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In Reply to: RE: For a mere 7700 dollars you can have some Magnavox amps. posted by Michael Samra on August 14, 2016 at 22:17:02
He says they are 50 watts per and then he recommends 95 db speakers as a minimum? With 50 per you should not even have to worry about the sensitivity of your speakers.
Follow Ups:
"With 50 per you should not even have to worry about the sensitivity of your speakers."Vinnie, there are quite a few "Watt Hog" speakers out there, for which 50 WPC would prove insufficient.
Paul Joppa's 102 dB. rule is useful in matching amps to speakers. "Joppa's Rule" states that for "average" volume listening spaces, an amp/speaker combo should be capable of 102 dB. SPL peaks at a 1 M. distance.
Where things can become highly problematic is the derating sometimes necessary when commercial speakers are mated to tube power amps. A nominally 4 ohm speaker whose claimed sensitivity for 2.83 V of drive is 89 dB. is "really" 86 dB. sensitive, as 2.83 V. into 4 ohms is 2 W., not 1 W. Another "gotcha" is impedance curve. Large dips in the curve, particularly in the deep bass, require reducing the nominal impedance and allowing for the consequent reduced sensitivity.
Big Thiel speakers, with their dips down to 1 ohm, are (IMO) very poor candidates for mating to tube amps. The power O/P needed is less important than a very large damping factor. BTW, those big Thiels will wreck mass market SS equipment, should it be connected up.
Eli D.
Edits: 08/15/16
with even typical dynamics the peak to RMS ratio of Recordings are 15-18dB. I just fired up my B&K 2270 sound analyzer and placed the microphone a meter away.... talking at a normal voice level - like a telephone call yields 91dB peak - Dropping my mouse onto its pad from 4 inches generates 101.81dB peak levels (1 meter away) This is not a snare rim hit! dropping my mouse onto the desk surface without a pad from 4 inches gives a peak level of 113.6dB! a hand clap gives me 130dB peak at 1 meter
I remember taking the sound meter to a Jazz Club (seats about 50 people) 10 years ago and measuring the concert from the back of the house. Piano topped 110dB peaks, snare topped 120dB and even the trumpet was over 105dB. Now the maximum RMS levels (A weighted) rarely topped 100dB. Live music impulsive sounds typically have a 24-30 dB crest factor (the Ratio of the Peak to the RMS values) - most (almost ALL) recordings use limiters that drop this to 15dB or so. This is the SHAME of the music and recording world.
IMO a system that can't reproduce over 112dB PEAKS risks clipping the amplifier on Dynamic music transients. I have measured 112dB peaks from my listening seat from my very inefficient MMG (83dB/watt@ 1 meter) loudspeakers driven by amplifiers that clip at about 1000 Watts. By this standard an 93dB/W@ 1 meter speaker would need a 100 Watt power amplifier.
"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius
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