Speaker Crossover Modification - 102

Real Capacitors

Real capacitors are actually pretty complex.  We like to think of them as being purely capacitative but they actually behave like capacitors, inductors and resistors.  Of the  component types you'll use they are probably the most complicated in the real world.

If the goal of a designer may be to maintain the Farads, while reducing the inductance and resistance then the answer is usually to use multiple small capacitors rather than one large one. Modern capacitors are much much better and smaller than they were even 15 years ago though, so the benefit with high quality caps and at audible frequencies is a hotly debated issue.

For those of you who prefer to try for themselves, I offer you this pair of experiments. The first simple and cheap, the second simple and painfully expensive.

With both approaches we show you below it's important to keep the total capacitance to vary no more than 1% of the original value, or you leave simple capacitor upgrading for the realm of crossover redesign.

Multi Capping

One thing to try after your first mod is multi-capping. Multi-capping is an accepted practice to reduce high frequency inductance and to get just the right values. It's not in and of itself an esoteric practice reserved for the lunatics. What makes it esoteric or crazy is that we bother in audible frequencies. That's what drives the engineers mad.

A universally accepted use of this technique is to get the right capacitance. For instance, if your design calls for a 7.5uF capacitor, only one audio capacitor company I know of (SCR/Solen/Axon) makes them.  If you don't have access to them, or don't want to use them, you could create an equivalent capacitor from almost any other brand by combining a 6.8uF capacitor and 0.68uF, yielding 7.48uF, a difference of 0.3%, well within most tolerances.

For the lunatics however, who want to reduce ESR or some other magical benefit, we do this where it appears to be otherwise unnecessary. The benefits of multi-capping is, in theory, more important with larger caps since they can become the most inductive. I generally don't bother to multi-cap anything under 5uF.

Here's an example:

As you can see, the 10uF  of C1 has now been broken up among C1, C2 and C3.  The total new capacitance is 10.08uF, less than 1% difference.


When looking to try this, keep price in mind. Some brands are sold strictly on uF, so the cost with one or 3 caps will be very similar, while other brands have a hefty minimum price, which can really increase the final cost.

Bypassing

Bypassing is just a term-of-art I use to differentiate from multi-capping.  While in multi-capping you use the same capacitor type for all the values, with bypassing you may use entirely different types of capacitors. At it's simplest, capacitor bypassing is to take a larger, often less expensive capacitor with high storage density (i.e. small size for the uFs) and bypass it with a film or foil capacitor of a much  smaller value, making a more ideal capacitor than with just the larger capacitor.  This is a common practices in many types of electronic designs outside of audio especially in power supplies where a large, electrolytic is used for it's storage and small size, while a tantalum or film cap will ensure the effective impedance at high frequencies remains near-linear. The designer saves money and space compared to using an all-film solution. What engineer wouldn't love that?

It is a reasonable, and common, option in speaker crossovers to take a bipolar electrolytic capacitor and bypass it with a nice film capacitor. 

Sadly, audiophiles leave reason behind here by bypassing a perfectly good film capacitors with another perfectly good film capacitor. The main goal of bypassing film caps for us in the crazy world of audiophilia is to color, or remove coloration of sound from existing capacitors. Engineers will state, correctly, that there's no accepted measurements for doing this, and little proof of it's merit at audible frequencies besides actually changing the total capacitance and ESR.  To which I say simply, listen for yourself and spend no money your ears don't compel you to.

Doing capacitor by-passing in speaker crossovers well almost always forces us into the land of expensive and exotic capacitors. It's definitely not for the faint of heart or bargain hunters.  Some would argue that at best it's psychosomatic, at worst charlatanism. It seems like Homeopathy, a practice completely discredited in some parts of the world. I think of it much more like layering in cooking. Regardless of whether you agree with the practice, I'll explain the basics. It's ultimately your ears and wallets that should determine the value.


Now, let's get into some examples.

 Here we have bypassed C1 with an 0.1uF capacitor. It's important NOT to bypass with more than 1% value of the original.  So if you have a 3.3uF cap you'd need an 0.033 uF bypass.

Next, don't bypass crappy caps.

I've had really good luck using copper foil bypass caps like the Audyn True Copper, but their minimal size is 0.1uF and largest is 2.2uF.  A sadly limited range for such a good sounding capacitor. Their smallest size is too big for anything less than 10uF, and the largest size is still too small to use as a prime cap most of the time.

Tweeter caps often run in the range of 2.2uF to 6.8uF. That's fine but to get 1% of 2.2uF we'll need 0.022uF which practically forces us into the land of expensive exotic capacitors, and this is why I don't recommend bypassing as the first thing a new modder should try.

There are a couple of things to keep in mind. These exotics are often physically HUGE! Make sure you look at the sizes before you purchase.  Also, in some cases they are so expensive you may be better off with buying entirely new caps.  For instance, the Duelund Precision Bypass caps, even at a discount are still around $100.  You may be better off buying a new Jupiter 100V Copper Foil or Duelund 100V RS as the base cap, and foregoing the bypass idea altogether.

Here's some brands that have values very useful for bypassing smaller tweeter caps:

• Mundorf Silver in Oil (not for me, but many others rave middle of the road cost)
• Jupiter Copper Foil 600V
• Duelund Silver Precision Bypass
• Duelund Copper Foil 600V RS (Silver is better, but check current prices)
• Cornel Dubelier ( best bargain , find through Mouser or Digikey )
• Clarity MR 600V ( great prime caps! never tried in bypass, middle of the road cost )

 

Combining Bypassing With Multicapping

The astute reader will wonder though:

If bypassing and multi-capping are based on the same principles, shouldn't I just do both? 

Sound reasoning which only experience can challenge. My thoughts are that this introduces too many variables at once, but it's your money so go ahead.  You could for instance take the multi-capacitor example and replace C3 with an Audyn True Copper 0.68uF capacitor.  From the stand point of Farad math, that's just fine but most with experience suggest if you are going to mix your capacitor types to avoid mixing in more than 1% from a different type.  0.68uF / 10uF = 6.8% so it is definitely far beyond my recommendations here.  Again, your money.  More interesting and of higher value is for you to try both approaches and pick the one you hear sounds best, if either.

Additional Reading

One of the most often referenced, but not perfect, listing and review of capacitors is the Humble Home Made Capacitor review.  I particularly disagree with the rating of the Mundorf MKPs.  I think they are better than listed, but to each their own.