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Old 25th November 2011, 03:27 PM   #21
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally Posted by Brian Oshman View Post
If it is listed as 1 watt into then it is 1 watt no matter
what the impedance is as it is 1 watt into that load.
Hi,

Problem is for the sensitivity of 4 ohm drivers this simply isn't true.
Sensitivity for hifi is for 2.83V at 1m, otherwise it is not sensitivity.

Drivers with the same sensitivity sound as loud as each other
with the same voltage drive, that is how it is intended to work.

Sensitivity of 4 ohm speakers is not measured with 2V to compensate
as this would mean a 4ohm mid unit would no longer match a 8 ohm
tweeter if they are selected for the same sensitivity.

Compare some 4 and 8 ohm versions of hifi drivers, you'll soon see.

rgds, sreten.
__________________
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When your only tool is a hammer, every problem looks like a nail - Abraham Maslow

Last edited by sreten; 25th November 2011 at 03:32 PM.
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Old 25th November 2011, 07:56 PM   #22
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Join Date: Jul 2010
Location: Stewartsville, NJ
Quote:
Originally Posted by sreten View Post
Hi,

Problem is for the sensitivity of 4 ohm drivers this simply isn't true.
Sensitivity for hifi is for 2.83V at 1m, otherwise it is not sensitivity.

Drivers with the same sensitivity sound as loud as each other
with the same voltage drive, that is how it is intended to work.

Sensitivity of 4 ohm speakers is not measured with 2V to compensate
as this would mean a 4ohm mid unit would no longer match a 8 ohm
tweeter if they are selected for the same sensitivity.

Compare some 4 and 8 ohm versions of hifi drivers, you'll soon see.

rgds, sreten.
You are missing the point. It depends on the method used to measure the sensitivity.

If you are measuring at one watt then the variables are the load and the voltage.

If you are measuring at 2.83 volts then the variables are the load and the wattage.

Sure if you are comparing a 4 ohm and an 8 ohm speaker then the sensitivity will be different if simultaneously connected to the same source but if they are connected to individual sources then the sensitivity would be the same if the spec were based on 1W/1m. They would of course be different if based on 2.83V/1m.

In the first rating we are adjusting the wattage to match based on load, in the second rating we are adjusting the load to a constant output.

This is why I said that it is how the measurements are derived that matters and how to really determine the given sensitivity and make a comparison.
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Old 25th November 2011, 10:28 PM   #23
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally Posted by Brian Oshman View Post

You are missing the point.
Hi,

No I'm not. I know what sensitivity is and what "efficiency" dB/W is.

That they are often confused is not my problem, or that 4 ohm drivers
are often misdescribed as dB/W when it is fact actually dB/2.83V.

The problem is rife in car audio, with 2 ohm drivers being 6dB out.

dB/W is meaningless because real driver impedance is not considered.
Nominally 4 ohm drivers are not measured with 2V, nor
are nominally 2 ohm drivers measured with 1.41V.

Honest specs for a 4ohm driver might say :
93dB/2.83V/1m (90dB/W/1m)
For a 2 ohm driver :
96dB/2.83V/1m (90dB/W/1m]

Only for an 8 ohm nominal driver is sensitivity the same as "efficiency".

rgds, sreten.
__________________
There is nothing so practical as a really good theory - Ludwig Boltzmann
When your only tool is a hammer, every problem looks like a nail - Abraham Maslow
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