A quick guide for understanding audio capacitors.

Capacitors are an important component to any speaker, they restrict lower frequencies, allowing high frequencies to pass through unimpeded.

  • The higher the value of a capacitor, measured in microfarads (uF), the lower the frequencies allowed to pass through the capacitor.
  • They come in a variety of sizes, shapes and materials, each with their benefits and drawbacks.

Common varieties include:

  • Electrolytic
  • Polycap
  • Film/paper & foil

Electrolytic Capacitors

These are the cheapest capacitors found on the market.
They are made using an electrolytic gel suspended between the cathode an anode of the capacitor.

They offer high capacity in a small package, however for audio they tend to smear the signal as they cannot discharge as quickly as other capacitors, losing clarity compared to other types of capacitors.

They also have a typical shelf-life of roughly 10-15 years. As they age they will often start to dry out, and their capacitance will reduce over time, hurting their effectiveness and usable frequency range. We recommend replacing these with a good, budget polycap whenever possible.



A generic term for a variety of metalized film capacitors which are made using a very thin, plastic film which has been coated in a layer of tin or other conductive metal. Most common varieties use polyester, polystyrene or polypropylene films as their dielectric.

This variety of caps offer the best performance on a budget.
Compared to electrolytic caps, they are much faster discharging, offering better detail & resolution, especially at higher frequencies.
However, they will be much larger than their electrolytic counter parts, even at the same values.

Common brands include: Bennic, Dayton, Solen, Audyn, Jantzen and Mundorf.

High-end Polycaps

Like their budget counterparts, these caps are often made from tin-coated plastic films, but typically use less common dielectric films or metals, which can often further improve clarity, discharge rate, or even influence the tone of a capacitor, some may even include aluminum, copper, gold, silver or platinum, with some also offering oil impregnation to further influence the sound and performance of the capacitor.

They are often larger and much more expensive than budget polycaps of the same values.

Sonicaps are our personal choice for their balanced tone and excellent clarity at a reasonable cost, but there are many other options available on the market that fit this category.

Foil Capacitors

These are often the largest and most expensive capacitors on the market. Foil capacitors use metal foil strips separated by a thin poly-film, may even use wax/oil impregnated paper or a coated paper and film, or may employ the use of other custom dielectric materials. Many are also oil/wax impregnated, and some are cast in epoxy resin.

Most foil caps use a high-purity metal foil, and you may also see options made with copper, tin, aluminum, silver, or platinum foil, or even a combination of metals (Silver+gold or copper+tin).

These capacitors are often designed to provide “richer,” “fuller” or even more “musical” sound, with their sound profile depending on the combination of materials they are made with. They can give up some clarity and finer details over high end polycaps, but may offer a much larger, more open, soundstage.

These capacitors are also often much more expensive than any of the other capacitors on the market, and it is not uncommon to spend $50 or even $500+ per capacitor, especially for larger values.

Despite their high-price, they aren’t necessarily “better” than most high-quality polycaps, but are often a means to tune your speakers/system to suit your personal taste.

Notable brands producing include Jupiter, Miflex, Duelund and Mundorf, among others.

These capacitors often make for excellent bypass capacitors.

 Bypass Capacitors

While not a specific “type” of capacitor, the term “bypass cap” refers to any small capacitor used in parallel with a larger capacitor.

Bypass caps are used as a “cheat” to improve the performance of a larger or cheaper capacitor. They can also be used to influence the tonal character of the primary capacitor.

In a Mid or Bass circuit, bypass caps should be kept at or below 1% the value of the main cap. This is to prevent phase issues at the crossover point(s).

In the tweeter circuit, bypass caps should be kept to 0.22uF, or smaller, and should be kept to high-quality capacitors to gain the most benefit. The smaller the value, the less impact a bypass has on the main capacitor.

Copper foil bypass caps typically adds “smoother” or “richer” quality to the sound.
Tin, gold and platinum are more neutral options, while Silver foil adds improved clarity with some extra sparkle at the top, but may come off as “clinical” or “bright” to some.

A high-end polycap bypassing a large film & foil cap can help improve focus and clarity without affecting the overall tone. 


What about capacitor polarity?

Audio capacitors found in a passive crossover are always non-polarized.

For the sake of consistency, we recommend orienting the “input” before the text, and the “output” as after the text.

You won’t hurt anything if a capacitor is placed “backwards.”

Polarized capacitors are most commonly found in electronic devices that are designed to run on DC power.


 Materials & Tone

Capacitors can be made with a wide variety of metals and dielectrics which will often contribute their own tonal differences to a particular capacitor. The information given below are common tendencies in regards to differences in tone for capacitors, which can be influenced by the combination of the other materials used in their construction. But the information below is offered as a handy guide help you tune speakers tone to fit your own tastes.

Tin: Tin is the standard metal used in the vast majority of metalized film capacitors, and is typically regarded as “neutral” towards tone.

Copper: Copper is typically only found in high-end film/paper & foil caps. Copper is mainly regarded as “natural,” “smooth,” “warm” or “rich” which makes them ideal for pairing with “bright” or “hard” sounding drivers. Their sound can be further influenced by the use of wax or oil damping, some of which can potentially make the caps sound “veiled” or “dark” compared to other materials on this list. 
Some manufacturers will offer tinned-copper foil caps which can offer a balance between a richer tone & clarity.

Aluminum: Aluminum is often the main metal found in cheaper electrolytic caps, but can also occasionally be found in some higher end film/paper and foil caps. Aluminum foil, while generally quite neutral, they can have a tendency to be “hard” at the edges, and should be paired paired with or “smooth” or “soft” sounding drivers. Like copper, their sound can be influence by other materials used, especially oil and wax which can help to soften some of that edge in the tone.

Silver: Silver is almost the exact opposite of Copper, it’s often considered “bright”, ” forward” or “analytical” sounding and adding a lot of extra top-end “sparkle.” Typically we’ve seen silver used as small bypass caps (0.01uF) to brighten up “dark” sounding capacitors or. It can enhance detail, but depending on the rest of your system, may come across as overly “analytical,” “clinical,” or even “brittle” In some cases can leave the treble feeling separated from the mid range within the soundstage.

We generally recommend avoiding silver, or using it sparingly as a tiny 0.01uF bypass capacitor.

Gold: Gold is rarely used on its own, often due to cost, but is usually seen paired with silver to help soften the “edge” of silver-based caps, but they can still be quite bright and overly detailed sounding capacitors compared to other caps.\ 

Platinum: Like Gold, Platinum is very expensive, so it’s quite uncommon to see capacitors made with it. However, like Tin, it is a very neutral sounding metal, making it ideal for occasions where improved clarity and detail is desired over tin without coloring the tone of main capacitors. (like bypass capacitors and high-pass filters)

Oil/Wax: Oil and Wax are used to dampen resonances within a capacitor, and fill the gaps in paper based dielectrics. and can also be infused into the dielectric, which is infused between the elements. They often tend to soften “hard” edges, leading to a smoother more “natural” sound, but can also lead to loss of detail & top end extension. Caps that contain oil or wax tend to require a lot extra of burn-in time over non-oil caps, often 400-500+ hours. When fresh, they can have a very “flat” soundstage, and often wont hide the edgy characteristics of some metals & they will need a lot of extra time until it settle into it’s final sound. 
Also keep in mind that oil-based and especially wax-based caps are sensitive to higher temperatures and should be kept away from sources of heat (ex: inside enclosed tube amps/preamps)

Resin: Most polycaps on the market will have resin caps on the sides simply to hold them together and prevent oxidation, but some manufacturers will take it a step or two further, casting the entire capacitor in resin to completely isolate the internals. This method reduces internal vibrations and any micro-phonics that, in theory, could otherwise be generated both within and outside of the components themselves, which is intended to improve clarity & soundstage performance. Some high-end speaker manufacturers may even encase an entire crossover in resin for these very same reasons.

Dielectric material: The type of poly-based dielectric used mainly influences the discharge rate with some materials better suited for different factors which can influence things like clarity, detail and soundstage. Cheaper options include polystyrene & polyester films aren’t ideal for clarity, but are still much better than options than electrolytic caps. Higher-end caps often use polyethylene, polypropylene, Teflon, and occasionally may use custom dielectrics which are better suited to the manufacturer’s preferences.

Dielectric thickness: The thickness of a dielectric also plays a roll in how the caps sound. The thinner a poly-based dielectric is, the faster it can discharge as the anode and cathode are closer together, allowing for faster discharge and better clarity & detail over a thicker material. However, make the dielectric too thin, and they may not be able to handle the voltages the speaker will see at higher volumes, which means will eventually burn through the dielectric, creating a short, putting gear or drivers at risk. Too thick and you start to lose those fine details & top end extension. Typically caps with thicker dielectric will be rated at a higher Voltage, (400-1000V range, vs a more typical 100-300V range) and will be much larger than lower voltage counterparts. Some manufacturers will make the caps longer instead.
When possible, we recommend sticking closer to the 200-250 Volt rated caps over the higher rated options.

Cheaper retail speakers often use capacitors rated for 100V or even 50V due to their lower cost, but due to the cheaper quality of the dielectric used, there often isn’t much in the way of benefits to such low-voltage capacitors.


Capacitor Burn-in

An ever controversial subject, but we’ll just stick to providing information and recommendations based on our experience.

Capacitor burn-in to put it simply is the process of changes within the dielectric material that separates the cathode & anode of a capacitor as the signal passes through it. The amount of difference burn-in makes will depend on the quality of the components in your system, along with the quality of the music & your gear, as well as your speaker’s placement within the room, and the room itself.

In general, fresh high-end capacitors may sound a bit “hard,” “stuffy” “dull” or even “harsh” at first, with much of that smoothing out over time. You should also notice improvements with the soundstage over time as well, namely in separation and layering, but also in width in some cases. Many fresh, Film/paper and foil and especially “oil-damped” caps may often have a very “flat” soundstage, almost like the soundstage is just a large, flat piece of cardboard. 
The amount of time a capacitor requires will depend largely on the dielectric of the capacitor being used.

For most retail speakers, there is very little improvement to be gained from burn-in, if any, especially with cheaper or budget models that are using the cheapest of components. This especially applies if the speaker loaded with iron-core inductors & electrolytic caps, which simply cannot provide the same level of clarity and detail as even basic budget air-core inductors and polycaps can provide, leaving lots of performance on the table.

  • Budget polycaps will typically experience small and gradual changes from the burn-in process, typically settling by 50-100 hours.
  • Hi-end polycaps, like Sonicaps, typically require roughly 200 hours of use before they are fully burned in, with consistent, but fairly gradual improvements. Some caps can go also through phases of better/worse before they settle into their final sound.
  • Film/paper and foil capacitors, (especially oil/wax-damped varieties) will require the most burn-in time, easily 400-500+ hours. Some caps may also exhibit rather dramatic changes during this process, especially during the first 100-200 hours, where at some points they can sound very good, and other where they sound quite bad, even when nothing in your system as changed. Continue putting time on them until they finally settle into their final sound, where they will be much more stable going forward.

Burn-in Tips:

The easiest, and fastest, method to burn in capacitors is to simply let them play music as much as possible. Anything at or above a whisper will keep the process moving along. We typically recommend using a cheap class-D amplifier or old receiver so as not to put any unnecessary wear and tear on high-end gear or tube amplifiers.

  • Play music through the system for 22 hours per day, then 2 hours with the system turned off. This gives the dielectric plenty of opportunities to “settle” or “cool” between the extended burn-in sessions. This is most helpful with foil and oil-damped caps.
  • You can also vary the volume at different times of the day, whisper levels at night, moderately low levels during the day, with occasional louder sessions in the evening.

See also:

We definitely recommend you take a look at the Humble Home made Hifi capacitor shoot out if you are curious about the performance and tonal characteristics of a given brand or model of capacitor and to help find which caps may be best suited to your tastes.

Humble Home Made Hifi Capacitor shoot out.