John Dunlavy On "Cable Nonsense"

Dunlavy talks about the transmission line properties of the cables he designs. I guess I have not forgotten as much as John Dunlavy because I clearly remember my Electrical Engineering professor saying that an audio cable would have to be many miles long before transmission line properties would come into play. It is at 100's of megahertz that a 1 or 2 meter cable can display those properties. I feel that that we need to investigate better methods of measurement.

There are some DIY cables that can be made very cheap. I can find the site and post it if you like.

I know for a fact that cables can react with a system and have bad results. I watched on an oscilloscope an amplifier pruduce a beautiful 1.2 MHz sine wave when connected to some unusually high capacitance DIY cables similar to John Risch's design. It is clear that cables and systems can interact but sometimes that can be in a productive manor!

Liguy, I commented on the idea of "transmission line" theory applying to audio frequencys. I do not dispute the charterisic impedance of a cable even if it is only a centimeter in length. Do you happen to recall how long an IC would have to be to get even ONE standing wave in it at any audio frequency? (it is way more than a few feet)

Frank, I am not sure what all effects the sound of cables, but I do feel safe to say (quoting a friend in the know) "everything makes a differance".

I do feel that no connector is better than a connector and there is a lot of connectors with wider bandwidth than a RCA plug. A BNC is one just for starters.

Lets get some oppinions on this ...... Chris

Gregm, I could not agree more. As my system evolved into the current collage of stuff, I tried different cables to achieve the sound that I desired. I have a mixture of silver plated and plain copper. What I use is not important to this discussion but the fact that they work in my system is. I have taken some cables to other systems and found the synergy is not there. I can clearly identify with the concept of matching cables to a system and the owner's taste.

Abe, It is common practice for a system owner to change interconnects in an attempt to 'produce' the sound he desires. I think you can agree that they can alter the sound. Speaker cables are the same way.

Now to make a point about the lack of quality power cable behind the outlet. I have opened at least a hundred models of audio electronics. I have found very poor quality wire inside the units. I have tried many different cables with these units and have heard differences. I have changed three inches of wire inside a unit and have heard a change. Do you really believe that all high quality electronics and speakers are wired with high quality wire? If hundreds or even thousands say they can hear the difference in speaker cables does that mean they ALL are listening to speakers that are wired with high quality wire inside? I think not.

Our ears have the ability to distinguish differences that the audio community has now figured out how to measure. I was trained in the precision measurement field of electronics. I understand the current forms of measurement pretty well and we are not even close to making measurements that can tell us what a piece of equipment sounds like. As an example of just how foolish a measurement means to audio, consider this. A normal low frequency speaker will easily produce over 1/2% distortion. Then how is it we can tell a difference in the bass performance of loudspeaker cables. The cables do not produce more than 1/100 of the distortion of the speaker.

Now on to the topic of AC power. If we use a similar analogy to the power cable it stands to reason that even a few inches of wire could make a difference. I agree that it could be even more important if the wire behind the outlet is high quality. (I believe it enough to have rewired my house with the stereo in mind) It is false to assume that the AC to DC converter (the power supply) is not effected by what comes in the power line. Our equipment is connected to the power grid. That power grid stretches all over the country and every minute of every day lightning is hitting the grid. Heavy machinery is dumping transients on the grid every second. It is imperative that this noise does not get onto the DC buss inside our equipment. It is next to imposable to stop a transient from passing thru the diodes and dumping a charge onto the filter caps. I believe that power line filters are our first line of defense to this grunge. Who is to say that a power cord does not have some property that helps in filtering this trash and keeps it out of our systems?

And to answer your question: YES I believe a AC power cord, just like a speaker, cable can be selected to 'adjust' the sound to one's liking. Most people feel that a tone control can be used to 'adjust' the sound and so therefore a cable is a form of tone control.

Chris

Abe, I really do agree with you 100%. It does seem silly to spend dollars a foot on power cables when the Romex is roughly 10 cents a foot. I do not plan on spending my stereo allocation for the next six months on a power cable. Because of my electronics and electrical background, I will make my own. I started out by putting a heavier gage cord on my power amp. It helped, but I did not go farther with power cords because, like you, I felt that size was the issue.

I then got introduced to this and other forums, and all the talk about hospital grade outlets. I had a friend tell me about a hospital grade power cord. He sent me one and I compared it to a shielded IEC cord I had found. Both cords were a lot better than a standard computer cord. They both were even better than the heavy gage cord. The shielded cord had a ferrite 'bead' and may have been responsible for the lower noise floor and better focus of the images. I do not have the answers. I wish I knew what it is that makes a power cord change the sound.

I think we all can agree that a filter of any sort on the power line can have a positive effect on removing high frequency transients from the AC power. I have three filters in series on my power amp! I feel that it is possible that some of the high end cords might, because of their geometry, have special filtering capability. This could be at ultra high frequencies where the mutual capacitance of a big heavy inductor in an after market noise filter just passes it through, but the cord stops it.

My experience in industrial electronics has educated me to the hazards of a poor electrical connection. I have seen the results of a loose connection on a motor. The motor overheated from the reduced voltage and melted the insulation on the windings. Every connection in our systems can be a source for problems. Heavy current flow into the power amp could easily be restricted by a less than perfect connection on an outlet or cord. I had to put a slow turn on circuit in my amp to prevent blowing the 20 amp breaker in the distribution panel! I know that a magnetic circuit breaker can pass many times its rated current for a short transient before it will trip. My amp was likely trying to draw over 60 amps at powerup. Some will not believe that 12 gage wire can supply that much transient current. I know it to be true! I wired a 12 gage 100+ foot circuit going to a pump wrong and when I applied power to the pump it popped a 100 amp fuse instantly. Those little 12 gage wires handled in excess of 100 amps and did not melt or even burn the insulation.

The point that I am trying to make is that I feel we do not understand all the interactions that affect the sound of a system. My ranting(s) are for the purpose of shedding a little light on areas that may affect what we hear. I am sure that many 'discoveries' are waiting to be exposed. I know that discussions like this stimulates me to look deeper for a possible answer. I look forward to more discussion on this topic. Ideas or questions placed on this forum can be the spark that sheds light on a new understanding. I am certainly ready to uncover some of the *snake oil* in the high priced cables so that the less finically fortunate can afford good sounding cables.

Chris

I personally know Tom. I would be interested in his comments on cables and controlled listening. I have done some controlled listening with him. Plus4dbu, please give us a report.

I do believe that cables can be 'engineered'. When you change the capacitance and inductance of a cable you are effecting a parameter called the "charateristic impedance"(I will use CI for short). In normal zip cord type wire, the CI is approximately 90 ohms. In RF theory it is said to be very important to match the load impedance to the CI of the cable.

If this theory was applied to speaker cable then we need to design cables with a CI of 8 ohms. The problem with designing a cable to 8 ohms is that a speaker is only a NOMINAL 8 ohms (or 4 ohms) and varies with frequency. It would be practically impossible to build a cable that could match the impedance curve of a speaker.

A few years back I investigated the effects of lowering the input impedance of my power amp. I tried some 75 ohm video cable as an interconnect and a 75 ohm RCA with a 75 ohm termination on the circuit board of the amplifier. This combo sounded very close to the best interconnects I had used in a more conventional manner. My preamp has a very high current output and can in fact drive a 8 ohm speaker at low volumes. It was important to drive the amp with this pre amp but it was less important what interconnect I was using. The differences that I heard in interconnects when the input impedance of the amp was 20,000 ohms was far larger than the differences when the input impedance was down around 100 ohms.

I do not know if it was the reduction of reflections due to the matching of the cable to the load. It may have also been the contribution of a lower noise floor due to the reduced thermal noise of the lower input resistor. I believe that musical enjoyment can come from the contribution of a number of factors, combining in a manner that makes the sound pleasant to YOUR ears. I kept the low input impedance in my amp for about a year until I got a different pre and had to take it out cause the new pre could not drive the load!

Testing is a good idea but no pratical computer test equipment has a noise floor exceeding 96 db. Our hearing has a dynamic range of about 110+ db. That makes our ears many times more sensitive that any test equipment. Chris

Trappist: The quick answer ... No I do not have any recomendations for equipment. The resolution om a 16 bit system mathamaticaly is around 86 db. It would be higher for a higher bit a/d converter but that is not the problem with making high accuracy measurements. Yhe problem is the noise floor of the analog front end of the converter. Therman noise and resistor noise (thermally related btw) would limit the actual resolution of the system. It would require cooling (like liquid nitrogen) to get the thermal noise low enough to get 110 db range accuratly. I do not believe a computer can be effeciently used in a near absolute zero enviroment. Chris

Gpalmer, your test results have blown me away. I would have not expected them to be that different. I would like to see several people try to measure the differences and give a detailed report. Chris

Lets pretend (cause it probably will not happen in real life) that your speaker has a strong impedance dip and drops from a nominal 8 ohms to say .25 ohms. If both cables were of simular guage then the longer ones could have a little more resistance in them and not deliver the exact same current to the speaker that the shorter one did at the frequency of the impedance dip. This type of situation is where the difference could be frequency selective.

I am impressed with your testing method. Three identical measurements with test signals would imply valid results. I for one feel that the differences are very large and would like to have others see if they can find results of this magnitude. Was the test conducted while only one speaker was playing? That would help to remove some reflection problems and the effects of the other speaker. Chris