Tuesday, November 5, 2013

A Resistor Review? You Bet!

When it comes to coaxing that last bit of fidelity from your speaker design, sometimes people overlook the importance of the modest resistor. Typically used as attenuators in crossover networks, notch filters, and Zobel networks, resistors play a huge roll in their ability not only matching individual acoustic output levels between multiple speaker drivers but also to uniformly pass high frequency signals. Using inexpensive wire-wound resistors is tempting because of their low price and in some cases they may work fine. But the higher the frequencies that are involved in using a resistor, the more likely there will be an audible effect of using wire-wound resistors as opposed to non-inductive types.

For example, if you are attenuating a screeching low-quality HF driver, you may want to use wire-wound resistors to help roll off the HF content to this driver and tame its fingernails-on-the-blackboard edginess. But if you are using quality home speaker drivers, always use the non-inductive varieties to achieve the most open and natural sound.

The results of using non-inductive resistors in audio circuits are well worth the insignificant incremental price difference. I personally use T-pad attenuators not only to match acoustic output levels of drivers but also to reduce the effects of standing waves between the amplifier and crossover network. Several online calculators are available, of which this one is my favorite:

The issue with the simple resistor is that it is non-linear, that is, as the frequency changes so does the value of the resistor. Some resistors are more stable than others, that being the non-inductive variety. HAM radio technicians understand this issue well where very high frequencies play havoc on stable equipment, but high-end audio gear can benefit from it also. Some folks may say that the frequencies are too high to impact the audio spectrum and with current understanding of the physics involved, they are correct. BUT as it is with thoroughbred horses and formula one race cars, trying to get that extra edge means trying things that are unconventional and certainly contrary to conventional wisdom. Such attitudes win races and in audio, similar attitudes create really good sounding gear.

All resistors "work" and the cost-to-return ratio steepens as audio nirvana is reached. One way to get an edge on this curve is to swap out those pesky low-cost resistors. Give it a shot: they're pretty cheap and you may be surprised what a simple 1:1 substitution will achieve.

Yours for higher fidelity,
Philip Rastocny 

I do not use ads in this blog to help support my efforts. If you like what you are reading, please remember to reciprocate, My newest title is called Where, oh Where did the Star of Bethlehem Go? It’s an astronomer’s look at what this celestial object may have been, who the "Wise Men" were, and where they came from. Written in an investigative journalism style, it targets one star that has never been considered before and builds a solid case for its candidacy.


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