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Does anyone know what Yamaha means when it says its new A/V receivers have "linear damping factor." It explains this by saying damping is applied across the audible spectrum, but I would have thought that would be the case with any damping applied. Why the "linear"? Also I note that a number of the new models, even more expensive ones, state the damping factor is 80, while with more expensive or top-of-the-line models in the past it was 200. I realize that the damping at the speaker will be lowered by the size of cable used, and this normally will lower it considerably, but that appears to leave 80 as far less effective than 200. How much should one worry about damping factor?
 

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spurge,


Some people don't feel damping factor is all that important.

I personally feel "system damping factor" is quite important to the sound. I'll give you my thoughts on it.


Damping generally effects the "tightness" of bass frequencies. The higher the number the better.

It's the amplifiers ability to control or damp the speakers voice coil oscillations. When a signal is sent to a speaker and then stopped, the speaker cone continues to move, and creates or presents a back voltage to the amplifier. If the output impedance of the amplifier combined with the impedance of the interconnecting speaker wires is very low (read a short) then this oscillation is damped and the bass sounds very tight. The higher this combined impedance, the more the speakers voice coil will continue to move and effect the sound.


This of course is where the bass mushy-ness of tube amps comes from. Tube amps generally have an attribute unlike solid state amps that their output impedance is usually unacceptably high and is non-linear and rises as the frequency increases. You can see how this non-linearity, besides being a source of distortion (read "warm" sound) in the damping formula makes a tube amp pretty undesirable if you're looking for accuracy. But, some people like the sound of distortion, that's their business.


Anyway, damping factor is a ratio of the load impedance (generally considered a flat 8ohms) to the output impedance of the amplifier. Very nice, but generally in practice though, you have to take into consideration the impedance of the wire connecting the two devices and the fact that speakers with passive crossovers are an extremely non-linear device.

Again, the short answer is that the higher the number the better.


The long answer is that in most solid state amplifiers the output impedance is fairly constant (read linear) and very, very low over the entire audio spectrum and as such can almost be ignored in the formula because the system impedance is overwhelmed by the non-linearity of the speakers crossover plus the interconnecting wire resistance. This is the reason to ignore small differences in amplifier specs of damping. It's usually insignificant in relation to the effect of the speaker wire. I'll show you why shorter speaker wires are better.


Lets look at the formula for damping using a figure of 300 for damping. This yields about 0.026 ohms output impedance:


(speaker impedance) / (amplifier output impedance)

= 8.0 / (0.026 ohms)

= 300 ,this is a very acceptable amplifier damping factor.


Now add in a typical connecting wire of 12 feet of 12 guage zip cord.

12 gauge at 12 feet yields about 0.039 ohms of pure resistance. Capacitive reactance can be ignored as insignificant, as can inductive reactance at the lower frequencies and this short length. I calculate at 100 Hz that inductance would only add about .0015 ohms to 12 feet, so I'll ignore it.


(speaker impedance) / [(amplifier output impedance) + (wire impedance)]

= 8.0 / (0.026 + 0.039)

= 123


Anyway, you can see how the system damping factor dropped quite significantly even when using very heavy gauge wire. It shows the importance of using a low gauge interconnect and the importance of using short speaker wires.


My advice would be to look for a high damping factor number in an amplifier, but don't turn an amp down if the number is a little low. Yamahas advertising claim of linear damping factor can be ignored. If a solid state amp didn't have a linear damping factor in the audio spectrum, then you better get it fixed.....


brucek
 

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How can one determine the amplifier output impedance? I don't see this as a number that is usually published on specs.


Can it be derived from Output Level/Load Impedance? This figure is provided as mv/kohms exp: 1.2V/10kohms for the Denon 3802.


Mike
 

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Mike,


Nope, you may be a little confused. The specification you're stating would be applicable to input sensitivity/ input impedance.


This spec would tell you the level of input required to drive the input to full scale and reference its input impedance.


But you're quite right, they don't normally spec the output impedance of a power amp. This is because they normally give you the damping factor. If you divide the damping factor into 8 ohms, you will derive the output impedance.


brucek
 

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I haven't seen the damping factor published on may receivers. This is also true about slew rates, which is another one of those debatable numbers.


Mike
 

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is one way to help system dampening factor.:cool:


Bruce speaks truth as regards short and fat on the speaker cables.


On a slightly different note it is not uncommon to find that an amp's output impedance (solid state) rises with frequency. And it does this in a linear fashion. This is one reason that the frequency spec, when published, for the ouput impedance is always low. Seems I remember 1 KHz or below. So yes it is linear, just not constant.


Even though it may rise with frequency it starts off tiny, tiny, tiny so it just ends up tiny.

Almost always swamped by the cables, xovers, etc.
 

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I agree with the idea of short and fatter cables are better, however, what should one do if they wire all of their speakers from one source? Is it better to have all wires run the same length, or should one opt. to put the receiver close to the fronts and have a long run to the rears?


I ask this since my front speakers system mirrors my rear speakers. That is they are all the same type. 4 towers and 2 centers. I'm not able to have the receiver in the middle of the room due to logistical problems and not to mention the way the cable would get in the way.
 

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Well, practicality has to win out here. I wouldn't worry about it. The rears are going to have to accept the longer speaker cables as these would be considered the less critical.

This is certainly one reason people prefer monblocks. They can locate them directly behind each speaker.


brucek
 

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Bruce,


So you're saying it would be better to run short for the fronts and long for the rears?


Secondly, if one runs monoblocks, don't you still have to run long interconnects from the pre/pro to the monoblocks?


I heard somewhere it's prefferable to run long interconnects, but why would this be true?


Mike
 

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Mike,


Yep, since the rears would be considered the least critical, I would recommend the long speaker runs to the rears from a receiver if given the choice....


Theory says that when there is a question between which should be shorter, speaker wire or interconnect, the speaker wire is your choice.


It's really not a question of susceptibility to noise, it's a question of which situation has the greater negative effect.

The interconnect between a pre amp and power amp is a low level, high impedance connection and is indeed susceptible to noise in long lengths, but this is taken care of very nicely in the home environment by using the standard coaxial cable - so there's no real problem there.

The interconnect run, as I'm sure everyone knows, doesn't care about power transfer. It's a high impedance connection where the preamp acts as a voltage source. There's almost no current here, only voltage. You could use 20 gauge or 10 gauge and it would have zero affect on the voltage feeding the power amp. Noise is the only important issue on an interconnect interface - and as I said before it's taken care of quite well by using properly shielded cable.


Alternately, the speaker connection is a very low impedance, high level connection and you would have to be arc welding on top of it to induce any noise, so again there's no noise problem. Ever wonder why speaker cable aren't shielded? Because it's not necessary.


So, the deciding factor for the length question is the resistance of the cable run, which can be ignored in the interconnect, but is relatively important in the speaker run.

The shorter the length, the lower the resistance. The speaker run, operates in the current domain. This is an extremely low impedance connection. We have the output impedance of most amplifiers at less than 0.1 ohms feeding a speaker and crossover system with impedance's that vary from 4 to 8 ohms. You have to appreciate the upsetting factor that simple cable resistance and inductive reactance can add to this scenario. Now we're talking power transfer.


Because the speaker connection is in the order of 4 - 8 ohms, a long speaker run, particularly one of high gauge can become an appreciable proportion of the speaker impedance and as such can affect a signal loss and change of system response and decrease system damping. The system damping formula is almost exclusively driven by the speaker cables impedance, which is a function of its resistance and inductive reactance (capacitive reactance can be ignored here).


It's really the main advantage (besides channel separation) in owning monoblocks. Place the monoblock as close as possible to the speaker and run long interconnects. Interconnects are affected by capacitive reactance (makes them a bit of a low pass filter), so choosing interconnects with as low a capacitance would be advisable, but simple RG-6 is a pretty good and cheap solution......


brucek
 

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I went from cheapo 10 gauge speaker wire to supposedly better 12 gauge wire and I don't think its as good. My speakers are bi-wirable, so I guess if I bought 2 lengths of stranded/braided 10 gauge wire as short as is practical and bi-wired my speakers, it should be an improvement over a non-bi-wired single longer 12 gauge connection? The old cheaper 10 gauge wire is braided while the 12 gauge is not. Does that make a difference? It does make it easy to trim for connecting though :)


What is the thickest gauge wire practical to use in the home anyways? 10 or 8 gauge?


What about this idea for people who have non-biwirable speakers:


OK. So with the idea of using the lowest resistance connection possible, what about getting 2 identical length wires of the lowest/thickest gauge you can afford and using both for each speaker? Of course, you'd have to couple them at the speaker and at the amp, but it should work to reduce the overall resistance, correct? If the lengths were as identical as possible, you shouldn't have any problems with phase difference, should you, since electrical signals are already moving literally at the speed of light? Is it electronically wrong to separate the outputs and join them at the speaker? Maybe thats bad?


Could the above be applied to each bi-wire connection for a total of 4 wire pairs per speaker? They won't be long, so maybe its worth it? Is it not correct? Is it overkill?
 

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Bruce. thanks for the explaination regarding the difference between interconnects and speaker wire.


The option you're presenting of buying a long interconnect seems to be a challenge. I don't think I've seen too many long running interconnects. Usually they are limmited to 3m runs.


BTW, pardon my ignorance, but you mentioned coaxial cable. I thought this was used for video and digital audio spdif connections? Is this the proper cable to connect a pre/pro to a monoblock/external amp? I thought the usual RCA type audio cables were used.


Mike
 

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cpc,


That's a lot of questions in one post.

I'm afraid as far as bi-wiring is concerned, you'd probably be better off using bi-wire with your speaker straps reinstalled. At least then you'd take advantage of the extra gauge realized by combining two cables to each speaker. I'm not about to argue the positives or negatives of bi-wiring. I've read all the explainations and they all are meaningless when you apply the superposition theorem and know that all those signals can co-exist on a single wire quite nicely without interfering with each other. Any first year electrical engineering student knows this. If you like bi-wire, then use it, no harm done......It's ineffective, others will disagree.


Speaker cable length and phase differences? Forget about it. Yes, electricity does travel near the speed of light in a wire depending on its velocity factor, but that's not important here. This speed is approximated to about a nanosecond a foot. The accepted explaination would be that if you had one speaker wire 50 feet longer than the other, then that signal would arrive about 50 nanoseconds later than the other. Well, this is about 1000 times less than human hearing can even begin to detect, so don't worry about the lengths of your cables and phase differences.


Mike,


Audio cables are coaxial cables.


brucek
 

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Damping factor is not important because the amp's output impedance is in series with the DC resistance of the speaker, and the DC resistance is at least an order of magnitude larger than the amp impedance. A nominal damping factor above 10 is sufficient. What is important is that the output impedance of the amp be constant, or constant enough (explained below), across the audible frequency range (20 Hz to 20 kHz) to not induce frequency response changes due to resistor divider effects between the amp's output impedance, the speaker cable, and the speaker's input impedance. There are still many solid-state amps today that do not have constant output Z across the audible spectrum. For example, Crown amps tend to have lots of damping factor in the bass and midrange, and then go down in the treble.


"Constant enough" means that the amp's impedance throughout the audible frequency range does not vary enough to cause more than 0.1 dB of frequency change. This is actually a conservative measure, as you could have looser requirements if you considered human hearing models and capabilities.


--Andre
 

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Discussion Starter #15
Thanks Andre, that's very interesting. Is it possible to know from published specs how much an amp's impedance changes across the audible spectrum?
 

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Spurge,

Thanks Andre, that's very interesting. Is it possible to know from published specs how much an amp's impedance changes

across the audible spectrum?



Sorry, that information is usually not available publicly from most amp manufacturers. When Audio magazine was around, their amp reviews would always have a measurement of this spec.


--Andre
 

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OK. So all things being equal, make your speaker cables as short as possible and use the thickest gauge speaker wire possible. Don't worry if your speaker wires have to be longer than what would be ideal, because the difference won't out-way the convenience of making it work.


I will likely try Bi-wiring because with 12 or 10 gauge wire that I use, its hardly worth worrying about the cost of the wire. The wire I use is reasonably priced.
 

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Bruce et all,


I thought there was a difference between a 75 ohm (video or coaxial cable) and standard interconnects/audio cables. Is this just a marketing gimick?
 

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Mike,


Generally, you wouldn't use audio cables for a video interface because they may not have sufficient shielding and may not be 75 ohms. But you may indeed use video 75 ohm cables for both audio and video.


An audio interface is a high impedance interface. We don't need to be concerned with the characteristic impedance of the cable. A 75 ohm video cable will be fine.

Indeed, both the digital and video interfaces in your systems are fairly close to 75 ohms and require cable impedance matching because of the possibility of reflections, but not the audio interfaces.

At these frequencies the wavelength is very long. So as far as standing waves on a 1 meter piece of coax, when we're dealing with a 10 kilometer wavelength, well, the 1 meter portion appears as DC. No reflections possible.


The audio interface is a low level, high impedance connection where almost no current is drawn and we want to present a relatively low voltage to the amplifier input with as low a noise floor as possible. The preamp acts as a voltage source. So the main concern is noise and to a lesser degree cable capacitance. A properly shielded cable is important. Wouldn't matter if it was 50ohms or 200 ohms characteristic impedance. So don't get concerned.


A member of this forum, Chris White has done an excellent job of outlining on his web site how to make RG-6 cables that can be used for all audio, video and digital connections relatively inexpensively. You should visit.

http://www.bus.ucf.edu/cwhite/theater/DIYCable.htm


brucek
 
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