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In Reply to: RE: SUB CONNECTION; speaker wire or interconnects? posted by Duster on December 03, 2016 at 11:19:20
What about if you come off the main speaker and connect to the plate amp
Follow Ups:
I wouldn't consider doing that, since the EMF backwave of the main loudspeakers will affect the signal that's run to the high-level subwoofer inputs, not unlike the issue that a bi-wire configuration addresses. It's best to connect the high-level cable(s) directly to the binding post outputs of the main power amplifier.
"I wouldn't consider doing that, since the EMF backwave of the main loudspeakers will affect the signal that's run to the high-level subwoofer inputs, not unlike the issue that a bi-wire configuration addresses. It's best to connect the high-level cable(s) directly to the binding post outputs of the main power amplifier."
Those two options are electrically identical.
The electrical connection options are quite different. Besides, bridging the signal from the binding posts of a loudspeaker to a subwoofer includes the poor connectivity of two cables run in tandem.
The EMF backwave is pollution created by the *motor function* of the woofer. This pollution can affect the high-pass crossover section of a loudspeaker in a detrimental way unless the high-pass section is connected directly to the binding posts of the main amplifier, which will then avoid the affect of the magnetic energy backwave created by the woofer. This is the nature of a bi-wire configuration.
As it pertains to a high-level subwoofer cable interface, connecting the high-level interface cable directly from the binding posts of the main amplifier, then to the high-level subwoofer inputs also avoids the affect of the EMF backwave produced by the magnetic energy of the woofer. Magnetic energy pollution sounds like the noise that it is. Best to avoid it at all costs...
You are correct that they are not electrically IDENTICAL, but in the frequency range over which the subwoofer operates, the speaker cable impedance doesn't matter. The back-EMF of the loudspeaker doesn't really affect that frequency range either.
Thanks for being civil, Dave_K. Yes, of course the two interface methods are not electrically identical. If by speaker cable impedance you mean it does not matter if two speaker cables are connected in tandem, then of course it does not matter from a resistance POV for a high-level interface, but from a signal purity POV, it's sub par and not advisable. As for the EMF backwave, I don't see how the issue is dependent on frequency range, since the high-level input circuitry of the subwoofer may still be detrimentally affected by the energy of the EMF backwave, regardless of what frequencies are ultimately filtered as the subwoofer signal output. I don't see how the subwoofer input circuitry is any less sensitive than the tweeter high-pass circuitry if the EMF backwave is not shunted at the main power amplifier output circuitry.
The subwoofer high level input is a high impedance input buffer, likely 10k ohms or greater. That's 3-4 orders of magnitude greater than a typical loudspeaker impedance, so the presence of the subwoofer connection is effectively "invisible" to both the amp and speaker.
Also, a typical speaker cable resistance is 0.01-0.1 ohms, which is 5-6 orders of magnitude less than the input impedance of the subwoofer. And the cable reactance is insignificant at very low frequencies. So the subwoofer response is far, far less affected by the cable impedance than the loudspeaker response.
Regarding back-EMF, on second thought I think you're right. I was thinking that since amplifier damping factor is usually highest at low frequencies, back-EMF wouldn't be as much of a problem. But I neglected to consider that loudspeaker resonances are typically strongest in the bass, and in a typical small two-way + sub combination the port resonance of the loudspeaker is going to be within the transition band of the sub's crossover.
I measured the speaker (high level) input impedance of three different sub Plate amps I have and the input impedance measured from 5600 Ohms to 21500 Ohms
One of the Plate amps (The one with the lowest impedance) has a High Level High Pass output (Series inductor followed by parallel capacitor) which effects the DC and AC impedance measurement.
I personally prefer all the bass management to be done at the low level (high impedance (RCA or Balanced) level. More control, Less RF and Hum likelihood.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
5-6 orders of magnitude , not 5-6 times
Cable impedance of 0.01-0.1 ohms, subwoofer input impedance of 5600 to 21500 ohms, that's 5-6 orders of magnitude, right?
I agree with you that high level is preferable and arguably better.
Just to make sure I understand the crux of the discussion here... ;)
However, since most of us use fairly heavy gauge speaker wire, there is likely to be no audible difference in the two connection schemes. For example, I use 10-gauge speaker wire and my wires are 10-feet long. Their resistance is less than 0.02-ohms per channel. This is the resistance of 20-feet of 10-gauge wire for each channel--one ground wire and one signal wire for each speaker. I doubt there will be any audible difference whether you connect the subs to the main speaker terminals or whether you connect them directly to the power amplifier terminals. On the other hand, if you're fanatical about it, use Case 2. ;-)
Best regards,
John Elison
Yep. I like the amp terminal idea.
Just run 2-pair unshielded to the plate amp.
Might even be a good DIY experiment... use a couple of pairs out of a CAT5e or CAT6 cable. I would just use dual banana jacks for the main speakers then pop another pair of banna-jacks into the back of them.
Some audiophiles might insist that you need to use the *exact same* speaker cable as they suggest when bi-wiring or bi-amping.
And this will drive them patently nuts! ;)
Cheers,
Presto
There is no need to use the exact same speaker cable for a high-level interface, since the current draw is miniscule in comparison. However, if the same quality of cable with a similar design concept is selected, it might be of help to provide a more homogeneous integration with the main loudspeakers vs. a cable that presents a very different type of sonic signature. In this case, a similar "house sound" might be advantageous, but experimentation should be a worthy effort to explore in order to find out how cable sensitive the interface might be, and if one type of cable or another simply performs better according to a particular listener's system configuration and/or taste.
I don't know if you've ever listened to a subwoofer without the main speakers playing, but there isn't any sonic signature to be found. All you hear is thump, thump, thump. If you hear anything intelligible, your sub is doing way more than it's supposed to be doing. In other words, I seriously doubt you will be able to hear a difference between different types of wire using a subwoofer to make the comparison.
Good luck,
John Elison
> The electrical connection options are quite different.
I think you need to take a course in electricity. As Kal correctly stated, the two are electrically identically.
Yeah, it doesn't matter. It's a parallel circuit with low impedance path to speaker and high impedance path to the plate amp. Doesn't matter if you "sample" the output voltage at amp terminal or speaker terminal. Any voltage difference at the speaker terminal versus amp terminal due to speaker cable impedance will be negligible.
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