Sensitivity and Impedance: What it means and how it matters

[spwath]

Lets start with definitions:

 

Voltage Sensitivity: The volume produced by a driver per unit voltage. In speakers it is usually measured as dB/2.83V at 1 meter, in headphones it is usually measured as dB/mV.

 

Power Sensitivity: The volume produced by a driver per unit power. In speakers it is usually measured as dB/W at 1 meter, in headphones it is usually measured as dB/mW.

 

Impedance: The resistance a component will have to alternating current. Measured in Ohms(Ω).

 

Now, how does this affect you?

 

Lets start with Impedance:

Impedance determines how much power will be producing noise. Ill start with speakers for simplicity sake.

An amp is rated for 100w at 8 Ohms. That means that it would produce 200w into 4 Ohms, and 50w into 16 Ohms (assuming it is rated for those impedances and wattages, don't want to kill your amp)

It seems like this would matter a lot then, however, 200w is NOT twice the volume as 100w. Ill get into this in sensitivity and efficiency.

 

Now for Sensitivity:

Usually a headphone or speaker will just have one of these specifications listed, and often it is hard to tell which one, however, it matters a lot.

If a speaker has and sensitivity of 98dB/W (very sensitive, often in pro audio) then that means if an amp outputs 1w (assuming that is at the same impedance of the speakers), it will make 98dB of sound. However, a 100W amp will not make 980dB. Im not going to go into all the details of this now, as this is less related to this topic, but just keep that in mind.

 

 

Sensitivity is the main determining factor of how hard a headphone is to drive, and what volume you will receiver.

For the most part, in headphones, Impedance can be ignored. In speakers it makes a bigger difference, because the numbers are lower, and make a bigger difference.

 

That is essentially it. I will add more information if I feel the need to.

I know @Dackzy you will be happy to have this to direct people to.

[Dackzy]

4 minutes ago, spwath said:

SNIP

yep, I think that I have written this  over 50 times now, never thought about a post  

I kinda have a bit with it in my DAC, amp thread, but this is going to be very neat to have to link, when I am lazy.

Might aswel put this in my signature.  

[SSL]

Incorrect information.

 

Your definition for "efficiency" is actually power sensitivity. Sensitivity can be expressed as either voltage or power sensitivity.

 

Efficiency is a ratio, usually expressed as a percentage, of useful power output divided by power input. Efficiency can of course be calculated from sensitivity.

 

Impedance is the resistance of a circuit to alternating current when voltage is applied. It is not simply another word for "resistance", and it definitely doesn't mean "resistance to power".

 

I have links in my siggy that explain these things.

[spwath]

3 minutes ago, SSL said:

Incorrect information.

 

Your definition for "efficiency" is actually power sensitivity. Sensitivity can be expressed as either voltage or power sensitivity.

 

Efficiency is a ratio, usually expressed as a percentage, of useful power output divided by power input. Efficiency can of course be calculated from sensitivity.

 

Impedance is the resistance of a circuit to alternating current when voltage is applied. It is not simply another word for "resistance", and it definitely doesn't mean "resistance to power".

 

I have links in my siggy that explain these things.

Ah, Ok, that makes sence, ill fix these, dont want wrong information here.

Thanks.