HOW TO UNDERSTAND DIFFERENT IMPEDANCE RATES?!!!

John Woodgate jmw at jmwa.demon.co.uk
Tue Jun 10 00:58:29 EST 1997


In article <339ca63a.419115 at news.pacbell.net>, God <god at almighty.com>
writes
>>You really are a most unsatisfactory god, you know (of course you
>>know!). If this goes on I shall have to stop worshipping you, and then
>>where will you be? You have the inequality sign the wrong way round; at
>>least, I suppose you did not mean 'greater than'!
>
>Would you quit picking on my name? It has nothing to do with whether
>you or I am correct. And yes, the signs should be reversed. If you
>caught this, you should understand my final point.

Anybody who claims to be <god at almighty.com> must expect to be twitted
about it, especially in terms of omniscience and fallibility!

>
>>>3) We assume that both "speakers" in 1) and 2) have the same
>>>efficiency (and identical except for their impedances.)
>>
>>Yes, the following reasoning is correct if, and only if, you mean
>>efficiency in the strict sense of sound power out divided by electrical
>>power in, but hardly anybody uses that because it is difficult to
>>measure and not of great practical use.
>
>No, John. THIS WAS A PREMISE STATED BY THE ORIGINAL POSTER. I was
>merely breaking down his premises + conclusion into an easy to
>understand format.
>
>>>4) Ergo, a 16 ohm speaker is less sensitive than an 8 ohm because at
>>>the same WATTAGE, the former produces a lower SPL ** from 1) and 2)
>>>
>>>He did prove his
>>>point that the higher impedance speaker would produce lower SPL at a
>>>given voltage. However, when he translated this to lower SPL at a
>>>given wattage, he committed the fallacy of four terms, a non sequitur
>>>fallacy of ambiguity. 
>
>
>>If by 'he', you mean me (John Woodgate),
>
>Since I was replying to you, he would have to be someone else. Of
>course, you didn't committ fallacy of four terms, dolt. :-)


The attributions seem to have become totally confused. I have been
convinced for at least two previous exchanges that that is exactly what
you did accuse me of. Double dolt (;-).
>
>> I certainly did not 'translate
>>that to a lower SPL at a given power' (I would even more certainly not
>>have written 'wattage' - ugh!). I fail to disceren any meaning at all in
>>the phrase 'a non sequitur fallacy of ambiguity'. A non sequitur is
>>false reasoning - the conclusion 'does not follow' from the premise(s).
>>An ambiguity is a language-dependent construct - what is ambiguous in
>>one language may not be in another (e.g. if the ambiguity arises from a
>>pair of homophones).
>
>N.B.: This is where your inexperience with formal logic comes in. The
>group non sequitur comprises the formal fallacies, fallacies of
>irrelevance (ignoratio elenchi), and the FALLACIES OF AMBIGUITY. The
>fallacies of ambiguity group comprises amphiboly and equivocation,
>which includes composition/division AND FALLACY OF FOUR TERMS. You're
>out of your league here, John.

What was it you said about not expressing weights in newtons 'in
practice' ? If you are a logician, please be more consistent. In my
naive way, I assumed you were using the words 'non sequitur' and
'ambiguity' in the normal dictionary sense, not in the strict sense of
the technical terms in formal logic.
>
>Take the time to look back at my numbered summary of the original
>poster's (which is not you, John) argument. All of the numbered
>bullets except for the last are the poster's premises. The last
>numbered bullet is the poster's conclusion. 
>>>
>>>>The
>>>>article in question assumed sensitivity was inversely related to
>>>>impedance and then proved it from the same starting point. That 'begs
>>>>the question',without doubt.
>>>
>>>He never made that assumption. Read the post again.
>>
>>If one says that 'the loudspeakers are identical except for their
>>impedance' (whether 'efficiency' is mentioned explicitly or not), that
>>is indeed a statement in which it is inherent that sensitivity,
>>correctly expressed as pascals per volt (these are quantities of the
>>same nature, known as 'field quantities', which can rigorously be
>>presented as a ratio), is inversely proportional to impedance. That is
>>where the question was begged - it applies ONLY to transducers that are
>>identical except for impedance.
>
>I give you credit for trying, John, you're still not DIRECTLY
>addressing where the petitio principii occurs. Just because his
>conclusion only applies to transducers are identical except for
>impedance does not constitute begging the question. I seriously want
>to understand you, John, but it's very difficult to interpret this to
>be what you say it is.

Maybe we have a language difficulty. In British English, what I
described is exactly 'begging the question'. I don't know about the
interpretation of that phrase in Valhalla^H^H^H^H^H^H^H your location.
>
>>>Then how on earth can the software ACCURATELY calculate the reference
>>>efficiency from the sensitivity referenced to 1 watt. As far as I
>>>know, JBL speaker shop does not have a random number generator for its
>>>speaker parameters.
>>
>>Wanna bet? (;-) Why not ask JBL how they do it? I suspect they include
>>the directivity index without telling you.
>
>Well, if they include the directivity index, it must not be that
>critical a variable. Or, are you implying that JBL made an egregious
>error in its Speaker Shop software (not shareware or PD, BTW)?

I still say you should ask JBL. The only way to get from on-axis
'sensitivity' in SPL/W to efficiency (sound power/ electrical power) is
via the directivity index (DI). The DI is the factor that allows for the
fact that the SPL is different in different directions - all
loudspeakers are directional, at least in some part of their frequency
range. It cannot be omitted from the calculation, and it is far from
uncritical.
>
>>Well either you want a proper technical discussion, in which precision
>>is necessary, or you want a thread full of folk-lore and hand-waving. If
>>the latter, I will not join you.
>
>I don't see how you can take it as the latter, but let's put it this
>way. You seem to be challenging a fairly solid source on this matter.
>You would make your case a lot better if either
>a) you are a higher authority on this matter

I am chairman of the British Standards committee responsible for
standards on loudspeakers. I designed loudspeakers for an international
manufacturer for more than 20 years.

>b) you produce a reference from a more reliable source

Look at the International Standard IEC268-5

>I'm willing to entertain the possiblity that JBL screwed up, John. 

I doubt that, I think the software doesn't tell you everything. I  don't
have access to the JBL software to see what it does. Maybe I'll ask
around to see if anyone I know has it.
>
>>>> You call making unjustified assumptions about people's
>>>>motives for posting 'courtesy'?
>>>
>>>What other motive can you offer for why your response was so rude? Is
>>>it in your nature? 
>>
>>Oh, dear, accused of blasphemy, now! Peccavi. Mea culpa. Mea maxima
>>culpa.
>
>te absolvo. :-)
>
>How did I accuse you of blasphemy in that sentence, an interrogative
>one at that?

Being rude to a deity is blasphemy, but of course your e-mail address is
not a claim of deity, as you have now told me.
>
>>If you think what I wrote was rude, you are very inexperienced in
>>Abusenet! However, I did not intend to be rude, and if you feel that
>>something I wrote was rude, I regret that. My intention is only to
>>hinder the propagation of factually incorrect information.
>
>Okay. 

-- 
Regards, John Woodgate Tel. +44 (0)1268 747839
Fax +44 (0)1268 777124. OOO - Own Opinions Only
Alternative e-mail address: jmwa at thenet.co.uk
That means I get double spam with everything (;-(



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