Submitted by dpedigo on Thu, 01/05/2012 - 12:00am

So about a week ago my neighbor asked me to help his friend (who also lives in our neighborhood) design a home theater for his basement on a pretty tight budget. No problem, this is what I (and most of those who will read this blog) do. I equate my skills to owning a truck, once someone finds out that I know how to design a proper home theater, I am their new best friend. Honestly, I love it because I can help out a friend and keep my design skills going.

So, I take a look at his basement, tell him what projector, screen, speakers and amplifier that he should buy and say that I will help him install the cable and speaker wires so that they are done properly. I also advise him that he needed to purchase a 25’ high speed HDMI cable.

At 25’ we are not talking about a significant long haul capability and that as long as the cable is considered high speed, or high speed with ethernet, he should be fine as the projector that he is purchasing is definitely entry level and there is an easement to pulling new cables if needed.

So to get to the point… on Saturday I was called by my new friend in a panic. I told him that the high speed cable should cost a few hundred dollars and not to get sucked into big box talk of having to go with the worlds greatest cable. Unfortunately, I was still recovering from surgery and missed the call and when I called him back I was informed that he purchased a cable for 3 times the amount that I said he should purchase for the following reasons.

1. Because his projector is 120 Hz, the normal high speed cable is not fast enough and that the super expensive cable is faster than high speed. That if he did not purchase this cable, he would lose resolution and not be able to see things like a hockey puck on the normal high speed cable. The super expensive cable is rated for in wall installations but the reasonably priced cable was not (despite it being a UL listed, in-wall cable right on the box).

Thus, I was asked to escort my new friend to the local big box store to straighten things out, which I happily obliged, as I love a good argument. When I got there, I somehow lucked out as the two salesmen and the manager of the department were there to “discuss” their reasoning. The manager was instantly condescending (to be fair, he was cool later and at one point said, obviously you know more than me, so teach me and we spoke for a about 30 minutes) asking me slowly “do you have dial up or do you have high speed internet.” I didn’t take this kindly and asked him to get to his point quickly.

His response was that the expensive cable was silver and the cheaper one was copper, just like dial-up vs. high speed internet. I proceeded to ask the manager “are you referring to velocity of propagation or are you talking about attenuation?” to which he responded “I don’t know those terms, I just know that silver is faster." At that point the bully beat down began (I was already pissed that he was speaking to me slowly).

I explained to him that conductors have a velocity of propagation rating and that rating is based on the conductor and the dielectric, and that the VOP # is somewhere between 65% and 80% of the speed of light, thus even at 65% it is still traveling at approximately 120,000 miles per second, and that what he was really referring to was signal attenuation (silver is a better conductor and has lower attenuation rates than copper but the difference in attenuation rates between copper and silver can be easily overcome by increasing the gauge of the copper conductors).

At this point, the two sales people leave and the manager continues the dialogue. I then took the time to point out a few other issues, such as 120 Hz doesn’t matter on the cable, as there is no broadcast standard (source) above 60 Hz and that LCD’s utilize frame interpolation (in this case the projector acting as a sink), and it is not completed on the cable. We also discussed that the speed of the cable is actually measured in its throughput or data rate. At that point we went back to both boxes, looked at the speed and what do you know, they were both rated to the exact same speed which was ….10.2 Gbps. We concluded the discussion by talking about the symptoms of an HDMI cable which doesn’t work because the resolution is too high, and described that digital signals do not replicate a loss of resolution as found on analogue devices, and instead there will most likely be sparkles/noise or no picture at all.

I ended the conversation by asking them if they would like for me to bring test equipment into the store and we could test both cables together including testing the bit error rate at all formats including 1080P 24, 1080 12 bit, 3D frame compatible and frame packing etc. My offer was politely declined and we ended our discussion. I left grinning from ear to ear and my friend returned his cable and got hundreds of dollars back. Of course, to make sure that the cable actually met specs I tested the cable and surprisingly, after 4 tests, they all came back with 0 bit errors at all recognized formats. Victorious.

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