Why Are Driver/Speaker Cones - er, CONE-Shaped?

[SurferJoe46]

I asked about some cabinet positions and got an interesting sidebar (OT) statement about the shape of the cones as not being important - or sumpthin' like that.

I was looking into the aspects of sound coming straight off the cone - and since it is shaped tapering to the center where the motor is and I was thinkin' <again> about the sound waves coming off at angles that force interception of each other from the same pulse - why is a cone shape so common and not a different shape?

Is it for the square inches or some stability considerations?

I mean - a 15" cone should be equal to a 15" flat driver - right?

Is it about flex and cone distortion?

Don't the sound waves actually run into each other coming off the cone and at each other from the points around the periphery of the cone?

It looks like the funnel shape would induce comb filtering or whatever if the sounds do run into each other coming out of the cone-shape.

I have a pencil. paper and a scanner and I can make one of my famous drawings if you don't understand what I'm asking.

[eyeballkid]

awaiting famous drawing...
just cos....

[zachoff]

No idea, but I always thought the Kicker Solobaric designs were interesting & always wondered what, if anything, makes them better than their competition.

[Sartori]

This thread might get pretty sciencey.

[SurferJoe46]

Originally Posted by eyeballkid

awaiting famous drawing...
just cos....

One drawing on the desk - as soon as I scan it, it will be here.

BRB --- Got It!



So what is the real situation - and can one assume that there is or is NOT a sonic interference and collision going on caused by the cone's shapes?

[SurferJoe46]

Nice drawing, if I say so myself.

[fu22ba55]

Originally Posted by Sartori

This thread might get pretty sciencey.

I'm puttin' on my science-listening pants... this should get good.

[SurferJoe46]

Originally Posted by fu22ba55

I'm puttin' on my science-listening pants... this should get good.

It's going for 11:30PM on the Left Coast, so there may NOT be too many audio-geeks here at this hour - or there's a gig to play or whatever.

I'm gonna take a shower and get right back here so I can see if the bait works or not.

I think this can become a contact sport if we're not careful though.

Last edited by SurferJoe46 : Today at 11:32 PM. : Shower's done and no risers yet? Hrumph!

While I have everybody's attention - I still need that small piece of TORT

[DukeLeJeune]

The cone shape is for strength. A cone of paper won't bend nearly as easily as a flat sheet.

There is indeed interference/cancellation from the sound emanating from various parts of the cone at short wavelengths, but it is caused by the cone's size rather than its shape. This partial cancellation of short wavelength energy results in a phenomenon known as "beaming", by which the radiation pattern becomes progressively narrower as we go up in frequency. The larger the cone, the narrower its pattern at a given frequency. This interference also occurs between two separate cones that are on the same baffle. The classic example is the 4x12 guitar cab, and the "icepick" concentration of high frequenciy energy in a relatively narrow beam out in front of the cab.

Look at drawing "A". See where the lower arrow from the left-hand side crosses the upper arrow from the right-hand side? The arrows are different lengths at that point. At the frequency where the difference in lengths between the two arrows is equal to 1/2 wavelength, one of them is 180 degrees out-of-phase with the other, and they cancel each other out. This is the mechanism that causes beaming.

Back to cones. Different cones have different profiles. A straight-sided cone is the stiffest, but when it finally does begin to flex its behavior is usually pretty nasty. A curved-sided cone will start to flex earlier, but its behaviour is more likely to be pretty good even when it's flexing. Another name for cone flexing is "breakup".

[SurferJoe46]

Originally Posted by DukeLeJeune

The cone shape is for strength. A cone of paper won't bend nearly as easily as a flat sheet.

There is indeed interference/cancellation from the sound emanating from various parts of the cone at short wavelengths, but it is caused by the cone's size rather than its shape. This partial cancellation of short wavelength energy results in a phenomenon known as "beaming", by which the radiation pattern becomes progressively narrower as we go up in frequency. The larger the cone, the narrower its pattern at a given frequency. This interference also occurs between two separate cones that are on the same baffle. The classic example is the 4x12 guitar cab, and the "icepick" concentration of high frequenciy energy in a relatively narrow beam out in front of the cab.

Look at drawing "A". See where the lower arrow from the left-hand side crosses the upper arrow from the right-hand side? The arrows are different lengths at that point. At the frequency where the difference in lengths between the two arrows is equal to 1/2 wavelength, one of them is 180 degrees out-of-phase with the other, and they cancel each other out. This is the mechanism that causes beaming.

Back to cones. Different cones have different profiles. A straight-sided cone is the stiffest, but when it finally does begin to flex its behavior is usually pretty nasty. A curved-sided cone will start to flex earlier, but its behaviour is more likely to be pretty good even when it's flexing. Another name for cone flexing is "breakup".

OT @ DukeLeJeune - recognize this?

That's just what I wanted to know - there will, of course, be more questions though.

1) Is it advantageous to have one shape or angle verses another for bass notes opposed to higher or guitar notes?

2) Does the angle of the cone vary enough with 'flex' or break-up matter at singular freqs like a bass produces? I imagine a multi-freq reproduction is gonna cause all sorts of comb filtering when there are so many different freqs coming off the cone all at once.

3) IF the radiating material of a flat driver were driven hard enough and therefor with enough compliance to the desired frequency - is there any other negative trade off, not counting the power consumption needed to drive it?

4) Wouldn't a flat driver be a lot less susceptible to distortion and comb-filtering since the sound would have to emanate straight from that singular flat surface (no sounds crossing-over and colliding inside the cone periphery)?

I wonder about the planair (sp?) flat panels that were used in the Sense-A-Round theater systems of 50 years ago. I know they took serious power to run them but their sound production was a real shirt flapper in the audience.

[Jazz Ad]

A speaker is a piston. The shape of the cap has no relationship with the pulse width frequency.

[SurferJoe46]

OK ---- er.

That's confusing.

It's after midnight here and I gotta cop some Z's - so I'll be back ASAP tomorrow.

[fu22ba55]

Originally Posted by DukeLeJeune

The cone shape is for strength. A cone of paper won't bend nearly as easily as a flat sheet.

Would there be any advantage to using a dead-flat piece of plastic / carbon-fibre / something more rigid than paper? Or is the flexing important (and necessary).

I imagine in this day and age there must be a material rigid enough for the task?

[JimmyM]

Originally Posted by fu22ba55

Would there be any advantage to using a dead-flat piece of plastic / carbon-fibre / something more rigid than paper? Or is the flexing important (and necessary).

I imagine in this day and age there must be a material rigid enough for the task?

ask larry hartke's opinion.

[BassIan]

Originally Posted by fu22ba55

Would there be any advantage to using a dead-flat piece of plastic / carbon-fibre / something more rigid than paper? Or is the flexing important (and necessary).

I imagine in this day and age there must be a material rigid enough for the task?

A benefit to the cone shape was mentioned above as "strength". True: The planar driver would be prone to buckling. Arguably more important than strength is the stiffness. Regardless of the material, a cone shape will be stiffer in the direction of motion for a given mass than a planar shape. So, paper, aluminum, carbon fiber, wood, you'll always be able to make a cone sufficiently stiff with less mass than a plane. The mass of the cone combined with the stiffness of the suspension are two primary factors that dictate a driver's free air resonant frequency. In a simplified spring-mass system, resonant frequency is indicated by sqrt(k/m) where k is stiffness and m is mass.

Others have mentioned cone "breakup" or resonance. Indeed the cone shape is subject to higher-frequency resonant modes, which is some cases are used to increase high-frequency response. Whizzer cones are an extreme example, where the inner portion of the cone is assumed to receive direct higher-frequency drive from the voice coil and is augmented by a secondary, stiffer cone.

As for direction of air movement, the best way to clarify this is to think of how Vd (maximum displacement volume) is calculated. This is the product of projected cone area (Sd - the circular area of the moving portion of the cone) and Xmax (the maximum linear excursion of the cone). This is the "swept" volume of the cone. If one were to perform a fluid Finite Element Analysis on the movement of air driven by a speaker cone, there would perhaps be some shear flow and turbulence along the angled portion of the cone, but I have trouble imagining the effect as significant.

[Jim C]

Thanks Duke; only 9 posts and I get a well crafted answer to an interesting question that is understandable by all

Wonder what the Vegas line is for:
* Number of posts that offer only smart a$$ answers
* Number of posts that are inaccurate opinions
* Number of posts that actually add anything positive

[billfitzmaurice]

Originally Posted by fu22ba55

Would there be any advantage to using a dead-flat piece of plastic / carbon-fibre / something more rigid than paper? ?

The added weight makes it impractical for wide bandwidth drivers. Large flat dustcaps are used in some subwoofer drivers, where the higher mass isn't a problem. Like this Lab 12, for instance:

ask larry hartke's opinion

A reference to aluminum, and there are no particular advantages to it, other than visual, i.e., marketing. Magnesium does have some advantages over paper, and it's used in some very good hi-fi drivers. There are advantages to more exotic metals with tweeters, where titanium is commonly used, and beryllium is the preferred material for those who can afford it.

[SurferJoe46]

Originally Posted by Jazz Ad

A speaker is a piston. The shape of the cap has no relationship with the pulse width frequency.

OK - a night's sleep and I can make a little more of this - at least the words don't blur right now.

I understand that the shape has nothing to do with the displacement of the air/volume and that's a given.

I was just thinking that the angles on the sidewalls of the cone play a part in forcing the sound waves to gather at the center of the area where the intersecting lines drawn from 90º to the paper cone sides, would run into each other and would be problematic.

Original drawing so one doesn't have to switch back and forth to view it again:::



It appears to me that if you propel air from a flat surface, then none of the waves have an opportunity to collide at such a close proximity near to the center of their 'birth', if you will, than if they went out straight and didn't have this initial collision and forcing them to move perpendicular to the surface of the cone.

So to imagine that we had two drivers (like the A driver above) and they had waves coming out of them at those induced angles, then more collisions are going to happen when the angled waves run into each other's sound waves in a side-by-side driver configuration.

If the signals went straight out from the drivers (like B) along their linear axis from a straight direction, then wave collisions and resultant comb filtering would not exist.

Going straight from their point of generation would negate the possibility to collide with a signal from another driver.

So far this is very informative and I appreciate the info provided. Thanks all.

[billfitzmaurice]

Originally Posted by SurferJoe46

OK - a night's sleep and I can make a little more of this - at least the words don't blur right now.

I understand that the shape has nothing to do with the displacement of the air/volume and that's a given.

I was just thinking that the angles on the sidewalls of the cone play a part in forcing the sound waves to gather at the center of the area where the intersecting lines drawn from 90º to the paper cone sides, would run into each other and would be problematic.

Original drawing so one doesn't have to switch back and forth to view it again:::



It appears to me that if you propel air from a flat surface, then none of the waves have an opportunity to collide at such a close proximity near to the center of their 'birth', if you will, than if they went out straight and didn't have this initial collision and forcing them to move perpendicular to the surface of the cone.

So to imagine that we had two drivers (like the A driver above) and they had waves coming out of them at those induced angles, then more collisions are going to happen when the angled waves run into each other's sound waves in a side-by-side driver configuration.

Your theorem leaves out a most critical bit of information, wavelength. At 100 Hz a wavelength is some 11 feet long, so there's no directionality from the various points of the cone, and no comb filtering or beaming. At 4kHz a wavelength is about 3.4 inches long, so there is directionality from various points of the cone, and there is combing and beaming, as explained by Duke.

If the signals went straight out from the drivers (like B) along their linear axis from a straight direction, then wave collisions and resultant comb filtering would not exist.

That also depends on the wavelengths involved and the distance between each 'source', be they multiple drivers or different points on the same cone. When that distance exceeds 1 wavelength the sources will reach the ear of the listener at different angles of phase and response will therefore be comb filtered. If you want to eliminate combing and beaming the only way to do so is with a radiating plane no more than 1 wavelength in dimension. That's why tweeters are smaller than midranges and midranges smaller than woofers.

[SurferJoe46]

Thanks BFM.

If so, then phasing and comb filtering are mutually the same thing - or perhaps without one the other would not exist.

For a broader appreciation, perhaps the effect of having a stereo speaker in a home stereo system with the polarity reversed is approximately the same.