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RE: Need assistance..... again!!! Thanks

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JBen

In Reply to: RE: Need assistance..... again!!! Thanks posted by neolith on September 18, 2012 at 18:07:59

Thanks, Neo. I meant low pass "section" of my setup, not the function of this filter itself which is a high pass, as you well indicate.

In my case, this particular HP filter affects only the low pass of the bi-amp. It is in series at the input of and tuned to this 2nd order low pass. The HP filter for the tweeter is separate.

However, in Atank's case the high pass filter we are talking about would affect the full panel, meaning both drivers. The big question would be if this could be enough for Atanks needs. In my case, I boosted the low end "acoustically", and then I lowered it back down with the filter. Thus, I was able to start much higher up than 80hz.

By starting higher, the shallow 1st slope removes more of the very bottom bass signal under 40hz while achieving a near parity where I wanted it further up (because of the acoustical compensation).

If Atanks starts with 80hz, 6db down at 40hz may not be enough for his purposes...then again, it could be. Perhaps he can also test adjacent values up from 80hz? The acoustics in his room may make a contributing difference, which partly happened in mine.

Failing the above, I guess he would need an active filter to support sharper slopes, something that I have contemplated but keep avoiding, for now.

In any event, it is inexpensive to try the passive approach with small-value caps, and quite easy. For resistors, the PRP have turned out to be the ticket to transparency in this kind of line-level application and cost for this top resistor quality is no issue from the start.

Follow Ups:

RE: Need assistance..... again!!! Thanks - neolith 05:36:28 09/19/12 (0)
Thanks for the clarification. I agree about the PRP resistors and I remember that Al Sekela recommended them for the Zoebel to eliminate RFI. I found that the Rel-cap RTE film caps (polystyrene-tin) work very nicely for PLLXO's.
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RE: Need assistance..... again!!! Thanks - atanks 05:32:53 09/19/12 (10)
Thanks NEO, JBEN
It is unbalanced. Now to accomplish this i would need a "for dummies" explanation/diagram. Im an AUDIO INFANT just born this year and already have the fever. I know what i like and dislike but dont know how to "fix" it. Definetly appreciate the help!
- RE: Need assistance..... again!!! Thanks - JBen 10:44:52 09/19/12 (8)
  Ok, I see that Neo included the schematics. Check to make sure that you understand this. Don't be afraid to ask if you don't understand.
  
  When I get home this evening, I'll try to do a "simplest prototyping rig" with whatever I have at hand and take a picture.
  
  Can you do basic soldering or should I try to avoid it for now?
  - RE: Need assistance..... again!!! Thanks - atanks 13:21:56 09/19/12 (7)
    Simple is better, thanks! Im outta my league at the asylum right now but soon with all the help i have been getting here (thanks again, everyone) I will learn enough to help someone else one day. I can solder pretty easily. I dont mind spending a few bucks to get good parts. I can wire a house with my eyes closed but havent messed with electronics much. I can put something together but dont yet understand how it works or what each thing actually does. Some years ago i designed parts for a manufacturing company using Autocad (self taught)and can read fabrication prints because i was familiar with the symbols and meanings but with electronics im just not familiar with it. I scratch my head and say now whats that squiggly line that looks like Charlie Browns hair??? :^))
    - RE: Need assistance..... again!!! Thanks - JBen 00:22:43 09/21/12 (6)
      Ooops! I thought I posted it last night but it was left in preview instead.
      I put this filter rig together very quickly in just one of several possible manners. There are other types of connectors, including project boards at Radio Shack. I just happen to like these bars because they can "sound" like a final assembled set. Thin wires do need to be checked for proper contact.
      The completed filter assemply should be placed/wired closest to the power amp.
      This is a top view of the "quick filter rig" no solder. Input is the Right side. The parts values are random, for illustration purposes only. Just one channel is shown. The second one can be added right next to it on the same connector bar. The RCA cables, in this case, are female. They were cut from a perfectly good "Y" just for this. You can choose other options for cabling. In electronics, "RED" is the "+" or signal. Black, white or other colors are used for "-" or ground. Yes, those are rubber bands holding things down. BTW, do mind the "base"...I used the top of a project box but a more solid object, like a piece of wood, is better to avoid resonances.
      
      This is my burn-in rig, which at times also serves as a quick prototype set. In this case, I had received 2 more new Dynamicap E caps for the low pass and I placed all (new and old) configured properly to burn in together. Dynamicaps are great but are among the slowest caps to break in. This set spent 2 weeks hooked up to a separate CD player & power amp (no speakers). The CD has music and pink/white noise mixes looping 24/7. The final circuit is placed in a box later and that box set also gets at least 24 hours of burn in (to cure any new solder joints quickly.)
      
      Edits: 09/21/12
      - RE: Need assistance..... again!!! Thanks - atanks 05:55:31 09/21/12 (5)
        
        In Reply to: RE: Need assistance..... again!!! Thanks posted by JBen on September 21, 2012 at 00:22:43
        
        Thanks Alot! OK so i can easily see how to do this. I can vizualize making it look nice in a box also. Now , what is the resistor and caps actually doing. If i understand whats going on behind the scenes i can try differ values. The higher the number equals? The resistor does what? The caps are for Etc... Etc...? Lety me get this right, this "filter" works by lowering the db on 80hz down(if the cap/res are for that value)? So in order to fix the problem area i try differ cap/res values to "target" the problem area? The problem area can be found by measuring along with listening in other words i can hear the problem but dont know if its at 90,80,70hz etc..? Sorry for all the questions but i really want to learn.
        
        RE: Need assistance..... again!!! Thanks - JBen 16:59:28 09/21/12 (0)
        
        In Reply to: RE: Need assistance..... again!!! Thanks posted by atanks on September 21, 2012 at 05:55:31
        
        Bummer! I just got home and looked at the beautiful contraption that I built...scratching my head...and suddenly it hit me.
        
        It seems like Neo and I have to stop drinking this same cheap tequila stuff. We both know that what we really want is a high pass filter, right? Yet, we made a low pass. The whole thing may be even simpler for you, or just about the same by swapping the cap & resistor positions.
        
        'be back later...switching to the cheap vodka and advising Neo to do the same. : - ))
        
        RE: Need assistance..... again!!! Thanks - JBen 14:52:11 09/21/12 (3)
        
        In Reply to: RE: Need assistance..... again!!! Thanks posted by atanks on September 21, 2012 at 05:55:31
        
        Atanks, re your: : "I can vizualize making it look nice.." Are you implying that this is not beautiful art! LOL
        
        I am just passing by. I'll be back in the evening when I get home.
        
        RE: Need assistance..... again!!! Thanks - atanks 17:37:33 09/21/12 (2)
        
        In Reply to: RE: Need assistance..... again!!! Thanks posted by JBen on September 21, 2012 at 14:52:11
        
        JBEN, I did not intend the "i can visualize" statement to offend you, but i must admit i would not want the looks of that thing to be seen by anyone that came over!!! :^))
        
        RE: Need assistance..... again!!! Thanks - JBen 20:49:01 09/21/12 (1)
        
        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.
        
        RE: Need assistance..... again!!! Thanks - atanks 11:47:42 09/22/12 (0)
        
        In Reply to: RE: Need assistance..... again!!! Thanks posted by JBen on September 21, 2012 at 20:49:01
        
        Thanks for taking the time to do that! Much appreciated!
- RE: Need assistance..... again!!! Thanks - neolith 08:33:33 09/19/12 (0)
  Check out my spreadsheet for PLLXO's which is written for LibreOffice (or Open Office) - free off the internet. It will allow you to calculate filters for other cutoff frequencies.
  Here's a schematic for a HP filter.
  
  It may be feasible to not use the series resistor (R) and use only the series cap. This is what Magnepan did with their XO-1 unit.
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  Edits: 09/19/12 09/22/12

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