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#1
Posted to rec.audio.tubes
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Speaker cable revelation?
Posted by Jim Lesurf on uk.rec.audio:
"I've just put up a new webpage that provides some measurements on the properties of a variety of loudspeaker cables. The page is at http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html "It is an expanded version of the article published in 'Hi Fi News' a few months ago." Wadya think? Ian |
#2
Posted to rec.audio.tubes
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Speaker cable revelation?
"Ian Iveson" wrote in message ... Posted by Jim Lesurf on uk.rec.audio: "I've just put up a new webpage that provides some measurements on the properties of a variety of loudspeaker cables. The page is at http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html "It is an expanded version of the article published in 'Hi Fi News' a few months ago." Wadya think? Ian Pure unadulterated nonsense of zero meaning or consequence. Maybe you didn't realize it but audio frequencies are ALL below 100kHz. Your measurements are in the megahertz range. What possible effect do they convey to sound quality? Be imaginative in your explanation we're all ears! |
#3
Posted to rec.audio.tubes
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Speaker cable revelation?
Bob Eld wrote: "Ian Iveson" wrote Posted by Jim Lesurf on uk.rec.audio: "I've just put up a new webpage that provides some measurements on the properties of a variety of loudspeaker cables. The page is at http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html "It is an expanded version of the article published in 'Hi Fi News' a few months ago." Wadya think? Pure unadulterated nonsense of zero meaning or consequence. Maybe you didn't realize it but audio frequencies are ALL below 100kHz. Your measurements are in the megahertz range. What possible effect do they convey to sound quality? Be imaginative in your explanation we're all ears! Maybe you'd like to join my crusade about Jim Lesurf's daft imaginings in uk.rec.audio. I gather he's an 'academic'. I found this recently from some 'academics' and to think this is what they're teaching for degrees ! " Audio systems are designed such that the output from the amplifier is matched to the impedance presented by the speaker. This maximizes power output, and mimizes reflection between the two. The same principle applies to microwave systems; we want the output of a source to be matched to the input of the next stage. If two components are connected (e.g. a transmission line to an amplifier), there will be a reflection if their impedances are unequal, reducing power transfer. " http://bmf.ece.queensu.ca/mediawiki/...he_Smith_Chart This wasn't even the case in the days of tube amps where the 'impedance selector' simply presented the right tap for optimum output vs plate dissipation. FYI I left University College London's EE course after a year since I could see most of the lecturers were totally out of touch with reality. Luckily I found a better course later. Graham -- due to the hugely increased level of spam please make the obvious adjustment to my email address |
#4
Posted to rec.audio.tubes
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Speaker cable revelation?
"Eeyore" Maybe you'd like to join my crusade about Jim Lesurf's daft imaginings in uk.rec.audio. I gather he's an 'academic'. ** Jim is a former member of the academic staff ( means now dead wood ) at the University of St Andrews where John Cleese ( of Faulty Towers fame) was the Rector between 1970 and 1973. Founded in 1410, the university also still has a thriving faculty of Divinity - god knows why !! The Science faculty allegedly gives out degrees in golf physics. Not an engineer in sight ..... ..... Phil |
#5
Posted to rec.audio.tubes
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Speaker cable revelation?
Phil Allison wrote:
"Eeyore" Maybe you'd like to join my crusade about Jim Lesurf's daft imaginings in uk.rec.audio. I gather he's an 'academic'. ** Jim is a former member of the academic staff ( means now dead wood ) at the University of St Andrews where John Cleese ( of Faulty Towers fame) was the Rector between 1970 and 1973. Mr. Cleese is likely ca. 60 miles due west of me right now. |
#6
Posted to rec.audio.tubes
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Speaker cable revelation?
Bob Eld wrote:
Posted by Jim Lesurf on uk.rec.audio: "I've just put up a new webpage that provides some measurements on the properties of a variety of loudspeaker cables. The page is at http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html "It is an expanded version of the article published in 'Hi Fi News' a few months ago." Wadya think? Pure unadulterated nonsense of zero meaning or consequence. Maybe you didn't realize it but audio frequencies are ALL below 100kHz. Your measurements are in the megahertz range. Jim, not me. Jim Lesurf. He writes for Hi-Fi News. My view is that there is pretty much nothing left to write about, so the comics compete to write about nothing. What possible effect do they convey to sound quality? Be imaginative in your explanation we're all ears! Imaginary rather than imaginative, I'm afraid. Although he doesn't say so in the article, he has defended it by saying it was intended to be a "heads up" to amplifier designers. The concern, he claims, is that some amps may be inclined to instability, and that this condition might be exacerbated by some cables. He is unable to cite any such amplifiers in reality, and doesn't say why publication in HFW is a legitimate conduit for such a warning, or why the warning isn't mentioned in the article itself. I could add that any designer stupid enough to need warning about the need for unconditional stability wouldn't be any the wiser after reading it. He also says he's concerned that amplifiers with relatively high output impedance may be particularly susceptible to some consequence or other, but this line of defense seems to disappear into hand-waving and if-you-don't-know-by-now-you-never-will snootiness. But don't take my word for it, have a look over at uk.r.a. I was dismissed as a troll, I'm afraid. I can see why, although it's something of a misuse of the term. Considering he's a professional writer, I'm disinclined to educate him, so I just took the ****. It's not easy to argue against determined nonsense anyway, which is exactly what the snake-oil merchants rely on. Watch your ankles, there's a couple of nasty poodles. Finally, he is concerned that audio engineers without his experience of working with high frequencies may not understand what he's on about. So, I wonder, is there anyone here who found the charts he produced, using his fancy-pants machine "intended for another purpose", in any way enlightening? Is there anything there that you wouldn't expect, following a moment's thought? It's occured to me that I don't think anyone has used the word "significant". That might be a question worth asking: "Apart from the red herring about stability, what is the significance of whatever effects you are on about?" He's not going to listen to me, so someone else will have to ask. I'm going on about this because I am genuinely outraged, and embarassed to be English in the company of audio enthusiasts. English engineers have always been snooty and lacking in culture, but now they're mostly daft as brushes, to boot. Incidentally, has anyone been to rec.audio.tech recently? I was going to post there but someone must have really upset the spambots Ian |
#7
Posted to rec.audio.tubes
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Speaker cable revelation?
"Ian Iveson" Bob Eld wrote: Posted by Jim Lesurf on uk.rec.audio: http://www.audiomisc.co.uk/HFN/Cables3/TakeTheLead.html Jim Lesurf. He writes for Hi-Fi News. My view is that there is pretty much nothing left to write about, so the comics compete to write about nothing. What possible effect do they convey to sound quality? Be imaginative in your explanation we're all ears! Imaginary rather than imaginative, I'm afraid. Although he doesn't say so in the article, he has defended it by saying it was intended to be a "heads up" to amplifier designers. The concern, he claims, is that some amps may be inclined to instability, and that this condition might be exacerbated by some cables. He is unable to cite any such amplifiers in reality, and doesn't say why publication in HFW is a legitimate conduit for such a warning, or why the warning isn't mentioned in the article itself. I could add that any designer stupid enough to need warning about the need for unconditional stability wouldn't be any the wiser after reading it. ** While it is possible for some hi-fi amplifiers to become unstable because of the use of a high parallel capacitance speaker cable - the shame here is there are NO such examples in the list of cables that Lesurf tested !!!!! ALL the cables in his list are low capacitance types ( ie figure 8 types ) hence quite benign and can be used with any amp and over any length. The one example that is not figure 8 ( the Isolda ) has feed inductors fitted at the amplifier end by the makers rendering it particularly benign. Lesurf is CRYING WOLF in a similar way to notorious charlatans like Matti Otala in 1973 with his phoney " TIM " distortion and Jung and Marsh in 1980 with their phoney ideas on selecting capacitors for audio. The harm done to honest audio manufacturers by the latter complete nonsense was enormous and is still going on today - with an army of net based snake oil merchants flogging exotic capacitors and phoney up-grade kits for amplifiers to fools. My " heads up " to pseudo-science types like Lesurf, who feel compelled to pontificate on the world of hi-fi audio, is that when deciding to CRY WOLF to the world - be sure you are not just making technical howlers. ...... Phil |
#8
Posted to rec.audio.tubes
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Speaker cable revelation?
On Sat, 15 Aug 2009 04:38:33 +0100, "Ian Iveson"
wrote: Bob Eld wrote: What possible effect do they convey to sound quality? Be imaginative in your explanation we're all ears! Imaginary rather than imaginative, I'm afraid. Although he doesn't say so in the article, he has defended it by saying it was intended to be a "heads up" to amplifier designers. The concern, he claims, is that some amps may be inclined to instability, and that this condition might be exacerbated by some cables. The standard practice in audio power amplifier design for at least 35 years to put a parallel connected RL filter at the amplifier output. This is usually implemented by using a few ohm a few watt resistor and wind a few turns around this "core" and connect it in parallel with the resistor and connect it between the actual amplifier output (from which the feedback is actually taken) and the speaker terminal. At low (audio) frequencies, the inductance of the few turns have no practical effect, but at ultrasound frequencies, the inductive reactance is high and the impedance is dominated by the resistor, effectively isolating the load from the feedback loop, which otherwise could cause instability. Electrostatic loudspeakers are practically pure capacitive reactance at high frequencies, causing potentially stability problems, unless there is some isolation between the feedback loop and load at ultrasound frequencies. Also some special loudspeaker cables with artificially high capacitance could cause stability problems without the filter. He is unable to cite any such amplifiers in reality, and doesn't say why publication in HFW is a legitimate conduit for such a warning, or why the warning isn't mentioned in the article itself. I could add that any designer stupid enough to need warning about the need for unconditional stability wouldn't be any the wiser after reading it. Some especially "high-end" manufacturers seems to be keen on displaying how well the amplifier is reproducing a 20 kHz square wave. In order to produce such a waveform purely, the amplifier must have a good amplitude and phase accuracy at odd harmonics (60, 100 etc. kHz). With a properly RL output filter, the amplifier is _not_ going to produce a clean 20 kHz square wave, no matter how good the amplifier itself is. In order to get a clean square waveform, some "high end" manufacturers omit this output filter, causing stability problems with difficult loads and hence sound coloration when high capacitance speaker cables are used. In order to produce a clean square wave, some "high-end" manufacturers also omit the input filtering, allowing potentially very steep input signals, which the amplifier can not handle due to slew rate limitation, driving the input stage into saturation and generating TID. In a proper power amplifier input there should be (before any feedback stages) a low pass filter attenuating ultrasound signals in order to avoid slew rate limitation effects as well as avoiding EMC problems due to high field strength RF breakthrough, which could be rectified in a small signal stage and there would be audio breakthrough from a local AM radio station. Some "high end" manufacturers have some special features that they are keen of, emphasizing it to a point that good engineering practice is ignored in other points of the design. He also says he's concerned that amplifiers with relatively high output impedance may be particularly susceptible to some consequence or other, but this line of defense seems to disappear into hand-waving and if-you-don't-know-by-now-you-never-will snootiness. If the amplifier has a high output impedance, this is a sign of low (or non-existing feedback) so at least there should not be no stability issues :-). So, I wonder, is there anyone here who found the charts he produced, using his fancy-pants machine "intended for another purpose", in any way enlightening? Is there anything there that you wouldn't expect, following a moment's thought? Those curves are of interest when you are trying to use some random conductors e.g. speaker cables to run Ethernet or other high speed signals. Unfortunately Ethernet over speaker cable (or Ethernet over barbed wire :-) would use more sensible termination impedances. Of course the impedance charts are quite as expected for a mismatched transmission line, when the cable effective length is greater than about 1/10 of the free space wavelength. Paul |
#9
Posted to rec.audio.tubes
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Speaker cable revelation?
"Paul Keinanen" ** Sci fi is right on the money with this dude. The standard practice in audio power amplifier design for at least 35 years to put a parallel connected RL filter at the amplifier output. This is usually implemented by using a few ohm a few watt resistor and wind a few turns around this "core" and connect it in parallel with the resistor and connect it between the actual amplifier output (from which the feedback is actually taken) and the speaker terminal. ** Correct. At low (audio) frequencies, the inductance of the few turns have no practical effect, but at ultrasound frequencies, the inductive reactance is high and the impedance is dominated by the resistor, effectively isolating the load from the feedback loop, which otherwise could cause instability. ** Only if some dope puts an actual capacitor of the right value across the output terminals. Electrostatic loudspeakers are practically pure capacitive reactance at high frequencies, ** Not all of them show a sudden impedance drop to very low ohms at high audio frequencies - the famous Quad ESL63 and it close relatives are notable exceptions. http://www.quadesl.com/graphics/quad..._impedance.jpg causing potentially stability problems, unless there is some isolation between the feedback loop and load at ultrasound frequencies. ** WRONG - the impedance dip is never in the supersonic range. It is very much in the audible range where almost any amp made is perfectly stable. Also some special loudspeaker cables with artificially high capacitance could cause stability problems without the filter. ** High capacitance in the cable is the only potential issue - but it has got to be damn high like 2000-3000 pF per metre. No such troublesome cable was presented by Lesurf. Some especially "high-end" manufacturers seems to be keen on displaying how well the amplifier is reproducing a 20 kHz square wave. In order to produce such a waveform purely, the amplifier must have a good amplitude and phase accuracy at odd harmonics (60, 100 etc. kHz). With a properly RL output filter, the amplifier is _not_ going to produce a clean 20 kHz square wave, no matter how good the amplifier itself is. In order to get a clean square waveform, some "high end" manufacturers omit this output filter, causing stability problems with difficult loads and hence sound coloration when high capacitance speaker cables are used. ** Even with no output inductor, the speaker load is never an issue. Even with a ( now rare or impossible to find) very high capacitance cable, any resulting instability is in the RF range. In order to produce a clean square wave, some "high-end" manufacturers also omit the input filtering, allowing potentially very steep input signals, ** From where ?????????????? Space aliens singing in ultrasound on Blue Ray audio DVDs ??? which the amplifier can not handle due to slew rate limitation, driving the input stage into saturation and generating TID. ** ABSOLUTE CRAPOLOGY !!!! If the amplifier has a high output impedance, this is a sign of low (or non-existing feedback) so at least there should not be no stability issues :-). ** Correct. But none of the cables Lesurf presented would upset ANY amplifier. Of course the impedance charts are quite as expected for a mismatched transmission line, when the cable effective length is greater than about 1/10 of the free space wavelength. ** BTW: Do you buy the quoted 0.22C speed figure for the Isolda flat cable ?? Does not compute with the known dielectric constant for polyester insulation ( 4.1 to 5.2 ) as used by the makers " Townshend". ...... Phil |
#10
Posted to rec.audio.tubes
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Speaker cable revelation?
On Fri, 14 Aug 2009 16:39:56 -0700, dave wrote:
Phil Allison wrote: "Eeyore" Maybe you'd like to join my crusade about Jim Lesurf's daft imaginings in uk.rec.audio. I gather he's an 'academic'. ** Jim is a former member of the academic staff ( means now dead wood ) at the University of St Andrews where John Cleese ( of Faulty Towers fame) was the Rector between 1970 and 1973. Mr. Cleese is likely ca. 60 miles due west of me right now. How is he doing? (If you know). Any public performances? |
#11
Posted to rec.audio.tubes
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Speaker cable revelation?
On Sat, 15 Aug 2009 16:16:55 +1000, "Phil Allison"
wrote: "Paul Keinanen" Some especially "high-end" manufacturers seems to be keen on displaying how well the amplifier is reproducing a 20 kHz square wave. In order to produce such a waveform purely, the amplifier must have a good amplitude and phase accuracy at odd harmonics (60, 100 etc. kHz). With a properly RL output filter, the amplifier is _not_ going to produce a clean 20 kHz square wave, no matter how good the amplifier itself is. In order to get a clean square waveform, some "high end" manufacturers omit this output filter, causing stability problems with difficult loads and hence sound coloration when high capacitance speaker cables are used. ** Even with no output inductor, the speaker load is never an issue. Even with a ( now rare or impossible to find) very high capacitance cable, any resulting instability is in the RF range. In order to produce a clean square wave, some "high-end" manufacturers also omit the input filtering, allowing potentially very steep input signals, ** From where ?????????????? Space aliens singing in ultrasound on Blue Ray audio DVDs ??? From a signal generator of course :-) and the signal output is viewed on an oscilloscope. This is how many amplifiers were advertized and apparently some audio amplifiers still appears to be designed in this way. which the amplifier can not handle due to slew rate limitation, driving the input stage into saturation and generating TID. ** ABSOLUTE CRAPOLOGY !!!! In the 1960's many designers had discovered that even a bad design could get very impressive performance figures by applying plenty of feedback. The drawback was that some additional voltage amplification stages was required, but since the cost of transistors had dropped significantly, so adding a few voltage amplification stages was not a cost issue (as it had been in the tube era). In order to make many of these designs stable, quite conservative frequency compensation had to be used, making the amplifier quite slow. A typical power amplifier has a differential pair in the input with quite significant open loop gain. A steep transition at the input could drive the input transistor out of range, before the slow global feedback would bring the differential pair into linear operation. Fortunately, this problem can be solved by making each stage sufficiently linear by using local feedback so that excessive global feedback is not required. At the differential pair input stage, adding some emitter degradation resistors is often enough. Of course, the input voltage slave rate must be limited by a low pass filter to less than the output slew rate capability divided by the closed loop voltage gain. Of course the impedance charts are quite as expected for a mismatched transmission line, when the cable effective length is greater than about 1/10 of the free space wavelength. ** BTW: Do you buy the quoted 0.22C speed figure for the Isolda flat cable ?? Does not compute with the known dielectric constant for polyester insulation ( 4.1 to 5.2 ) as used by the makers " Townshend". Yes, those figures looked quite strange. I have used microstrip resonators on PCBs ("infinite" ground plane and a strip with a well controlled width in an other layer) both below and above 1 GHz, in which the velocity factor (and hence required resonator length) is assumed to be constant at least for a specific line impedance (typically 50 ohms). However, looking at some reference documents, the velocity factor drops by some tens percent at very low impedance levels (= wide signal conductors). The Isolde cable has a ground plane with the same width (15 mm) as the signal conductor (not infinite ground plane as in microstrips) so this might also affect the quite low propagation velocity. Looking at the impedance chart for the 5 m section, the 1/4 wave resonance (both open and short) at 3.2 MHz would rule out any lumped capacitance hiding inside the cable. The frequency is consistent with a velocity factor of 0.2-0.25. The listed inductances and capacitances would also be consistent with the claimed velocity factor and impedance. Looking at the huge capacitance of 2800 pF/m for a 15 mm wide strip, would suggest about 0,2 mm insulation between the conductors, if er=5. To make a home brew Isolde cable, take a 15 mm long tubular capacitor, cut it open and unroll the foil and at both ends, attach banana plugs to the both foils :-). You may have to add some mechanical strengthening to it. Paul |
#12
Posted to rec.audio.tubes
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Speaker cable revelation?
Hi RATs!
Some geezer gets a little cash for a silly article in an audio advertising rag and you lot get huge erections ... the rockers on your hobby horses are bent, strangely. "A concise history of the Great Wars of the Aural Age of Enlightenment ..." such depth of field! Whatever gets you through the long, dark, teatime of the soul - August in London. Happy Ears, my snarling friends, Al |
#13
Posted to rec.audio.tubes
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Speaker cable revelation?
"Fu Knee" Some geezer .. ** A famous audio industry person, former university academic and dominant member of the newsgroup " uk.rec.audio". gets a little cash for a silly article in an audio advertising rag ** That event never caused at a murmur - as no-ne on the NG reads the rag. Publishing the same bogus info on the NG and thereby inviting comment was what did it. and you lot get huge erections ... ** Physical impossibility, for any of the rabid, needle dick poms that haunt "uk. rec.audio". Happy Ears, my snarling friends, ** Remember: on usenet - NO-ONE CAN HEAR YOU SCREAM !! ....... Phil |
#14
Posted to rec.audio.tubes
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Speaker cable revelation?
Al ventured:
Some geezer gets a little cash for a silly article in an audio advertising rag and you lot get huge erections ... the rockers on your hobby horses are bent, strangely. "A concise history of the Great Wars of the Aural Age of Enlightenment ..." such depth of field! Whatever gets you through the long, dark, teatime of the soul - August in London. Happy Ears, my snarling friends, http://www.bigeye.com/donotgo.htm Ian |
#15
Posted to rec.audio.tubes
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Speaker cable revelation?
On Aug 14, 9:52*am, "Ian Iveson"
wrote: Wadya think? Mpffff..... I think that straightened steel coat-hangers, if properly insulated and terminated will do just fine for 99-44/100ths of typical applications. That I use standard #12 stranded THHN wire spun in a drill (for ease of handling, not for any magic electrical properties due to spinning) is because it is cheap, tough, can be pulled through walls without damage and is amenable to longish runs - such as to my rear speakers in the library - 35 foot runs. "Difficult loads" - that would be the speaker, perhaps? Doncha think? I guess one gets what one pays for - and if one pays enough for a 'difficult load', it will be produced as needed. YIKES! Peter Wieck Melrose Park, PA |
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