker cable to act as a RF interference antenna. The interference can sneak in thru the feedback loop to the sensitive input stage. Impedances in this path are not low.

b] Jim Brown suggests a Unshielded Twisted Pair (UTP) for speaker cable.

c] If a foil shielded (STP) is used, the shield should be attached to the amp's metal chassis. It's a shield, not a ground.

d] Very long shielded speaker cables, may make some amplifiers unhappy.

 

[DVDdoug]

Plus, foil shield is rarely used where the cable will be flexed. They are normally used in walls or inside equipment, etc.

...of a well-known brand,

I wouldn't trust a company that sells shielded speaker cables, assuming they are marketed as "speaker cables".

 

[flightops]

I've got 20+ foot runs of plain old 12 gauge speaker wire in my home system. I use 12g for everything. Not because I think just because it's "thick" that it's better in some way, but because many moons ago I found three 250 foot spools on clearance for 15 bucks a roll. so now I use it everywhere I need speaker wires. Still haven't used all of even the first roll.

I've never had a noise problem on the speaker runs. Home, auto, etc.....anywhere.

Interconnects? Have had some "noise" that was solved mostly by changing the connection, swapping out/cleaning any tarnish/corrosion and rerouting the lines.

Never speaker wires though. Mine have always "just worked".....

 

[egellings]

The shield should be unnecessary unless the system is located in a high RFI environment. In that case, power cords might also need the same treatment.

 

[mhardy6647]

I can't imagine a domestic setting in which loudspeaker cables would ever need to be shielded. I cannot imagine many commercial settings where it might be necessary. Maybe with a few feet of a megawatt radio transmitter, radar station, or a high-field NMR spectrometer -- or perhaps a Tokamak.

 

[Speedskater]

The shield should be unnecessary unless the system is located in a high RFI environment. In that case, power cords might also need the same treatment.

Yep, Jim Brown (again) points out that all cords and cables can act as RF interference antennas.

 

[egellings]

Yep, Jim Brown (again) points out that all cords and cables can act as RF interference antennas.

Agree.

 

[Punter]

Audio equipment is not designed to work with radio frequencies so an RF field would have to be excessively strong to pass through it. Induced RF voltages are in microvolts even with strong fields. The only time I have observed true RF interference in audio equipment was in the early days of GSM mobile phones. A presenter had his new GSM phone in the studio with him when it received a call. The response from the transmitter in the phone was able to induce itself into the mixing console and the buzz actually went to air. Following this, we had to ban GSM phones from all studios. the nature of the GSM signal was loaded with fast rise-time pulses which were great at interfering with any sensitive electronics in the near vicinity.

GSM is an obsolete format now so its off the menu as far as RFI is concerned. However, the interference from GSM would not be audible because it had been induced into the speaker or speaker wiring. The interference was audible because it was being induced into the amplifier circuit. ESD diodes in the amplifier circuitry would be the most likely candidate by rectifying the signal. It stands to reason that any signal in microvolts that may have been induced into a speaker cable where a signal in volts would be present, would be inaudible.

Subsequently, adding a shield to a speaker cable to eliminate induced radio frequencies is an exercise in futility. If one was to do so anyway, the only plausible way to connect the shield would be at the amplifier end to the chassis ground.

 

[egellings]

I lived in Shorewood, WI (USA) a long time ago near an antenna farm, about a block away from my apartment. WTMJ and WISN TV (might have been others, too) and radio had large transmitter towers there. My system was vacuum tube based, which is a bit less susceptible to RFI than a SS system would be. I was soaked in RFI and my system was unusable. Shoot, the filling in one tooth acted as a detector in my mouth and I could pick 'TMJ up, no radio needed. Only solution was to move.

 

[Moonbase]

I think if rf is so strong that you need screened speaker cable, so interference is the least of your concerns.
I keep mains cable at least 5cms away from rca and Ethernet cables.

 

[egellings]

I think if rf is so strong that you need screened speaker cable, so interference is the least of your concerns.
I keep mains cable at least 5cms away from rca and Ethernet cables.

I would have had to place the entire system, speakers & all, and maybe me too, inside a big chicken (bedawk!) wire or hardware cloth box, which would act as a Gaussian shield to keep the RFI out, and a serious RFI filter would be needed at the power inlet. It was simply overwhelming. Moving was the only way I could see to remedy that.

 

[Punter]

WTMJ puts out 50kW on AM during the day! Now that's what I call RFI

 

[mhardy6647]

I believe I've mentioned this before elsewhere on ASR: When I was a lad, we lived a just few miles as the wave flies from the transmitter and towers a moderate-powered AM radio station* in Baltimore (WFBR). One of my father's loudspeakers (a 'fullrange' Electrovoice Wolverine LS-12 twincone 12 inch driver in a large BR enclosure) would, when the hifi was not switched on, play WFBR quietly but unmistakably. My father's theory was that the speaker wire (18 gauge lamp cord) was acting as a long-wire antenna, and something about the loudspeaker motor (e.g., a 'flaw' in the voicecoil) was acting as a detector. The very sensitive EV driver was responding to the detected signal as best it could.


a pair of LS-12 drivers, unbaffled.
Sensitivity of the LS-12, if memory serves, is ca. 96 dB/watt @ 1 meter (calculated from the driver's published EIA sensitivity specification)

_______________
* not a "peanut whistle", but also not 50 kW (as, e.g., was, and still is, WBAL-AM @ 1090 kHz). I think WFBR may have been 5 kW (@ 1300 kHz in those days).

 

[NTK]

How about San Francisco's Twin Peaks neighborhood right under the Sutro Tower? >6 MW.

RF Exposure Levels — Sutro Tower - Official Site

www.sutrotower.com

 

[EERecordist]

Hi, I have a question about shielding speaker cables. Out of curiosity I opened a shielded cable of a well-known brand, to see what the shield was connected to and to my surprise I saw that the shield (aluminium foil) is not connected to anything, neither on the amplifier side nor on the speaker side. I wanted to ask if this configuration makes sense or if it can lead to problems. thank you all.

I had shielded 18 ga speaker wire when I lived near a large radio transmitting tower. It was some kind of Belden with foil and an 18 or 20 drain wire. It worked fine without grounding the drain. Unshielded cable picked up the radio station. Magnetic shielding for the speakers - MuMetal is to keep the magnetic fields of the drivers in, so they don't interfere with the deflection coils of CRT displays, a problem we don't have now. YMMV.

The famous contemporary artist Nam Jun Paik used CRT displays because that was what was available at the time. He illustrates the impact of a permanent magnet on a display. The variable magnetic field of a speaker would have an effect depending on the speaker and the distance.

 

[Alice of Old Vincennes]

I wear a tin hat. Also, keeps UFO's at bay.