Speaker cable length - does size really matters ?? ;)

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  • Gadgets
    Junior Member
    • Dec 2003
    • 19

    Speaker cable length - does size really matters ?? ;)

    Well... tunneling my cables to the rear speakers was quite a mission... 45' of stranded copper.. but as going through the walls i only needed 33' for the rear left speaker & 45' for the rear right speaker - i bet you thought about it yourself once or twice.. well the question is - should i cut both cables to 45' (with 12' of leftovers) so i won't have any difference in the signal strength, or need i cut it 33' & 45' and could never tell the difference.. scientificly i guess it's the 1st. choice... any audiophile advice ?
  • Scarp
    Senior Member
    • Mar 2003
    • 632

    #2
    Originally posted by Gadgets
    Well... tunneling my cables to the rear speakers was quite a mission... 45' of stranded copper.. but as going through the walls i only needed 33' for the rear left speaker & 45' for the rear right speaker - i bet you thought about it yourself once or twice.. well the question is - should i cut both cables to 45' (with 12' of leftovers) so i won't have any difference in the signal strength, or need i cut it 33' & 45' and could never tell the difference.. scientificly i guess it's the 1st. choice... any audiophile advice ?
    Audiophily and with leaving nothing to chance, cut them both the 45'. However do *NOT* bunch up the extra 12' or wind it up in a circle. Ideally, lay the cable roomy enough that you do not get windings, but still get correctly to the end.

    Quite long distances btw, can't you put your equipment closer?

    Comment

    • Gadgets
      Junior Member
      • Dec 2003
      • 19

      #3
      Well... There's a big sofa between those rear speakers lol... but i guess i can cut another 2' from the distance.

      Comment

      • Lex
        Moderator Emeritus
        • Apr 2001
        • 27461

        #4
        Absolutely, same length is best for timing issues. Now in all truth, it likely would not be audible by your ears. But that doesn't mean the difference doesn't exist, and it's on that basis that most true audiophiles would seek the grail, and make them the same length.

        Lex




        Cable Guy DVD Collection
        Doug
        "I'm out there Jerry, and I'm loving every minute of it!" - Kramer

        Comment

        • Andrew Pratt
          Moderator Emeritus
          • Aug 2000
          • 16507

          #5
          if you're speaking from an engineering perspective yes the cables should be the same lenght....BUT in the real world for you to be able to hear any difference between two cables of unequal lenght they would have to be extremely different lenghts (as in 1 inch vs 1 mile) and you couldn't move an inch from the perfect sweet spot. Short answer is don't worry about it just use what you need. Its actually far worse to have excess cable that's coiled up to maintain the same lengths as it would be to just trim off the extra and use what fits.




          Comment

          • ThomasW
            Moderator Emeritus
            • Aug 2000
            • 10934

            #6
            The signal moves through the wire at the speed of light (~300,000 kilometers per second or 186,000 miles per second) 8O

            As a result a few feet of wire one way or another isn't going to cause timing issues. It's possible that the increased L/C/R of the wire is enough to cause minor voicing changes.

            If you have enough spare wire cut a 30' & 45' length and give them a listen before putting them in the walls. That will answer your question.

            As Scarp noted don't 'coil' any excess wire, it should instead be 'fan-folded' to avoid creating an inductor....




            theAudioWorx
            Klone-Audio

            IB subwoofer FAQ page


            "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

            Comment

            • Gadgets
              Junior Member
              • Dec 2003
              • 19

              #7
              Well ... i've just cut them both to 45' and tossed the leftovers under the big sofa... LOL apparently this sofa is a big disadvantage & a small advantage after all.. :LOL:

              Comment

              • brucek
                HTG Expert
                • Aug 2000
                • 303

                #8
                Speaker cable length affecting phase differences, timing issues? Forget about it.

                Yes, electricity does travel near the speed of light in a wire (depending on its specific velocity factor), but that's not important here. This speed is approximated to about a nanosecond a foot.

                An acceptable example would be that if you had one speaker wire 50 feet longer than the other, then that signal would arrive about 50 nanoseconds later than the other. Well, this is about 1000 times less than human hearing can even begin to detect, so don't worry about the lengths of your cables and phase differences.

                If you hear the difference, you won't need a receiver to listen to local radio stations, your ears will do the job for you...... :LOL:

                Comment

                • Lex
                  Moderator Emeritus
                  • Apr 2001
                  • 27461

                  #9
                  While that is likely very true, it does not change the fact that there is "a" timing difference, even if miniscule in size. I still like to keep things equal, as do a lot of other people. Why have any difference at all if you don't have to? That's my thinking on it. I don't sell someone a 5 meter RCA cable, and a 1 meter. I sell them like sizes normally. Speaker cables should be no different. That's why they are called a pair, if they aren't the same, they really aren't a pair.

                  Lex




                  Cable Guy DVD Collection
                  Doug
                  "I'm out there Jerry, and I'm loving every minute of it!" - Kramer

                  Comment

                  • Andrew Pratt
                    Moderator Emeritus
                    • Aug 2000
                    • 16507

                    #10
                    Why have any difference at all if you don't have to?
                    because more often then not there's a difference in the distances between the and and right speaker and its better to cut the cable to match the required lenght then to coil up excess.

                    As for their being a difference sure there "is" but its going to be masked by so many other variables why bother worrying about it.

                    I'm not opposed to people keeping them the same lenght just so long as they're not comprimising something else as a result.




                    Comment

                    • brucek
                      HTG Expert
                      • Aug 2000
                      • 303

                      #11
                      because more often then not there's a difference in the distances between the and and right speaker and its better to cut the cable to match the required lenght then to coil up excess.
                      Exactly. And here we've only focused on phase issues - which I think we've established as a non-issue.

                      With respect to the far more significant increased low pass filter effects exacerbated by longer cable lengths, why would Gadgets leave an extra 12 feet of low pass filter crammed behind his couch when he can cut it to length as Andrew suggests and realize a benefit for that speaker at least?

                      brucek

                      Comment

                      • Lex
                        Moderator Emeritus
                        • Apr 2001
                        • 27461

                        #12
                        We'll agree to disagree here. As far as this being "masked", masked by what? I'm sorry but that makes no sense. If we are talking 2 channel, there's one thing going on with music and it's the music coming out of 2 channels. Other than accoustics, there's no other variables. Those 2 speakers are either timed as close as the electronics will allow, or they are not, it's your choice. I've made mine and decided what I recommend. It's a small difference, granted, probably couldn't be heard by the best golden ear. But that still doesn't mean he wants to leave it to chance.

                        Lex




                        Cable Guy DVD Collection
                        Doug
                        "I'm out there Jerry, and I'm loving every minute of it!" - Kramer

                        Comment

                        • Andrew Pratt
                          Moderator Emeritus
                          • Aug 2000
                          • 16507

                          #13
                          As far as this being "masked", masked by what?
                          Slight differences in the crossover components (actual values), one cable running // to a power cord, your head moving 1" to the left of perfect centre etc. any one of those would have a great effect on what you hear then a difference in a couple of feet of cable




                          Comment

                          • David Meek
                            Moderator Emeritus
                            • Aug 2000
                            • 8938

                            #14
                            Is a variation in resistance a possible issue? Not being a poobah on things EE, I'm curious. . . . :huh:




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                            Comment

                            • brucek
                              HTG Expert
                              • Aug 2000
                              • 303

                              #15
                              Those 2 speakers are either timed as close as the electronics will allow, or they are not, it's your choice.
                              Is a variation in resistance a possible issue? Not being a poobah on things EE, I'm curious
                              Mmmm, so our question is whether 12 feet extra of speaker cable has a greater effect on (timing of the electrical signal) or the (frequency response) of the signal. We certainly always want the best sound possible, so it's worth looking at.

                              Well, an extra 12 feet of cable would cause the signal to end up at one speaker about 12 nanoseconds late. This calculates to a hearing requirement needed to perceive this signal delay of about 83 MHz - read megahertz (which is just below the FM radio broadcast spectrum) . Humans can hear up to 20Khz (that's kilohertz). I think we can put that issue to bed.

                              Regarding wire length, if we're using 12 gauge wire, what length would significantly disrupt frequency response and system damping.
                              Well, that's a tough one to answer as each listener is different. The question is always , "How much performance am I willing to lose"? - because, no matter what, you'll always lose performance with any speaker wire. The longer it is - the worse it gets.
                              The best caveat is of course to keep your speaker wires as short as possible. Monoblocks are desirable because you can place them close to the rear of the speakers and use super short speaker wires.

                              There are lots of rules of thumbs for acceptable percentage loss in signal across a speaker wire. Most people would find the values unacceptably high. The rule says you shouldn't lose more than 10% of your power in your speaker cable and that a system damping factor of greater than 10 is OK. I don't find those figures acceptable, but there you are...
                              It's easy to calculate your losses at certain frequencies for a given wire and amplifier and speaker impedance, but its boring and better to stick to making sure you keep speaker wires as short as possible.

                              Anyway, I'll give you an example of our 12 gauge at 12 feet.
                              Typical 12 gauge cable exhibits a DC resistance of about 1.619ohms per 1000ft. This DC resistance is not frequency dependant and can be calculated as to the loss you'll experience for every foot in relation to an 8 ohm speaker for example. Basic math.
                              Next value to consider is inductance per foot of the wire. A pretty good estimation of inductance per foot for most gauges of speaker wire is about 0.20 microhenrys/foot. Yes, the higher the gauge (smaller wire), the higher the inductance, but it's really, really insignificant.
                              Inductance (and capacitance) are both properties of wire that create frequency dependant resistance (this is AC resistance).

                              For inductance, as the frequency goes up, the resistance increases. This resistance is actually called inductive reactance - no matter. What matters is that it is a resistance that is in series with the speaker loop and it will create a loss.
                              The fact is, the higher the frequency, the higher the resistance caused by the inductance, and remember, the longer the cable, the more inductance increases.
                              For capacitance, since this a low impedance connection, we can essentially disregard it and the bypass reactance it causes. Capacitance is only a player in high impedance connections such as interconnects between preamps and power amps. It's too small an effect to be considered in a speaker connection.

                              Let's pick two frequencies of interest - 100Hz and 20KHz.
                              The DC resistance is the same at both frequencies and calculates to 0.039ohms for 12 feet
                              The inductive reactance (XL impedance) at 100HZ and at 20KHZ is:
                              @100Hz = 0.0015 ohms
                              @20KHz = 0.30 ohms

                              So a 12 foot piece of speaker cable has an approximate impedance at the two frequencies of:
                              @100Hz = 0.039 + 0.0015 = 0.04 ohms
                              @20KHz = 0.039 + 0.30 = 0.339 ohms

                              So how is that significant in relation to an 8 ohm speaker:
                              @100Hz = power loss in speaker cable of 0.5%
                              @20KHz = power loss in speaker cable of 4.1%

                              Assuming a typical solid state amplifier output impedance of .05 ohms yielding a damping factor of 160, then at the 100Hz impedance of the wire where damping factor is significant, it will be lowered to about 88.

                              What's this mean? Well, it means 12 feet of 12 gauge is pretty darned good, but at 20KHz you can see that the inductive reactance is starting to overwhelm the formula and a loss is creeping in, evidenced by the 4% power loss figure and resulting in a softening of the upper audio frequency range (essentially this is a low pass filter - did I hear someone say wire doesn't matter). Well, no way you'll likely hear that loss, but the conclusion I come to on this question is:

                              If you have an extra 12 feet of speaker cable not used, it will affect the frequency response and will not affect the timing. Cut the wire to length.

                              brucek

                              Comment

                              • David Meek
                                Moderator Emeritus
                                • Aug 2000
                                • 8938

                                #16
                                Excellent post, Bruce! Thanks for the information. :T




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                                • Andrew Pratt
                                  Moderator Emeritus
                                  • Aug 2000
                                  • 16507

                                  #17
                                  The best caveat is of course to keep your speaker wires as short as possible. Monoblocks are desirable because you can place them close to the rear of the speakers and use super short speaker wires.
                                  i thought that since speaker wire was far less likely to pick up interference so you should always opt for longer speaker cables then interconnects?




                                  Comment

                                  • brucek
                                    HTG Expert
                                    • Aug 2000
                                    • 303

                                    #18
                                    i thought that since speaker wire was far less likely to pick up interference so you should always opt for longer speaker cables then interconnects?

                                    It's really a question of which situation has the greater negative effect.

                                    The speaker to power amp connection, operates in the current domain. This is an extremely low impedance interface. The output impedance of most amplifiers is less than 0.1 ohms feeding a speaker and crossover system with impedance's that vary from 4 to 8 ohms. You have to appreciate the upsetting factor that simple cable resistance and inductive reactance can add to this scenario even in relatively short lengths.

                                    Because the speaker is in the order of 4 - 8 ohms, a long speaker run, particularly one of high gauge (small wire) can become an appreciable proportion of the speaker impedance and as such can affect a signal loss and change of system response combined with decreased system damping. The system damping formula is almost exclusively driven by the speaker cables impedance, which is a function of its resistance and inductive reactance (capacitive reactance can be ignored here).

                                    The interconnect between a pre amp and power amp is a line level, high impedance connection which is essentially a voltage bridge and is indeed (as you stated) susceptible to noise in long lengths, but this is taken care of very nicely in a home environment by using standard coaxial cable with a good (100%) shield - so there's no real problem there.

                                    There is (almost) no power transfer in an interconnect interface. The preamp acts as a voltage source and as such almost no current here, only voltage. So you could use 20 gauge or 10 gauge and it would have zero affect on the voltage feeding the power amp. In that regard the DC resistance of a long length isn't a factor to be considered as it is with a speaker cable. The only concern with the interconnect is cable capacitance which increases with length. The resulting capacitive reactance shunt has an appreciable effect on high output impedance devices such as passive pre amps and tube preamps. In those cases a short interconnect is preferred. But in solid state pre amps with their very low output impedance the minimal low pass effect of a long interconnect wins out over the long speaker cable.

                                    It's really the main advantage (besides channel separation) in owning monoblocks. Place the monoblock as close as possible to the speaker and run long interconnects. Choosing interconnects with as low a capacitance would be advisable.

                                    The problem of course is that reality steps in and because of equipment location concerns etc., you often have to compromise on this long/short deal. Myself, because my two channel is so important to me, I have my power amps close to my mains and my preamp close to the power amp. It allows me to use both short interconnects and short speaker cables of 9 gauge. For my rears (where I don't really care, nor consider 5.1 critical listening) I have long speaker cables.....I don't really care if I lose a few percent in the speaker runs to the rear.

                                    brucek

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