Wednesday, August 6, 2014

Capacitors: All Things are NOT Created Equal - Part 1

When buying speakers or electronics, designers always begin a project with a budget and an idea of what can be done with that budget. In the lab behind the curtains, designs take on a very different look than what finally gets out the door. Bread-boarded amplifiers, cobbled-together cabinets, and recycled power supplies are common items jockeyed about in an engineer's inventory never seeing the light of day, at least from the consumer's eyes.

Part 1 - The Budget

An evolution occurs in an audio design where once a fundamental parts count is achieved, juggling the costs of these individual parts makes a difference in how the total comes in line with the budget. For example, the budget for a small 2-way speaker could look something like this (actual values vary but this is just an example to make a point):

  • 8" Woofer: 20%
  • 1" Tweeter: 10%
  • 2,500Hz BW-2 Crossover: 15%
  • Cabinet: 20%
  • Shipping box:: 5%
  • Misc. Materials: 5%
  • Labor: 25%
  • Raw Cost: 100%
  • Selling Price: 5 X Raw Cost

A similar budget is created for any piece of electronics gear with a far greater granularity but you get the general idea. What typically happens is that one of these items runs over budget so the designer must start juggling numbers to stay within the budget OR increase the budget (something the bean counters hate). So if the design must stay within budget, something has to give if the design is to make money. What typically is compromised first is the quality of the parts used in the design (what is on the bench rarely makes it into production).

If the designer can make a crossover network for less and stay within budget, this is one option OR use cheaper drivers OR a cheaper cabinet. Sourcing alternative drivers while possible is harder to do if a certain sound is to be maintained and the price difference for a typical 8" woofer can range from $20 to $80 (4x difference). Sourcing alternative cabinets is an option, especially if cabinet resonances can be disregarded and price differences are similar (2x-4x). 

But the cost of a quality capacitor or inductor can be hundreds of times higher than the least expensive form available. For example, a 2.2uF/100V Deuland Cast PIO is $443, a 2.2uF/600V Mundorf Supreme is $22.50 (about 20 times lower in cost), and a 2.2uF/100V non-polar electrolytic is $0.50 (886 times lower in cost). So the parts count can be identical but the cost for these parts can be adjusted so that the design stays within budget.

But what do you give up for the lower cost?  A good analogy to answer this question is to look at the MSRP of new automobiles. All of them will go 70mph but why does the TATA Nano have a MSRP of $3,056 (the cheapest car built) and the LAMBORGHINI Veneno have a MSRP of $4.5 million (BTW, the last one of the nine built sold for $7.6M)? Is the Veneno worth 1,472 times more than the Nano? Well that is what the high-end is all about, right? And if you believe that the Veneo is worth it, then you are truly a hopelessly hooked audiophile like me.

The Lamborghini Veneno

So to build a Nano, one uses the lowest cost parts possible (here the non-polar electrolytic capacitors) and does not include much in the way of an audio system and for the Veneo cost is truly not an issue (here the Deuland Cast PIO capacitors). BTW, the Veneno comes with a hand-tuned custom-built Monster(TM) audio system and the Nano doesn't. So it is with audio design and the allocation of its budget that determines what is and is not possible. (Does your automobile go from 0-60 in 2.9 seconds? The Veneo does and the Nano doesn't!)


The Tata Nano

Matching the links in the audio chain becomes as important as the budget to which this speaker is assigned. Again as an analogy, would you suspect to find the Monster audio system of the Veneo in the Nano? No. And why not? I am sure that this question need not be answered.

The question becomes one of applying the right money to the right design to fit into the right system. One would not appreciate the $400 Deuland capacitor in a $100 boom box but even in this modest system one would appreciate a minor capacitor upgrade from a $0.50 non-polar electrolytic to something a little more esoteric at just twice the price.

So now that you understand a little about budgets and how things fit into the overall audio chain, in Part 2 we will look at why it costs what it does to make a good sounding capacitor and what some of the major design considerations are.

Related articles:
The Vishay 1837 Review and Modification
Bypass Capacitors
Mundorf Supreme Capacitor Review - Part 1
Mundorf Supreme Capacitor Review - Part 2
Capacitors: All Things are NOT Created Equal - Part 0
Capacitors: All Things are NOT Created Equal - Part 1
Capacitors: All Things are NOT Created Equal - Part 2
Capacitors: All Things are NOT Created Equal - Part 3

Yours for higher fidelity,
Philip Rastocny

Skeptics are essential to keep us sane; skeptics do little to keep us inspired. Philip Rastocny, 7-16-2014

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