Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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Re: Ping John Atkinson

Posted by John Atkinson (R) on December 12, 2006 at 07:00:15

In Reply to: Ping John Atkinson posted by tomservo on December 11, 2006 at 09:53:25:

> I owe you an apology, clearly your magazine does have speaker
> measurements, some are atypical too, like seeing the responses for
> each driver.

No apology necessary, Tom. But I do owe you one for the tardy
response. I don't surf Prop Head Plaza, so I was puzzled no longer
to be able to find our discussion in the Critics forum. I wanted to
tell you that my skepticism over your speaker's claimed sensitivity
was misplaced, due to the mistaken assumption on my part that it was
a domestic design, where 87dB/2.83V/m is a typical figure. I read
your pdf with interest, as in the world of sound reinforcement, you
can apply solutions that are not domestically applicable or feasible.

> I have either mistaken yours with another publication, or, the tone
> of it has changed in the intervening years.

A bit of both. We implemented our policy of accompanying reviews
with measurement data at the end of the 1980s. Not only does it
provide our readers with relevant information, but it serves to
differentiate Stereophile from its competition.

>In any case, I applaud you for have what to me seems like more than
>average data.

Thank you.

>http://stereophile.com/floorloudspeakers/506ap/index4.html
>A spherical projection of the speaker’s radiation is more intuitive
>than the polar data shown about half way down on this page.

Earl Geddes has made the same point, and sent me some of the graphical
presentations he would find more easily interpreted and therefore
more meaningful. When I have time (and those words present a
mountainous threshold), I will experiment along these lines.

> The TEF machine with Tef polar is what I use. The TEF machine uses
> Richard Heyser’s “Time delay Spectrometry” for taking its gated
> measurements.

I am a big admirer of the late Richard Heyser, but I never found the
original TEF analyzer intuitive to use, which is why I have relied
DRA Labs' MLSSA system over the years. I am also experimenting with
Fuzzmeasure for the Mac, which calculates the impulse response from a
chirp signal, because I can run it on my laptop and it is thus more transportable.

> An advantage of it is that unlike MLS etc, it actually does measure
> acoustic phase as opposed to calculating it based on a minimum
> phase assumption.

I see that Bill Waslo has also addressed this, but the DRA MLSSA
system does show true phase (from which, if you want, you can subtract
the Hilbert-Transform-related phase error to show the "excess phase,"
which is really want you are interested in). The only measurement
system I have tried that only shows the Hilbert-related phase, not
the actual phase response, is LMS, which assumes that the speaker is
a minimum-phase system. I note that you mention Smaart in another
message. I have only tried that out at AES Conventions, but as, IIRC,
it doesn't calculate the impulse response, I would not be surprised
that it too only shows the amplitude response-related phase.

Thanks for getting back to me, Tom. Always happy to talk speakers.
BTW, I gave a presentation at the 1997 AES Convention on the
development of my speaker test regime for the magazine. You can find
this reprinted in slightly different form at: http://www.stereophile.com/features/99/ ,
http://www.stereophile.com/features/100/ , and
http://www.stereophile.com/features/103/ .

John Atkinson
Editor, Stereophile

John Atkinson
Editor, Stereophile

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