[earplay]

Well, I'll be!

In disassembling a troublesome pre amp, I came across what I recognized as two identical zobel devices (a cap in series with a resistor). According to Wikipedia, when installed in a speaker, they can be used to "cancel out the reactive portion of loudspeaker impedance".

David Kan discusses them favorably in this 6moons article http://www.6moons.com/audioreviews/ring/ring.html.

So, without calculation (see http://diyaudioprojects.com/Technical/Speaker-Zobel/), using just what I removed from the pre amp, I attached the free cap leads to the positive terminals of my speakers and the free resistor lead to the neutral terminals. This is NOT the OCOS implementation Kan describes, but I took a flight of fancy and thought I could try and see what happens. 

WOW! More extension on both ends, smoother and more detailed. 

I would like to hear if others have done this and what their results were. In my case, VERY noticeable, VERY cheap and VERY cheerful.

[Letitroll98]

Congrats on your Zobel network working well for you.  Did you by any wild chance measure frequency response before and after?  Often a reduction of high frequency energy can make things sound more complete, images have more body, and there's less listener fatigue. 

If you're using high capacitance, low inductance speaker cables, the zobel may be eliminating ultrasonic ringing, which could also result in what you're reporting.  MIT cables used (is using?) them for years and lots of folks swore by them.  I wonder what would happen if you used that L/C calculator you linked to, prolly mess up the sound, right?     Anyway, glad it worked.

[earplay]

No measurements, just my ears.

It's interesting that a reduction of high frequencies can make things sound more complete. I didn't know that. The cable I'm using temporarily is Blue Jeans 10 guage 5000 series Belden cable. I don't know if that's a high-capacitance, low-inductance cable.

I'm not sure what you mean by "more complete". I can say that the my impression was that the sound was more extended on both ends, more detailed and smoother. AFTER I heard the results in my system, I read on Wikipedia that "Zobel networks were formerly widely used in telecommunications to flatten and widen the frequency response of copper land lines, producing a higher quality line from one originally intended for ordinary telephone use." I would say that description squares with what I am hearing. David Kan and Srajaen accord on this.

Of course, what do I know? Nothing about electronics, that's for sure! YMMV

[Letitroll98]

The Blue Jeans 10 guage SC is Belden 5T00UP and is moderate in capacitance and inductance at 26 pF/ft and .15 uH/ft.  For comparison some Goertz SC can be as high as 1500 pF/ft capacitance, but ultra low inductance at .004 uH/ft, which is more in line with what I was talking about.  This is why you'll hear some audio engineers disparagingly refer to these types of cables as "filters".  Zobel networks are very popular with Geortz cables for these obvious reasons.  Not to pick on Goertz, it's just an example I know of.

As for "flatten and widen the frequency response of copper land lines, producing a higher quality line from one originally intended for ordinary telephone use", this was referring mainly to Mhz ranges and transmission line theory.  Now I'm of a mind that ultrasonic ringing can have effects in the audio bandwidths, but most audio engineers will tell you I'm wrong, the frequencies are too high and the cables too short.  The effects I'm hearing are easily located directly between my ears in some rather unsubstantial grey matter fields.  Not being an engineer, I can only respond from my areas of expertise and note that you can almost never disturb one part of a system and not have effects on the other end of the system, even if you can't measure what they are.  This argument garners little sympathy.

Thus I've been playing devils advocate with you and trying to generate some interest and explanations of why you hear what you do.  So far it's just you and I talking which i'm quite sure from my end is viewed as poor illumination on the topic.  Perhaps we can get someone with real knowledge to weigh in here, huh? 

[Speedskater]

I'm not at all sure how a high impedance pre-amp output network could work as a low impedance power amplifier output - speaker Zobel Network.  A speaker Zobel might have values of maybe 0.05uF and a 8 Ohm resistor.  I have never seen anything like that in a pre-amp output.

[earplay]

Well, if you are looking to me for a technical electronic response, that's out of my ball  park.

I'm just wondering if anyone has tried this and would care to weigh in.

What I heard was substantial. I cannot rule out a placebo effect, but, to be honest, what I expected was nothing or, possibly worse. I was neutral in my expectations, AFAIK. I had doubts and stood ready to turn off the amp as quick as I could. As far as I am concerned, the odds were equal for a nocebo effect. What prompted me to post was the very obvious improvement.

Maybe I have a weird amplifier. Well, I'll be honest, I do have a weird amp. It's modified Sonic Super T-amp along the lines suggested by M Mardis. The speakers are 2-way, rated at 86 db with a simple crossover. It's a small room and I don't play loud.

I am certain that the values involved are larger than ideal, as Speedskater says. Still, either I am highly suggestible or I am hearing something valid. Even if I am THAT suggestible, I thought the chances were only 50/50, at best, to expect an improvement. Actually, I was thinking more along the lines of a three-way split: worse, no change, better. I should get someone else to listen and see what they think/hear. It won't be double-blind, just a simple preference test. Hmmm.... 

Thanks for your thoughts.