how much current is enough?


I know that to gain 3db of additional headroom from your speakers you need to double the power from your amp...given that, its easy enough to calculate how many watts will be suficient to reach your speakers rated max volume level before compression...or to see if your amp will play loud enough for your particular listening habits...
and i know know that watt/sq.rt of resistance = current ...so i can calculate how many amps my amplifier will put out into various loads, but i dont know how many amps are enough for a given speaker...or if the difference between say 10 amps and 12 amps is a lot?

with regards to a specific difficult to drive speaker the Totem Mani 2 how much current is enough??

its specs are
4 ohm nominal...it drops down to 2 ohms, all resistive
81 db sensitivity at 1w/1m

and it uses an isobaric configuration which i gather makes it require more current than normal..but again i dont know why or how to calculate it...

so from a mathematical point of view how do i figure this out...

and in terms of the ability of am amp to put out lots of current what specs are the most important to look at?

thanks
mbacinello
"Another simmilar question...so if the mani-2's (which I dont as yet own...but am considering) are 81 db sensitive...that means that they will play 81 db with 1 watt, 84 with 2, 87 with 4 etc. That means that to get to the 110db, which their spec sheet says is their maximum volume level they would need 1024 watts of power."

Yes, your process is correct but I didn't check your arithmetic.

"..two things...is the sensitivity measured at 8ohms?"

No. 'Sensitivity', a term that became popular with solidstate amps, is the acoustic output measured 1 meter away from the speaker when driven with a signal that produces 2.83 volts into an 8-ohm test load (which happens to be 1 watt) and driven by a constant-current amp, which means solidstate, not tubed. 'Efficiency' is measured with 1 watt of input INTO THE APPROPRIATE LOAD, and that term is NOT used much anymore. So...sensitivity is measured with 2.83 volts into 8 ohms while efficiency is measured with 1 watt (into the load equal to the speaker's rated impedance). See below about Totem's rating.

"...such that a four ohm nominal speaker draws twice as much power from the amp?"

Yes, generally.

"...in which case those numbers should all be double and it would draw 2048 watts at 4 ohms to play 110 db?? and secondly, that's way more watts than the speakers can handle. Does that mean that they could never actually play as loud as there specs suggest??"

Well, sort of. As merge03 indicated, these things never work out exactly because, at least partially, they're based on subjective measuring techniques.

Merge03 also is absolutely correct in his statement that high listening levels are FAR easier and less expensive to achieve with more-sensitive speakers than with very-high-power amps. Also, it seems that achieving a sense or feeling of dynamic 'ease' is much-more difficult with low-sensitivity speakers and high-power amps than with higher-sensitivity speakers and less amplifier power.

BTW, the Totem Mani-2's sensitivity is eighty-FIVE, not 81dB, at least according to their website. That will reduce your power requirement to 300 - 400 watts for 110dB. And it appears to me they specify it inconsistently--"Sensitivity 85 dB/W/m.". If they're claiming to indicate efficiency, that indeed is stated in output at 1 meter with 1 watt of input. If they're claiming to indicate sensitivity, that's measured with an input of 2.83 volts into 8 ohms. There's a real difference.

Also, and this is STRICTLY personal, and I know NOTHING about Totem speakers, so PLEASE don't anyone overreact to my comment here: any audio-equipment manufacturer that says "Regardless of specifications, “Mani-2” channelizes primal energy and force into “being”" goes WAY down on my shopping list. That had to have been written by some marketing idiot who specializes in obfuscation, not elucidation.

And Blkadr is correct in writing that you need to try different amps with the speakers you love; I too should have emphasized that.

Personally, if high-quality sound at high listening levels were important to me, I'd start with a more-sensitive speaker.
There website does state they are 85 db /w/m, however when stereophile reviewed them they found them to be 80.7 db/w/m...
Finding those reviews is the proverbial search for the needle in the haystack.

What's the exact term 'Sterophile' used for its sensitivity/efficiency rating?
they use the term sensitivity...the mani-2 original..reviewed in 1995 measured 80.7db(b)/2.83v/m the mani-2 signature is 84.5db(b)/2.83v/m
Stereophile measured SPL at one metre. Probably at 1kHz, BTW which is an indicative but hardly final measurement. It is however useful./ Since CURRENT was mentioned, and adding onto Jeffreybehr informative post, the 4ohm nominal indicates the need for twice as much current as in the standard 1W/8ohm/(1kHz) ratings... for 2ohm, four times the current all else being equal.
As such, it seems difficult to achieve 110db (spl) with those speakers UNLESS the drivers are extremely resistent both mechanically and thermally. Or maybe, the 110 db is an indication of in room spl levels, both speakers driven (even then, each speaker would have to stomach nearly 1/2kW rms). Maybe they mean "peak" (1-3ms)? Or, the 80db spl is wrong???