The most important think to do is learn. You surprise me.
You fail to understand the technical issue, you use bad test methodology for what is discussed, you put up irrelevant scope displays, and claim success.
Why do you think I estimated ten years for the audio world to understand?
If you were really serious, you would put together a step source capable of 350 picosecond rise times at 10 volts into an 8 ohm load with an output impedance less than 100 milli ohms to eliminate the source as a confounder. Your voltage measurement at the amp and load shows how little you really understand about what I have been saying, you should be looking at current at the load vs input signal. If you recall, I offered you a resistor capable of high slew rate with zero b dot error, do you really think I do not understand this?
Your casual dismissal of me as pushing pseudoscience is laughable, and quite below your level. I certainly expect better of you, "hey look, a squirrel" does not work with me.
Oh, the step source, I did that back in '81, almost 4 decades ago, as well as some of the measurements. In many aspects of this discussion, you are 40 years behind me. Alternatively, I would never question your abilities and understanding in your expertise, you are head and shoulders above me there, it would be laughable for me to do so.
If you are wondering about where I got 350 picoseconds from, look up Mercury wetted reed relay, and Tek 109.
Perhaps 10 years is an underestimate...sigh
Jn
10 to 90% has been chosen to reflect in a more accurate way the real behavior of an audio amp, getting rid of marginal bad behaviors near the rails that we are not supposed to reach.While you may be correct, I was just explaining slew rate as a definition of signal, as opposed to the slew rate def as 10 to 90 percent.
For the same reason, we usually take a little margin to the MAX power, measuring distortion levels.
It do not affect comparators, as well, because the detection thresholds are widely included in this range.
I am unaware of any results from those who were acquiring dual coil cones. Me, I just bought a mini mill so that I can actually make parts out of metal for various test setups and fixtures. Strangely enough, no matter how hard I try, I can't find any wood with permeability over vacuum. Even ironwood is not magnetic
so, metal it is.I consider my hobbies to be part of the long game. I will eventually get stuff done, but give my understandings freely so that the "yoot" of the world can run with it. I'll eventually retire, grow a long beard and a huge head of hair, get a lab coat, glasses, and practice my mad scientist laugh..
As an offshoot, I was discussing a setup with one of the beam physicists to rapidly modulate the magnetic field of a quad focus/de focus magnet by the use of an aluminum disc spinning in the flux gap of the return legs. By spinning in the flux, the aluminum will drag the flux along the spin direction and increase the path reluctance. She was amazed at this possibility, as it's never been done before and is so easy!!!
So I gigged her...told her that speaker manufacturers and audio guys have known about this for decades, and how come particle beam physicists didn't???
Shameful, I know, but I had to have some fun with her..after all, she was a physicist...
Jn
It is technically not quite a servo drive. And while it may be conceptually complex, to do it in practice is very simple.
Jn
Same for most critical listening.
Please, what is the bit depth and sample rate used for the measurement?
On my side, my first DIY speaker (just before the dinosaurs disappear) was servoed, with the usual coil in the back, and a little one in the front. With the advantage that there were no magnetic coupling between them. Never tried an other after this.
Because the fashion is, nowadays , to the active wireless Wifi speakers, I think I would rather choose an optical sensor (laser) inside the enclosure, to measure the position of the cone. With the advantage that we should be able to do it without significantly increasing the mass of the moving assembly.
Last edited:
Joan/Pavel
Most audio amplifiers have a small inductor in series with the output. Often a few microhenries. This just adds to the phase/frequency response issue a tiny bit. It also not surprisingly raises the output impedance at higher frequencies (say 5 MHz) where transmission line effects may begin to show if there were any signal around to be bothered by it.
JN
When I get around to it I can do a frequency sweep of an audio power amplifier into a noninductive (actually just really low) 8 ohm resistor through 25' of cable. That should be more accurate than calculating it. I already have observed the issue on long cable runs.
One fellow tried a gizmo similar to a PC add on loudspeaker tester to measure the frequency response of a ballpark cable. His results showed it rolled off mid band. Very easy to demonstrate when the test signal generator cannot produce enough current to properly drive the cable capacitance.
Most audio amplifiers have a small inductor in series with the output. Often a few microhenries. This just adds to the phase/frequency response issue a tiny bit. It also not surprisingly raises the output impedance at higher frequencies (say 5 MHz) where transmission line effects may begin to show if there were any signal around to be bothered by it.
JN
When I get around to it I can do a frequency sweep of an audio power amplifier into a noninductive (actually just really low) 8 ohm resistor through 25' of cable. That should be more accurate than calculating it. I already have observed the issue on long cable runs.
One fellow tried a gizmo similar to a PC add on loudspeaker tester to measure the frequency response of a ballpark cable. His results showed it rolled off mid band. Very easy to demonstrate when the test signal generator cannot produce enough current to properly drive the cable capacitance.
Sample rate is 50MHz, bit depth is 9bit. It is unimportant, because one can make measurement with shorter time base and more Y sensitivity. However, it is unimportant. Nothing interesting is happening there. Time difference between the plots is quite exactly 150ns.
One has to keep in mind that it is only 6m of cable and we speak about audio frequencies, and kilometers of wavelengths, not about nanoseconds and centimeters or meters of signal wavelengths.
Sometimes I have a feeling that many people do not make a difference between seconds, milliseconds, microseconds and nanoseconds or just are unable to transform it into frequencies or wavelengths. They just look at the signal shape without taking into account time axis.
Audio signal is too slow to create any cable reflections or energy storage if cable length is few meters. The only signal that might create cable reflections is HF EMI interference.
That’s exactly why I always separately spec what I call ‘small signal’ rise time which is typically 1V pk~pk and slew rate which is 10% to 90% of the full pk ~pk output voltage.
Sorry but i don´t understand your question, could you please rephrase?
Sorry, but no. Slew rate is a maximum of signal derivative, Max(dv/dt).
Interestingly wiki has it
Slew rate - Wikipedia
Last edited:
Haha, basically, is acoustic rise time synonymous with electrical signal rise time and a fourier transformer can be performed in the same way?
My apology. I have overlooked the "why I always separately spec".
There are 32 screens that are averaged - for the calculation. Of course every screen shown is a "single shot", 32 screens are in a memory.
Not a bad place to look first. At least you know they are not there before looking elsewhere. Maybe even tie a piece of string to the lamppost and start walking round in a spiral. Might not ever find them, but you will definitely know where you started from.
Standard methodology
ToS
Last edited:
- Status
- Not open for further replies.