Speaker sensitivity is only related to the driver alone ??? Or it depends on the cabinet too ???

Naveenbnc

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Hi Guys...

Mid range (in terms of cost) bookshelfs generally have a sensitivity around 86db.

Mid range Floorstanders have slightly higher sensitivity around 89 to 90db.

So I'm just wondering sensitivity also depends on the cabinet size and shape also ???

Higher sensitivity speaker is easy to drive generally. So how is it easy for an avr to drive an Fs with multiple drivers, as compared to a BS having single driver. (Assuming the same driver is used in both cases)

Just asking to understand...any suggestions please...

Thanks in advance
Naveen
 
Naveenbnc- For an amplifier I believe the important factor is the total load of a speaker and it does not care about the no of drivers that contribute to the total load. The higher the impedance/sensitivity the easier it is to drive a speaker and vice versa. This comes from basic physics, Ohm's law

The 1st part is explained by the equation (V=IxR). If you increase the level of resistance (R) i.e impedance in a circuit then you need lower amount of current (I/Amp) to achieve the same volt (V).
The 2nd part of this equation is the Power (Watt) calculation which is how we measure the amplifier power. The equation is Power(P) = Volt(V) xI (Current/Amp).
So when resistance i.e impedance increases, the amount of current drops to get the same volt and when the amount of current drops the power coming from the 2nd equation also drops. This is why an amp needs to work less harder to drive a high impedance/high efficiency/sensitivity speakers.
I don't believe that speaker cabinet plays any role in this equation.
Thanks.
 
Very interesting question indeed. Let's try to see what are the things at play, when a speaker is being driven by an amplifier.

Firstly, lets be clear that the sensitivity mentioned is the Sound Pressure Level it produces at a distance of 1 metre by 1 watt. Then onwards, any increase of 3dB demands double the power. So, a 86dB speaker would need 1 watt to produce 86dB of SPL at 1 metre, it would need 2 watts to produce (86 + 3) 89 dB, 4 watts fot 92 dB and so on. But this has a caveat, this is true assuming the impedance remains constant throughout the SPL and frequency.

Next we need to know that there are broadly, three types of electrical loads, Resistive, Inductive and Capacitative. A speaker is a combination of all three of these and together they define the impedance of a speaker. Since these load characteristics change with frequency, we have a far more complex behaviour of a speakers electrical character when we take the crossover and speaker cables into the total LCR Circuit.

Keeping the above points in mind, we can say that whether a speaker of 86dB will require either more than or less than 2 watts to produce 89dB of SPL depends on what frequency it's going to reproduce at that instant. That's the reason why the instantaneous power delivery depends on the source material too.

Let's come to the cabinet part now. Imagine trying to force a driver to stop while its making sound. Any external damping applied to the driver would change it's impedance characteristics and produce back EMF. A smaller cabinet would contain less volume of air in it. So the compressibility resistance of the air is higher and hence the driver damping is more. Incase of a larger cabinet the compression factor is logarithmically less and if used with 2nd order or higher crossover then the phase differential compression from different drivers would make the damping less. That would result in different impedance curve based on cabinet volume, and hence the amplifier's drivability comes into picture.

Along the impedance curve of a speaker there are regions where "voltage leads current" and "current leads voltage". These role reversals take a lot of additional "pressure" on the power supply of the amplifier. If the AVR is sufficiently powerful to handle these then I don't see any theoretical issue of not being able to drive slightly inefficient speakers.

Please keep in mind that to indentify the compression artefacts of an underpowered speaker is extremely difficult, atleast just by listening.
 
Hi Guys...

Mid range (in terms of cost) bookshelfs generally have a sensitivity around 86db.

Mid range Floorstanders have slightly higher sensitivity around 89 to 90db.

So I'm just wondering sensitivity also depends on the cabinet size and shape also ???

Higher sensitivity speaker is easy to drive generally. So how is it easy for an avr to drive an Fs with multiple drivers, as compared to a BS having single driver. (Assuming the same driver is used in both cases)

Just asking to understand...any suggestions please...

Thanks in advance
Naveen

Floorstanders from the same model series using the same drivers usually have higher sensitivity because they usually use multiple mid-bass drivers reproducing the same same frequency range and as a result the tweeter does not have to be attenuated (volume lowered) to match the sensitivity of the midbass. Higher sensitivity = louder speaker not easier to drive speaker. I think you are confusing normal speakers with higher sensitivity with some very impedance stable high sensitivity speakers adored by class A tube amp enthusiasts.
 
Last edited:
Indranil,Otpidus & danielnaveen,

Thank you so much for your inputs.... let me study and understand properly .... thanks a lot for your time ... :)
 
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