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Thread: Short IC/long speaker vs. long IC/short speaker runs

  1. #1

    Short IC/long speaker vs. long IC/short speaker runs

    Quote Originally Posted by Myles B. Astor, PhD View Post

    Maybe Jim can start out talking about the pluses/minuses of short IC/long speaker vs. long IC/short speaker runs?
    Myles,

    It took me a while to get back to you, because this is a detailed question. My preference is for longer interconnects and shorter speaker cables. But, like everything else in life, there's a caveat. To have the longer interconnects, you must have equipment that can drive low impedance loads. As an example, if you are using a passive pre-amp, then you could not use long interconnects, because you'd need to be concerned with the capacitance of the cable. Or, another example: if you are using a computer running into a small DAC that uses a IC stage that does not have a current drive for long interconnects, you probably should not use long interconnects.

    To help with calculating the treble cutoff frequency of your cable, this calculator may be a helpful start: http://www.sengpielaudio.com/calculator-cable.htm .

    Concerning the speaker cable, is that the speaker itself possesses a very low impedance. Typically, you're talking from 1-16 Ohms impedance. Here, Ohm's Law prevails. The cable length itself also has an impedance. Both of these will begin working together. The cable will consume power from your amplifier, and one of the things you do not want is for your speaker cable to become hot, or in other words, to create resistance. As it creates resistance, you start having frequency dropouts of your speaker cable. That is, it will roll up or roll down.

    So, how long should cables be? Is there a "rule of thumb"?

    With true balanced, you can pretty much go any length from 1m to 100m. With RCAs, you need to be a little more cautious. I'd say anything from 1m to say, 20m should work fine. It also depends on the equipment being used and whether it can support that length.

    With speaker cables, I'd say anything from 1m to 4m. Most of the high-end manufacturer's equipment I have seen should not cause an issue, so long as you pay attention to the gauge. Say, a 14 gauge down to 8 gauge, you should not have an issue. If you go the other say, say 16 or up, you need to start being concerned for the speaker cable length.

  2. #2
    Hi Jim
    Thanks for answering this Intersting Topic
    The way i understand it is i want the Output impedance of my Preamp to be as low as possible for running long interconnects.
    What dictates how great the capacitance of the Cable can be without causing high frequncy roll-off.
    Regards
    Analog: Acoustic Solid Wood MPX Reference Microcontroller, SME M2-12, Ortofon Cadenza Bronze
    Digital: Rega Apollo, Chord 2 QUTE
    Amp: Roksan Caspian M2 + DX-2 Ref Phono
    Speaker Kef-LS 50
    Cables: all MIT Magnum M3, M1 Phono, Magnum AC1

  3. #3
    Quote Originally Posted by Billy Shears View Post
    Hi Jim
    Thanks for answering this Intersting Topic
    The way i understand it is i want the Output impedance of my Preamp to be as low as possible for running long interconnects.
    What dictates how great the capacitance of the Cable can be without causing high frequncy roll-off.
    Regards
    Morning, and hope the weekend treated you well!

    Cable loss can be described as a low-pass filter model. For example, your preamp has an output impedance of 100 Ohms, and your capacitance of your cable of your 1 m is, let's say, 100 pf. Your high frequency cutoff would be around 16 million.

    Let's do another example. Say your preamp has an output impedance of 50k, and everything else stays the same. The high frequency cutoff would be around 32k. If we increase the capacitance to 1000, the cutoff becomes 3k.

    The basic idea is that the more capacitance and interference you have, the shorter length the cable needs to be to avoid high frequency cutoff.

    To figure your cable length, you need to know your capacitance of your cable per meter, and your source impedance. These numbers are usually found in the manufacturer's specs. If not, give them a call or email. Then, I'd use a calculator like the one here: http://www.sengpielaudio.com/calculator-cable.htm

    We're lucky to have sites like this one. Used to, you had to do all of this by hand or slide rule (see attached if you'd like the formula).

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  4. #4
    Thank you for that reply Jim

    If i do the Math the loss from IC seems to be less of an issue than i had anticipated.

    If we take a avarege 600ohm output impedance and a 6 meter 300pf/meter cable the cut off would be 147366 Hz.
    Considering frequencys over 60 Khz are mostly unwanted anyway i now understand your preference for longer ICs...
    Analog: Acoustic Solid Wood MPX Reference Microcontroller, SME M2-12, Ortofon Cadenza Bronze
    Digital: Rega Apollo, Chord 2 QUTE
    Amp: Roksan Caspian M2 + DX-2 Ref Phono
    Speaker Kef-LS 50
    Cables: all MIT Magnum M3, M1 Phono, Magnum AC1

  5. #5
    Another item to consider regarding the output impedence of your preamp is that the specified impedence may not hold true for the range of 20hz-20khz. I have a valve preamp in a smaller system with a measured output impedence of 36 ohms. This increases to almost 125 ohms at 20hz. This change in output impedence will be variable with different amplifier input impedences and cable capcitance.

    This is another reason the higher end preamps have more robust power supplies and output stages.
    Last edited by dan31; 09-10-2015 at 03:53 PM. Reason: Corrected output impedence of preamp

  6. #6
    Quote Originally Posted by dan31 View Post
    Another item to consider regarding the output impedence of your preamp is that the specified impedence may not hold true for the range of 20hz-20khz. I have a valve preamp in a smaller system with a measured output impedence of 36 ohms. This increases to almost 125 ohms at 20hz. This change in output impedence will be variable with different amplifier input impedences and cable capcitance.

    This is another reason the higher end preamps have more robust power supplies and output stages.

    Good points, especially about the pre-amps, Dan!

  7. #7
    Quote Originally Posted by Jim View Post

    My preference is for longer interconnects and shorter speaker cables.
    Allow me to expose my point of view.

    I do not understand about impedance, capacitance or resistance.
    But in the last 3 years ive tried a few diy experiences with cables. And what became my concerns? I care about cross-talk, vibrations and external interferences.

    I think the interconnects, often have better design and effective shielding than speaker cable. Maybe is because the signal is weaker and, as a baby, extra care is absolutely necessary. Maybe, just maybe, this is the reason why you prefer longer interconnects.

    This is true about construction, but is also true about the handling. Usually, we do not see interconnects dying on the floor, as we see in the speaker cable.

    I think the longer the cable, the more you should treat with caution the signal path.
    In a longer cable, a good shield is absolutely important, or it may become an RFI antenna. But a bad application may cause some electro-magnetic turbulence / interference (EMI).
    So, my point is: interconnect or speaker cable, have extra care with the longest.

    PS: my opinion is just valid until the next experience

  8. #8
    Unless I missed it... I have found the longer the run (either interconnects or speaker cable), the more you need to raise the cable off the carpet or floor. I assume a cable's direct contact with a rug or floor acts like an added dielectric.

    Mike's room is ideal:


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    Founder: AVShowrooms- over 15,000,000 video views! featuring video reports of audio shows, company tours and reviews. Resume' includes; the absolute sound, Stereophile, Listener Magazine, founder Philadelphia Audio Society. Top articles: Lamm ML3- TAS, YG Anat III Signatures- TAS, Ayon- TAS, Kronos Ltd. video review- AVS, Audionet- AVS, Single Ended Survey- TAS, Fisher 500c- Stereophile, Bozak CGs- Stereophile, Box Sets- Listener, Dynaco ST70-Listener. Best catch phrase: Bugatti of Audio.

  9. #9
    Quote Originally Posted by peteravshow View Post
    I have found the longer the run (either interconnects or speaker cable), the more you need to raise the cable off the carpet or floor. I assume a cable's direct contact with a rug or floor acts like an added dielectric.
    Totally agree.
    Is that kind of care that i spoke about.

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