[BuGsArEtAsTy]

So, this may not come as a surprise to you, but nonetheless it's the first time I've actually noticed a real difference by swapping out the speaker wires.


I moved into a house last year that had an ex-garage turned into a home theatre room. The wiring wasn't in-wall, but for the surround speakers' wire they had run inconspicous very small wire covers (white plastic tubes) along the corner of the ceiling and wall.


Well, I noticed that the surrounds always sounded quiet, probably partially because of the setup of the room and the small speakers... but also probably because they had run 20 gauge wire. The run was about 40 feet, but I suspect they had almost twice that there, as at each end there was a lot of coiled unused wire. So perhaps 75' of 20 gauge wire.

After struggling with the surround output levels I finally decided to remove all the wires and put new 14 gauge wire in.


To make a long story short, the surrounds now seem a bit louder, although not by a huge amount. Not a big surprise to you I know, but it was actually the very first time that speaker cable made any noticeable audible difference to me. Better? I dunno, but it does seem a bit louder.


I am still wondering though how much of that difference truly is though. My question is how do I calculate the impedance loss between say 75' of 20 gauge wire and 50' of 14 gauge wire, and correlate that to dB change? (My speakers are nominal 8 Ohm.) I have seen some online descriptions, but I'd like to go through the exercise of doing the actual calculations. The guidelines I have seen suggest to me that the volume difference between the two sets of wires is probably less than 1 dB. That's significant, but it may be hard to notice unless you're specifically listening for it (like I was).


P.S. Some of you are probably wondering why I chose 14 gauge wire for 40'-50' runs. Well, I did so partially because it's considered relative OK by some of the guidelines, and 14 would fit a heluvalot easier in the existing wire covers. With 12 gauge I probably would have wanted to rip out the existing wire covers as well and replace them with bigger ones, adding effort and expense. I probably could have actually fit standard 2 x 12 gauge wire in the existing wire covers, but if you've ever used them, you'd know how much of a pain it is to stuff thick wire into them once they've already been mounted on the wall.

 

[XanderMoser]

Seen this page?

http://www.roger-russell.com/wire/wire.htm


It's the first hit from google with a search for "speaker wire"


Good info.

 

[BuGsArEtAsTy]



Quote:
Originally Posted by XanderMoser /forum/post/15396945


Seen this page?

http://www.roger-russell.com/wire/wire.htm


It's the first hit from google with a search for "speaker wire"


Good info.

Yes. In fact, it is one of the guidelines I was talking about.


However, unless I'm missing something, it doesn't tell n00bs like me how to do the do the actual calculations.

 

[XanderMoser]

Warning: I am not an electrical engineer. I will have a bachelor's in mechanical design in a few months. But I have built a few speakers and have experience running concerts and troubleshooting systems. So I'm not guaranteeing any of this is right. Someone back me up or shoot me down...



The real gain in higher gauge wire is that your frequency response will be more even, not just louder.


We are going to use resistance rather than impedance so we don't have to measure and calculate at every frequency...good enough for now I hope.


20 gauge wire has a resistance of .0119 ohms/foot. 75' = .8925 ohms


14 gauge wire has a resistance of .00297 ohms/foot. 40' = .1188 ohms


You can already see that the resistance of the 20 gauge wire was 8 times more than the 14 gauge wire, and more than 10% of a nominal 8 ohm speaker. Very very bad for the frequency response...


The rule is that doubling voltage results in a 6db gain, while doubling power results in a 3db gain.


To get a realistic voltage/current level of your amp...let's put you at 10 watts into an 8 ohm speaker. That makes the voltage 8.94 volts. (V^2=PR). That makes the current 1.12 amps (V=IR)


Voltage of your amp will stay constant with different loads. The current will change, resulting in more power (watts).


So...


20 gauge speaker wire with 8 ohm speaker:


8.94V = I*(8+.8925ohms)

I=1.005 amps

P=8.94V*1.005amps = 8.985 watts


14 gauge speaker wire with 8 ohm speaker:


8.94V = I*(8+.1188ohms)

I=1.101 amps

P=8.94V*1.101amps = 9.843 watts


So 8.985 watts versus 9.843 watts.


9.843/8.985 = 9.5% increase in power


It looks like you are seeing a db increase of 0.4 dB (using a power to db calculator)


I'd say that would be very very hard to tell the difference in pure output.


However, the difference in sound quality would be audible, mostly a more even frequency response.

 

[BuGsArEtAsTy]

Wow thx.


So 0.4 dB on average, but I do understand your statement of "mostly a more even frequency response". Perhaps my "louder" I'm interpreting is actually more consistency. I was hearing a few things I wasn't hearing before. Anyways, like I said, this was the very first time I've ever noticed a difference due to speaker cable, and I tend to be a skeptic about these things. Obviously, I can't do a blinded test though.


BTW: That impedance difference is rather striking:

Quote:
20 gauge wire has a resistance of .0119 ohms/foot. 75' = .8925 ohms


14 gauge wire has a resistance of .00297 ohms/foot. 40' = .1188 ohms

P.S. Googling your Ohm/per foot numbers brings me up to this page which suggests to double the numbers, because speaker wire is in a loop.


So a 14 gauge impedance is 0.00297, but should be doubled to 0.00594. He also states that instead of 10%, 5% should be used as maximum impedance vs. speaker impedance, and compared to minimal speaker impedance (which is may be 2 Ohms as a rule of thumb). However, I wonder if he's talking about average 4 Ohm speakers, and not 8 Ohm speakers. (I only own 8 Ohm speakers.)


In any case, assuming a 5% max for speaker wire vs speaker impedance, a minimum speaker impedance of 4 Ohms, and per/foot loop impedance of 0.00594 Ohm/foot, then a 50' foot wire would have an impedance of:


.00594 x 50 feet = 0.3 Ohm


That's a bit more than the 0.2 Ohm that I'm inferring would be his recommendation. (The run is 40', but I have about 5' extra on both ends.) (In contrast, the more lax criteria you suggest would say that my run is 0.15 Ohm, which is only 1.9% of 8 Ohm.)


So again, 12 gauge would be the recommendation. Oh well. Perhaps I will swap out all the wiring, and the wire covers) in the room for 10-12 gauge, if I can find a cheap but good quality 200' spool of it somewhere, and if I get better quality surrounds. However, I doubt I'd hear any difference.


Actually my fronts are only 16 gauge, but the runs are less than 20' there.

 

[XanderMoser]



Quote:
Originally Posted by BuGsArEtAsTy /forum/post/15397781




P.S. Googling your Ohm/per foot numbers brings me up to this page which suggests to double the numbers, because speaker wire is in a loop.

Good call, didn't catch that. Certainly very important

Quote:
In any case, assuming a 5% max for speaker wire vs speaker impedance, a minimum speaker impedance of 4 Ohms, and per/foot loop impedance of 0.00594 Ohm/foot, then a 50' foot wire would have an impedance of:


.00594 x 50 feet = 0.3 Ohm

I like the 5% rule better myself. I did mention 10% though, that's the absolute max I'd ever suggest for someone else, if they were trying to save money for instance.


Anyway, you get the point. Glad you learned something, I did too.

 

[XanderMoser]

Oh, and since everything in those equations is linear, the .4 dB difference should double to .8 dB I think...which would be noticeable. Not drastic, but probably noticeable.

 

[BuGsArEtAsTy]



Quote:
Originally Posted by XanderMoser /forum/post/15398912


I like the 5% rule better myself. I did mention 10% though, that's the absolute max I'd ever suggest for someone else, if they were trying to save money for instance.


Anyway, you get the point. Glad you learned something, I did too.

Yeah, thanks. Definitely learned something.


To further the set of calculations:


If I use your 8 Ohm, I'd get 3.8%.

If I use an inferred 4 Ohm, I'd get 7.5%.

If I use his recommended 2 Ohm, I'd get 15%.


For 50' and 12 gauge (at 0.00374/ft):


If I use your 8 Ohm, I'd get 2.3%.

If I use an inferred 4 Ohm, I'd get 4.8%

If I use his recommended 2 Ohm, I'd get 9.4%.


For 50' and 10 gauge (at 0.00236/ft):


If I use your 8 Ohm, I'd get 1.5%.

If I use an inferred 4 Ohm, I'd get 3.0%.

If I use his recommended 2 Ohm, I'd get 5.9%.


So, in essence, he's recommending 8 gauge (!) for 50', whereas that Roger Russel guy would recommend 10-12 gauge, with 14 the minimum for 8 Ohm speakers that drop down to a minimum of around 5ish Ohms. It seems he isn't doubling the numbers, which is one reason for the difference in recommendations. (He also uses the 5% cutoff.)


Dunno about my surrounds, but some of my 8 Ohm speakers have a rated minimum impedance of 4 Ohms according to Paradigm.

 

[DMF]

Don't worry about it. 14 AWG is fine. Whatever tiny difference there might be in volume can easily be corrected when you calibrate the levels.


Besides, it's not like the surrounds carry much information.

 

[Aaron Gilbert]

Well, I just made a run of about 35' 16 gauge to my surround back speakers, which are four ohm - so that's 70' round trip. It turns out that puts the resistance at 8.3% of the nominal speaker impedance, oops. I'm not about to change it out though, it was too much of a pain to run. Plus, it's a neat bundle of four wires in one round jacket, which works perfectly for my setup. I'm skeptical that I would ever be able to tell the difference with a thicker gauge at this length, based on the excellent page XanderMoser posted, specifically the Stereo Review paragraphs. Plus, I don't think the ears are nearly as accurate for sounds immediately behind the listener, not to mention the receiver will take care of any level mismatches.

 

[BuGsArEtAsTy]



Quote:
Originally Posted by Aaron Gilbert /forum/post/15411711


Plus, I don't think the ears are nearly as accurate for sounds immediately behind the listener, not to mention the receiver will take care of any level mismatches.

Actually, the receiver won't. One of the reasons I was a bit concerned was not just because of the level differences overall, but the fact they vary by frequency.


This is from that page that was linked earlier:

This is a hypothetical example (extra 1 Ohm resistor), but it gets the point across. The difference in volume (red vs. green lines) ranges from 0.5 dB to 2 dB.


I do agree that you may or may not hear any difference, esp. with surrounds. However... I sympathize with your desire not to change the wiring because of the hassle (see above), but I do note that while many consider 14 gauge OK (albeit marginally so) for my 50' run with a nominal 8 Ohm speaker, most recommend against 16 gauge for a 35' run with a nominal 4 Ohm speaker. For you that Russell guy also recommends 14 gauge (and some others might recommend even bigger).