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Old 18th November 2008, 10:13 AM   #1
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Default How to convert sensitivity values

Please could some one help me with a simple conversion:

A driver that I am looking at is rated SPL: 94.2 dB 2.83W/1m

What is this the equivalent to in dB/1W/1m?

Thanks in advance.
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Old 18th November 2008, 10:40 AM   #2
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Hi,
You mean 94.2 dB 2.83V/1m not W.
2.83 V is only equivalent to 1 W in 8 Ohm.
All drivers are measured using voltage source, so it is a fallacy to express sensitivity in dB for 1W/ 1 m, despite many manufacturers still do it.
The main concern of a DIY buider is sensitivity : what will be the output for a given voltage ?
Power calculations are related to efficiency and are not of much practical value.
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Old 18th November 2008, 11:08 AM   #3
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Forr: Thank you for your reply.

Parts Express must have made a typo :

http://www.partsexpress.com/pe/pshow...number=290-386

The DIY designer stipulates a min sensitivity of 97dB/1W/1m :

http://www.lampizator.eu/SPEAKERS/PR...20Kitchen.html
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Old 18th November 2008, 11:27 AM   #4
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Hi Dublin,

Parts express : typo just for this driver..

Endrophine :
"Minimum sensitivity dB/1m/1W
is 97 dB"
(1m and 1W inverted)

Usually,
it is expressed as dB/1W/1m,
it should be read
dB for 2.83V at 1 m
See Beyma docs for a good example.
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Old 18th November 2008, 03:17 PM   #5
Ron E is offline Ron E  United States
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The difference is 10*log10(8/Re), where Re is the DC resistance of the voice coil. This does not account for the fact that most 8 ohm drivers are 6 ohms, but such is life when you are dealing with irrelevant specs.

Some will say that the 2.83V figure is cheating, and others will say that the 1W figure is meaningless. I am of the latter camp. Your amp doesn't put out watts, it puts out volts - solid state or tube. If you hook up a speaker with a 97dB/2.83V of any impedance to any amp and feed it 2.83V, you will get 97dB. Go to the next speaker that is 94dB/2.83V you will get 94dB from any amp and so on and soforth. This means matching a woofer to a tweeter with varying rated impedance is easier with the 2.83V spec.

If you hook up a 4 ohm speaker that is 97dB/2.83V and feed it 1Watt, you get 94dB. This is where the tube amp, who is "voltage challenged" will cry "not fair, that's an exaggeration". If you hook up a 16 ohm speaker that is 97dB/2.83V you will get 100dB if you feed it one watt - now which spec is "exaggerating".

An 8 ohm woofer doesn't match the 8 ohm resistive rating (although it might be 6+5.3i ohms) anywhere within its passband anyway, it may range from 5.5 to 50+ ohms, so you can see that the 1W figure is more ambiguous because it could be 1W into 8 ohms nominal (meaning not actual, where Re is actually in the 5.5-6.2 ohm range) or 8 ohms Re. If you really wanted a true "1Watt" sensitivity rating, it would have to be a curve, because the impedance of the speaker is constantly changing.

The 2.83V figure is less ambiguous because it means that whatever amp you hook it up to, if you feed it 2.83V, you will get the rated SPL. Now that assumes that everyone is being perfectly honest in their specs Have I made my point?
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Old 18th November 2008, 03:59 PM   #6
sreten is online now sreten  United Kingdom
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Quote:
Originally posted by dublin78
Forr: Thank you for your reply.

Parts Express must have made a typo :

http://www.partsexpress.com/pe/pshow...number=290-386

The DIY designer stipulates a min sensitivity of 97dB/1W/1m :

http://www.lampizator.eu/SPEAKERS/PR...20Kitchen.html
Hi,

It is no typo at PE, all drivers are measured with the equivalent
of 2.83V @ 1m, e.g. 2V at 0.5m gives the same level readings.

This is often quoted as 1W at 1m, which is meaningless once
you start looking at a drivers or loudspeaker impedance curve.
This is often quoted to mislead for nominally 4 ohm loudspeakers.

Zu for example claim 100dB/W/1m by using a high impedance region.

However the simple answer to your question is for an
8 ohm driver the two values are effectively the same.

/sreten.
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Old 18th November 2008, 04:02 PM   #7
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The typo is the 2.83W instead of 2.83V
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Old 18th November 2008, 04:49 PM   #8
sreten is online now sreten  United Kingdom
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quite right, sorry about that, /sreten.
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Old 18th November 2008, 05:32 PM   #9
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Thanks for your help.

RonE: excellent explanation - thanks.
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Old 18th November 2008, 06:58 PM   #10
Pano is offline Pano  United States
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Ditto for me. As a DIY guy, I'd like to see the the sensitivity given at a set voltage, not power.
For the reasons stated above.

If it's 2.83V - that's fine by me.
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