Sound Quality Vs. Measurements

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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.

Thanks to a friend's largesse, I 've gotten to hear the organ in Disney Hall a few times now, including that nearly-infrasonic lowest note. Very very impressive, and a great hall for it.

Also Sprach Zarathustra was done, and the organ was nicely balanced rather than being overpowering. I remarked that I was hearing the piece as if for the first time, and even consented that properly-recorded and reproduced multichannel might really be worth the trouble! (I'd not been fully convinced at that point, although I liked a lot of what I'd heard of John Eargle's recordings, a man who is sorely missed).
 
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.

http://theaudiocritic.com/back_issues/The_Audio_Critic_20_r.pdf

Article starts on p14 and shows how useful the Powercube plots can be. I was amused to see that one of the amps in the chart was Jan Didden's early high power effort from Audio Amateur.
 
20Hz is not that great, considering harmonics and reverberating echos that can be produced. If you want 20Hz, design for 10Hz

Example: if you cut off a guitar amp just below the low E, you lose atmosphere.

Moral of this story, design with lower and higher frequency response then you think you need.

Today is Heinrick Hertz birthday.
 
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 :eek:

Mine is much humbler. :D
 

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diyAudio Member RIP
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http://theaudiocritic.com/back_issues/The_Audio_Critic_20_r.pdf

Article starts on p14 and shows how useful the Powercube plots can be. I was amused to see that one of the amps in the chart was Jan Didden's early high power effort from Audio Amateur.

That's a very engaging, albeit controversial and lengthy article. His discussion of output stage topologies is refreshingly clear and almost comprehensive, particularly unusual for a review. Thanks for that link!

I remember when I ran into Bascom King (whom I didn't know but knew of) at CES one year, probably 1986. I'd read his review of the Jadis in TAS, one of the rare ones that said much of anything about the details of the design of a product under review. Although Rich doesn't mention it in his excerpt, one of King's speculations was that tube rectification in the power supplies might have some correlation with sound quality (which clearly ties into some of the remarks about soft recovery diodes in this thread). I hoped to get him to "open up" a bit more about these issues, but I caught him on a very bad day, his having drawn the short straw which sentenced him to duty in the Infinity multimedia suite, featuring projection video and IRS speakers playing the predictable action movies of that year on laser (was it, among others, Top Gun?). I believe he had a terrible headache, and when I mentioned having read his TAS review he looked at me as if he wished to kill me.
 
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AudioGraph also used to have a unit that connected to an Audio Precision system and used that to generate signals, read values and do the data presentation. That unit basically was a bunch of load resistors and switches, driven by AP like the AP switch units.

jan

When I inherited the supposedly-99%-complete h/k TC600 amp, designed by a succession of engineers (in chronological order, Andy Hefley, and together Rich May and Brad Plunkett), when I started work with Harman Electronics in 1990, I was asked to measure the performance into a subset of the PowerCube loads by the intracorporate customer Harman Kardon, and at that point got acquainted with Zanfino. He insisted on the amp's delivering a 20Hz burst into an aggressive 60-degree inductive load. I rummaged in the JBL speaker lab and found an L-shaped iron-core inductor that served, but even at a fairly low duty factor I had to immerse it in water to complete the test :eek:
 
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.

So, here is something valid that we could be doing. I would probably have guessed that same ranking. I suspect the people paying for the back cover ads would not like it. Funny you mention Nak. My CA-5 preamp just came so it is about time to subject my wife to some listening tests. Any recommendations on SACD for strong swing jazz ? Something in the vain of Harry James. My Schefeids are just plain CD's.
 
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 :eek:

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


Thanks for the response Brad, i was a fan of such a test method and wondered why it had fallen out of or why it was not used anymore ...



http://theaudiocritic.com/back_issues/The_Audio_Critic_20_r.pdf

Article starts on p14 and shows how useful the Powercube plots can be. I was amused to see that one of the amps in the chart was Jan Didden's early high power effort from Audio Amateur.

Yes didn't notice that before , i had read that many moons ago and never made the connection here ...
 
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.

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.

For something like a sinc pulse, (i.e looks like a half sine wave) the frequency response is sinx/x, with maximum Y amplitude at 0 frequency (DC) and the more narrow the pulse, the higher the frequency extension.
It may sound counter intuitive, but to properly reproduce a cymbol hit, you need (almost) DC response. Of course, in that case you can only replay what was recorded by the microphone.
A lot of people talk about organ notes and lowest sting on a bass, etc, completely ignoring the frequency response of transients, which music is full of.

I guess I missed the thread on balancing LF and HF. Are you saying the LF and HF product needs to be related to something else?
 
diyAudio Member RIP
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Thanks for the response Brad, i was a fan of such a test method and wondered why it had fallen out of or why it was not used anymore ...

This came up because FT is writing some material for installers and asked me about power amps. He is now rattling cages at Harman to get the powercube testing reinstated, so this may lead to some actual improvements in testing methodology there.
 
Why talk about LF response? Already been there?

Well, in a discussion about Sound Quality Vs. Measurements, if you break down music into octaves, which is how we (the ear) hears it, the first 4 octaves are below 320 Hz.

There are 10 octaves of audible frequencies.

Half of the action happens below 640 Hz.
 
less than half, more like 1/4 - look up critical band/bark scale

roughly we lump everything in 100 Hz wide bands together below 500 Hz, and ~ 20% fracton of the center frequency bandwidths above

with ~24 critical bands only 6 are below 640 Hz

also look at loudness curves - dynamic range is much reduced compared to mid frequency as well

which given the lumpy frequency response from modal behavior of small rooms its probably just as well we don't resolve that well at low bass
 
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 :eek:

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

Thank you, I get it now. Frankly, this is the first I have ever heard about it, so it's good that I did.

As for Richard Miller, the HK 680 is one of his designs which I own. An impressive piece of work, in my view.
 
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.

The LF content can also be dangerous. Some time ago, I noticed that when I tune to a local FM station, I get some wonderful LF transients which I barely hear, but I can see the bass membrane pushing air like crazy. The subsonic filter cured that. My speakers will go down to below 40 Hz in a room.
 
So, here is something valid that we could be doing. I would probably have guessed that same ranking. I suspect the people paying for the back cover ads would not like it. Funny you mention Nak. My CA-5 preamp just came so it is about time to subject my wife to some listening tests. Any recommendations on SACD for strong swing jazz ? Something in the vain of Harry James. My Schefeids are just plain CD's.

Not really. Generally, I hesitate to recommend anything to anybody, having experienced what different tastes can do to what I feel is a good choice. All my comments are related to my taste and system only, I make no other claim.

Just yesterday, I was visiting a friend I both like and respect, who spared no effort to praise his German made, MB active speakers, driven by a tube preamp. He just loves it, while I can honeslty say it's been many a year since I heard a system sound so closed in, so shut and so lifeless. Of course, I passed on comments. To each his own.
 
The LF content can also be dangerous. Some time ago, I noticed that when I tune to a local FM station, I get some wonderful LF transients which I barely hear, but I can see the bass membrane pushing air like crazy. The subsonic filter cured that. My speakers will go down to below 40 Hz in a room.

Really good reason to use dedicated woofers. That extra LF does not as much sonic damage to my sealed peerless woofers as it would do the the 6 inch woofers in my main speakers. I would not call them subs, as most consider that for movie sound effects. Just my 60 to 20Hz. woofers that happen to do pretty good wit movies too.
 
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