ULTRA 55 Review - Michael Fremer of Stereophile Magazine

Apr 3, 2017
Hong Kong
I doubt a 1 watt signal would fry the tweeter
Using an xover and could you be more specific about JA measurements , what about it is incomplete or sub optimal ..?
The downward-sloping distribution of frequencies across the audible spectrum typical in the vast majority of recorded music shows a significant drop in the range reproduced by the tweeter relative to the bass frequencies (see links below). Historically, the 60-80Hz region has been on a red-hot melt-up during the past few decades, with the advent of electronics and hip-hop/rap music.

Try playing a demo/test disc containing warble tones, and the half-octave centered around ~4kHz (where the ear is most sensitive to) is painful to listen to even at 85dB, not to mention 88dB (double the power), or god forbid 91dB (quadruple the power). Even assuming that the typical loudspeaker has a low acoustic tweeter output sensitivity at the listening position of 85dB/1W, it will only require 4W of power to produce 91dB (assuming power linearity).

The typical delta of -24dB between 200Hz and 4kHz (limiting the range to be music-genre neutral) implies a power factor difference of 2^8, or 1/256. Normalizing the tweeter reproducing 4kHz with 1 watt of power, that’s 256W into the woofer (ignoring room boundary reinforcement effects in the bass and absorption/diffusion effects in the treble).


http://eecs.qmul.ac.uk/~josh/documents/2013/Pestana Ma Reiss - AES135.pdf B90D533A-6D98-4CE1-BE4A-C8798118DC08.jpeg
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Likes: Duke LeJeune
Apr 3, 2017
Hong Kong
As for my assertion that most of the published data in the Stereophile review of the Ultra 55 is faulty or incomplete, let me take a stab at it later, when I have more time. As a long-time subscriber (30+ years) of Stereophile, and admirer and owner (20+ years) of Von Schweikert loudspeakers, I can’t help but wonder why there were so many holes in the measurements.
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WBF Founding Member
Apr 21, 2010
Manila, Philippines
Well a technique is a technique. Often times it isn't so much how the data plots out but rather how well the interpreter of the data is able to correlate his graph with what is observed. Stereophile has been using this method for a very long time. I like that because of the consistency it brings but I also understand that what is in reality a niche publication can not afford an anechoic chamber and to do complex testing as that found at a serious manufacturer's facilities much less acoustic laboratories. The plot has holes simply because of the limited samples. That however in my opinion, does not rob it of all merit and utility. It just is what it is :)
Likes: GSOphile

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