Using Bypass Caps in Speakers

Discussion in 'Speakers' started by shacky, Jan 14, 2008.

  1. shacky

    shacky Addicted Member

    I just used 0.1 uF Dayton film bypass caps in my EPI 201 project and am very happy with results. These were not well functioning before my resto so can't make A/B comparisons (and they would be from memory anyway).

    I used the bypass because of a suggestion from somone at another forum for a NLA project I was doing a while ago. He told me the following in regard to adding the bypass to NLA:

    "The 0.1 uF cap reduces hysteresis in the electrolytics and therefore, distortion."

    Can someone explain the theory in simple terms?

  2. shacky

    shacky Addicted Member

  3. avguytx

    avguytx AK Subscriber Subscriber

    I can't get too technical about it but using one along with a cheaper electrolytic (or poly, etc) will impart some of the better caps characteristics. They were used in a lot of speakers thru the years. I've had 3 pairs of Polk SDA's that I rebuilt the crossovers in that used 750pf bypass caps on the electrolytics. When I rebuilt the crossovers with new Solen poly caps, I didn't use bypass caps...not needed. But, as anything, it's personal choice.
  4. dshoaf

    dshoaf That high voltage buzz Subscriber

    I believe this was a JBL quote that I've seen floating around on various forums but was taken out of context. I've got a mid-80s JBL Technical Note on the 4425/4430 Studio Monitors discussing the use of bypass caps that uses a similar phrase but offers no specific reasoning - I see the quoted phrase as much marketing fluff as anything else. BTW, I've had 4425s and they, indeed, had 0.01mf bypass designed into the crossovers.

    If you're interested in discussions about the bypassing of capacitors used in crossover networks for speakers, I'd suggest you Google around a bit to find _plenty_ of discussions that, I found, lead to nowhere in particurlar. It is much like discussions of relative merits of various wines, IMHO, as everyone has an opinion. I've bypassed caps in some crossovers during rebuilds but haven't hear much difference with or without them.

    I could buy into the idea that capacitors today used for crossovers are of better quality and made with more understanding of the effects of materials like film, mylar, and electrolyte paste have on them. And that most caps today are spec'd at closer tolerances than in decades past. For these reasons, I could understand why this technique isn't really needed like it might have once upon a time.


  5. Zilch

    Zilch Curve Junkie Subscriber

  6. Snade

    Snade humble AK member

    I recently recapped my JBL Decade L26 speakers with a Solen 8.2uF cap and a Theta 0.01 bypass cap.

    I think the majority view is the Solens do not benefit much from a bypass because they are such good caps. And some think the Dayton is just as good as a Theta for bypass and is cheaper.

    All I can say is the spaciousness and detail in the old JBLs is greatly improved. The total cost for the caps was 20 bucks and I think this is one of the best investments I've made in my vintage gear. These speakers play big and sound beautiful.

    Cheers, Snade
  7. FalconEddy

    FalconEddy Audio Mastering Engineer

    Here's some general information on an article I wrote last year about using bypass capacitors in speakers:

    In order to make a noticeable difference in a speaker application when using a bypass cap, you really need to find the right value bypass cap to use in parallel with the larger value cap.

    Bypass caps work in this type of application by adjusting certain issues within the component(s) it's bypassing. If you're using a simple crossover using a first-order high pass filtration design, you adjust the crossover point(s) by using a certain value capacitor to achieve the desired crossover frequency. The lower the capacitor's value, the higher the crossover point.

    However, since many larger value capacitors have so many feet of tightly wrapped foil in them, you've now introduced a small level of spurious inductance into the equation. Even a tiny amount can sometimes be noticed since it appears as a small percentage of 90° out of phase in the circuit.

    Two things you don't want to introduce in a simple first-order high pass filtration design, are inductance and additional resistance. This limits a percentage of the actual capacitance ability in the higher frequency range.

    Adding a properly sized lower value bypass cap in parallel with the larger cap allows this combination to appear to have a much lower value of spurious inductance. This partially cancels the unwanted spurious inductance effect and will allow a much higher percentage of upper range frequencies to reach the speaker. Thus, allowing the larger capacitor and it's bypass cap to work more efficiently at the higher frequency ranges above the crossover point it's controlling.

    This effect will generally be more noticed when employing this bypass technique with a lower quality main capacitor.

    When properly sized, it lets through the slight amount of 'air' it's designed to handle; but, improper sizing can sometimes create unwanted harshness.

    . . Falcon
  8. analog addict

    analog addict Glory or Death! Subscriber


    now that you've teased us....:D

    How do you determine the right value?

    Is there a formula????:scratch2:
  9. spkrdtr

    spkrdtr spkrfixer Subscriber

    "...How do you determine the right value?

    Is there a formula????

    Analog Addict"...

    I believe the rule of thumb is use something in the range of 1% to 10% of the primary cap value.
    An old North Creek Music white paper on bypassing recommended cascading the bypass caps in gradually reduced levels of uF. However, I think that was a try at selling more caps.
  10. spkrdtr

    spkrdtr spkrfixer Subscriber

  11. pat5jfet

    pat5jfet New Member

    Every cap is also an inductor, ever measure the inductance of a large cross over cap (10 mfd)? It is there and it is in your crossover. Every resistor (especially the wire wound in cement) is also an inductor. So we are in some delusion if we think crossover designs really work exactly the way the math states.
    Parallelling smaller caps to acheive a value is one way to reduce inductance.
    Bypassing nonpolar crossover caps with high end caps does help to contain the sonic nasties. They seem to take on the flavor of the smaller cap. Modifing the values of the bypass cap can also help to zero in on a specific value of the crossover cap for both speakers. Nonpolars can be 10 to 20 percent off spec.
  12. photoman2

    photoman2 Member

    Where can I order the better caps? I have a pair of old Infinity RSb's and a set of RS 2001's I would like to do .. I also have a set of newer Advents Floor standing speakers that could do better with a upgrade..
    There Advent AS2'sAny good url? Any god post's for a specific modding of the crossover in any or all of these speakers.. Thanks! George
  13. tarior

    tarior Dirty pool, old man?

  14. Zilch

    Zilch Curve Junkie Subscriber

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