RLG Posted February 4, 2003 Share Posted February 4, 2003 I will be running speaker wire for my rear speakers up through the attic. Should I keep the wires the same length for both speakers or can one be 12 feet while the other is 30 feet? Thanks for any help. Quote Link to comment Share on other sites More sharing options...
DrWho Posted February 4, 2003 Share Posted February 4, 2003 since light travels at like 300,000 km/sec and electricity isn't that much slower...i don't think you will be able to notice a difference in the sound, especially considering that sound travels a mere 3km/sec. that means that a difference in length of cable would mean your speaker placement would have to be 18/100,000 feet closer for the sound to arrive at the same time. (this is all speculation, but i think it works out that way) anyways, all that to say, go ahead and use the shorter cable. but im sure others would tell ya otherwise. Quote Link to comment Share on other sites More sharing options...
lynnm Posted February 4, 2003 Share Posted February 4, 2003 The only suggestion I would make is that given that one of your runs is longish don't go any smaller than AWG 12. As DrWho implies the transmission time is essentially irrelevant but with longer runs resistance can become a factor. That said AWG 12 is plenty big enough. Quote Link to comment Share on other sites More sharing options...
rjb294 Posted February 4, 2003 Share Posted February 4, 2003 I don't think the cable length makes a difference. I ran my speaker wire throught the attic as well, and I am sure they are different lengths. I didn't even stop and think that it would make a difference and they both sound great, so I am sure it does not matter. RJB Quote Link to comment Share on other sites More sharing options...
WMcD Posted February 4, 2003 Share Posted February 4, 2003 Whoops, I think some error crept into DrWho's calculation. Maybe it is the scarf. Speed of sound in air is 344 m/sec. Or 0.344 km/sec. It is interesting to note that: Speed of sound in water is 1525 m/sec. Speed of sound in copper is 3353 m/sec. Speed of sound in steel is 4877 m/sec. Naturally the final two refer to when you bang a hammer on one end of a rod and determine how fast it travels to the other end. This is not the speed of an electrical signal in a wire. Gil Quote Link to comment Share on other sites More sharing options...
DrWho Posted February 4, 2003 Share Posted February 4, 2003 when i mentioned that sound goes like 3km/sec i was thinking about lightning striking and every 3 seconds is 1 mile (close to 1km)...but i did my math wrong cause 1km/3seconds = 333 m/s like you said what can i say? i was in the middle of a lecture and had to look like i was paying attention... anyways, lynm brings up a good point about a difference in resistance...i don't think it's a big issue here (as long as we're not using extremely thin wire), but it's something i never thought about. (hah, that's why i like this forum, every1 looks at stuff differently) Quote Link to comment Share on other sites More sharing options...
WMcD Posted February 5, 2003 Share Posted February 5, 2003 Sorry to be a stickler. People have to know they can trust information from the Tardis. Sound travels at 13500 inches per second in air. That is fairly close to 1 mile in 5 seconds. So the delay between lightning and thunder (Blitzen and Donner, maybe that what the poet was thinking of) is 5 seconds for every mile. In bed as a kid, I'd count "1 allegator, 2 allegator, 3 allegator . . . . " to estimate the time. I still do. Working the late shift of the forum in ORD land, Gil Quote Link to comment Share on other sites More sharing options...
Malcolm Posted February 5, 2003 Share Posted February 5, 2003 Don't think you will have a problem because of the difference in arrival time of the signals due to cable length. The difference between your ears and each of the speakers is going to be a much bigger factor. An electrical signal travels much, much faster through a cable than sound does through air. Could be a small difference in frequency response due to different capacitance and inductance in the two cables. Doubt you can hear it. BTW the speed of sound changes with the density of the air, which is affected by many factors, including humidity and temperature. That is why supersonic aircraft have mach meters. Quote Link to comment Share on other sites More sharing options...
duckloads Posted February 5, 2003 Share Posted February 5, 2003 I went throught the same decision when I got my new Klipsch speakers. Life is kind of short to agonize over something like this, so I made my (2) rear cables the same length and the (3) front cables the same lenght. It's only cable. When I opened up my ksf-8.5's and saw the wire inside, I started to wonder if anything matters. It was REAL small. Good luck Quote Link to comment Share on other sites More sharing options...
DrWho Posted February 6, 2003 Share Posted February 6, 2003 uh-oh...do i sense a fellow doctor who fan? hehe, sorry...im obsessed with that show (tom baker rocks! in fact, i got every episode with him on videotape). and just for the record, though i claim there's no difference in sound, i still end up using the same length cables. it just sits better in my head that way Quote Link to comment Share on other sites More sharing options...
fini Posted February 6, 2003 Share Posted February 6, 2003 It's been recommended one use in-wall rated speaker wire for your attic runs. Don't ask me to explain it. Same reason you don't use extension cords inside walls. Marksdad is an electrician, he'll know! fini Quote Link to comment Share on other sites More sharing options...
michael hurd Posted February 6, 2003 Share Posted February 6, 2003 The reason for using an in-wall rated wire is to ensure that you meet electrical codes and also, for fire resistance. If you light normal zip cord or speaker wire on fire, the flames travel fast. In-wall wire has fire retardants in the jacket which slows flame spread. Quote Link to comment Share on other sites More sharing options...
redwood forest Posted February 7, 2003 Share Posted February 7, 2003 The length of both cables should be the same regardless of the distance to each speaker. This is to assure that both speakers have the same signal due to length and quality of the wire. This is why cable companies sell cables in pairs using the same length and quality of wire. Actually it is better to have long interconnects leading to a stereo amplifier half way between both rear speakers. In this way the quality of the signal can be better maintained and the length of the speaker wires can be kept the same. Quote Link to comment Share on other sites More sharing options...
lynnm Posted February 7, 2003 Share Posted February 7, 2003 Quote: "The length of both cables should be the same regardless of the distance to each speaker. This is to assure that both speakers have the same signal due to length and quality of the wire. This is why cable companies sell cables in pairs using the same length and quality of wire. Actually it is better to have long interconnects leading to a stereo amplifier half way between both rear speakers. In this way the quality of the signal can be better maintained and the length of the speaker wires can be kept the same. " Redwood I fear that I must disagree . Your reasoning makes sense but neglects two critical factors - the speed of electricity - essentially the speed of light - and the resistance to that transmission - more accurately impedance to A.C. current flow when we speak of audio signals, (resistance is most properly described as a measure applicable to Direct Current which need not take signal frequency into account as in a DC situation there is no frequency change - while impedance needs to take frequency of a signal into account because a given conductor - eg. a voice coil does in fact present varying degrees of current flow -) per foot of wire.< Common Example: Place an Ohmeter across the terminals of a speaker rated at 8 ohms and you will read a resistance of anywhere from 0 to 1 ohms because the meter is measuring the DC resistance of the speaker. If however one were using a meter designed to read the AC impedance of that speaker fed with a 1 Khz signal then the reading would likely be something near the 8 ohm reading.[bR> The ability of a conductor to pass a signal varies widely depending on the AC frequency of that signal. That is why the term "Nominal Impedance" is used to describe the "Impedance" of any speaker is universally used. In other words a manufacturer will specify the impedance of a particular speaker as 4 ohms or 8 ohms. The reality is that the impedance of any speaker will range anywhere from 0 ohms up to several hundred ohms. The nominal impedance generally refers to the impedance presented at some overall average frequency measured over time when an "average" range of frequencies are presented to the speaker. The notion that speaker wires should be of precisely same length to ensure temporal equality would likely be relevant if we were dealing with the task of transmitting signals AC or DC over vast distances. Every electrical conductor has a certain amount of resistance/impedance and the longer the wire the greater that resistance/impedance but realistically 12 guage wire will negate any such differences in even the most elaborate systems encountered in a residence. Quote Link to comment Share on other sites More sharing options...
sculpin Posted February 7, 2003 Share Posted February 7, 2003 RLG Don't worry about the length, especially for the surrounds. I try to keep my lengths the same but the only difference it seems to make is to the company who gets to sell me more speaker cable! If you worried about cable length that closely, it would seem you would have to also worry about exact speaker placement and delays as even a small difference in distance would impact the arrival of sound to your ears and probably make the whole discussion irrelevant. Just enjoy! My only recommendation is to buy decent in-wall cable so that you only have to do this once. Not much that is less fun than running cables in walls and attics! Quote Link to comment Share on other sites More sharing options...
bkrop Posted February 8, 2003 Share Posted February 8, 2003 You should keep the length of the speaker wire the same for each pair of speakers, not because of any difference in sound quality, but because you should have the same resistance presented to your amp L/R. It is a miniscule difference but might matter long term. Quote Link to comment Share on other sites More sharing options...
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