Subsonic Filter

Really?

Why do you think the clipped signal sounds distorted?

 

hmm....

it's a thinker

but still - acceleration is proportional to current, right?

 

Sure, but when you cease current increase and voltage increase, you cease acceleration.

Seriously, what you see on an ociliscope in a musical pattern, is exactly what the cone of the speaker is doing (well, at least we hope so )...

Here's something for you to try, hook a 9 volt battery to your speaker, and tell me what happens to the cone. Essencially what we are doing when clipping the signal is the same thing.

I think I know where there is a great example in a flash, so gimme a minute... I'll link it here for you

 

http://www.bcae1.com/speaker.htm

I can't link directly to his flash, but hopefully this goes directly tto the page. About 1/3 of the way from the top, directly beneath the tri-axial speaker section, you will see how the driver mimics the input signal. Now, imagine what the speaker would be doing if the ttops of the signal were clipped.

I swear he used to have a flash on there for it, but I just don't see it right now

If I can find it, I will post it for you to examine

 

okay, i see that

but since it's directly proportional shouldn't you change what you said to:
...when you cease current increase and voltage increase, you cease acceleration
increase.

cause there is still acceleration - constant acceleration.

okay, maybe i'm just messed up, confused

 

I'm sure you understand momentum.

When you throw a football, you only are applying force on the footbal as long as it's in your hands.
When the ball leaves your hands, does it just drop out of the air, falling to the grass just outside the reach of your fingertips?
No, momentum carries it... far!

Now, picture a woofer.
With a clean sine-wave test tone as input, the woofer will move outwards rapidly (as the sine wave heads upwards), but progressively slowing down (as we reach the peak of the sine wave)... then, begins accellerating rapidly as it heads back towards the center "at rest" position...(as the sine wave curves back down) flying right by it, of course (as we pass the point where the sine wave crosses the center line)... moving inwards rapidly (as the sine wave heads downwards), but progressively slowing down (as we reach the low trough of the sine wave)... then, begins accellerating rapidly as it heads back towards the center "at rest" position...(as the sine wave curves back up) flying right by it again as it starts it's way through the next wave.

Those peaks of the sine wave control the cone motion... they progressively decellerate the cone, so that it can smoothly change direction.

Now, if you feed a cone a square wave, what would happen?
The woofer will move outwards rapidly (as the square wave heads upwards)... but suddenly it levels off!
Does the cone instantaniously halt, frozen in place, until the square wave heads back down in the other direction?
No!
Essentially, for the whole top portion of the square wave, there's no force on the cone, pushing it out, or pulling it in... rather, a simple DC force trying to hold the cone in a position that's "out" some distance.
So, momentum carries it outwards... then the suspension will pull it back.. momentum again overshoots the distance the DC current is trying to hold the cone out to, so it pulls the cone back in that direction... no doubt overshooting again... oscillating like that, until that moment in time occurs where the square wave does pull the cone back downward... only to repeat exactly the same sort of distorted behavior in the rearward half of the wave.

Make sense?

 

hmm... a square wave is comprised of sine waves of infinite frequencies

but if there's constant current, there's no acceleration?
it just 'stays' in one place?

doesn't seem correct... gotta think more

edit:
I don't think it's momentum, per se, that's making the cone have small oscillations
I think it's the constant supply of current that's still trying to force the cone out
(or in) that causes the small oscillations, with the suspension constantly forcing
it back

 

No, describing a square wave as "infinite frequencies" isn't accurate...
It's got a frequency... it's number of cycles per second... same as a sine wave.

Don't think about it too hard... it's not complex.

Cone motion replicates the sine wave, if you will.

Here, an easy example:
Draw a sine wave on a sheet of paper.
Draw a horizontal line through it, bisecting it.

In terms of a signal, the X-axis line you just drew represents time, and the Y-axis represents current, where the area over the line is positive current, the line itself is 0 voltage of course, and the area below the line is negative current.

This is the current that is fed into a speaker, and it causes excursion... positive and negative excursion, relative to it's "at rest" position.

As far as how it translates into excursion, in simple terms, think of it this way:
Where the Y-axis was labeled "current" before, erase that and label it "mm of excursion", where the area over the line is positive excursion, the line is 0mm "at rest" position, and the area below the line is negative excursion...
And the X-axis is still time.

So, as you feed current into a subwoofer, you cause excursion, proportional to the signal that's fed into it.

Now, go back and read my previous post, it'll make more sense, I think. B)

 

Also, consider what happens when you apply DC electricity to a speaker...
Go grab a 9v battery from the smoke detector and give it a try.

The speaker will move OUT (or in, depending on which way you apply the battery), and stay there... holding it's position, until you remove the battery.

For the "peak" of a square wave, essentially it would be exactly the same thing, for that brief moment in time (the top of the square wave, or bottom of the square wave).

 

yeah, i see what you mean
I think i get it


but take the fft of a square wave, and you get "infinite frequencies"