Sensitivity Issues

gregm3,252 posts04-07-2001 6:19pmEleonida, excellent afvice, IMHO!. A few rules of the thumb waiting for cognoscenti. The Ohm load doubles (or halfs, as it were) per 3 db rating. I would pounce on 91 vs 88 dbs (the difference could mean a bigger amp, try getting THAT past yr wife -- or mine, for that matter). Resistance plays with the sound spectrum and average 8-4 ohms is, usually, happily dealt with by most amps. It doesn't compensate in the way I think you think it does (i.e. make things easier, low load but low resistance, so my amp loses on one and gains on the other). Beware of low resistance, it requires mamouth efforts to control... in other words, it'll suck the juice (the life) out of yr amp.
Concluding, if U like yr music at reasonable levels and, worse still, listen to classical, go for sensitive -- 89 upward -- speakers, and check out their lowest resistance rating. Most modern speakers play around a minimum of 4; yr Pass can easily match that.


~~~~~~~~~~~~~~~~~
Excellent post, Now i clearly understand the ohm thing. 
Yes FR/WB/High sens speakers are amp friendly = higher ohms vs the xover design.

89db+.. I'd suggest 91db is the cut off point. 
All FR/WB/ high sens speakers, all specs start 91db ++
89db is still xover low efficient type. 


**and wosre still if you listen to classical music*** Yes classical music, demands/equires higher sens speakers. 
xover  designs fail at classical due to lower sensitivity. 
Very glad you posted the classical music as a drain on efficiency of a  amplifier. 

 If you can, go for 90db (which is fine)

~~~~~~~

 Close but no cigar
90db is still in xover territory
91db is the lowest acceptable rating for a  true wide band/higher sensitivty speaker. 

system.I wouldnt go below 90 dB's with the Pass.I can hear the difference between 1 dB up or down in a speaker.

~~~~~~~~~~~~~~~~~
Yep
1 db makes a  difference. 
My Seas Thors at 87db, are unacceptable for classical music, And this goes for all dome tweeters as unacceptable to voice classical music due to  its high demands.
xover speakers usually are below 90db , rarely if ever 91db, making xover speakers unacceptable for classical music. 
If you like jazz only, wel then xover designs wil work for you.
But lets say you like both genres, Well now you will need  2 sets of speakers,
Or just get a  higher senstivity speaker which can voice both genres. 

eleonida, to answer your question; as a rule of thumb efficiency drops with impedance. Your amplifier's power increases because current flow increases as long as your hand can pass the current. 
As another rule of thumb, any high end system should be able to hit 100 dB. This assures you can handle all peaks gracefully. Most of us never listen this loud. Power doubles with every 3 dB. So if you have a speaker with 87 dB/1 watt/meter, 90 dB requires 2 watts, 93 dB requires 4 watts, 96 dB 8 watts, 99dB 16 and 102 dB 32 watts. This is wonderful except nobody listens to their speakers at 1 meter. Depending on the room sound pressure levels can be an easy 6 dB down at the listening position. So your 87 dB/1 Watt/meter becomes an 81 dB/watt/meter speaker and with 30 watts you are only going to make it to 95dB. 95 dB is a reasonable loud level that many rockers will listen at and if you do with 30 watts you will be clipping the peaks and the sound will be distorted. So, with your amp you should have speakers with a sensitivity of 93 dB/watt/meter or above and there are many available such as the Klipsch Heritage series speakers. If Your Class A Pass amp is a wonderful sounding amp and will drive a Klipsch loudspeaker to very pleasing levels without clipping. You can't expect rock concert levels out of it but those levels damage hearing. If a system has adequate low end you do not need to play at those levels to get the effect of being at a live concert. Unfortunately, most systems do not but, that is another subject.