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???Why The HUGE Discrepancy in Sensitivity Ratings???

I'm shortlisting speakers & have noticed a HUGE difference in the sensitivity ratings provided by manufacturers & what they actually measure.For example the Martin Logan Motion 35XT is specd at 92db.sens.@1 watt & yet actually measured at 87db!At least 4 different pair of speakers on my list are the same,specd at 90db or better @1 watt yet NONE measured better than 87db so what gives?
freediver
philjolet's avatar
philjolet
2,262 posts
 
are any of them made by Volkswagon?

...

;^)
newbee
4,093 posts
 
Measurement techniques perhaps? Did yours match the manufacturers?
tls49's avatar
tls49
1,318 posts
 

If the sensitivity is measured in a room instead of an anechoic chamber, it will be 2-3db higher. Some manufacturers have been known to spec room sensitivity. Also, some specifications say 1 watt and others say 2.83v. If the speaker is 8 ohms, it doesn't matter, they are the same. They are not the same with a 4 ohm speaker. If the spec says 2.83v, that is 2 watts with a 4 ohm speaker, and the 1 watt spec will be 3db lower.

timlub
1,649 posts
 

The only fairly accurate way to measure is 1 watt 1 meter anechoic...

even then,  many speakers are  not adequately impedance compensated.  As posted above... 1 watt @ 8 ohms is 2.83 volts, 1 watt @ 4 ohms is 2.00 volts.... a big difference in power for rating a speaker... Many speakers are called 8 ohm that stray down to even 3 or 4 ohms and those measurements can be quite flawed....

Plus when put in them in a room setting, you know deal with peaks in the room, so someone could easily rate at its highest peak rather than 1k or over average frequency response. 

Not sure that there is anyway to win here.

These are just a few of the problems when quoting sensitivity...

If they are using off the shelf parts, like a seas, scan speak, audax, etc,  you could take a look of individual drivers and go from there... If manufactures are truly trying to give you a flat response,  the lowest sensitivity of any single driver should be very close to the sensitivity of the entire speaker,  but even that is flawed... Tough call.

Tim



erik_squires
5,268 posts
 
FYI, sensitivity and efficiency are two different things, and is rarely the same for any given speaker.

Efficiency is measured at 1 Watt, and is also called "Power Efficiency." Sensitivity is measured at 2.82 Volts and is also called "Voltage Sensitivity." If the speaker is purely resistive and measures exactly 8 Ohms, then these two figures will be the same.

Efficiency explains how much work is required to produce a certain volume level, while voltage sensitivity cares nothing for the amount of work, and only thinks about what happens when a certain voltage is applied. Take for instance a 1 Ohm speaker, remember the old Apogees?

At 2.83 Volts, an 8 Ohm speaker draws 1 Watt, a 4 Ohm speaker 2 Watts, 2 Ohm speaker 4 Watts, and a 1 Ohm speaker draws 8 watts.

Sensitivity could be accurately called 85 dB, but at 1 Ohm it would actually be drawing 8 Watts, so the efficiency is actually a lot lower, probably around 78 dB or so.  I've gotten quite forgetful about the precise math, but you get the idea.

This matters more to tube amplifiers, which have the same power output regardless of the transformer taps. For those with reasonably beefy solid state amplifiers, and speakers with impedance curves at 3 Ohms or higher voltage sensitivity matters more.



Best,


Erik
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