Bypassing Caps - what is it really about?

https://components101.com/articles/decoupling-capacitor-vs-bypass-capacitors-working-and-applications#:~:text=The%20Bypass%20capacitor%20is%20used,spikes%20on%20the%20supply%20lines.

The main capacitors, or AKA "filter capacitors" in an amplfiier will together with the power transformer(s) influence sound quality overall, but most importantly have great impact on the level of clarity and transient response in fast-paced music; also important for resolving nuanced details in slower tracks.

So I’m not talking about bypass circuits. I’m taking about what hi-fi people call "bypassing a capacitor", which is running two capacitors in parallel, typically using a small value to piggy back the main value.

Larger capacitors act as inductors at AC frequencies. The larger the cap and the higher the frequency, the higher the "resistance" presented by the cap. This can impede or roll off frequency response (impedence). A small value cap across the large value cap allows those frequencies to pass. Kinda like overtaking a slower semi on a small road.

Larger capacitors tend to have higher inductance and dielectric absorption affecting higher frequencies the most.  Bypassing with smaller capacitor (creating alternative path at high frequency) improves overall performance.  It also allows to use cheaper main capacitor for cost reduction.  Huge electrolytic caps (with higher inductance)  in power supply seems to be ideal target for bypassing (speaker current closes thru them), but low ESR bypassing caps in parallel with inductance of main caps can create parallel resonant circuit.  Using many filter capacitors in parallel reduces overall inductance.  There are better, lower inductance "Slit Foil"  BHC (now KEMET) electrolytic caps, but they only go to about 80V and are expensive. 

noromance has it more or less. Bypassing caps has it's basis in good EE design, especially older but also best bang for the buck designs. 

Think of actual caps as a series of parts:

--> Capacitor --> Inductor --> Resistor ---> 

As the frequency goes up the cap no longer acts like a perfect cap and the inductance becomes a problem.  By bypassing this with the appropriate values of smaller, higher quality caps you can get maximum value for your money.  Imagine a situation when you need 100uF.  The cheapest option may be an electrolytic but may become inductive too soon.  So you buy a 100uF and bypass it with something pricier (per uF) but smaller, like a 2uF film or tantalum cap to overcome the internal inductance. 

The reality of audio gear however is complicated.  Sometimes a good bypass cap can help, sometimes it does nothing.  I like Clarity CMR caps a great deal, but at values larger than 4uF or so they do audibly benefit from a small bypass cap.  Below this value I've not found a bypass cap to help at all.  

I suggest you get a pair of Audyn TruCopper 0.1 uF film caps and experiment for yourself.  The argument of the value of bypassing or not is not ever going to be solved in an online forum. :) 

This is why JBL uses them. See below: page 3 see section High Resolution Dividing Network. 

Mike

https://www.lansingheritage.org/html/jbl/catalogs/1982-home.htm

Bypass capacitors in crossover circuits are, in my opinion, useless. The reason bypass capacitors are used is to lower the overall impedance at frequencies where the equivalent inductance of capacitors has the dominant impedance, which is above the resonant frequency of the capacitor’s inherent RLC. That frequency is way above the audio range.

If you take, say, an exact 10uF crossover cap and bypass it with an exact 0.5uF cap, all you have is one 10.5uF cap. However, if that 10uF cap has a tolerance of 5%, then it can have a 10.5uf capacitance on the high side. Which is exactly the same thing as the 10 plus 0.5 cap in parallel. So I don’t see what benefit piggybacking a cap does to a crossover.

In power supply circuits, the RFI can easily exceed the resonance of the filter caps. That is why bypass caps are used, to lower the overall impedance at those frequencies to shunt the noise to ground.

Thanks for the answers! I would not have intuitively thought about this because the caps I’ve used (Audio Note, VCap, Jupiter, etc) all seem to have fantastic high frequency sound, even if their ESR measures this way or that. (I kind of wonder what kind of person uses VCap teflon or Deuland silver and still doesn't hear enough high frequencies detail) 

I do have a 350uF industrial filter cap on the preamp plate, and that seems like a target for bypassing to experiment with.

Also, from reading articles from various "tone" guys. they seem to bypass based more on blending the sound of their caps. For example I’ve blended electrolytics on each wave of the rectifier, it seems strange each get a different brand of cap, but it did "split the difference" in sound...one Elna was too noisy, the other Kaisei was too intense.

The 10uF film capacitors we use behave like near ideal capacitors almost to 1MHz. Bypassing that capacitor with a smaller one is not going to have any benefit.

I am not an electronics expert, but I know speakers well. For crossovers, this bypassing of a large capacitor with a small one, from what I have read, often very small, sounds like an urban myth that became real.

The effect of a capacitor in a crossover is related to its impedance at the frequencies you need it to work. Others have mentioned the capacitive element and inherent resistance and inductance. A 0.1uF capacitor is going to have lower inductance than a 10uF capacitor, but the resistance may be high, and at the same frequency, the effective of capacitance is 1/100. That 0.1uF capacitor is not going to fix any perceived issue with the 10uF capacitor. Maybe a 1uF and a 10uF, but then you have a much different capacitor and perhaps a 10% change in crossover frequency. Maybe if you are using first order crossovers, bypassing an electrolytic with a film capacitor if the film capacitor is a significant portion of the electrolytics values could be beneficial in a shunt location, by preventing frequencies at say 10x the crossover frequency. I am clutching at falling straws at this point.

Maybe in an amplifier or pre-amp bypassing an electrolytic audio coupling capacitor with a small film capacitor will have a benefit over the full frequency range, but I will leave that answer to the EEs.

. For crossovers, this bypassing of a large capacitor with a small one, from what I have read, often very small, sounds like an urban myth that became real.

That's your problem right there.  Research without experience.  $40 in parts and a weekend is worth more than all of the Internet.

See that’s your problem right there. You confuse $40 in parts and a weekend with experience. I have been designing speakers for professional applications for the better part of 2 decades. When you lack experience, you may be able to convince yourself with $40 in parts and a weekend that bypassing a capacitor that is ideal up to nearly a MHz provides some benefit other than just changing the total value. I don’t have such a luxury.

Pick a large respectable high end speaker manufacturer. Magico, B&W (high end), Wilson. Do they bypass their large capacitors with much smaller ones? No. Could they afford it? At those margins, of course, small capacitors are inexpensive. Why don’t they? It will have no benefit. Do you honestly believe these companies don’t know any better?

My comment is specifically about crossovers. I will leave power supplies to those that know better, and the same for capacitors passing audio signals in amplifiers and other electronics.

That’s your problem right there. Research without experience. $40 in parts and a weekend is worth more than all of the Internet.

I can see a stuffy sounding vintage cap with poor high frequency transparency being bypassed by one that does to create some layering (?).

But that could create some weird situations - imagine caps which image poorly with a very mono sound, being bypassed in the high freq with a high fidelity cap. So the high frequencies image 3d dimensionally on top of an old low fi midrange? Or is that effect the goal? It could be interesting....?? 

When you lack experience, you may be able to convince yourself with $40 in parts and a weekend that bypassing a capacitor that is ideal up to nearly a MHz provides some bene

When you lack an open mind you may be able to convince yourself your measurements and models are always adequate.

Takes an open mind and discerning ear to realize when one or the other has fallen short, and this topic is impossible to argue online.  That's why I make suggestions to audiogoners to experiment inexpensively and come to their own conclusions.  Or they can listen to you stroke your beard and tell us nothing is left to be learned.

@clustrocasual ,

If you means capacitors passing signals in electronics maybe there are some effects. In speakers though, you have to look at the combined effect of the capacitor and driver. If I bypass a 100uF (was mentioned above) electrolytic with a 1uF, there is no benefit because where the 1uF starts to provide any benefit, the driver has no output.

Oh come on. Do you think with million dollar development budgets that we never listened to anything?  What do you think companies who develop speakers do? Listening confirms measurements and measuring confirms listening. It is always a two way street.  Your "stroke your beard" comment is out of line. Just experiment sounds simple, but if you don't understand the basics, like how capacitors perform in a crossover, you are likely to make a flawed experiment and convince yourself of something incorrect. Then you will come on here and tell others about it like it was true.

There is lots still to learn. How to interpret the electrical characteristics of a capacitor and apply that to a crossover is not one of them. There are parameters of different capacitor constructions that some believe are audible. Dielectric absorption already mentioned and mechanical resonances being two, electrical resonance potentially being a 3rd influenced by ESR in the operating range a 4th. A small bypass capacitor will not solve any of those issues, nor make any change that is not swamped by component to component variation.

Do you really think these high end speaker companies have never thought of bypassing large capacitors with a much smaller one to make a better speaker?

When you lack an open mind you may be able to convince yourself your measurements and models are always adequate.

Takes an open mind and discerning ear to realize when one or the other has fallen short, and this topic is impossible to argue online.  That's why I make suggestions to audiogoners to experiment inexpensively and come to their own conclusions.  Or they can listen to you stroke your beard and tell us nothing is left to be learned.

Oh come on. Do you think with million dollar development budgets that we never listened to anything? 

I'm 100% sure that you are sure there was nothing to be heard.