[AMPS] Watt meters and PEP

[Jim Reid]

Earlier,  John,  GW4RFX wrote,  in part:

> .......... I'm no longer a hi-fi journalist
> within the meaning of the act -- chiefly because consumer 
>audio nowadays is dominated by bullshit, hype and assorted 
>marketing-driven crap.

I have always believed that Paul Klipsch was among the
most honest spokesman and designers of equipment
for the true high fidelity reproduction of audio.  I  do not
know if Paul is still living.  His first loudspeaker patent,
so far as I know,  was granted about 1941;  at least,
his initial paper about his "corner horn"  design was
published in The Journal of the Acoustical Society
of America in October, 1941.

In the late 1960's,  early 70's, Paul was publishing data about 
modulation distortions in loudspeakers: Journal of the
Audio Engineering Society,  April 1969;  JAS, February, 1970,
and JAS,  December, 1972.  All three papers were illustrated
by him using photos of the displays from an audio frequency
spectrum analyzer.

I  corresponded with Paul frequently during that time,  as I
was quite interested in promoting the idea of using
the intermodulation product "intercept point"  as a  valid
measure of loudspeaker performance,  much as it is
used today to evaluate the "goodness" of certain
RF components:  mixers,  RF amplifiers,  and the 
IMD performance of transceivers.

One result was that Paul went out and purchased,  what was
then  the new Hewlett-Packard audio frequency spectrum
analyzer;  all of his published data in the papers mentioned
above were done using the Tek. 564 storage scope, a
3L5 audio spectrum analyzer,  and the 2B67 time base.
The new HP gear was clearly a better machine.

With that Paul continued his data collection.  His interest
from early time,  had been in illustrating the FM distortion
introduced by Doppler frequency shifts occurring to
tones being radiated by a speaker cone moving at
differing frequencies because of the complex signal
components in musical chordal tones from orchestral
instruments.  He had written much about that,  as his
corner horn loaded speakers seemed to show much
lower radiated frequency distortion than some of 
the competing loudspeaker systems offered to the hi-fi
market.

The horn is an impedance matching device between the
relatively high impedance of the moving speaker cone,
and the lower impedance of the air in the listening room.
The benefit is lower cone movement required for a given
sound pressure level in the room;  lower cone movement
means less required amplifier power for an given room SPL,
and also lower distortion as the smaller cone movement
results in less nonlinearity in the restoring force of the
cone suspension.

I sent to Paul comprehensive measurements of the
IMD distortion,  using IP theory applied directly to
several of his published spectrum photos in the
articles mentioned above.  He was very interested,
and did get behind the IP characterization idea --
of course,  because I had showed to him that
his design was clearly  better than a direct cone
radiator,  at least as far as radiating IM tones, and had 
the highest measured IMD intercept point.  

However,  I tried to educate Paul about the value of
measuring the IMD and IP of tones arising from the
IM of tones within a musical chord,  all tones within
the same octave,  not separated by decades of
frequency!  Third order IM's of two tones within the
same octave,  also fall within that octave!!  And the
HP analyzer could clearly show them,  and the horn
loaded speaker generated the lowest IM's during a 
spectrum analyzer run.

Paul continued to supply me spectrum data and I wrote
up a paper,  and submitted it to the JAS editorial review
group.  That kicked off a very inflammatory round of
correspondence among the reviewers which,  in time,  
frightened off Paul's support for my work,  even though he 
did understand it.  He evidently did not care to risk his 
already established standing in the community,  and you 
could not blame him!!

I revised the paper per all the required comments and
additions desired by the many members of the review
committee.  Paul was on the committee;  and wrote 
what I considered the "death knell" to publication;  he
noted that what I was writing he now doubted!!  I was
shocked.  But that was sufficient to cause Gordon
Knight ( he of fame from the analysis of the erasures
from one of Nixon's tapes )  to hold my rewritten paper
in his office for an interminable time.  I at last contacted
him,  and it was he who revealed to me Paul's
penciled notation on one of the reviewer's copies.
The result was that  Knight brought up a new "knit"
not attacked by other reviewers,  and chose to quarrel 
with the mathematical details of my Taylor Series error
expansions about the loudspeaker's operating parameters 
from where the higher order IM products derive.  I could
not out "mathmatic" him,  and then and there the 
paper and the idea of introducing the IP to loudspeaker
performance characterization seems to have died.  The
fame of Knight and Klipsch,  plus the rage of others
about clearly inferior performance of other speakers,
at least as far as in-octave IM's could be shown,
overwhelmed the effort.  I know Paul,  in his heart,
understood,  but chose to back away.

I was exhausted,  dropped the work,  lost contact
with Paul Klipsh,  except for one brief personal
meeting a few years later,  1979 I think,  at which
he seemed to just barely recall me,  except as
that  fellow who had had what seemed to be
some interesting ideas "some years ago".

Well,  anyway,  Paul K.  still remains my audio hero;
still in our living room stand three of his speakers,
two corner horns,  and the needed,  per him,  center
speaker,  this the smaller "Belle Klipsch".

End of my hi-fi story and attempt to contribute.

73,  Jim, KH7M





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