From: email@example.com (N. Thornton)
Subject: Re: Bullshit wins v. science
Date: 8 Nov 2002 19:16:27 -0800
NNTP-Posting-Date: 9 Nov 2002 03:16:27 GMT
"Kevin Aylward" wrote in message news:...
"N. Thornton" wrote in message
(I took my time to explain it clearly here, somewhere near the bottom
of this hopefully it will start to get clearer. It'll take 2 readings.
>> The approach and industry practice you describe for measuring
>> distortion only measure certain types of distortion. They do not
>> _define_ distortion.
>In practice it does. Its what is meant by using the term distortion,
I agree that is what it is normally taken to mean.
I think it thru beyond what is printed in the text books, because I
discovered this issue when trying to produce a super efficient
speaker. I went for a resonant design for best efficiency, and
encountered a problem that made me rethink the generally accepted
concept of distortion.
Resonance causes a non flat freq response, which can be corrected, but
it also causes something else. Resonance does make what you hear
different to the signal analogue, and that dfference is conceptually
distortion. I accept we probably won't agree on that. More later...
>For example if someone was referring to phase aberrations,
>on would have said "phase distortion".
Sure, granted. You're talking about accepted conventions there, I am
going past them. I am saying accepted convention is not the whole
picture, and although accepted, is not entirely accurate.
>The issue here is that you are simply not conversant with standard
Sure I am. I just believe there more to it now. My muddy speaker
proved that to me.
> Lets take a really clear example to illustrate. Lets say you delay
> your audio signal by 1 second twice, and add the 3 signals: the
> original one, the 1 sec delayed one, and the 2 sec delayed one. Any
> speech put through that would be unintelligible. According to the
> _definition_ of distortion, it is indeed distorted, badly distorted.
> But if you measure the THD of this distorting process, it is zero.
>In fact if had taken probably any course on this in university,
>example, it would have been pointed out that delay distortion is not
>usually refered to as "distortion".
Sure, I quite agree. But the example I gave still is distortion, even
if its not what's measured and referred to as distortion in the
>> I am perfectly aware that THD is the usual figure used, and am also
>> aware that it does not, contrary to popular ignorance, give a
>> picture of a speaker's distortion.
>It gives a proper indication of its non-linear amplitude distortion,
>understood by anyone knowledgeable in the field.
>There is no contrary to
>popular ignorance on this matter at all. Only ignorance concerning
>standard terminology really means by novices.
I think you may have missed what I'm saying. I hope I will be clearer
>THD has never implied
>anything about what the frequency response of a speaker is.
The delay/ time spread type of distortion caused by resonance, and
uneven frequency response, are 2 separate things: I am talking only
about the former, not of anything to do with unflat freq response
Of course resonance is prone to causing both of those. But they can be
separated, and are 2 different effects of resonance. I'm not sure I'm
putting this too clearly though :)
>> they don't quote the _real_ distortion figure, it would be far
>> and not as simple to test.
>You still pissing in the wind. Give it up. You wont change the
>establishment one little bit.
I am not seeking to.
>Frequency response variations are called the frequency response of
>system, and this is indeed specified for speakers. A decent data
>will contain graphs of *both* distortion and frequency response, and
>both are quite easy to test. It would confuse things no end to refer
>frequency response as distortion.
Sure, but that's not what I was looking at.
Have you ever tried putting sound through a resonant transducer and
flattening the frequency response? When I did, I discovered something.
Although the final freq response may be flat, or near flat, the sound
is still, to the ear, very distorted. It has a 'muddy' blurred'
character. It is harder to make out the words, everything sounds a
mess. But the frequency response was perfectly reasonable, and the
linearity quite good.
The cause of this, what I would call distortion, is that the sound
reflects back and forth across the speaker surface, and thus an input
at time t comes out at times t, t+1, t+2 etc. The example I gave above
is a simplified version of this type of distortion.
What I was attempting to say originally, and maybe I was being muddy
about it myself, is it is this type of distortion that bass reflex
speaker cabs cause at low frequencies. And its for the same reason,
because they are designed to be resonant at the bottom of their f
And that is why the bass from a bass reflex cabinet always sounds
different to that from a simple closed cabinet. It is less clear. A
bass note will have slower attack, and delayed decay.
Now I'll address this:
>> Distortion means, and I quote:
>> "The state of being distorted, or twisted out of shape or out of
>> position; crookedness; perversion."
>> That is the _meaning_ of it.
>Your pissing in the wind. An engineering definition of distortion is
>the same as an English language definition of distortion. Try looking
>the definition of an "Observable" in Quantum Mechanics, e.g.
I agree the accepted eng. concept of it is not what I have given. What
I am saying is that the accepted concept isn't the full story.
I dont asume you'll agree with what I'm saying, but I like to say it
nonetheless :) I guess I like discussing and developing concepts.
I hope I've managed to explain better this time.