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"Frank Dresser" wrote in message ... wrote in message oups.com... AT http:/www.kiwa.com/rxtips.html, A nice publication on "Tips for Imporivng Receiver Performance" [snip] However, the Kiwa article doesn't mention detector distortion, which can be a significant source of distortion, at least with diode detectors. The subject of detector distortion has been beaten to death here and on other forums. One post I seem to recall involved some simple mods to a common diode detector which significantly reduced distortion but also reduced output by about 3db. [snip] Frank Dresser Or AGC distortion. Fast AGC can be a huge cause of distortion as it varies the gain of the receiver with the bass energy in the modulation. Slow AGC can make a huge improvement. Tom |
FWIW, the diode used in the AM demod of my HP334A distortion analyzer
is a fd2387. There is nothing on the net about the diode. Specs are thd 0.3% from 550Khz to 1.6Mhz, 30% modulation 3 to 8 v carrier thd1% for 1.6Mhz to 65Mhz (same conditions) |
Frank Dresser wrote:
I'm not sold on the necessity of heavy cables for speakers. The largest resistance on the speaker system isn't the cables but the speaker voice coil. A typical 8 ohm radio speaker will have a voice coil resistance of about 6 ohms. Even thin wires will have much smaller resistances in the milliohm range. I really can't imagine how going from cables with milliohms resistances to microohm resistance will make a difference in a circuit which a resistance of a few ohms. It dosen't, but the audiophools can't grasp that so they throw big bucks away on speaker cables with fancy names and tons of hype about performance. |
Frank Dresser wrote:
"Tony Meloche" wrote in message ... "High definition" speaker wire is jargonese for "heavy". Monster Cable is excellent, but much heavier than it needs to be. Some of the best audio engineers, while lauding Monster Cable, have also written that the difference in performance between Monster Cable (12 gauge, if memory serves) and 14 gauge wire is purely for late-night debates, not anything truly hearable or usually, even measurable (to a significant degree). I'm not sold on the necessity of heavy cables for speakers. The largest resistance on the speaker system isn't the cables but the speaker voice coil. A typical 8 ohm radio speaker will have a voice coil resistance of about 6 ohms. Even thin wires will have much smaller resistances in the milliohm range. I really can't imagine how going from cables with milliohms resistances to microohm resistance will make a difference in a circuit which a resistance of a few ohms. I'd guess the resistance of the voice coil changes more with temperature than the amount of resistance change you'd get from going from 14 gauge wires to 20 gauge wires. The "conventional wisdom" (interpet as you wish) is that the thinner the speaker wire, the higher the resistance of the wire itself. With strong, bass-heavy passages at fairly high volume (I listen to a lot of organ music CD's recorded in European cathedrals) a portion of the amplifier power coming down that wire is dissipated as heat. Thin speaker wire also changes the damping factor - not for the better, again according to "CW", though it's debateable if it changes it to a severe enough level to make any real difference. I have always used 14 gauge speaker wire, but if it disappeared from the face of the earth tomorrow, I would shrug and use 16 gauge wire without a care in the world. 18 gauge wire I consider acceptable if the run isn't too long, but I, personally, would never use anything thinner than that from a 100W amp to my speakers of (nominal) 6 ohm impedance. And 50 feet of 18 gauge zip at my local hardware store is about $6.50 50 feet of 14 gauge speaker cable I can get for $15. For a one time $8.50 price difference, I think the 14 gauge is well worth it. 12 gauge wire, though, is a waste of money, IMO. Tony ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
On Wed, 18 May 2005 19:22:23 -0400, Tony Meloche
wrote: I have always used 14 gauge speaker wire, but if it disappeared from the face of the earth tomorrow, I would shrug and use 16 gauge wire without a care in the world. 18 gauge wire I consider acceptable if the run isn't too long, but I, personally, would never use anything thinner than that from a 100W amp to my speakers of (nominal) 6 ohm impedance. And 50 feet of 18 gauge zip at my local hardware store is about $6.50 50 feet of 14 gauge speaker cable I can get for $15. For a one time $8.50 price difference, I think the 14 gauge is well worth it. 12 gauge wire, though, is a waste of money, IMO. Tony I use powered subwoofers (a form of biamplification) so I don't have to worry about high power on my 16g speaker wires. That being said, the Rane Pro Audio Reference spake thusly: ''damping factor: Damping is a measure of a power amplifier's ability to control the back-emf motion of the loudspeaker cone after the signal disappears. The damping factor of a system is the ratio of the loudspeaker's nominal impedance to the total impedance driving it. Perhaps an example best illustrates this principle: let's say you have a speaker cabinet nominally rated at 8-ohms, and you are driving it with a Rane MA 6S power amp through 50 feet of 12 gauge cable. Checking the MA 6S data sheet (obtained off this web site, of course), you don't find its output impedance, but you do find that its damping factor is 300. What this means is that the ratio of a nominal 8 ohm loudspeaker to the MA 6S's output impedance is 300. Doing the math [8 divided by 300] comes up with an amazing .027 ohms. Pretty low. Looking up 12 gauge wire in your handy Belden Cable Catalog (... then get one.) tells you it has .001588 ohms per foot, which sure ain't much, but then again you've got 100 feet of it (that's right: 50 feet out and 50 feet back -- don't be tricked), so that's 0.159 ohms, which is six times as much impedance as your amplifier. (Now there's a lesson in itself -- use big cable.) Adding these together gives a total driving impedance of 0.186 ohms -- still pretty low -- yielding a very good damping factor of 43 (anything over 10 is enough, so you don't have to get extreme about wire size). [Note that the word is damp-ing, not damp-ning as is so often heard -- correct your friends; make enemies.] '' http://www.rane.com/digi-dic.html |
wrote in message oups.com... You need to look at it from the viewpoint of what does the lower resistance buy you, and it is not insignificant. Low end amplifiers have damping factors of a few hundred. A high end product (say a Jeff Rowland design) can have a damping factor of 1000. So your high end amp has an output impedance of 8 milliohms, and maybe 30 milliohms for the average amp. http://www.epanorama.net/documents/w...esistance.html Let's ignore the skin effect for the sake of simplicity, i.e. will will deal with DC resistance. [The skin effect at audio isn't that big of a deal.] Using cheesy 18 guage wire, you have 7.5milliohms per foot, while 12 guage is about 2 milliohms per foot. For twenty foot runs (i.e both sides of the cable), this yields 150 milliohms and 40 milliohms. Thus you spent all that money on a amp to control the speaker, but the wire resistance is at least 5 times greater than the output impedance of the amp. Sure, but is there really much difference between a dampning factor of 1000 or 100 or whatever? What if we could arrange an infinite dampning factor? An infinite damping factor should control the voice coil as much as it can be controlled. Imagine, for the purpose of illustration, a speaker with it's terminals dead zero ohms shorted. Can the voice coil be moved without any electrical input? Yep. Back emf (or current) or not, it can be moved pretty easily. It can be moved at any frequency. Sure, with the speaker shorted, the voice coil will try to act as an electrical brake, but it's a pretty lousy brake. I doubt an infinitely damped speaker would control unwanted motion any more completely than a shorted mechanical meter movement. I imagine the voice coil would be a much better electrical brake if it didn't have any electrical resistance. But it does have electrical resistance. The majority of most speaker's impedance is electrical resistance. So, as I see it, voice coil resistance is the limiting factor in all these wire size/dampning factor considerations. I can think of one way to get around the effects wire size has on dampning factor. Just run another pair of thin sensor wires from the speaker terminals back to the amplifiers feedback network. Voice coil resistance effects could be greatly reduced if somebody would wind a sense coil on the voice coil form and run sensor wires back to the amp. I'm not convinced such extraordinary damping factor designs would be worth the effort. After all, tube amps have a comparatively crummy dampning factor, yet still can sound pretty good. Is heavy wire a good idea? Yes, Does it have to be fancy stuff? No. There is another school of thought called biwiring. Here you wire the drivers (or more corectly the input to the crossover filter) individually. This is related to the damping factor as well. Since the wire has resistance, the back EMF of the woofer (which is significant) can find it's way back to the tweeter since the amplifier, no matter how well damped, is connected to the speaker with a resistor (aka wires). If you bi-wire, the woofer back EMF, which can contain higher order harmonics, gets damped at the amp. There is good science behind many audio tweaks, but often the science gets lost in the argument. For instance, Kiwa suggesting to yank ceramic bypass caps is just plain stupid. There may be arguments to yank them in the audio chain, but low inductance ceramic caps are really a requirement for good power supply bypass. Keeping this remotely on topic, I use that bad ass speaker cable wire you get from the hardware store as an "extension" cord from my cigarette lighter outlet to a power distribution breakout box. This way when monitoring out in the field, I can set up my gear outside the SUV and have a little elbow roon. Speaker cable is quite flexible, so the setup packs up nicely. Eventually I'm going to set this up so that I can have gel cells to run the gear, but use the car battery to supply some of the power. What you need to do is prevent the situation where the gel cell power flows back to the car. I'll probably end up using power schotky diodes unless some clever linear circuit comes to mind. |
Some people like the loosely damped sound of tube amps, even if it is
less accurate. Your proposal for a Kelvin connection to a speaker isn't exactly marketable since the amplifiers would have to be designed with a sense input. There are already motion feedback speakers, generally for woofers. Typically they use a piezo accelerometer to sense the motion, not a second coil.. Velodyne has done this for over 20 years. I wouldn't mind infinite damping. Sounds like a good idea. |
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