I agree, its not the technology, its who is liable for it.
Two points:-
First point. If the credit card companies are offering such an onerous deal to the merchants then it seems to me there is a gap in the market for a payment system that does share the liabilities around more fairly.
Second point. What is a card number and pin anyway? It looks a bit like a username and password to me. Do you know of any other computer systems that restrict you to a numerical username and a 4 digit numerical password?
My bank sent me a little gadget that I can put my bank card into, enter the pin and it returns "pin correct" and an authorization code. The machine is stand alone and looks like a pocket calculator. If I was in possession of a stolen card I could use this gadget to brute force the pin. Ok it might take me 80 hours to go through all 10,000 pin's by hand, but I bet I can get it a lot quicker for many cards. Start with numbers like 1940, 1941, 1942... up to about 1990 and similar strategies.
Its not just I^2R loss that is the problem with speaker cable, if it were, all you would have to do is turn the volume up or use a bigger amp.
I don't think its to do with speed of signal propagation either. at least not on typical length speaker cable. I agree that the terminals of the speaker are going to be in-phase with the terminals of the amp as near as makes no difference at AF over a few feet.
It has to do with the speaker being an electromechanical thing ie an electric motor obeying Flemings right or left hand rule (which ever one it is). The speaker cone is not going to move at the speed light.
I'm not mathematician enough to do this formally but think about the step input response. Start with 0V across the terminals of the speaker, as near instantly as you can, change this to +10V and watch what happens to the speaker cone. If the speaker were perfect it would move forward about 1mm and stop instantly, and then maybe, burn out after a while. What really happens is the speaker starts at rest, accelerates, slows down, overshoots, returns, undershoots and eventually settles back to rest at the new position and then maybe burns out. All the while it is moving it is generating a back emf, all the while it is moving, ie long after (milliseconds) the step was applied.
Part of this momentum or resonance is due to the mass of the speaker cone and its suspension springiness. Part due to the springiness and mass of the air and part due to the electrical momentum, ie the reactance, of the speaker motor. Careful cabinet design can help but the advantage of short, fat speaker cables is that there is not much resistance between the regulated terminals of the amp and the unregulated terminals of the speaker. The amp can adjust its output to compensate for all these back emfs coming from the speaker. With a higher resistance the speaker cone can flap about as it pleases. It is insulated from the controlling influence of the amp by high cable resistance.
Hmmm, Randi missed his target. Randi overshoots his target. Maybe?
Speaker cable should be short and fat. Some would argue short and fat and twisted. The resistance of a wire is proportional to its length and inversely proportional to its cross section. so twice the length = twice the resistance, twice the cross sectional area = half the resistance unless you are dealing with extreme frequencies or extreme powers and that doesn't apply to speaker cable. The reason is that a loud speaker is a reactive load, when the amp drives the speaker, the speaker drives it back or tries too. The amp combats this by having a low output impedance and negative feedback. The problem is that the speaker wire and the speaker are not part of the feedback loop. An analogy might be to imagine that you have lost the remote control for your tv. Being lazy you get a long cane from the garden shed and tape a pencil eraser to the end and use this to sit in your chair and prod at the buttons on the telly with your cane. Dont knock this, I've seen it done. Clearly the longer, thiner and more springy the cane the more difficult this will be to do. You will keep overshooting and over correcting and the end will bounce up and down. not an exact analogy as you can see the end of the cane, but close.
Loud speakers often have an impedance of about 8 ohms so a 1 ohm resistance in the cable and connectors is getting on for significant.
As for twisted, twisting a cable improves its performance at higher frequencies. I don't know if this is significant in the audio spectrum.
According to en.wikipedia.org/wiki/Oxygen-free_copper oxygen free copper has a lower resistance than ordinary copper, a whole 1% lower. It is probably cheaper to add 1% more copper to the cable (to the thickness, not the length) than it is to use a more expensive material. If you are rich you could use gold or silver for the wires both are better conductors than copper.
If you look at the frequency plot for a loudspeaker eg www.jblpro.com/pages/components/maxout.htm you will see a very jagged line and wonder why they work as well as they do. I would think that imperfections in the mechanical bit of the system are going to overwhelm imperfections in the electronic/electrical part of the setup.
Anyway, after twenty odd years playing with loud PA systems I doubt if I could tell the difference between a $7000 set of speaker leads and a bit 1.5mm^2 mains wire. Just don't use woolworths bell wire and you should be ok.
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Two points:-
First point. If the credit card companies are offering such an onerous deal to the merchants then it seems to me there is a gap in the market for a payment system that does share the liabilities around more fairly.
Second point. What is a card number and pin anyway? It looks a bit like a username and password to me. Do you know of any other computer systems that restrict you to a numerical username and a 4 digit numerical password?
My bank sent me a little gadget that I can put my bank card into, enter the pin and it returns "pin correct" and an authorization code. The machine is stand alone and looks like a pocket calculator. If I was in possession of a stolen card I could use this gadget to brute force the pin. Ok it might take me 80 hours to go through all 10,000 pin's by hand, but I bet I can get it a lot quicker for many cards. Start with numbers like 1940, 1941, 1942... up to about 1990 and similar strategies.
No wonder there is fraud.
Not only that but I'm about at the limit of my depth. Nice chatting with you.
I don't think its to do with speed of signal propagation either. at least not on typical length speaker cable. I agree that the terminals of the speaker are going to be in-phase with the terminals of the amp as near as makes no difference at AF over a few feet.
It has to do with the speaker being an electromechanical thing ie an electric motor obeying Flemings right or left hand rule (which ever one it is). The speaker cone is not going to move at the speed light.
I'm not mathematician enough to do this formally but think about the step input response. Start with 0V across the terminals of the speaker, as near instantly as you can, change this to +10V and watch what happens to the speaker cone. If the speaker were perfect it would move forward about 1mm and stop instantly, and then maybe, burn out after a while. What really happens is the speaker starts at rest, accelerates, slows down, overshoots, returns, undershoots and eventually settles back to rest at the new position and then maybe burns out. All the while it is moving it is generating a back emf, all the while it is moving, ie long after (milliseconds) the step was applied.
Part of this momentum or resonance is due to the mass of the speaker cone and its suspension springiness. Part due to the springiness and mass of the air and part due to the electrical momentum, ie the reactance, of the speaker motor. Careful cabinet design can help but the advantage of short, fat speaker cables is that there is not much resistance between the regulated terminals of the amp and the unregulated terminals of the speaker. The amp can adjust its output to compensate for all these back emfs coming from the speaker. With a higher resistance the speaker cone can flap about as it pleases. It is insulated from the controlling influence of the amp by high cable resistance.
Hmmm, Randi missed his target. Randi overshoots his target. Maybe?
Speaker cable should be short and fat. Some would argue short and fat and twisted. The resistance of a wire is proportional to its length and inversely proportional to its cross section. so twice the length = twice the resistance, twice the cross sectional area = half the resistance unless you are dealing with extreme frequencies or extreme powers and that doesn't apply to speaker cable.
The reason is that a loud speaker is a reactive load, when the amp drives the speaker, the speaker drives it back or tries too. The amp combats this by having a low output impedance and negative feedback. The problem is that the speaker wire and the speaker are not part of the feedback loop.
An analogy might be to imagine that you have lost the remote control for your tv. Being lazy you get a long cane from the garden shed and tape a pencil eraser to the end and use this to sit in your chair and prod at the buttons on the telly with your cane. Dont knock this, I've seen it done. Clearly the longer, thiner and more springy the cane the more difficult this will be to do. You will keep overshooting and over correcting and the end will bounce up and down. not an exact analogy as you can see the end of the cane, but close.
Loud speakers often have an impedance of about 8 ohms so a 1 ohm resistance in the cable and connectors is getting on for significant.
As for twisted, twisting a cable improves its performance at higher frequencies. I don't know if this is significant in the audio spectrum.
According to en.wikipedia.org/wiki/Oxygen-free_copper oxygen free copper has a lower resistance than ordinary copper, a whole 1% lower. It is probably cheaper to add 1% more copper to the cable (to the thickness, not the length) than it is to use a more expensive material. If you are rich you could use gold or silver for the wires both are better conductors than copper.
If you look at the frequency plot for a loudspeaker eg www.jblpro.com/pages/components/maxout.htm you will see a very jagged line and wonder why they work as well as they do. I would think that imperfections in the mechanical bit of the system are going to overwhelm imperfections in the electronic/electrical part of the setup.
Anyway, after twenty odd years playing with loud PA systems I doubt if I could tell the difference between a $7000 set of speaker leads and a bit 1.5mm^2 mains wire. Just don't use woolworths bell wire and you should be ok.