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  • By pass caps?

    What do by pass caps do on a speaker xover? I just watched a video on it but want to know others opinions.

  • #2
    Don't listen to me - I have not sold any $150,000 speakers.

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    • #3
      Can open.........worms everywhere.

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      • #4
        Regardless of whether it actually works or not...what is the bypass cap supposed to do, according to those who would argue for one?

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        • #5
          Nothing starts an internet flame war better than something whose effect can't be measured, but people swear they can tell the difference.
          Isn't it about time we started answering rhetorical questions?

          Paul Carmody's DIY Audio Projects
          Twitter: @undefinition1

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          • #6
            Keep in mind that I'm NOT very experienced with any of this. This is mostly just parroting what I've been able to find/read so far.


            The hope is to get some of the qualities of Poly or Foil capacitors while keeping the size/uF and price benefits of NPE capacitors when they're together parallel.

            Some things that people might be aiming to avoid (or bypass) are ESR and inductance.
            Some of the controversy comes from how much benefit or difference you'll realistically gain....for example, ESR (the resistance of a capacitor that's often not listed in specs) is very frequency-dependant. NPE capacitors will have higher ESR/resistance at lower and lower frequencies and larger uF capacitors will have less ESR/resistance and it'll start climbing at far lower frequencies. This makes ESR much less of an issue because it naturally occurs in frequencies below where you'll likely use the capacitor anyway. It's a difference, but it typically happens where you won't notice much or possibly at all.

            I'm also unsure how effective a smaller bypass capacitor will help when its smaller value naturally impedes lower frequencies more effectively than the larger capacitor it's paired with...so I'm doubtful of how much help a 1/10'th size bypass cap would offer against ESR at low frequencies a ways below the XO point when the smaller bypass capacitor naturally wants to block those lower frequencies as much or more because of its low uF value.
            A bypass cap should still help against ESR at higher frequencies, but this is often less than 1ohm even without the bypass, so the difference is very small and too little for most people to hear.

            Inductance, on the other hand, should still be quite tweakable with a bypass capacitor. That said, I don't know how much inductance is typical for larger or smaller NPE caps. I also haven't been able to find/read whether NPE typically has higher or lower inductance compared to poly or foil (though it also looks like different build/styles of higher-end caps can have different inductance values via different design tweaks).

            Would really help if PE listed the inductance and maybe a graph of ESR for their PE/Dayton capacitors.
            In many cases these traits aren't inherently "goodVSbad", but simply something you can plan your build around when you KNOW they're there. Which would be a LOT easier to do if they were more commonly listed in the specs!
            My first 2way build

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            • #7
              There are also arguments out there that the ESR is reduced in that leg of the crossover - the theory goes that since net resistance is always something less than the lowest value of any two components in parallel, adding a small resistor with very low ESR results in very low net ESR. Since most people use a LIMP jig or a DATS, it is difficult to actually verify ESR - much less confirm audibility.

              There are also compelling arguments that paralleling two capacitors that are not the same value/type actually degrades the sound. I can't remember the physics behind that, but I'm sure somewhere on DIYAudio there is a 9,000 page thread talking about it.

              Don't listen to me - I have not sold any $150,000 speakers.

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              • #8
                To answer the OP's question directly, bypass caps make some people happy. They believe, correctly or incorrectly, that the sound is improved. It is very difficult to justify any improvement electrically, but hey, it makes them happy.
                Francis

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                • #9
                  The technique is a way to save money on crossover capacitors in the networks that you build. What you do is you use a less expensive capacitor for most of the value of the crossover capacitor. Then you buy an expensive but very small, say 1 mF, capacitor and you use that to "fill out" the value of the capacitor. The "built" capacitor supposedly takes on the better sonic characteristics of the small value better capacitor.

                  Originally posted by daryl View Post
                  Re: Uncharted Crossover Design Waters

                  Bypassing has it's roots in power supply rails for equipment where low impedance is required through the radio frequency range or at some distance from the main capacitor bank where the inductance of the supply line necessitates additional local capacitance.

                  At radio frequencies a large capacitor becomes an inductor or at least the supply line will if the large capacitor isn't right near by a critical point for an active circuit.

                  A small capacitor in such an aplication will become the controlling element providing a low impedance point for your circuitry.

                  At audio frequencies for the purpose of a speaker crossover all capacitors are always in their range and behaving like capacitors.

                  Even the infamous non-polar electrolytic capacitor performs far beyond the capability of the best drivers.

                  The difference between film capacitors and non-polar electrolytics is measurably dramatic but when you build them into the speaker the performance is dominated by the characteristics of the drivers and the capacitors become insignifigant.

                  A bypass capacitor in the limited audio range simply contributes to the circuit in the same ratio in which it is implemented.

                  That is if your bypass capacitance is 1% of the total for the main and the bypass then the bypass capacitors characteristics are contirbuting 1% to the circuit and the main capacitor is contributing 99% of it's characteristics.

                  So if you use a non-polar electrolytic capacitor for your main capacitor and even though it's performance is beyond that of the best drivers in the world you decide to bypass it anyway with 1% of the total capactance coming from some type of film capacitor, then the difference will simply be a mere 1% of the way along the line between the performance of the non-polar electrolytic and the performance of the film (99% of the performance being determined by the non-polar electrolytic).

                  Should you increase your bypass to 10% of the total then you simply have 90% of the capacitor performance being determined by the main capacitor.

                  In a crossover filter a bypass capacitor always is a minority element while the main capacitor has near total control of the circuit.

                  Another misunderstanding in audio is that crossover componets do not influence the circuit most at high frequencies.

                  You've heard it said a million times that in the top octave is where you really hear the clarity or sweetness or what ever BS with a certain capacitor.

                  Truth is that crossover componets have their greatest influence near the corner frequency of the filter created with them (crossover frequency) where their impedance is comparable to that of the circuit.

                  As you get further from the a filter's corner frequency the impedance of crossover componets will go very high or very low and their influence over the circuit becomes less and less (the componets effectively are removing themselves from the circuit as you get further from the filters corner frequency).
                  https://techtalk.parts-express.com/f...243#post322243

                  All of that being said, for a few bucks extra I tried it on the last crossover I built and I honestly couldn't say if it does or doesn't improve things - I couldn't really hear a difference.

                  I do think there is certainly an area of acoustics and human perception that isn't currently covered by science/available to measure. For instance its only relatively recently that the ear/brains equivalent "sample rate" capability is understood proving that it is possible at some level for us to at least perceive a "difficult to explain" difference between analogue and digital source material - proving that all those early 'nut jobs' who thought they could hear a difference correct. (explained really well here: https://www.youtube.com/watch?v=r_wxRGiBoJg&t=163s)

                  And I'm also conscious of the fact that there is a lot of advise given that, should it be taken in its entirety, as a sum total, would result in the worlds crappiest loudspeaker. One expert says caps don't matter, you cant measure the difference, use electrolytic everywhere, another says use any old wire - science says the copper in your power point is perfect, another says cabinet construction doesn't matter use 1/4 inch everywhere with a few braces, another says any driver costing over 30 bucks is a waste of money...and so on and so on, each piece of advise coming from a "seasoned veteran". I wouldn't want to be in the same room as the resultant speaker.

                  At the end of the day, just use the best quality caps you can at a cost point that makes sense for the overall investment in the speaker. My philosophy is that a speaker is as good or bad as the sum total of its flaws and compromises. But I'd say bypass caps aren't going to add any noticeable benefit.
                  Last edited by DeZZar; 06-25-2021, 08:54 PM.

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                  • #10
                    Originally posted by Paul Carmody View Post
                    Nothing starts an internet flame war better than something whose effect can't be measured, but people swear they can tell the difference.
                    This can be measured. If the lower ESR of the bypass cap has an effect it will show up in the frequency response. Of course you'd have to go to the trouble of measuring the result with an NPE and then measure it with a smaller NPE plus a bypass that results in the same total capacitance. What's pertinent about those who insist that they can tell the difference never provide the measurements that would prove it. But for that matter those who insist that you can't tell the difference don't provide measurements either.
                    www.billfitzmaurice.com
                    www.billfitzmaurice.info/forum

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                    • #11
                      I did a little bit of searching for capacitor inductance information but couldn't find much. Does anyone have advice or experience or a link with some information (even just rough information or averages) about the typical inductance you can expect to see from NPE VS poly VS foil caps, and/or typical inductance differences you might expect from larger VS smaller cap uF values?

                      Do some types (NPE/poly/foil) or some sizes/values tend to have negligable inductance while others have significant amounts?

                      Is it common to expect up to 0.05mH+ from some types and uF values or is it more of a golden-ear thing or even just a radio frequency concern?
                      My first 2way build

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                      • #12
                        Wow great info guys thanks, I just didnt know bypass caps were this controversial like speaker cables. I just watched a vid of someone mentioning by pass caps and explaining why he used it in his crossover design. I also thought that these caps wouldnt have a specific name but P.E. calls them bypass caps.

                        I am going to try some 0.1uf film foil by pass caps and wire them parallel to my 125uf NPE caps to see if it makes a difference as they are only around a buck fifty each.

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                        • #13
                          Originally posted by Unbiasedsound View Post
                          Wow great info guys thanks, I just didnt know bypass caps were this controversial like speaker cables. I just watched a vid of someone mentioning by pass caps and explaining why he used it in his crossover design. I also thought that these caps wouldnt have a specific name but P.E. calls them bypass caps.

                          I am going to try some 0.1uf film foil by pass caps and wire them parallel to my 125uf NPE caps to see if it makes a difference as they are only around a buck fifty each.
                          I would try something around 1uf. Not saying it will be audible, but it couldn't hurt. Something like this...https://www.parts-express.com/Jantze...acitor-027-261

                          Your 125uf cap is probably plus or minus 10uf, or more. Adding 1uf should have negligible impact on the xo region, If it changes for the better on the top end, then enjoy the improvement. If you hear no difference, add the caps to your parts box. The .1uf caps can be quite handy too.

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                          • #14
                            I tried Cornell Dubilier 940C 0.01uF 500Vac which this guy raves about here http://www.humblehomemadehifi.com/Cap.html.

                            Tony Gee must be able to hear ants fart to write the stuff he does comparing caps so I take all this with a pinch of salt.

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                            • Unbiasedsound
                              Unbiasedsound commented
                              Editing a comment
                              THanks for the link.....In your opinion which cap on that site do you think is the best?

                            • DeZZar
                              DeZZar commented
                              Editing a comment
                              I certainly don't have any personal experience with the greater majority of caps shown here but so far I don't think there is really any substantial justification for spending any more than the Jantzen Superior Z. And depending on the kind of speaker you're building (overall budget etc) I've been very happy with the standard z cap and cross cap depending on where it's used.

                          • #15
                            Originally posted by rpb View Post

                            I would try something around 1uf. Not saying it will be audible, but it couldn't hurt. Something like this...https://www.parts-express.com/Jantze...acitor-027-261

                            Your 125uf cap is probably plus or minus 10uf, or more. Adding 1uf should have negligible impact on the xo region, If it changes for the better on the top end, then enjoy the improvement. If you hear no difference, add the caps to your parts box. The .1uf caps can be quite handy too.
                            Ok thanks I will try that as I already have that exact Jantzen 1uf standard Z cap.

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