HOW TO UNDERSTAND DIFFERENT IMPEDANCE RATES?!!!

God god at almighty.com
Sat Jun 7 03:19:14 EST 1997


>> 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.
>
>You're totally missing the point  You are confusing voltage level with
>power levels.
>
>You are putting LESS POWER into the 16 ohm speaker which results in a lower
>sound level.  This has absolutely nothing do do with efficiency which is
>function of the physical engineering design of the speaker and the
>enclosure.
>> 
>> The assumption, of course, is that both speakers have the same efficiency
>
>> and are, in fact, identical except for their impedances.
>
>If thet are of identical impedances, puting 1 watt of power into either
>speaker will result the EXACT SAME sound level!
>> 
>> John Fields

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) of both drivers is the
same, they will produce the same SPL at a given power level. 
As an aside, the argument is not begging the question (petitio
principii) although it does seem to be. After all, 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. 



More information about the Audiolog mailing list