HOW TO UNDERSTAND DIFFERENT IMPEDANCE RATES?!!!

John Woodgate jmw at jmwa.demon.co.uk
Sun Jun 8 01:38:35 EST 1997


In article <339c4542.1672239 at news.pacbell.net>, God <god at almighty.com>
writes
>>>John Fields is absolutely correct in this respect and hit it right on
>>>the money. If you consider sensitivity to mean SPL as a function of
>>>voltage, then the original theory is correct: the higher impedance
>>>speaker would produce lower SPL at a given voltage. However,
>>>sensitivity generally refers to SPL as a function of power. As John
>>>Fields said, if the efficiency (dB @ 1W, 1m)
>>
>>You can't be god, because that is wrong. Efficiency relates power in and
>>*power* out. SPL is not power. 
>
>Apparently, you are a little disgruntled because you incorrectly
>identified a petitio principii.

Being a god, you' know that of course, even if I deny both your
assumption and your critique. Just becuase you know the Latin name for
something does not mean that you could see one if it bit you. 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.

> Not that this in particular makes your
>most recent assertion incorrect.

Oh.
>
>But let me quote you:
>"If the reference efficiency, ho, is unknown, it can be accurately
>calculated from the sensitivity if the sensitivity is referenced to 1
>watt." -- JBL Speaker Shop help file

Not that alone, you need the directivity index as well. Maybe that was
an inadvertent omission by JBL?

>Essentially, sensitivity and efficiency say the same thing; it's just
>a difference in derived units.

Quoting manufacturer's literature as a technical authority shows extreme
naivety. The 'sensitivity' quantities that have been mentioned are all
dimensioned quantities. Efficiency is a pure ratio, and dimensionless.
>
>As an aside, you quoted the wrong passage from my post. If you note, I
>don't even use the word "efficiency" in the excerpt you selected.
>However, I extended you the courtesy of looking back to my original
>message to understand what you were referring to. 


I quoted the bit that was wrong, yes. I did not quote some bits that
were right. You call making unjustified assumptions about people's
motives for posting 'courtesy'?
-- 
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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