Speaker efficiency vs sensitivity

[Vaughan]

Hi guys,

Having a discussion at the moment concerning efficiency and sensitivity and some people are arguing that it's just a hair splitting semantic game.

If you have two woofers with similar efficiency but differing impedance then the sensitivity will differ. Surely ? If you have one 8 ohm woofer and another 4 ohm woofer, both have the same efficiency but the 8 ohm woofer will have - 3dB sensitivity given that it will only draw half the power.

Agree ? Disagree ? Is it technically accurate to say that sensitivity and efficiency are the same thing or should one separate both terms ?

[AndrewT]

efficiency is power output (acoustic watts) / power input (electric watts). Usually ~1% but some loadings can push this to near 50%.

Sensitivity is SPL (sort of equivalent to power output) at a specified voltage input.

These two equations show that the two definitions can not be regarded as the same.

You are right, changing impedance has an effect on the power delivered to the speaker driver. It changes the sensitivity. It cannot change the efficiency.

[picowallspeaker]

Hi guys,

Hi!

Having a discussion at the moment concerning efficiency and sensitivity and some people are arguing that it's just a hair splitting semantic game.

Math is not an opinion.

If you have two woofers with similar efficiency but differing impedance then the sensitivity will differ

Sensibility is measured by applying a 2,83 V voltage to the driver ,and measuring the response at 1 meter.

Surely ?

Math is not an opinion

If you have one 8 ohm woofer and another 4 ohm woofer, both have the same efficiency but the 8 ohm woofer will have - 3dB sensitivity given that it will only draw half the power.

For all kind of drivers ,they exhibit not a costant impedance over frequency and phase .Also , a 4 Ohm coil will have a minor Re and increase in power and current demand ,which is frequency- dependant and applyes to a non perfect resistive device.

Agree ? Disagree ? Is it technically accurate to say that sensitivity and efficiency are the same thing or should one separate both terms ?

Longer coils would store more groundside electrons

[Vaughan]

So then it's possible to have the same efficiency between two speakers but different sensitivities ? You guys are obviously more knowledgeable than I. : )

[Vaughan]

A guy on the forums essentially said that the efficiency is often referred to with reference to a specific frequency, but it could also be specified as average over the coverred band of the speaker and that sensitivity is the average output at a given voltage (directly proportional to power) over the band coverred. But looking at average sensitivity, and average efficiency of a speaker, they are related he said. eg The higher the sensitivity the higher the efficiency.

My understanding, as basic as it is, is that efficiency is different to sensitivity and perhaps can only be loosely associated with sensitivity. But it's not technically accurate to assume both are similar terms because they're not.

[AndrewT]

Originally Posted by Vaughan

(directly proportional to power)

directly proportional to square of power.

Both Efficiency and Sensitivity can be specified for a single frequency or and range of frequencies. The specification if done properly will make that quite clear.

Some business trying to pull the wool over your eyes may deliberately miss out part/s of the specification conditions and compare results that are not comparable.

[Vaughan]

BTW, thank you Andrew and Picowallspeaker for posting and offering your advice. If efficiency is power out/power in and sensitivity is power out/voltage in then obviously the two terms are not compatible since power is not voltage. I assume my understanding is correct but it's more than possible it's not.

The thing I was interested in was the fact that you can have identical efficiencies but differing sensitivities. As in the example I made earlier but two speakers having identical efficiency but since the impedance of both differ (8 ohm to 4 ohm) the sensitivity would be different between both. This would imply that both terms are not 100% compatible with each other, as in you can't exchange efficiency for sensitivity or vice-versa.

[Vaughan]

Originally Posted by picowallspeaker

Also , a 4 Ohm coil will have a minor Re and increase in power and current demand ,which is frequency- dependant and applyes to a non perfect resistive device.

Between a 4 ohm and 8 ohm speaker with similar sensitivity, wouldn't the 8 ohm speaker be more efficient since it's drawing half the power ? Correct me if I'm wrong but don't bulldoze me...

[Vaughan]

Originally Posted by AndrewT

It changes the sensitivity. It cannot change the efficiency.

I don't understand this. As I said to Pico, if you have two speakers with identical sensitivity but one is a 4 ohm and the other 8 ohm, wouldn't the 8 ohm speaker have higher efficiency since it's drawing half the wattage ?

[AndrewT]

if two near enough identical drivers are built witha 4ohm VC and an 8ohm VC and both have the same efficiency. Same motor, same Moving mass, same cone area etc.
Then it follows that each will need a different drive voltage to reach the same SPL.
The 4ohm will require 2V for it's sensitivity measurement i.e. XXdB/2V @ 1m in midband.
The 8ohm will require 2.83V for it's sentivity measurement i.e. XXdB/2.83V @ 1m in midband.

When these two sensitivities are changed to watts they come out the same, eg. XXdB/W @ 1m in midband.

The two drivers have the same efficiency and the same sensitivity, Well I said they were near enough identical.

The problem you are having is that some suppliers/manufacturers quote sensitivity differently and hide the fact they have quoted it differently to try and gain an apparent advantage over their competitors. They say 1W when they actually mean 2.83Vac of drive signal when the driver is lower than 8ohms nominal. And some will do the opposite and quote 1W for a driver that is over 8ohms nominal impedance. There must be sufficient in the specification to determine what way the sensitivity is being measured. If there is information missed out then it is likely that the manufacturer is trying to hide something.