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Quote:
Originally Posted by Kevio
Here's the math.
If you are feeding a 10 kohm input from a 1 kohm output, you'll experience a -0.8 dB attenuation. If you feed two 10 kohm inputs in parallel, attenuation is -1.6 dB. Both inputs will experience the same attenuation so no balancing is required - just turn it up 0.8 dB to compensate. I don't believe anything is overloaded or even straining in this scenario.
10 kohm is a typical minimum input impedance (actual input impedance up to 100 kohm or even 1 Mohm for op amp circuits is fairly common)
Output impedance on line outs for most modern equipment is 50 ohms. A 600 ohm standard was used on older equipment. The 1 kohm output impedance on your distribution amplifier example is unusual.
Thanks, but I didn't mean that part. I just meant that I didn't notice the Adcom specs worked out to 1:100 when I brought up the 1:10 rule.
Quote:
Originally Posted by markw
I incorrectly attributed that1:10 ratio to Pix when I should have given you the credit.
Mea maxima culpa.
No apology necessary. But thanks for the thought.
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you guys are really audio savy. You guys have your P.H. Ds in audio technology
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If anyone is still interested the problem was definitely phase. Just switching the cables left/right going to the sub input cured the problem. I really didn't realize the cables going into the sub made any difference.
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Quote:
Originally Posted by markw
Keep looking. I'm sure that somewhere you'll find one of the items under discussion that is an exception to the rule, but wouldn't that simply prove it?
You told me to give you some example, so I did. I admit that they are not amp or pre amp, but they are still products that might be utilize in an audio chain. So audio products with low input/output ratio do exist and can’t assume that everything have high ratio.
Even if we assume that voltage output will be alright, you still can not get around the disadvantages of shorting two inputs together via Y cable.
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Whatever you say, old man.
Quote:
Originally Posted by Smokey
You told me to give you some example, so I did. I admit that they are not amp or pre amp, but they are still products that might be utilize in an audio chain. So audio products with low input/output ratio do exist and can’t assume that everything have high ratio.
Even if we assume that voltage output will be alright, you still can not get around the disadvantages of shorting two inputs together via Y cable.
Sorry, guy. No-one "assumed" anything. We were talking specifically about preamps, power amps, and powered subwoofers. Why you brought them into the discussion is beyond me.
As long as it makes you happy to think this rationalizes your posts here and think it makes it appear that you knew what you were talking about, then you just go right ahead believing it, I think you're the only one that buys it, though.
But, what I do notice is that you have no qualms about jumping in feet first with your dire proclamations when disagreeing with someone, yet when confronted with incontrovertible evidence of your own errors, you try every trick in the book to try to justify your stance and try to weasel out of admitting you blew it.
That just makes you look worse than simply admitting you made an error and moving on. How can one NOT question your grasp of the subject matter at hand when rather than learn, you choose to fight to justify your incorrect beliefs?
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We're always interested in solutions.
Quote:
Originally Posted by Mr Peabody
If anyone is still interested the problem was definitely phase. Just switching the cables left/right going to the sub input cured the problem. I really didn't realize the cables going into the sub made any difference.
I'm glad it worked out. Perhaps I misread something but I really can't see where switching the cables R/L would make a difference, but I'm glad it did.
Now, that's another item for the checklist for solving subwoofer problems.
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Swapping left and right cables should make no difference. Either you've changed something else, your subwoofer has an unusual or defective input circuit or the placebo effect is in play.
The subwoofer should just mix the two line channels, pass the result through a low-pass filter and on to the internal amplifier and speaker. This is a symmetrical signal path with respect to left and right.
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Quote:
Originally Posted by Smokey
Even if we assume that voltage output will be alright, you still can not get around the disadvantages of shorting two inputs together via Y cable.
Connecting two inputs to a single output using a Y cable does not create a short circuit. You're perhaps confusing that with connecting two outputs to a single input.
If for some reason you don't want to use a Y cable when sending a single to multiple places, your alternative is to use a distribution amplifier. But be aware that a distribution amplifier actually has a Y cable on its circuit board. The legs of the Y connect to individual amplifier stages which isolate and drive the outputs.
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I think I'd know if I changed something else, and I didn't.
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Quote:
Originally Posted by markw
As long as it makes you happy to think this rationalizes your posts here and think it makes it appear that you knew what you were talking about, then you just go right ahead believing it, I think you're the only one that buys it, though.
To tell the truth, I did search Internet to support my arguments but did not find any. That just show you how much good information is on the net :D
But I still be weary of shorting two low noise, high dynamic inputs together.
Quote:
Originally Posted by Kevio
If for some reason you don't want to use a Y cable when sending a single to multiple places, your alternative is to use a distribution amplifier.
Thanks Kevio
Have an old equalizer laying around that have monitor output, and use that if need distribution. I just keep all of audio adjustments at 0 dB.
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Well, I'm glad this is over with.
Quote:
Originally Posted by Smokey
To tell the truth, I did search Internet to support my arguments but did not find any. That just show you how much good information is on the net :D
I respect you greatly for admitting that. Some things are de facto standards and can pretty well be relied upon. It makes our life much easier.
Quote:
Originally Posted by Smokey
But I still be weary of shorting two low noise, high dynamic inputs together.
It's not considered "shorting" inputs. It's considered "splitting" an output and you can put your fears to rest. Splitting one output into two inputs has been done with no ill (real-world) effects for as long as "Y" connectors have been around. In fact. that's WHY they are around.
Now, had it been two outputs into one input, then you might have a problem. Ask Hyfi.
Now, let's go get a beer.
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As I once stated this is an old sub, it's one of those that requires both left/right input to have a signal to run at it's full power, so I have confirmed both by accident and reliable source that the cables being switched can indeed cause a phase issue with the main speakers.
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Does the reliable source offer any technical explanation as to why swapping left and right cables would make a difference?
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Quote:
Originally Posted by Kevio
Does the reliable source offer any technical explanation as to why swapping left and right cables would make a difference?
"This question is more complex than an initial analysis would lead you to believe.
1. A single sub needs to add left and right channels together to get the full output. If left and right are out of phase the sub ends up subtracting instead of adding the signals, leading to a significant loss of bass,
2. The acoustic phase of the sub woofer needs to match the acoustic phase of what is now a midrange driver. Again this assures the acoustic output of the sub and midrange are in phase and that they sum together at the crossover frequency. Many subs contain a true sub to midrange crossover, often the low frequency of the mid is raised by this circuit reducing he work being done by the mid."
Now that I reread this I'm not sure if, subtract=out of phase. But this is what happens when drivers are out of phase. I also got to thinking if I was correct this should be repeatable. So I went and switched the cables back again and you couldn't really tell the sub was on, this was at a moderate volume of the preamp, then when I switched them again the low filled in. So it is a repeatable condition. This may all be moot as this sub is about 20 years old. I was really impressed a few years back at the new features on subs.
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OK, now my reliable source came back and says he agrees with you all that switching the cables wouldn't put the sub out of phase but I'm not convinced he understands the set up I have. My preamp channels are even so what could cause this condition?
Maybe I should clarify, the sub is NOT Y'd, it is receiving left/right signal from preamp. The Y just takes left/right to power amp. So left preamp channel is split to sub and amp, then same for right. So if the left/right to sub was opposite left/right to amp it shouldn't make a difference?
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Try stuff
No clue at this point. When I get stuck on a problem, sometimes I find it helpful to just try stuff, not with an aim towards solving it but just to collect more information that might lead to a bright idea. I'd try running the sub with only left or only right connected to it (and turn up the volume to compensate). I'd try flipping the cables to the power amp. And you're not gonna like this suggestion but, I'd try asking someone else to flip or not to flip the cables and verify that you can reliably tell the difference without being told how it's connected.
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Quote:
Originally Posted by Mr Peabody
OK, now my reliable source came back and says he agrees with you all that switching the cables wouldn't put the sub out of phase but I'm not convinced he understands the set up I have. My preamp channels are even so what could cause this condition?
Maybe I should clarify, the sub is NOT Y'd, it is receiving left/right signal from preamp. The Y just takes left/right to power amp. So left preamp channel is split to sub and amp, then same for right. So if the left/right to sub was opposite left/right to amp it shouldn't make a difference?
It depends on whether or not the sub has a true crossover. If it's a true crossover then the low end of what was the bass and is now the midrange will be controlled by the circuitry in the sub woofer. In other words, the sub has a high pass to drive the original left/right main speakers.
By using a "Y" adapter, an unmodified signal is fed to the left/right mains, this raises the possibility of incorrect acoustic sums in that portion of he spectrum where both sub and mains contribute to bass output. By feeding the mains from a signal derived in the sub woofer electronics the only remaining question will be absolute phase. Does the left/right main amp invert or not? Most good subs will havea polarity switch to solve this problem.
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In Mr. P's configuration, signals are only being delivered to the sub. There's nothing connected from the sub back into the system.
Since there's no HP on the mains, there's going to be problems with bass response as the mains and sub fight with one another in the acoustical space (i.e. there will be places and frequencies in the room where it sounds better than others).
We're looking for an explanation as to why swapping the L and R cables to the sub fixes all of this or even changes it at all.
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Quote:
Originally Posted by markw
When you combine two chanels into one with a simply "Y" connector, the entire signal is mono. ...not just there, but anywhere else in the signal chain.
Think of a long wire. Connect them in the middle. They are joined for the entire length, not just on one side of the join.
You need something that will combine two channels into a common mono channel and yet maintain the two original channels.
Something like this : http://www.nextag.com/Nady-CX22SW-2-...78/prices-html. While the crossover portion may seem redundant, I can't find a standalone combiner.
I just got off the phone with Bob from RHB Sound Dezign, who just completed the repairs and re-tubing of my recently acquired Counterpoint NPS-400 and asked him about this issue. He told me in most cases, the low level bass that would get sent to the sub is usually in both channels and only using 1 of the Pre outs should allow the sub to perform OK without combining both channels to mono. No Y needed.
I,m going to test it out tonight if I feel I still need a sub after dropping in the Counterpoint.
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