don't understand....what the heck does +/- infinity have to do with anything other than theoretical, non pragmatically applicable math...
Ok, let me back up.....
going back to your post #19
"It will take time to accelerate and so won't be at maximum velocity at zero crossing, there will always be an envelope, you can't ignore it"
Let me ask, what is the envelope of a sine wave?
And how does said envelope enter the discussion about the ability of a speaker to replicate a sine wave, without the speaker having full spectrum capability?
going back to your post #19
"It will take time to accelerate and so won't be at maximum velocity at zero crossing, there will always be an envelope, you can't ignore it"
Let me ask, what is the envelope of a sine wave?
And how does said envelope enter the discussion about the ability of a speaker to replicate a sine wave, without the speaker having full spectrum capability?
I think they're trying to say that (if a resting speaker is at 0 deg, the pressure peak is 180 deg and the rarefication minimum is at -180), then as a sine wave crosses the 0 axis it must be travelling at a certain speed. A speaker cannot accelerate from 0 to that speed instantaneously, it has to start its movement at a certain speed., therefore the time it takes to accelerate to that speed will affect the shape of the waveform.
Thanks for trying to help clarify Rob
Here's what i don't get...and why the reasoning as so far presented, confuses me...
I have a system at rest...a sub....i pop it with a one period sine wave of 50Hz.
The whole wave has a time period of 20ms...that's pretty darn slow really.
The signal to the sub starts at zero degrees, but is running at sine wave slope to reach its peak at 90 degrees at 5 ms...again slow slope, slow relative rate of time change, ....slow as molasses compared to higher frequencies.
I just can't buy that a 50Hz sine wave needs full spectrum bandwidth to be faithfully reproduced till i see, hear, and measure it ....
Here's what i don't get...and why the reasoning as so far presented, confuses me...
I have a system at rest...a sub....i pop it with a one period sine wave of 50Hz.
The whole wave has a time period of 20ms...that's pretty darn slow really.
The signal to the sub starts at zero degrees, but is running at sine wave slope to reach its peak at 90 degrees at 5 ms...again slow slope, slow relative rate of time change, ....slow as molasses compared to higher frequencies.
I just can't buy that a 50Hz sine wave needs full spectrum bandwidth to be faithfully reproduced till i see, hear, and measure it ....
At the crossing point (0 deg) the speaker needs to be moving at it's highest speed. It's basically decelerating from 0 to 90 degrees, then accelerating towards 0, and then decelerating from 0 to -90.
So how can the speaker start from stationary 'at it's highest speed' ?
The closer the wave gets to straight up and down the faster its moving..
That's how I see it at least.. ?
edit, so when you say it starts at 0 degrees it actually has to start decelerating towards 90 deg, not accelerating towards it..(it cant start at zero velocity and then get slower towards 'the peak at 90')
Edit2: think I made a mistake in post #25, should have been plus/minus 90 degrees not plus/minus 180 degrees.
So how can the speaker start from stationary 'at it's highest speed' ?
The closer the wave gets to straight up and down the faster its moving..
That's how I see it at least.. ?
edit, so when you say it starts at 0 degrees it actually has to start decelerating towards 90 deg, not accelerating towards it..(it cant start at zero velocity and then get slower towards 'the peak at 90')
Edit2: think I made a mistake in post #25, should have been plus/minus 90 degrees not plus/minus 180 degrees.
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Why can't it just follow the sine wave as it originates?
Why would we impose conditions in time before they existed?
It would have a vertical attack, horizontal sustain for the duration of one cycle and vertical release. It would look like a square window.
Thx for explaining the basis behind your comments.
If a square wave were the single pulse under discussion, then sure, it won't be replicated without extended bandwidth.
(And it wouldn't matter whether it is a single pulse or a continuous tone....)
Going back to WA's original post.....pls note he said single cycle sines.
So sticking to a single cycle sine, the question I have is how well will the speaker (subwoofer) replicate it.
I don't know, but I'm not willing to assume it can't accelerate fast enough from rest, or decelerate back to rest, in just one cycle.
I want to hear how it does ...and measure it if i can figure out a way.
Been thinking to start the one period sine pulse at various phase angles, keeping its duration one period, and listen for any difference.
Anybody have any other suggestions how to evaluate or measure how well the sub replicates the pulse?
If a square wave were the single pulse under discussion, then sure, it won't be replicated without extended bandwidth.
(And it wouldn't matter whether it is a single pulse or a continuous tone....)
Going back to WA's original post.....pls note he said single cycle sines.
So sticking to a single cycle sine, the question I have is how well will the speaker (subwoofer) replicate it.
I don't know, but I'm not willing to assume it can't accelerate fast enough from rest, or decelerate back to rest, in just one cycle.
I want to hear how it does ...and measure it if i can figure out a way.
Been thinking to start the one period sine pulse at various phase angles, keeping its duration one period, and listen for any difference.
Anybody have any other suggestions how to evaluate or measure how well the sub replicates the pulse?
would a single cycle of a sine even propagate or be heard?
since it's a single cycle wouldn't the pressure of the positive half not be cancelled by the subsequent negative pressure of of the second half of the cycle...?
where's wonderful audio? i wonder what he's is trying to do?
since it's a single cycle wouldn't the pressure of the positive half not be cancelled by the subsequent negative pressure of of the second half of the cycle...?
where's wonderful audio? i wonder what he's is trying to do?
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Why are you even bringing envelope up?
Are you saying the speaker reacts like the straight-ish window response you depicted as an envelope ??
Cause the sine pulse signal doesn't look like that, or have that envelope.....
Besides, envelope is a term normally used to describe the smooth curve fit to a waveform's extremes...you're right about me missing your point, as i totally miss why envelope is even relevant here...
A single cycle sine wave signal is the given in this thread imo.
The question in my mind is how much bandwidth is needed to replicate it.
I didn't. I've tried to explain, in slightly different ways, what has been mentioned in almost every post of this thread, including the first one, to help you understand what really happens.
Can you point me to some references, that explain what you think is happening?
I simply can't buy into the OP's assertion "With a real life driver, the oscillations take time to build and time to die .......(which is fine for music but not for my application.)"
That is, I can't buy in without personal testing/experience, or reading some cogent explanations about speaker rise and fall times vs a single sine..
(WA, what is your application?)
I think i've figured out how to measure this.
Seems simple enough...just send the single sine pulse, and look at speaker response via mic to scope.
I simply can't buy into the OP's assertion "With a real life driver, the oscillations take time to build and time to die .......(which is fine for music but not for my application.)"
That is, I can't buy in without personal testing/experience, or reading some cogent explanations about speaker rise and fall times vs a single sine..
(WA, what is your application?)
I think i've figured out how to measure this.
Seems simple enough...just send the single sine pulse, and look at speaker response via mic to scope.
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If there are extra oscillations, cant they be counteracted with factored signal? in other words record the single sine output from driver, subtract the original sine, invert and add to the original sine and use that as excitation signal instead?😀
Ok, i just made a single cycle 50Hz sine wave recording.
Realized that's even easier than doing the arb generator route....
Played it thru subwoofer only, which has a 72dB/oct linear phase LR low pass filter at 100Hz
Plays just fine...with authority...and sounds like a 50Hz dirac pulse for a sub.....just as i would expect.....
Some times it just pays to try things 😀
Realized that's even easier than doing the arb generator route....
Played it thru subwoofer only, which has a 72dB/oct linear phase LR low pass filter at 100Hz
Plays just fine...with authority...and sounds like a 50Hz dirac pulse for a sub.....just as i would expect.....
Some times it just pays to try things 😀
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