speaker sensitivity?

I have a set of alpine type S 5 1/2 speakers for up front of the car(92 db sensitivity)(40 watts rated)

and set of apline type R 6x9's for the rear(89db)(55 watts rated)

both speakers carry the same impedence

Is sensitivity a big issue that i need to have concern with?i remember reading soemthing about keeping the sensitivty close as possible.Is 89 and 92 a huge difference i need to worry about?

thanks so much.Mike

Sensitivity is a bunch of bull anyways, that measurement is mainly relative to the frequency in which they used for that reading.  An accurate efficiency  test would be to run an RTA on each speaker recording a sine sweep with a given amount of wattage, then compare the two.

If I were a speaker manufacturer I would  use the frequency that peaked/highest in the sweep for my SPL (sensitivity) measurement.

Beat: 

For someone looking to maximize the value of his system, reference efficiency of drivers is only one variable to consider.

That said, all the others have made excellent points.

Poormanq is correct:  you do want your front speakers to be hotter, many say even 10db hotter, than rear fill.  I wouldn't worry about rear speakers having lower efficiency.

Jeff is also correct:  it does take a doubling of power to overcome a 3db difference.  However, because of Poormanq's good point, it probably doesn't matter for the rear speakers; you don't want them to be the same loudness as your front speakers.

Zacdavis is correct as well:  most low/mid priced manufacturers aren't very honest or use cracked up methods of measuring reference efficiency.  However, if they are honest enough to list some of the driver's physical parameters you can calculate reference efficiency yourself.  If you do this for everyone's drivers then you can get an OK picture of how efficient different drivers are relative to eachother.  Adire has posted a Technical Paper on calculating reference efficiency correctly.  See https://www.adireaudio.com  for this paper.

Finally, I would like to assert that, for most car audio people, attention need only be paid to reference efficiency of the least efficiency driver in the system (often the subwoofer).  Why? Because most users want their bass more hot than the rest of the frequency curve.  In a correctly set system the gain of the highs and mids need to be TURNED DOWN to make the bass hotter relative to the highs and mids.  Please note and contrast this correct way to increase bass with what most car audio idiots do - jack up the subwoofer gain to inappropriate levels.  Also note that even those looking for a balanced system will likely need to reduce the gains or otherwise attenuate the mids and highs.  THUS, since system efficiency will almost always be attenuated relative to the least efficient driver (usually the subwoofer), it is fruitless for most car audio people to look too hard at midrange and tweeter sensitivity.  Instead, primarily look for the SOUND and FREQUENCY RESPONSE performance you want in a midrange and tweeter.  Indeed, for many car audio people, high sensitivity of the mids and highs will only INCREASE the tendancy to turn the sub-gain up too high to match the rest of the system.  In other words, who gives a rip about efficiency when 99/100 times you'll be attenuating the midrange / tweeter anyway.

Now, for the subwoofer, or the least efficiency driver in the system, it DOES become VERY important to consider efficiency if you are interested in SPL or showing off.  This is of great importance especially if you have a small alternator and/or a small amplifier AND like loud music.  In such a case you NEED to pay very close attention to efficiency.  If, on the other hand, you have electrical system room for a 600+ watt amplifier, efficiency concerns become less important.  Notice that I didn't say go away.  (Many of these concerns also fly away if you aren't interested in competing or SPL, but rather comfortable volume levels in-car. )  However, MOST car audio people will want to consider subwoofer efficiency in system planning if they have certain loudness expectations.

Nutshell of my hypothesis and conclusion:
1) Reference efficiency is of little importance for midrange / tweeters in a multi-amplifier and subwoofer system.
2) This reduced importance is because the midrange / tweeter will almost always need to be attenuated relative to the least efficient driver in the system (this is almost always the subwoofer). 
3) If you like showing off sub-bass then efficiency of the sub-bass system becomes very important.
4) Sub-bass efficiency importance is reduced if you have gobs of power.
5) While sub-bass efficiency importance is reduced, sophisticated system designers will still pay attention to efficiency.

KFR01] wrote:

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ow, for the subwoofer, or the least efficiency driver in the system, it DOES become VERY important to consider efficiency if you are interested in SPL or showing off. This is of great importance especially if you have a small alternator and/or a small amplifier AND like loud music. In such a case you NEED to pay very close attention to efficiency. I

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