Bob Cordell's Power amplifier book

[Bob Cordell]

Originally Posted by Joachim Gerhard

I find many things in your book that i do not find in Selfs or Duncans volumes.
To include measurements of all described designs whould make the page size double i am afraid.

Hi Joachim,

Thank you. I was actually very fortunate that McGraw-Hill let me put in as much as I did. When you try to cover a lot of topics there are sometimes some difficult decisions to be made about what to cut.

Cheers,
Bob

[Ian Finch]

Yay, my copy turned up yesterday! What a great work, right on target! - (on first take, at least!). What a pity though; the sad reviewer Mr de Velder (post #577) can't get his head around these new ideas in solid-state. His review is even more clearly prejudiced than that he gave of D. Self's Small signal audio publication.

Hurtful as they are, I don't think readers are going to see his comments stacking up with the publisher's or the text itself, even with regard to simple matters like book content. Still, I'm sure you'd rather not see such stuff in the major distributor's presentation, Bob.

I guess it's all part of some "equal-time" policy for airing contrary views as in the public face of many large corporations today.i

[Joachim Gerhard]

I did some measurements of speaker distortion at various soundpreasures as requested.
Note that my measurement amp is an inexpensive Alesis and i use a simple M-Audio Transit soundcard so some of the "grass" you see is from my electronics. Nevertheless the measurements confirm in general the monothonic nature of speaker distortion.
There are too much measuement to put in one post so i start here with a measurement of second and thrird harmonic at 75dB and 105dB in 1m. The driver is an Audio Technology 18cm midwoofer with filled Polypropylen membrane in a 35 liter bass reflex cabinet. I measured in 10cm so the soundpreasure scale looks way to high and i did not normalise.

[Joachim Gerhard]

i also looked at harmonic 5 if there is any raise of higher harmonics with level again at 75dB and 105dB.

[Joachim Gerhard]

Here is the spectrum of a 1.1kHz tone at 75dB and 85dB.

[Joachim Gerhard]

Here is the spectrum at 95dB and 105dB.

[Joachim Gerhard]

Here is the Spectral Contamination ( multitone distortion ) at 95dB. And the "Gerhard Test" also at 95dB ( sorry. i did not find a better word for it ). This a a wav. that you can play back.
I got it by putting in 30 frequencies over the range from 20 to 20kHz that are chosen not to stack up harmonics. I them supressed the tones digitally and did an invers FFT on the residuum to extract the time domain signal. I then converted into 16 bit 44kHz wav.
It is a good indicator of rubb and buzz and when you listen carefully you hear the "sound" of the membrane. Note that this distortion is at a very low level and i had to "blow" it up a lot to make it audible.

[Joachim Gerhard]

Gerhard Test and how this waveform looks in the time domain.

[Joachim Gerhard]

The wav. as a zip.

[Bob Cordell]

Originally Posted by Ian Finch

Yay, my copy turned up yesterday! What a great work, right on target! - (on first take, at least!). What a pity though; the sad reviewer Mr de Velder (post #577) can't get his head around these new ideas in solid-state. His review is even more clearly prejudiced than that he gave of D. Self's Small signal audio publication.

Hurtful as they are, I don't think readers are going to see his comments stacking up with the publisher's or the text itself, even with regard to simple matters like book content. Still, I'm sure you'd rather not see such stuff in the major distributor's presentation, Bob.

I guess it's all part of some "equal-time" policy for airing contrary views as in the public face of many large corporations today.i

Hi Ian,

Glad you got your copy and thanks for the kind words.

Negative reviews are just part of the territory. Some will have valid points, others will be a result of too quick a skim, and others may be the result of a technical philosophical difference. Moreover, no book can be complete and without error on every topic. The important thing is just like a vote. If those who like the book will write reviews, then the overall picture of the book will come out as more balanced. When you have only two reviews, one good and one bad, the picture is too lacking of data points. As more people read the book, I hope more reviews will be written.

Cheers,
Bob