HOW TO UNDERSTAND DIFFERENT IMPEDANCE RATES?!!!

God god at almighty.com
Sun Jun 8 17:03:50 EST 1997


The original fallacy:

>Consider an amplifier with an 8 ohm output impedance feeding 8 volts into 
>a speaker with an 8 ohm impedance.  The speaker will be dissipating 8 
>watts of power and will generate a specific sound pressure level.
>
>Next, consider the same amplifier putting 8 volts into a 16 ohm load.
>Since P = E^2 / R, the power being pumped into the load is 8^2 / 16, or 4 
>watts, which will yield a lower sound pressure level.
>
>The assumption, of course, is that both speakers have the same efficiency 
>and are, in fact, identical except for their impedances.
 
1) An amp driving 8 volts into 8 ohms will dissipate 8 W of power and
an SPL of  A.
2) An amp driving 8 volts into a 16 ohm load will dissipate 4W of
power and an SPL of  >A.
3) We assume that both "speakers" in 1) and 2) have the same
efficiency (and identical except for their impedances.)
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 you still insist that the fallacy is petitio principii, please tell
us DIRECTLY where this occurs.

>>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.

Well, if you don't want people to infer that, make it less obvious.
And I never claimed to be god.

> Just becuase you know the Latin name for
>something does not mean that you could see one if it bit you. 

Well, if  little flees bit your glutei maximi, you wouldn't be able to
see it either.

>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.

>>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?

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.

>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.

Christ, not for practical purposes. Force is a vector quantity, but we
don't say "this object has 450N, in the direction of the center of the
earth." 

> 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? 



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