A Question That Has Burned In My Mind For Years...

[MarkWComer]

Here ya are, Fisher XP4a and yes they sound great. Really good when your "Baked"

View attachment 50204 View attachment 50205

Now THAT is COOL!​

 

[MarkWComer]

Now THAT is COOL!​

Umm.. speaking of cool, what does that wrinkly pie pan do for scattering waves where you don’t want them to go? Or is the dispersion by design?

Given the years, what has become a chief failure for this design? Somehow I would expect the bonding between the different materials would be a fail point, large excursions ripping it apart.

 

[Wheel-right]

Haven't had any problems with them separating Mark. Powering them with a Harman Kardon 730, approx. 40 watts a channel. The weak point on these was the tweeter, 2" hemispherical with a 5 pound magnet, had to replace them, 12" Woofer, two 5" Mids. The port hole is not original, mine doesn't have any. Hard to find much info on them so who knows how the idea for the pan edges came about and what reasoning on using them.

 

[MarkWComer]

The port hole is not original, mine doesn't have any.

View attachment 50207

I was gonna ask if they were ported...

 

[pennysdad]

OK everybody...
Get your brains around this one.

 

[BlueCrab]

Interesting. It must be recording the harmonics since I would expect the fundamental would be the length of the string. Cool effect, though.

 

[pennysdad]

I'm calling it a fake.
There is no way a guitar string under so much tension is going to be able to bend to such a degree.

 

[laatsch55]

Interesting. It must be recording the harmonics since I would expect the fundamental would be the length of the string. Cool effect, though.

Funny thing about strings, tension seems to have quite an effect too!!

 

[MarkWComer]

I'm calling it a fake.
There is no way a guitar string under so much tension is going to be able to bend to such a degree.
View attachment 50220

You’re correct about the string- the second one does not bend to that degree. This is a video artifact having more to do about the way image sensors capture images. If the strings were horizontal, you may see disconnected segments of the string instead of a continuous sine curve. As a disjointed example, this is similar to motion pictures where a wagon wheel appears to rotate in the opposite direction of the wagon’s travel. The best way to view string vibrations is with a high speed flashing xenon light source, not a CCD image capture or camera shutter.

 

[MarkWComer]

Interesting. It must be recording the harmonics since I would expect the fundamental would be the length of the string. Cool effect, though.

Partially correct, possibly completely correct, depending on the image capture method. Although progressive video will capture a solid “frame,” the image is still “scanned” from the top to the bottom of the sensor, giving the string time to move between each scan line before the entire “frame” is captured.

Yes, the fundamental is the entire open string:

 

[Gibsonian]

Good stuff here, still amazes me that a driver can follow the squiggly lines of the complex waveform incoming, and reproduce it so well, being one mass, one VC (per driver here). It is no wonder that speakers are typically the biggest source of distortion in the chain, that is unless you might be a SET guy.

 

[Lazarus Short]

OK everybody...
Get your brains around this one.

Be aware that the vibration through the air vibrates the string on either side. This is the basis of the Norwegian hardanger fiddle and the Swedish nyckelharpa, which have sympathetic strings. It also affects the wire racks that some are so fond of.

 

[pennysdad]

Be aware that the vibration through the air vibrates the string on either side. This is the basis of the Norwegian hardanger fiddle and the Swedish nyckelharpa, which have sympathetic strings. It also affects the wire racks that some are so fond of.

It's the string going into square waves was the bit I was most focused on.

 

[Gepetto]

It's the string going into square waves was the bit I was most focused on.

Needs better video recording ...

 

[HotSauce]

I'm late to the party here so forgive me if it was mentioned, but check out "fourier transform." The remarkable discovery that many pure tones can be represented by one more complex tone. Which is absolutely NUTS when you think about it!

https://en.wikipedia.org/wiki/Fourier_transform

The woofer responds to the wave by moving to some position along its Z axis, say maximum inward deflection is -1 and maximum outward deflection is +1

If you look at a complex waveform like music, you can imagine that the driver is simply following the line by moving to the corresponding position on its Z axis and this reproduces the wave as a sound pressure wave moving through the vibration medium, air:

https://swphonetics.files.wordpress.com/2012/03/somvi01s.jpg

And then our brains have this remarkable ability to take that and break it up like this! (the bottom waveform is the complex one and the top three are its constituent sine tones)

https://hearinghealthmatters.org/wp-content/uploads/sites/9/files/2012/06/Fourier-Analysis.gif

 

[Pure_Brew]

How can a driver...say a woofer...reproduce frequencies from 30hz to 300hz , simultaneously....AND how does the ear hear these simultaneously?? Seems to me while a woof would be doing 30hz, it could not do anything else till that was accomplished...

I like to think of it this way:

move your handlike you are bouncing a ball pretty fast.

now without changing your speed, move your whole arm (with hand) up and down at slow rate.

Your hand then will be moving at the same rate, but also rising up and down slowly with your whole arm.

If you apply this to a speaker, it’s doing a similar thing.

Slowing things down, as an example, let’s say you have a woofer on the bench, and you can achieve 1hz with some good cone travel, or at least slow enough to see the cone moving way in and way out. Now if applied a much higher frequency at the same time, the cone would simply be making that high frequency during the full slow travel of the cone. Back to the hand/arm analogy.

In other words, the woofer/voice coil doesn’t have to return to its “at rest” or zero-crossing to make other sine waves. It’s making other waves as it travels on it’s outward and inward paths.

might look a bit like this:

From: https://courses.lumenlearning.com/physics/chapter/16-10-superposition-and-interference/

 

[Gepetto]

Have you watched a hard disk drive doing a butterfly seek test? Voice coil driven...

On a much larger scale, a shaker table for mechanical vibration testing? Much larger voice coils...

 

[laatsch55]

Ahhh...

 

[HotSauce]

It's understandable to be confused by this, because it requires accepting and understanding two very counterintuitive things at the same time! I did not really understand this until we covered it in one of my college sound engineering courses.

One of the more interesting things we did in the synthesizer composition class was to experiment with modulating waves with other waves. As you do this you watch the spectrum analyzer and you see all these sine tones moving around just from combining, say, a square wave with a sine wave and changing the frequency.

I like this animation for visualizing it:

https://upload.wikimedia.org/wikipedia/commons/7/72/Fourier_transform_time_and_frequency_domains_(small).gif

The math part isn't important but you see the red wave is the complex wave made up of all the simple sine waves. Then at the little end those vertical lines along that horizontal blue line are where each frequency is relative to one another from 20Hz to 20kHz, and how loud they are.