Electronic Design

Bob's Mailbox

Greetings Mr. Pease,

Re:  "All This Taguchi Stuff"

Right on!  Another pot of snake oil exposed for what it is.  My favorite skunks (changing metaphors) these days are:

1.  Concurrent engineering - as if that is new.  All projects, if done sequentially, will take too long.  Under time-to-completion pressures, parallel paths will be taken.  The skill and art of management is to keep the relative rates of progress balanced.  This management challenge existed before the Egyptians built the pyramids.

2.  Scheduling - as if dividing a project into a million little tasks, and arranging those tasks on a time-phased chart, means that the project's understood and can be managed.  My experience is that schedules will be generated to management's request.  The real job is to get the guys to think through what they do not understand about the project and what they are afraid to admit even to themselves.  Once that is accomplished, the project will take on a form and direction that makes the previous scheduling exercise impossible to relate to except in very broad strokes.

Keep it up man!

Lauren Merritt, Sunnyvale, Calif.

Experts are always bundling up a package of old stuff with new buzzwords-and sometimes it is of some value.-RAP

Dear Mr. Pease,

Recently, in a minor reorganization, I came across a few periodicals that had been set aside into a "later" pile over a year ago.  It included an Electronic Design magazine with one of your triple-column commentaries.  I regularly enjoy reading your works because, although your circuits display great practicality, your mind often tends to stray toward whimsy.  Most of us could do with more doses of levity, interspersed with handy hints.  Thank you.

The subject of that triple column was splices in wires to loudspeakers.  That brought to mind related facets of Esoteric Audio, like the perceived need for Litz wire run to loudspeakers.  The increased surface area of Litz wire is believed to reduce distortions, which would result from the use of Gigantic SuperFlex Cable (from your local Audio and Welding Center).

Those who engage in Esoteric Audio are far from united in their beliefs.  Like many other religions, the truth is often misinterpreted.  War may result.  One splinter group currently prophesies that the physical shape and relationship of the conductors colors the sound; they believe that the interconductor capacity is more important than the Litz-believers' surface conductivity.  As a result, they have developed rectangular conductors.  These are parallel strips of copper foil, laminated between insulating films, like an extended flexible circuit board.  This facilities few farads per foot, while maintaining reasonably low dc resistance.  It should be noted that this splinter group has, perhaps unwittingly, contributed greatly to the aesthetically satisfactory installation of loudspeakers in the home environment.  However, it is not due to the measurably minuscule interconductor capacity, but rather to the fact that speaker wires can be placed under carpeting with no visible ripples.  Zip cord may be doomed...

On a more scientific front, splices in speaker wires may cause grief, but only if they're poorly done.  Loose connections tend to transmit audio intermittently, and may oxidize.  Copper oxide is used to make low-voltage rectifiers for meters.  A rectifier in a speaker lead can produce nasty-sounding "crossover" distortion (a discontinuity when the current is reversing direction).  However, anybody who believes he can hear a proper splice is likely more artist than scientist.

Now on to a phenomenon for which I seek an explanation:  Several years ago, I was cautioned that the use of tantalum capacitors for audio could or would result in perceivable distortion.  I placed that into my Esoteric Audio fact file, and proceeded.  A few years later, I was developing yet another audio circuit.  It needed a coupling capacitor, and I had suitable value tantalum handy.  The circuit measured reasonably near perfect.  As is my practice, I listen to my circuits while I'm developing them, as the ear is often much quicker to detect a flaw and suggest a solution than are bench instruments (besides, this is audio; the ear is the ultimate judge of quality).  That circuit did not sound clean on orchestral program material.  But it sounded normal on signals from my oscillator.

I monitored the circuit at various points.  There was an obvious change in program quality when I monitored before and following the tantalum capacitor.  The polarity was correct.  I replaced it with a similar tantalum.  No improvement.  I replaced it with an aluminum electrolytic.  The program sounded normal.  Disbelief.  Then I replaced it with a different brand and style tantalum.  Bad again.  I repeated frequency response, THD, noise measurements.  Sine, square, and sawtooth waveshapes did not appear different than normal on the oscilloscope at any frequency or amplitude.  The meters gave the same numbers with either capacitor type.  But the program sounded slightly distorted, unclean.  Then I replaced it with another aluminum, different brand.  Good sound again.  I repeated the same measurements, and they were essentially identical.

The sound of orchestral music (from any good CD) was unquestionably altered by the type of capacitor.  I do not enjoy phenomena that are observable, but not measurable with my instruments.  Obviously, I didn't make the appropriate measurement.  I do not have access to an audio spectrum analyzer, perhaps that might show something.  Have you any experience with the good-measuring, bad-sounding tantalum coupling capacitor?

Keith Rauch, Senior Engineer, ACD Services, Santa Ana, Calif.

Someday I'll set up an A-B comparison of audio amplifiers with electrolytics vs. tantalums.  A side-by-side comparison will show us the difference.  But does anybody outthere know the answer already?-RAP

Dear Bob,

Lee Seelig's interpretation on why one steers right to turn left (which is called counter-steering in the motorcycle safety courses) is interesting.  I have another interpretation.  When you steer left, the tires move left.  When you steer left, the tires move left.  When this happens, the center of gravity is to the right of the roll axis (the line between the contact patches of the tires).  This causes the bike to fall to the right.  To keep from falling, you have to start turning right to inertia (centripetal force) holds you up.  Fortunately, the geometry of the forks and steering head naturally turns the front wheel in the correct direction.  To get the bike back upright, you turn harder.  This causes inertia to raise you up and also causes the tires to try to get back under the bike.  You can actually see this happen if you watch someone take a quick turn on a bike or motorcycle.  The tires actually move a bit to the left just before a right turn.  Understanding this was a boon to the designers of racing motorcycles.  They used to think they needed to keep the weight low to get fast handling.  Now they know they need to keep the moment of inertia low (along a front to back axis) so the tires can get out from under the bike quickly.

Of course, you can steer a bike without counter-steering (remember "Look Ma!  NO HANDS!").  Leaning right causes the bike to fall right and the fork geometry causes the wheel to turn right, catching the fall.  You can see this, too.  Just walk your bike by just holding the seat.

I wonder what would happen if the geometry were set up such that the wheel turned left when the bike leaned right (ouch!).

Carl G. Hayssen, Principal Engineer, Ungermann-Bass, Andover, Mass.

I still think a bicycle will work if you use tiny wheels (like a roller skate) or an ice skate blade where there's nogyro effect-RAP

Dear Bob,

I read your article on the BSEET degree with considerable interest.  I happen to work for the government and make occasional recruiting trips for engineers.  We have an interesting policy on hiring engineers - if they take and pass the EIT examination, we can hire them as engineers.  There is a considerable pay differential and greater opportunity, so it is quite an incentive to do so.  This might also work in the case of "Mr. X," but I agree with you he should pursue the "changed rules" path first.

...You also mentioned creativity versus education.  I more or less agree with you, but feel it is more a function of what type of school the engineer has attended.  I attended a technological school, and got my MS from a similar school.  Had I opted for more theoretical schools, I doubt I would be as creative or effective as I am.  My father, a chemical engineer, referred to my schools as "nuts and bolts" schools.  We learned to get our hands dirty, and never lost our desire to do so.  I work with a number of engineers with lots more textbook knowledge than I have, who are unable to apply it in their jobs.

And this applies to Professors as well.  I had a chance to teach for a year at Cal Poly in San Luis Obispo, in the EL/EE Department.  As I looked around at my fellow instructors.  I noted that the ones who were the most popular (and effective as well) were often the one without PhDs.

Mark S. Hutchenreuther, Computer Engineer (Yup, times have changed again..), Oxnard, Calif.

I'm with you; I like to get my hands dirty and operate in the "can do" mode.  If we can't apply theoretical knowlege, why have it?-RAP

Mr. Pease,

Over the past year or more, I have read "Pease Porridge" with a sense of anticipation, and pleasure.  You have an outlook that is quite refreshing in its humor, realism, and style.  Please keep dishing out the porridge.

I read your May article "What's All This Bachelor's Degree Stuff, Anyhow?" and felt that your comments were reflective of "real world" conditions.  I think the "engineer" in this case is getting screwed and should stick to his guns.  Your comments about "very good engineers who never got engineering degrees" hit home like a smart bomb.  In short Mr. Pease, "Encore!...Encore!...Encore!"

As you have probably guessed by now, I am a technician, with an associate degree in applied science, that has been in the "real world" for twenty years.  I have a long history of working with engineers (BS's and MS's) and have known both good and bad, but that's not what this letter is all about.  I would like to know what your readers (BS's,MS's,AAS's and tech school grads) feel about technicians and their role in the industry today.

I would also like to see information presented for technicians much like it is now presented for "Titled Engineers." The "Career Survey" is good information and helps keep me current.

For the past ten years I have filled an engineering position where I have had sole responsibility for all technical duties, and feel that I have done as well as any "Titled Engineer."  I like to call myself a "Pocket Engineer" - that is an engineer in every way except the money in my pocket.  Is this a commonplace occurrence and if so, does this reflect a trend in the industries?

I want to thank you for you comments about the "Negative Correlation" and "Most Creative Engineers," and please thank Frank Goodenough for giving you encouragement.  I know that technicians are not engineers, but in many cases we "Techs" are the ones that make things work.

Name and Address Withheld

Technicians are not only extensions of my hands; they are receiving antennas and filters for info which they help digest, and pass on to me.  Good ones are very valuable.  Comments, guys?-RAP

 

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