EFFICIENCY

oops that should be ohms.............my difficieny

I have A Classe amp rated at 100 watts per channel into 8omhs and 190 watts into 4omhs.I am looking at two speakers,one has an efficiency rating of 86 and the other 90.

Assuming both speakers are rated at 8 ohms, the 86 db rated speaker would put out 106 db at full 100 watt output on the amp. The 90 db speaker would put out 110 db with 100 watts. Note that 10db = twice as loud. so 110 db is twice as loud as 100 db. Also, the 106 and 110 db speaker output would be at 1 meter from the speakers.

How important is this difference in the final sound quality?
Pegasusxls

Not important at all to the sound quality. Power and efficiency specs have no more to do with sound quality then gas tank size and gas mileage ratings have to do with automobile quality.

Cheers,
John

Jmcgrogan2 is correct on how loud the peak sound pressure levels will be with each speaker. However, another thing to consider is how each speaker will sound (i.e. tonal balance), which will vary depending on not only the voltage sensitivity but the nature of the load. For this you need an impedance vs. frequency curve. For instance, many speakers have a combination of low impedance and a highly capacitive phase angle in the mid- to upper bass. If you use a tube amp you will probably run out of current in this region and the sound may become either lean in the bass and/or flabby and boomy in the bass. Since you are using a Classe solid-state amp you probably won't have this issue since SS amps usually have low output impendances, but still it is something to think about.

You should find out what the lowest and nominal impedance is for each of these speakers and that your amp is stable at this minimum impedance. Typically good quality amps are at least 2 Ohms stable. If your speaker dips below the amps impedance limit it will clip i.e overload the amp.

Speaker manufacturers usually suggest the power an amplifier should have to drive their speakers properly e.g 30-150 W @ 8 Ohms. Lets say both speakers have the same nominal impedance of 8 Ohms and minimum recommended power is 30W. This means that the 86db Speaker will need about 70W while the 90db speaker will only need 30W to produce the same volume.

Given your amp is limited to 100W the difference in efficiency can become significant as you would want your amp to run in effortless mode rather than strain as it gets closer to its limit.