speaker efficiency / required power

[aKnyght]

with regard to speaker efficiency and low powered [SET] amps, i saw this analysis a number of years ago:

1) in general, you typically want 102dB capability for fully satisfactory sound.

2) the amp adds 10*log(watts) dB to the speaker sensitivity (base 10 logarithm). some examples:

45 tube 2 watts = 3dB wants 99dB speaker
2A3 tube 3.5 watts = 5dB wants 97dB speaker
300B tube 8 watts = 9dB wants 93dB speaker

88dB speaker wants 14dB = 25 watts
90dB speaker wants 12dB = 16 watts

you can have lots of fun with less power... but this is the standard minimum.

math for the 8 watt example: 102 - [10 x log(8)] = 93

it would be good to hear others' practical experience in pairing speakers with amps in terms of efficiency and power.

is 93dB efficiency really enough for a 300b SET amp... or 99dB for a 45 tube amp?

[Al M.]

It not just depends on nominal efficiency, but also the nature of the drivers used. My old 15 W/ch push-pull triode amps could easily drive 90 dB sensitive monitors with 5 inch drivers, or 92 dB sensitive monitors with 8 inch drivers, but they were 'dying' on Goldmund speakers of nominal 96 dB sensitivity but with a large bass driver.

On the other hand, they also could easily drive the minuscule Rogers LS5/3A monitors of nominal sensitivity of 83 dB (these speakers were known to be tube friendly, also because of their benign impedance curve).

So nominal efficiency is a first hint, but there are other very important factors involved.

Don't get hung up on numbers only. A simple table like the above is not just simple, it is unfortunately also simplistic.

[the professor]

Of course you will need headroom above this also. Otherwise the dynamics will be compromised. I've heard that you need anywhere from 10 times the power on up.

[Mordante]

I think that impedance is just as important as efficiency.

The Blumenhofer Grand Gioa sounded a lot better IMHO with a powerfull amp then with a Nagra 300i. Personally I think that the flea power amps will never work great if you like big orchestral music or rock/metal.

[AJ Soundfield]

I think that impedance is just as important as efficiency.

Yes and since very few if any manufacturers include actual impedance measurements, audiophiles are left blindly throwing darts at boards for that magical and elusive "synergy".
Bob Cordell did an interesting workshop at RMAF many moons ago, to show attendees just how much power (using true power meters, not ornamental bling) was needed for uncompressed peaks, even at average (RMS) outputs of 1-2 watts. (Scroll down to The Peak Power Demands of Well-recorded Music)
http://www.cordellaudio.com/he2007/show_report.shtml
Then there is the fact that many (most?) of the these flea amps brag about zero NFB...which means they are equalizers, sometimes in the order of several db magnitude, tied to the shape of the impedance curve of the speaker! Horses for courses...

cheers,

AJ

[a.wayne]

with regard to speaker efficiency and low powered [SET] amps, i saw this analysis a number of years ago:



math for the 8 watt example: 102 - [10 x log(8)] = 93

it would be good to hear others' practical experience in pairing speakers with amps in terms of efficiency and power.

is 93dB efficiency really enough for a 300b SET amp... or 99dB for a 45 tube amp?

This is sensitivity not efficiency , 10 watt is not enough IMO for 93db/2.83v/M speakers..

For SET you want both high sensitivity and efficiency 8 ohm min Z with 12 -16 ohm being best..


Regards

[a.wayne]

100 watt amp is best with 93 db sensitivity, so a 103db sensitivity for 10 watts ....