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In Reply to: RE: Need assistance..... again!!! Thanks posted by atanks on September 21, 2012 at 17:37:33:
That bit of flattery towards my eccentric art design will gain you nothing but...applause from my wife. LOL
Anyway, here's a bit of basics in layman terms. I stay away from theory and math formulas...except myself for the initial phase of a design. After that, I can measure the actual results and listen. So, I can tweak up or down in values as close to reality as practical.
You are not being asked to measure because you can test/tweak values and evaluate with your ears if we get you close enough. That's why a prototyping rig may work best for you at first. It allows to quickly and easily change components. So here we go, in terms that are going to get me in trouble with the hardcore tweakers...
Resistors (alone) resist or impede all frequencies equally. Capacitors do a few things. Among them, they react to frequency variations. (Inductors do, as well, but are not useful for a role IN HERE). When resistors and caps are used in a circuit segment in certain manners, it may be called an "RC" segment. There are formulas for their joint behavior and these are affected by adjoining values. Thus, in calculating our RC filters, at least the input impedance value of the power amp is also required. That's what Neo did. He looked up the input impedance for your Emotiva.
The filter design that we showed you, by mistake, is a low pass filter. It will allow lower frequencies to pass on to the power amplifier but progressively attenuate or block higher ones after a certain point. This is the role of the capacitor. For any given value, it will favor higher frequencies and oppose lower ones. In this design, the attenuation slope, or curve, achieved is 6db/octave after a certain point. It is also called a 1st order slope.
In oversimplified practice, the resistor is just a qualifying or adjusting value. As far as frequencies, it lets EVERYTHING pass on equally, albeit somewhat attenuated depending on the value that was selected.
Yet, as soon as the signal hits the output side of the resistor it is "offered" a choice other than going to the power amp. The higher frequencies "see" less resistance if they take the route via the capacitor. The higher they are, the less resistance they see. So, SOME of it takes that route...and it gets "dumped to ground". They don't reach the power amp. Again, I am oversimplifying.
If you were building a PLLXO, this would be the most basic configuration for a low pass that would drive the woofer, for example.
OTOH, what we should have drawn & made for you, is a high pass filter. This one is the reverse of the previous. It will favor higher frequencies and "progressively" block lower ones from reaching the power amp.
The simplest form of it is, guess what?...a single capacitor in series to the signal path. It attenuates/blocks low frequencies and allows higher ones through, just like it did before. Except that now they are going to the power amp. Its proper value is still mainly qualified by the power amp's input resistance and if used, a qualifying resistor going to ground.
This resistor "dumping to ground" (like the cap does in the drawing) may not be needed in some cases. If a resistor is used in such segment, it is still a qualifiying value because we use the resistor to adjust the behavior of the joint components.
That's why I said that the same design we drew/made can be altered easily. If one swaps the positions of the cap and resistor in the circuit, it becomes a high pass filter.
The beauty of it is that, in some cases, a single good cap can do the trick. A high pass is what would normally be used for a tweeter. For example, as part of a PLLXO xover that includes a high pass and a low pass filter combo. A single cap could send anything above, say 3000hz to the tweeter and attenuate/block frequencies below this point.
Yet, in your case, it would affect THE WHOLE speaker. What we are doing is to "tune" the values so that a HP filter will allow all frequencies after, say, a nominal 80hz to go through. Anything lower than 80hz would be backwards-attenuated at a rate of 6db/octave. So, at 40hz the signal would be 6db lower. At 20hz, 12db lower.
This is the basic concept. There are implications, both good and bad. Nothing is free of trade-off in the electronics world. Luckily, the worst case if it doesn't work...is that you spent a few "fun bucks".
Well, also that you still get the pleasure of us boring you to death.
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Follow Ups
- RE: Need assistance..... again!!! Thanks - JBen 20:49:01 09/21/12 (1)
- RE: Need assistance..... again!!! Thanks - atanks 11:47:42 09/22/12 (0)
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