Big Box Bully Beat Down
Submitted by dpedigo on Thu, 01/05/2012 - 10:02am
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.
- 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.
Jeez, you opened a can of
by jgardner - 01/11/2012 - 2:36pm
Jeez, you opened a can of worms here, Dave.
But along with the worms came a great discussion and raised awareness.
Now I will throw my $.02 in;
Wouldn't the NEC rating on HDMI be CMX, CMR or CMP, rather than CL-2_?
I think CL-2 and CL-3 would apply to simple control or speaker cable with limited current compared to Class 1 electrical wiring.
I don't know because I honestly have never seen NEC ratings on a prefabricated cable like HDMI.
So am curious to see if anyone can answer this for sure. It would help in our classroom discussion about in-wall wiring. Hope you are having an inspiring CES week!
Jeff, The cable was
by dpedigo - 01/14/2012 - 10:32pm
Jeff,
The cable was clearly marked CL2. I understand your question, as there is a reasonable question as to is it a communications cable, (CM) or Class 2. In this instance, I assume that it is CM2 because there is more than just video going through (such as the DDC channel) and thus would fall under 725 Remote Control & Signalling.
I find all this very
by Troy Henderson III - 01/11/2012 - 11:04am
I find all this very interesting. I am currently an HDMI high speed EE and found much of this pretty entertaining. However there are a few things here that Dave did not take into consideration.
The performance of each product has to be determined not necessarily by its bit rate and bandwidth, but by the aggregate of the entire HDMI cable specification. He is correct in that the quality of the picture would not be any different between cables as long as both products supported the bandwidth, which I would imagine both did. The real issue is the cables reliability. The reliability is a far greater issue than the picture quality since once you have supplied enough bandwidth it would always look perfect. As I said, if both products really passed the necessary bandwidth the picture content would be the same.
There is little doubt that the biggest complaints with HDMI is it s reliability. So a cable has to be determined not only by its bandwidth, but also by its ability to provide its critical DC component that starts the system, the ability for a strong Hot Plug detection to take place and the quality of the DDC channel to successfully communicate the every so critical HDCP and EDID functions. Without all these operating up to a high standard the system will either not work, work with some products and not with others, fail intermittently, or fail over time.
So any time a product is produced ALL of these functions have to be taken into consideration, not just the video, which is just as important as the rest.
When you consider the character make up of the cable i.e gauge, dialectic, twist topology, skew (timing),etc one would have to also consider if a disproportionate weight is given to each wires within each HDMI cable.
For instance, since the clock channel of the video is only one tenth the speed of the video channels, those particular wires within the cable would not have to be as large in gauge as the others which is OK.
Or, if the DC wire inside the HDMI cable is really small to allow for more physical room to be applied to accommodate higher gauge video cable, like an oversized clock channel. In this case the system may not even start due to increased voltage drops that may occur over the DC wire limiting the necessary DC to activate the display. Without sufficient DC the system will not even start.
Same holds true for the DDC channel that supplies both HDCP and EDID. This is a serial based channel typically operating at 100 KHz. If these wires have poor integrity the capacitive loading of the cable will cause HDCP and EDID failures. I have found this to be very common.
So to say that a less expensive product has the same quality or reliability as a more expensive product may be an incorrect statement all together. It is all up to what was designed inside the jacket.
I have seen some less expensive cables built better than some expensive cables. So in reality the customer and retailer in many instances are lost and just punting when deciding on the purchase of these cable products.
To make matters worse, many of these parameters must be reconsidered to the cables length.
So there is much more here than many are willing accept.
T Henderson III
Thanks for the input, I was
by dpedigo - 01/14/2012 - 10:37pm
Thanks for the input, I was hoping that I could attract some cable mfg engineers. I would say that all of your points are correct. For me, in this instance since there is an easy way to be able to remove and reinstall a cable it was a no brainer. Using a very nice HDMi tester which was able to test for intr-pair skew and check the DDC channels certainly helped me feel very confident that this was a well constructed cable. But you stating that there us much more here than many are willing to accept is correct, which I why I hope that more who install HDMI systems consider purchasing an HDMI test device which can design.
I really appreciate your input.
Best regards,
Dave Pedigo
Dave, I enjoyed the article
by Cory Plummer - 01/09/2012 - 8:48am
Dave,
I enjoyed the article and instead of "nitpicking" it, understood what you were getting at. I have friends call me all the time in a panic about visiting Big Box stores and getting overwhelmed with talk of no picture if you use inexpensive product A instead of over-the-top expensive product B.
I understand my friends' and clients' needs vs. budget and get them the best system I think will meet those needs. If I feel they are making a mistake by overspending or underspending, I let them know. But I have never used a fear tactic to sell them something to make more money.
You did what I have always wanted to do (If I didn't fear confrontation...)
Thanks.
Sorry dpedigo, I see you
by Licensed - 01/06/2012 - 12:40pm
Sorry dpedigo, I see you were making a gallant effort trying to make sure everyone involved (including us readers) "knew" you had your technical hat on straight and jargon correct... But I had a really hard time reading the rest of your article after I read this comment: "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)."
In my world as a licensed AV contractor, UL rating has nothing to do with a CL2 or 3 rating, which by the way rates the wire as being usable safely in an in-wall installation. The CL ratings are an NEC code standard that all installers must know and follow, regardless of helping out a friend with his wiring. And for those that don't know, the NEC Code trumps any CEDIA Installer knowledge base and certifications.
Those ratings don't stop there. Much more to know about CL ratings and how they apply to the installation type... but I'll let you learn more about CMX, CMG, CMR, CMP in your own NEC book.
I wouldn't want to be responsible for burning anyones house down because the fire had wicked and traveled through the walls of someone's home spreading the fire because the wire I used was truly not CL rated.
If the wire clearly doesn't have printed on it (not the packaging) which CL rating it is, and it is geared to the application I'm using it for; I don't use it.
@ Licensed, I should have
by dpedigo - 01/06/2012 - 7:32pm
@ Licensed, I should have specified that it was CL2G rated, I didnt think I needed to get that specific in the blog, but obviouly I should. I am very aware of article 725 of the NFPA 70 (also known as NEC). UL listing is still very important. Underwriters labratories have very strict guidelines in their testing.
However, if you want to get technical, National Electric code is NOT National Code. The National Electric Code is a book written by the National Fire Protection Association (NFPA), much like CEDIA is an association. There is no National Electric Code in the manner of which you speak and does not "Trump any CEDIA Installer Base."
That said, most states and municipalities pass laws adopting NEC as their basis for their state and local regulations, which are then either adopted in part or whole by the state or local municipality (many states have much stricter code requirements than NEC). The codes are then enforced by the authority having jurisdiction.
I have served as a subect matter expert for several states regarding low voltage cables and their usage state and local requirements. I really do, after sounding very defensive above, appreciate your understanding of the various categories of cables, and their jacket rating.
Sincerely,
Dave Pedigo
Senior Director of Technology, CEDIA
Nice article Dave! Minor
by dpedigo - 01/05/2012 - 7:29pm
Nice article Dave! Minor typo "he was really referring to signal attenuation (which silver is a better conductor and has lower attenuation rates than silver," but otherwise well written and entertaining to read.
Thanks Bill, I fixed it from silver to copper. I appreciate the feedback! Happy New Year
Nice article Dave! Minor
by Bill Maxey - 01/05/2012 - 6:39pm
Nice article Dave! Minor typo "he was really referring to signal attenuation (which silver is a better conductor and has lower attenuation rates than silver," but otherwise well written and entertaining to read.
"high speed with
by Anonymous - 01/05/2012 - 5:15pm
"high speed with internet"
Wow, the whole internet in that one cable? Or did you mean high speed with ethernet? :)
Oops. Thats what you get
by dpedigo - 01/06/2012 - 7:48pm
Oops. Thats what you get when you write at 12:30 AM! Thanks, been updated