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#201
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More cable questions!
On Fri, 9 Jan 2004 21:14:31 +1100, "Tony Pearce"
wrote: "Stewart Pinkerton" wrote in message ... 25 years ago, I was using a slide rule, You were fairly slow to catch onto those "new fangled" calculators then :-) 30 years ago I was already using a HP35 calculator, having sold my slide rule. To be honest, I was probably using a Casio 25 years ago, but I still have three slide rules, including the redoubtable Otis King 'truncheon'. Eeee, them were't days! :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#202
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More cable questions!
On Fri, 9 Jan 2004 21:14:31 +1100, "Tony Pearce"
wrote: "Stewart Pinkerton" wrote in message ... 25 years ago, I was using a slide rule, You were fairly slow to catch onto those "new fangled" calculators then :-) 30 years ago I was already using a HP35 calculator, having sold my slide rule. To be honest, I was probably using a Casio 25 years ago, but I still have three slide rules, including the redoubtable Otis King 'truncheon'. Eeee, them were't days! :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#203
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More cable questions!
On Fri, 09 Jan 2004 10:47:11 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 21:14:31 +1100, "Tony Pearce" wrote: "Stewart Pinkerton" wrote in message ... 25 years ago, I was using a slide rule, You were fairly slow to catch onto those "new fangled" calculators then :-) 30 years ago I was already using a HP35 calculator, having sold my slide rule. TonyP. You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. I did get an HP35 when it came out though - I'm still paying the mortgage off! I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#204
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More cable questions!
On Fri, 09 Jan 2004 10:47:11 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 21:14:31 +1100, "Tony Pearce" wrote: "Stewart Pinkerton" wrote in message ... 25 years ago, I was using a slide rule, You were fairly slow to catch onto those "new fangled" calculators then :-) 30 years ago I was already using a HP35 calculator, having sold my slide rule. TonyP. You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. I did get an HP35 when it came out though - I'm still paying the mortgage off! I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#205
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More cable questions!
On Fri, 09 Jan 2004 10:47:11 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 21:14:31 +1100, "Tony Pearce" wrote: "Stewart Pinkerton" wrote in message ... 25 years ago, I was using a slide rule, You were fairly slow to catch onto those "new fangled" calculators then :-) 30 years ago I was already using a HP35 calculator, having sold my slide rule. TonyP. You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. I did get an HP35 when it came out though - I'm still paying the mortgage off! I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#206
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More cable questions!
On Fri, 09 Jan 2004 10:47:11 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 21:14:31 +1100, "Tony Pearce" wrote: "Stewart Pinkerton" wrote in message ... 25 years ago, I was using a slide rule, You were fairly slow to catch onto those "new fangled" calculators then :-) 30 years ago I was already using a HP35 calculator, having sold my slide rule. TonyP. You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. I did get an HP35 when it came out though - I'm still paying the mortgage off! I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#207
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More cable questions!
On Fri, 9 Jan 2004 22:12:09 +1100, "Tony Pearce"
wrote: "Don Pearce" wrote in message .. . You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. Yeah I sold my best one and kept my cheapie. Since it's never been out of the case in 30 years, I'm glad I sold the other while it was still worth something. Then again maybe there are slide rule collectors now paying silly money? Hmmmmm, there's a thought. I have an old circular jobby, and the classic Otis King 'truncheon' and Faber-Castell Novo Duplex, both in mint condition in their original cases. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. Isn't that what log books are for? I did get an HP35 when it came out though - I'm still paying the mortgage off! I know what you mean, it took me a year to pay mine off at the time :-( Even so I don't regret it. Don't programs like Spice seem like cheating these days? :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#208
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More cable questions!
On Fri, 9 Jan 2004 22:12:09 +1100, "Tony Pearce"
wrote: "Don Pearce" wrote in message .. . You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. Yeah I sold my best one and kept my cheapie. Since it's never been out of the case in 30 years, I'm glad I sold the other while it was still worth something. Then again maybe there are slide rule collectors now paying silly money? Hmmmmm, there's a thought. I have an old circular jobby, and the classic Otis King 'truncheon' and Faber-Castell Novo Duplex, both in mint condition in their original cases. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. Isn't that what log books are for? I did get an HP35 when it came out though - I'm still paying the mortgage off! I know what you mean, it took me a year to pay mine off at the time :-( Even so I don't regret it. Don't programs like Spice seem like cheating these days? :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#209
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More cable questions!
On Fri, 9 Jan 2004 22:12:09 +1100, "Tony Pearce"
wrote: "Don Pearce" wrote in message .. . You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. Yeah I sold my best one and kept my cheapie. Since it's never been out of the case in 30 years, I'm glad I sold the other while it was still worth something. Then again maybe there are slide rule collectors now paying silly money? Hmmmmm, there's a thought. I have an old circular jobby, and the classic Otis King 'truncheon' and Faber-Castell Novo Duplex, both in mint condition in their original cases. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. Isn't that what log books are for? I did get an HP35 when it came out though - I'm still paying the mortgage off! I know what you mean, it took me a year to pay mine off at the time :-( Even so I don't regret it. Don't programs like Spice seem like cheating these days? :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#210
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More cable questions!
On Fri, 9 Jan 2004 22:12:09 +1100, "Tony Pearce"
wrote: "Don Pearce" wrote in message .. . You've sold your slide rule? My Thornton is still sitting in front of me at the back of my desk. Yeah I sold my best one and kept my cheapie. Since it's never been out of the case in 30 years, I'm glad I sold the other while it was still worth something. Then again maybe there are slide rule collectors now paying silly money? Hmmmmm, there's a thought. I have an old circular jobby, and the classic Otis King 'truncheon' and Faber-Castell Novo Duplex, both in mint condition in their original cases. I still use it sometimes to explain logs to the new generation - the wonder in their eyes when at last they understand them is great. Isn't that what log books are for? I did get an HP35 when it came out though - I'm still paying the mortgage off! I know what you mean, it took me a year to pay mine off at the time :-( Even so I don't regret it. Don't programs like Spice seem like cheating these days? :-) -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#211
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#212
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#213
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#214
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#215
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More cable questions!
On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#216
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More cable questions!
On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#217
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More cable questions!
On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#218
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More cable questions!
On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce
wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
#220
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More cable questions!
Here are my opinions, whaever they are worth... :
(Bob-Stanton) wrote in message (Stewart Pinkerton) wrote in message I'm well aware of the underlying theory. It is not sensibly applicable to speaker cable. It may be that you object to using transmission line theory, because it is quite unnessary to do so. It's like killing a mosquito with 44 magnum. Nevertheless, the mosquito end up dead whether you hit it with your hand or shoot it with a magnum. Good analogy Likewise, either model method will give virtually the same answers. This is "experience" (see below) Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. My one objection toward component models of transmission lines is: how do you know the model is right? I previously asked you to give us a component model of 100 ft of 12 gage speaker wire, but you never did. I wanted to test your model to see if it met the simplest basic requirement of a transmission line model, that the signal takes a certain amount of time to pass through. Probably you would know this by experience. Just as you know the hand is enough to kill the mosquito. Of course, in case there is a doubt, grab the magnum and see if the mosquito dies. On my model, the group delay is 101.7 ns, which is about the velocity of light. (It neglects the velocity factor.) And oh yes, if you prefer shorter cables, my 10 ft long speaker cable model has 10.2 ns group delay. I don't mind that sound arrives 100 ns late to my ears. This tells me that RF models of cables ARE overkill (but applicable) and the great margin tell me that simpler models probably would do OK. And even if a really poor model would yield a delay of 1 ms, I would not mind. So, let us see your transmission line model. Let's see if it gets the basics right. It should have 101.7 ns group delay, and it's characteristic impedannce should be 300 Ohms. In my opinion, characteristic impedance and delay are unimportant in the audio case. What I wonder is if the transmission line model predicts frequency response changes in the audio band (like a simple RLC model does), given a frequency-varying load. If you take a typical, or better, a slightly ill-behaved load to get "worst case", how much effect will the cable have on the frequency response, within the audio band. I bet yo end up with less than 0.1 dB. IMO the frequency-varying load in combination with the series resistance and possibly inductance accounts for most of this level variation. Anyway, how does the transmission line model you use work, actually? Isn't it actually a large number of RLC elements connected in series ("one for each cm of the cable")? |
#221
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More cable questions!
Here are my opinions, whaever they are worth... :
(Bob-Stanton) wrote in message (Stewart Pinkerton) wrote in message I'm well aware of the underlying theory. It is not sensibly applicable to speaker cable. It may be that you object to using transmission line theory, because it is quite unnessary to do so. It's like killing a mosquito with 44 magnum. Nevertheless, the mosquito end up dead whether you hit it with your hand or shoot it with a magnum. Good analogy Likewise, either model method will give virtually the same answers. This is "experience" (see below) Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. My one objection toward component models of transmission lines is: how do you know the model is right? I previously asked you to give us a component model of 100 ft of 12 gage speaker wire, but you never did. I wanted to test your model to see if it met the simplest basic requirement of a transmission line model, that the signal takes a certain amount of time to pass through. Probably you would know this by experience. Just as you know the hand is enough to kill the mosquito. Of course, in case there is a doubt, grab the magnum and see if the mosquito dies. On my model, the group delay is 101.7 ns, which is about the velocity of light. (It neglects the velocity factor.) And oh yes, if you prefer shorter cables, my 10 ft long speaker cable model has 10.2 ns group delay. I don't mind that sound arrives 100 ns late to my ears. This tells me that RF models of cables ARE overkill (but applicable) and the great margin tell me that simpler models probably would do OK. And even if a really poor model would yield a delay of 1 ms, I would not mind. So, let us see your transmission line model. Let's see if it gets the basics right. It should have 101.7 ns group delay, and it's characteristic impedannce should be 300 Ohms. In my opinion, characteristic impedance and delay are unimportant in the audio case. What I wonder is if the transmission line model predicts frequency response changes in the audio band (like a simple RLC model does), given a frequency-varying load. If you take a typical, or better, a slightly ill-behaved load to get "worst case", how much effect will the cable have on the frequency response, within the audio band. I bet yo end up with less than 0.1 dB. IMO the frequency-varying load in combination with the series resistance and possibly inductance accounts for most of this level variation. Anyway, how does the transmission line model you use work, actually? Isn't it actually a large number of RLC elements connected in series ("one for each cm of the cable")? |
#222
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More cable questions!
Here are my opinions, whaever they are worth... :
(Bob-Stanton) wrote in message (Stewart Pinkerton) wrote in message I'm well aware of the underlying theory. It is not sensibly applicable to speaker cable. It may be that you object to using transmission line theory, because it is quite unnessary to do so. It's like killing a mosquito with 44 magnum. Nevertheless, the mosquito end up dead whether you hit it with your hand or shoot it with a magnum. Good analogy Likewise, either model method will give virtually the same answers. This is "experience" (see below) Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. My one objection toward component models of transmission lines is: how do you know the model is right? I previously asked you to give us a component model of 100 ft of 12 gage speaker wire, but you never did. I wanted to test your model to see if it met the simplest basic requirement of a transmission line model, that the signal takes a certain amount of time to pass through. Probably you would know this by experience. Just as you know the hand is enough to kill the mosquito. Of course, in case there is a doubt, grab the magnum and see if the mosquito dies. On my model, the group delay is 101.7 ns, which is about the velocity of light. (It neglects the velocity factor.) And oh yes, if you prefer shorter cables, my 10 ft long speaker cable model has 10.2 ns group delay. I don't mind that sound arrives 100 ns late to my ears. This tells me that RF models of cables ARE overkill (but applicable) and the great margin tell me that simpler models probably would do OK. And even if a really poor model would yield a delay of 1 ms, I would not mind. So, let us see your transmission line model. Let's see if it gets the basics right. It should have 101.7 ns group delay, and it's characteristic impedannce should be 300 Ohms. In my opinion, characteristic impedance and delay are unimportant in the audio case. What I wonder is if the transmission line model predicts frequency response changes in the audio band (like a simple RLC model does), given a frequency-varying load. If you take a typical, or better, a slightly ill-behaved load to get "worst case", how much effect will the cable have on the frequency response, within the audio band. I bet yo end up with less than 0.1 dB. IMO the frequency-varying load in combination with the series resistance and possibly inductance accounts for most of this level variation. Anyway, how does the transmission line model you use work, actually? Isn't it actually a large number of RLC elements connected in series ("one for each cm of the cable")? |
#223
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More cable questions!
On Sat, 10 Jan 2004 08:48:08 +0000 (UTC),
(Stewart Pinkerton) wrote: On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! I had a Z12, famous for going into meltdown at any power over about a watt. Can't remember the claimed "Peak Music Power", but it was something pretty enormous. d _____________________________ http://www.pearce.uk.com |
#224
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More cable questions!
On Sat, 10 Jan 2004 08:48:08 +0000 (UTC),
(Stewart Pinkerton) wrote: On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! I had a Z12, famous for going into meltdown at any power over about a watt. Can't remember the claimed "Peak Music Power", but it was something pretty enormous. d _____________________________ http://www.pearce.uk.com |
#225
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More cable questions!
On Sat, 10 Jan 2004 08:48:08 +0000 (UTC),
(Stewart Pinkerton) wrote: On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! I had a Z12, famous for going into meltdown at any power over about a watt. Can't remember the claimed "Peak Music Power", but it was something pretty enormous. d _____________________________ http://www.pearce.uk.com |
#226
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More cable questions!
On Sat, 10 Jan 2004 08:48:08 +0000 (UTC),
(Stewart Pinkerton) wrote: On Fri, 09 Jan 2004 19:13:31 +0000, Don Pearce wrote: On Fri, 9 Jan 2004 18:16:56 +0000 (UTC), (Stewart Pinkerton) wrote: I did look at a 45 with the 'magic' gold function button - but IIRC it cost more than my car! I always preferred the contemporaneous Texas and Casio jobbies, as I never did like Reverse Polish notation...... Did you never get a Sinclair than? Interesting device - he couldn't get enough memory to implement the trig functions properly, and it gave errors. Sexy red on purple display, though. IIRC, this beastie was indeed famous for being a calculator which couldn't do sums................... Just as the Sinclair X-10D amplifier was famous for having 0.1% distortion at full power - and exactly the same level of artifacts at any lower power! I had a Z12, famous for going into meltdown at any power over about a watt. Can't remember the claimed "Peak Music Power", but it was something pretty enormous. d _____________________________ http://www.pearce.uk.com |
#227
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More cable questions!
On 10 Jan 2004 01:33:35 -0800, (Svante)
wrote: Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. You would have thought that given enough Ls and Cs (ie dividing the lumped model very finely) you would end up with a perfect equivalent of the transmission line model, but you don't. You just end up with an ever steeper lowpass filter. Up to the cutoff point, this filter does indeed behave remarkably like a true cable, though. For much audio work a single L and C seem to do just fine, but there are problems - like what order should you put them in? In theory you can put the shunt C at either the start or end of the network, but if you are modelling a very unmatched situation this won't work. For example, if you are looking at an amplifier to a loudspeaker, the C must be put at the speaker end - it has no effect on amplitude at the amplifier end. In a matched scenario - equal impedances both ends, the capacitance must be split and placed both ends if the model is to work. So you must be careful in the application of a lumped model cable, and understand the significance of the impedances at both ends before you use it. The true transmission line model has the advantage that all this is taken care of, there is no anomalous lowpass filter effect to worry about and it is really easy to change lengths - you just alter the length term. It also works at any frequency. It is a sledgehammer to crack a nut, though, and representing a cable as Ls and Cs (given the caveats above) is perfectly proper, particularly if you are having to hand-crank the results, or just doing a back-of-an-envelope calculation. If you are using Spice, or something similar that possesses native transmission line models, then why not use them? They are easier to use, just as accurate for audio, and vastly more accurate outside the audio band. d _____________________________ http://www.pearce.uk.com |
#228
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More cable questions!
On 10 Jan 2004 01:33:35 -0800, (Svante)
wrote: Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. You would have thought that given enough Ls and Cs (ie dividing the lumped model very finely) you would end up with a perfect equivalent of the transmission line model, but you don't. You just end up with an ever steeper lowpass filter. Up to the cutoff point, this filter does indeed behave remarkably like a true cable, though. For much audio work a single L and C seem to do just fine, but there are problems - like what order should you put them in? In theory you can put the shunt C at either the start or end of the network, but if you are modelling a very unmatched situation this won't work. For example, if you are looking at an amplifier to a loudspeaker, the C must be put at the speaker end - it has no effect on amplitude at the amplifier end. In a matched scenario - equal impedances both ends, the capacitance must be split and placed both ends if the model is to work. So you must be careful in the application of a lumped model cable, and understand the significance of the impedances at both ends before you use it. The true transmission line model has the advantage that all this is taken care of, there is no anomalous lowpass filter effect to worry about and it is really easy to change lengths - you just alter the length term. It also works at any frequency. It is a sledgehammer to crack a nut, though, and representing a cable as Ls and Cs (given the caveats above) is perfectly proper, particularly if you are having to hand-crank the results, or just doing a back-of-an-envelope calculation. If you are using Spice, or something similar that possesses native transmission line models, then why not use them? They are easier to use, just as accurate for audio, and vastly more accurate outside the audio band. d _____________________________ http://www.pearce.uk.com |
#229
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More cable questions!
On 10 Jan 2004 01:33:35 -0800, (Svante)
wrote: Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. You would have thought that given enough Ls and Cs (ie dividing the lumped model very finely) you would end up with a perfect equivalent of the transmission line model, but you don't. You just end up with an ever steeper lowpass filter. Up to the cutoff point, this filter does indeed behave remarkably like a true cable, though. For much audio work a single L and C seem to do just fine, but there are problems - like what order should you put them in? In theory you can put the shunt C at either the start or end of the network, but if you are modelling a very unmatched situation this won't work. For example, if you are looking at an amplifier to a loudspeaker, the C must be put at the speaker end - it has no effect on amplitude at the amplifier end. In a matched scenario - equal impedances both ends, the capacitance must be split and placed both ends if the model is to work. So you must be careful in the application of a lumped model cable, and understand the significance of the impedances at both ends before you use it. The true transmission line model has the advantage that all this is taken care of, there is no anomalous lowpass filter effect to worry about and it is really easy to change lengths - you just alter the length term. It also works at any frequency. It is a sledgehammer to crack a nut, though, and representing a cable as Ls and Cs (given the caveats above) is perfectly proper, particularly if you are having to hand-crank the results, or just doing a back-of-an-envelope calculation. If you are using Spice, or something similar that possesses native transmission line models, then why not use them? They are easier to use, just as accurate for audio, and vastly more accurate outside the audio band. d _____________________________ http://www.pearce.uk.com |
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More cable questions!
On 10 Jan 2004 01:33:35 -0800, (Svante)
wrote: Nowadays, it is quicker and easier (less typing) to enter a transmission line model, than to type in a componet (L,C) model. Use whatever way floats your boat. OK, in my boat there are no transmission line models, but a lot of R, L and Cs. You would have thought that given enough Ls and Cs (ie dividing the lumped model very finely) you would end up with a perfect equivalent of the transmission line model, but you don't. You just end up with an ever steeper lowpass filter. Up to the cutoff point, this filter does indeed behave remarkably like a true cable, though. For much audio work a single L and C seem to do just fine, but there are problems - like what order should you put them in? In theory you can put the shunt C at either the start or end of the network, but if you are modelling a very unmatched situation this won't work. For example, if you are looking at an amplifier to a loudspeaker, the C must be put at the speaker end - it has no effect on amplitude at the amplifier end. In a matched scenario - equal impedances both ends, the capacitance must be split and placed both ends if the model is to work. So you must be careful in the application of a lumped model cable, and understand the significance of the impedances at both ends before you use it. The true transmission line model has the advantage that all this is taken care of, there is no anomalous lowpass filter effect to worry about and it is really easy to change lengths - you just alter the length term. It also works at any frequency. It is a sledgehammer to crack a nut, though, and representing a cable as Ls and Cs (given the caveats above) is perfectly proper, particularly if you are having to hand-crank the results, or just doing a back-of-an-envelope calculation. If you are using Spice, or something similar that possesses native transmission line models, then why not use them? They are easier to use, just as accurate for audio, and vastly more accurate outside the audio band. d _____________________________ http://www.pearce.uk.com |
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Stewart Pinkerton wrote:
That's likely true, but again, why bother to do *any* kind of speaker cable modelling? OK, since I started this whole horrible thread, I figure I can toss out an answer to this one. Pure knowledge. Modelling cables can prove what we know--that beyond a very easily obtainable point, cables are irrelevant. Furthermore, we can find out where that point is, and for lack of a better phrase, how irrelevant the differnt factors are. For instance, 12 gauge vs. 14 gauge wire isn't particularly important in speaker cables, but it's a lot closer to being a valid factor than say, capacitance or even worse, characteristic impedance. So modelling helps those of us who DON'T know this stuff to learn it. It also provides worthwhile information for those who are running long (maybe in-wall?) speaker cables; and for that matter, also for those who are designing their own amps. Of course, that doesn't address which model to use, and the answer is pretty obvious in any field: Use the model which most simply and closely matches your conditions. For audio of any sort, that does NOT mean a transmission line model! Anyways, my two bits worth on why I asked about cables in the very first place. Colin |
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More cable questions!
Stewart Pinkerton wrote:
That's likely true, but again, why bother to do *any* kind of speaker cable modelling? OK, since I started this whole horrible thread, I figure I can toss out an answer to this one. Pure knowledge. Modelling cables can prove what we know--that beyond a very easily obtainable point, cables are irrelevant. Furthermore, we can find out where that point is, and for lack of a better phrase, how irrelevant the differnt factors are. For instance, 12 gauge vs. 14 gauge wire isn't particularly important in speaker cables, but it's a lot closer to being a valid factor than say, capacitance or even worse, characteristic impedance. So modelling helps those of us who DON'T know this stuff to learn it. It also provides worthwhile information for those who are running long (maybe in-wall?) speaker cables; and for that matter, also for those who are designing their own amps. Of course, that doesn't address which model to use, and the answer is pretty obvious in any field: Use the model which most simply and closely matches your conditions. For audio of any sort, that does NOT mean a transmission line model! Anyways, my two bits worth on why I asked about cables in the very first place. Colin |
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More cable questions!
Stewart Pinkerton wrote:
That's likely true, but again, why bother to do *any* kind of speaker cable modelling? OK, since I started this whole horrible thread, I figure I can toss out an answer to this one. Pure knowledge. Modelling cables can prove what we know--that beyond a very easily obtainable point, cables are irrelevant. Furthermore, we can find out where that point is, and for lack of a better phrase, how irrelevant the differnt factors are. For instance, 12 gauge vs. 14 gauge wire isn't particularly important in speaker cables, but it's a lot closer to being a valid factor than say, capacitance or even worse, characteristic impedance. So modelling helps those of us who DON'T know this stuff to learn it. It also provides worthwhile information for those who are running long (maybe in-wall?) speaker cables; and for that matter, also for those who are designing their own amps. Of course, that doesn't address which model to use, and the answer is pretty obvious in any field: Use the model which most simply and closely matches your conditions. For audio of any sort, that does NOT mean a transmission line model! Anyways, my two bits worth on why I asked about cables in the very first place. Colin |
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More cable questions!
Stewart Pinkerton wrote:
That's likely true, but again, why bother to do *any* kind of speaker cable modelling? OK, since I started this whole horrible thread, I figure I can toss out an answer to this one. Pure knowledge. Modelling cables can prove what we know--that beyond a very easily obtainable point, cables are irrelevant. Furthermore, we can find out where that point is, and for lack of a better phrase, how irrelevant the differnt factors are. For instance, 12 gauge vs. 14 gauge wire isn't particularly important in speaker cables, but it's a lot closer to being a valid factor than say, capacitance or even worse, characteristic impedance. So modelling helps those of us who DON'T know this stuff to learn it. It also provides worthwhile information for those who are running long (maybe in-wall?) speaker cables; and for that matter, also for those who are designing their own amps. Of course, that doesn't address which model to use, and the answer is pretty obvious in any field: Use the model which most simply and closely matches your conditions. For audio of any sort, that does NOT mean a transmission line model! Anyways, my two bits worth on why I asked about cables in the very first place. Colin |
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