Quoting from Wikipedia :
Prior to modern computer graphics, Lissajous curves were typically generated using an oscilloscope (as illustrated). Two phase-shifted sinusoid inputs are applied to the oscilloscope in X-Y mode and the phase relationship between the signals is presented as a Lissajous figure. Lissajous curves can also be traced mechanically by means of a harmonograph.
In oscilloscope we suppose x is CH1 and y is CH2, A is amplitude of CH1 and B is amplitude of CH2, a is frequency of CH1 and b is frequency of CH2, so a / b is a ratio of frequency of two channels, finally, δ is phase shift of sin curve of CH1.
Prior to modern computer graphics, Lissajous curves were typically generated using an oscilloscope (as illustrated). Two phase-shifted sinusoid inputs are applied to the oscilloscope in X-Y mode and the phase relationship between the signals is presented as a Lissajous figure. Lissajous curves can also be traced mechanically by means of a harmonograph.
In oscilloscope we suppose x is CH1 and y is CH2, A is amplitude of CH1 and B is amplitude of CH2, a is frequency of CH1 and b is frequency of CH2, so a / b is a ratio of frequency of two channels, finally, δ is phase shift of sin curve of CH1.
AKSA said:
Hello Hugh
Yes I know 🙂
I'm slowly reading all the archive of the diyaudio forum, but it's very long to read. So for now I do search by using key word like JLH, soundstage, drivers matching, cob, vas, phase change, ltp, etc... And wen I see some names, like you Hugh, Nelson Pass, Carlos, Graham, Alex Kethel, Anatech, and few others, I read with more attentions since there is allway someting to learn from you and all of them. But there is some big thread that I can't read all of it.
Thank
Bye
Gaetan
This thread is indeed very old, but the subject of sound staging is nevertheless fascinating. There have been quite a few exchanges on the forum postulating the factors that give rise to good sound staging in an amplifier (speakers are a whole additional ball game).
I don't think there is a difinitive answer to this, although there appear to be some ideas. In the final analysis, whether as a designer you are from the zero feedback camp or the optimal feedback camp, an amp has to be voiced and this is probably where we can pool some knowledge, albeit subjective, to arrive at definitive conclusions. Where we are forced to use subjective assessments, we can rely on comparative assessments - e.g. after I changed this, it sounded worse/better etc. We may not end up with a guideline that says to get a good sound do xy but instead something that says 'don't do this'.
🙂
I don't think there is a difinitive answer to this, although there appear to be some ideas. In the final analysis, whether as a designer you are from the zero feedback camp or the optimal feedback camp, an amp has to be voiced and this is probably where we can pool some knowledge, albeit subjective, to arrive at definitive conclusions. Where we are forced to use subjective assessments, we can rely on comparative assessments - e.g. after I changed this, it sounded worse/better etc. We may not end up with a guideline that says to get a good sound do xy but instead something that says 'don't do this'.
🙂
Bonsai said:
Bonsai, since you have brought up this topic which I originally started, let me add something on the lines suggested by you.
Apart from the image either being projected slightly forward or backward, my guess is that amps which have a more dense presentation of the music sound far better than those that sound rather sparse and seemingly with a "hole in the middle" kind of presentation.
Let me give two examples:
1) Many years ago I was playing around with a 300 watt amp that appeared in Elektor. It had an opamp for the front end (NE 5534) a couple of BD 139/140s, MJE 15030/15031 for drivers and MJ15003/15004 for the outputs. While playing with very cheap interconnects, with one particular track I felt that the music was coming from a distance. I changed the interconnects to silver plated - teflon insulated type and found the image move considerably forward. Then I changed the opamp and used a TLE2141, the sound stage moved even more forward and the music content was also comparatively dense.
2) For outdoor use, for a couple of years I used Dynacord S1200 amps. For the day they were indeed good. But I always felt that the music was not dense enough and there was a "hole in the middle". The amp was also noisy. I owned 4 of the Dynacords so I can say that is how they all sounded. I compared this with QSC 2040 and the QSC was better. Now I have QSC 4050 which has a denser presentation compared to QSC 2040. Ofcourse, none of these come even close to a gain clone using LM3886 which is bettered by many discrete designs I have tried.
I have been helping a friend set up his system using a Krell 400 AVi and Dynaudio Audience 72 speakers. The Krell sounds very, very clean and "forward". But it is also very clinical, lacks warmth and does not sound dense. Overall a very dissatisfying musical experience, despite a very "forward" sound stage.
However, the very clean presentation of the Krell is very desirable. What I mean by clean is that the noise threshold seems way down, but I don't mean that it is timbrally accurate or revealing of inner detail.
In the quest to purse some of the desirable qualities of the Krell, in one N-channel mosfet design that I have been putting together, in the position of the Vas I used a 2SA1539 (the original used KSE350). I noticed improved inner detail and better speed but it is a wee bit less dense compared to the original. This Vas is loaded by a CCS. When I used a 2SC3423 in this position I noticed that the sound became excessively bright and thin. It sounds much better with a KSE340 in this position.
What I am trying to say is that, apart from forward/laid back aspects that I had referred to originally, there is another aspect of spectral(music) density which has a bearing on how we subjectively appreciate the sound stage and over all performance.
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