Sound Quality Vs. Measurements

[tvrgeek]

Originally Posted by dvv

Completely agreed.

It's just that my own taste runs into the bipolar group, as MOSFETs don't do it for me either. Although I am always open to new experiences. You never know, and I have had a few surprises in my time, and in both directions.

I was a MOSFET output fan until recently when I moved to JBT output amps of high enough quality. (Rotel and Parasound) I don't miss the "mist" or weak bass. (Sony, Sanyo, B&K, Haflers).

[tvrgeek]

I would have to agree that I would like to see distortion numbers at 1W as well as rated. While we are at it, how about a waterfall plot?

[bcarso]

Originally Posted by tvrgeek

[snip] While we are at it, how about a waterfall plot?

Won't that throw up more mist? Or at least make things etwas feucht? (apologies Dennis!)

[tvrgeek]

Only by a small factor.

[dvv]

Originally Posted by tvrgeek

I would have to agree that I would like to see distortion numbers at 1W as well as rated. While we are at it, how about a waterfall plot?

Sure, no problemo, just subscribe to Italy's "Suono" magazine, they have had it for over 20 years now.

And it can show up things. They once had a test of power amps, like 14-15 years ago. In it they had offerings from Harman/Kardon, Sony, Nakamichi and, to the point, Musical Fidelity. Well, H/Ks was absolutely clean up until about +1 dB, Sony's was good to 0 dB, Nakamichi's started to deteriorate at about +1.2 dB, while the Musical Fidelity's, the small model touted as Class A (which it really wasn't, it ran in class A until about 14 of its nominal 30 W/8 Ohms or so, so it was really a High Bias product), was a mess all around. The thing was running wild from about -5 dB upwards.

[a.wayne]

What about the power cube test , i don't see it being used anymore ......

[dvv]

Originally Posted by a.wayne

What about the power cube test , i don't see it being used anymore ......

Not sure what that is?

[BFNY]

What about the low frequency cut-off, and what value it needs to be?

I run into this one with FM tuners, where you need flatness to at least 3Hz on the detector out composite signal to get full stereo separation from the MPX decoder.

Also, though you can have a system where individual components have decent low frequency cut-off, when you put all the components in series, you create a bunch of serial low low pass filters. Then that "system" has a total low pass characteristic that's the sum of the components, (and cables used). This can be different for everyone, depending on how things "match". And this does not even yet include the speakers, but then yes, they have their own low pass cutoff.

And what is the music requirement for low frequency cutoff? Don't think about sine waves, think about transients. What is the relationship between the width of a transient and frequency content?

And when you roll off the low end, what does that do to the phase response, and can anyone hear the phase of, say, an 80Hz signal's harmonics?

I ask because I've read that many designer's feel there is a "sweet spot" for low end roll-off that "sounds good".

[DF96]

What is the relationship between the width of a transient and frequency content?

Roughly, the wider the 'transient', the lower the lowest frequency content. For a single unrepeated transient the frequency content goes down to DC, but that does not necessarily mean that the audio system has to go down to DC. We perceive very low air frequency air movements as a draught rather than sound.

You are right to say that LF cutoffs accumulate. Cables don't have an LF cutoff; they go down to DC. Rolling off the LF is necessary with any realistic speakers. My guess is that, apart from the special case of stereo decoders, the main need is to maintain channel balance on LF phase rather than worrying too much about the actual value. Having said that, you can reckon that there is a significant phase change up to about a decade in frequency either side of the -3dB point.

The 20Hz LF cutoff often quoted is not too daft, when you realise that the lowest note in music is 17Hz (?) and many speakers rolloff quickly below about 40-60Hz. Then there is the need to balance LF and HF cutoff, so the product of the two is in the right region. There was a thread about this last year.

[bcarso]

Originally Posted by dvv

Not sure what that is?

AudioGraph Power Cube - Stand Alone System

I brought this up with Floyd Toole a couple of days ago (having asked Martin Zanfino, now with Infinite Algorithms and formerly VP Engineering with Harman Kardon, what was that 2-d representation of a 3-d plot with different loads that showed how close to perfect voltage sources power amps were?), and he dug a bit and found the audiograph site. I love their water-cooled model

Marty remarked that when h/k started to characterize their and others' amps using their own version of the power cube, audiophiles remarked that it was one of the first measurements that seemed to correlate with perceived sound quality. The h/k amps were designed by Ritchie Miller, who according to Marty is still active although formally retired, and they emphasized high current capability as well as wide bandwidth.


Brad