John Curl's Blowtorch preamplifier part II

[john curl]

The problems with horn design are multi-fold and they are NOT easily solved. IF there are better solutions than others, so be it. However, I will stick to direct radiators for my apartment, they do the job, well.

[Chris Hornbeck]

About the time that we develope cars that work well at both 20 mi/hr and 20,000 mi/hr, we'll have perfected loudspeakers.

Thanks,
Chris

[fireworks]

Since IMD and similar topics recur frequently in this thread, here is an interesting article on IMD:

IMD - Something New

[bcarso]

Originally Posted by fireworks

Since IMD and similar topics recur frequently in this thread, here is an interesting article on IMD:

IMD - Something New

Nonlinearities that produce the third harmonic of a single sinusoid will produce IM products from f1 and f2 at 2f1- f2 and 2f2 - f1. You need a nonlinearity that will generate some second harmonic distortion from a fundamental, to generate |f1 - f2| and f1 + f2.

I'm surprised he couldn't find ample discussions of this.

BTW, this is a reason why second harmonic distortion is not so benign, unless you are listening to very sparse textures, like solo voice or other solo instruments. High frequency IM will generate difference-frequency energy often in regions of high aural acuity. Not good.

[john curl]

Well said, bcarso. I started looking for references to the problem, as well. It is known problem with 2 tone IM by the difference method.

[gpapag]

Originally Posted by bcarso

I love the beginning of that third volume and the story of the boy. For some reason I couldn't scan it adequately and deleted the post after noticing lines of type were cut off. I have the three volumes in storage so maybe I'll dredge them up and scan directly.

Here it is:

Adagio. Andante. Allegro moderato.

§ 450. The following story is true. There was a little boy, and his father said, “ Do try to be like other people. Don't frown." And he tried and tried, but could not. So his father beat him with a strap ; and then he was eaten up by lions.
Reader, if young, take warning by his sad life and death. For though it may be an honour to be different from other people, if Carlyle's dictum about the 30 millions be still true, yet other people do not like it. So, if you are different, you had better hide it, and pretend to be solemn and wooden-headed. Until you make your fortune. For most wooden-headed people worship money ; and, really, I do not see what else they can do. In particular, if you are going to write a book, remember the wooden-headed. So be rigorous ; that will cover a multitude of sins. And do not frown.
There is a time for all things : for shouting, for gentle speaking, for silence ; for the washing of pots and the writing of books. Let now the pots go black, and set to work. It is hard to make a beginning, but it must be done.

Volume III starts sarcastically and ends wisely ("Limitations on Scientific Prediction." p. 518-519)

George

[kgrlee]

Originally Posted by fireworks

Since IMD and similar topics recur frequently in this thread, here is an interesting article on IMD:

IMD - Something New

Thanks for this fireworks. I wish I still had my copy of the B&K 1902 manual where I had scribbled the equivalences of Harm. Dist. to each type of IMD test. I've insufficient brain cells left to redo the maths.

Nonlinearities that produce the third harmonic of a single sinusoid will produce IM products from f1 and f2 at 2f1- f2 and 2f2 - f1. You need a nonlinearity that will generate some second harmonic distortion from a fundamental, to generate |f1 - f2| and f1 + f2.

I'm surprised he couldn't find ample discussions of this.

When I did this in the early 80's, I couldn't find any sources for the maths either.

[jcx]

plenty online now: Volterra, Wiener nonlinear systems modeling papers for RF amp predistortion compensation, even a few on loudspeakers

the math horsepower is also freely available now with symbolic and numerical software like SageMath or SciLab, Octave

[kgrlee]

Originally Posted by jcx

plenty online now: Volterra, Wiener nonlinear systems modeling papers for RF amp predistortion compensation, even a few on loudspeakers

Got any recommendations on this specific topic .. Relation between Harmonic Distortion and various Intermod Products?

Especially for a beach bum hu kunt reed, rite oh ****.

[scott wurcer]

Originally Posted by bcarso

I'm surprised he couldn't find ample discussions of this.

BTW, this is a reason why second harmonic distortion is not so benign, unless you are listening to very sparse textures, like solo voice or other solo instruments. High frequency IM will generate difference-frequency energy often in regions of high aural acuity. Not good.

I agree Rod is a fun guy but this stuff has been hashed over from just about any angle somewhere. I assume his use of the term non-harmonic does not mean he believes in the creation of frequencies that are not n*f1 +- m*f2.

I'll have to read the whole thing.

EDIT - I read the whole thing. I like Rod but here he is speaking from a fairly hermetic naivete. You can derive all these results from a simple mathematical exercise, his comment about not being able to offer any references because there are none is baffling.