Does treble radiate from the centre of a cone only?

[Bill poster]

..in relation to full range cones.
I know the centre of a cone will vibrate at higher frequencies but do HF sound waves develop across the whole cone surface or mainly the centre?

[PeterDupont]

In a Lowther unit as an example, the voice-coil decouples from the cone at very high frequencies and radiates sound with the wizzer-cone and centerplug as a horn.

[GM]

Radiation from a Baffled Piston

[Bill poster]

Thanks GM- I'm still trying to understand lobing if using two identical drivers. So you have a main lobe and surrounding side lobe at high frequencies. I it the side lobes or centre lobe that cause lobing? Or is it sound waves from the 2 drivers cancelling each other out?
Still a bit confused.

[ByronInLawrence]

In a conventional driver, all frequencies radiate equally across the whole cone surface. The beaming of drivers at high frequencies is caused by waves from one side of the driver cancelling out waves from the opposite side of the driver. The cancellation only occurs in waves traveling at an angle relative to the plane of the driver. Also, cancellation occurs only (roughly, approximately) for wavelengths equal-to or shorter-than twice the diameter of the driver. I know I'll get grilled for that last statement because it's oversimplified. It's just a "rule of thumb"

On to lobbing between two identical drivers:
First, pretend that each driver is only a point, so all waves from each driver originate from only 1 point. I say "pretend" because this is patently false, but thinking this way helps to understand lobbing. Now imagine the drivers are side-by side, 10cm apart, and you are standing off to one side of a speaker. Waves which reach you are originating from the far (relative to you) driver, 10cm behind (0.00029 seconds later than) waves originating from the near driver. If the frequency the drivers are playing is low, the wavelength will be long enough that this 0.00029 second delay will be irrelevant. As the frequency increases and approaches 0.00029 seconds/cycle, the waves will start to cancel each other out, until they completely cancel each other out at 0.00029 cycles/second or 3430Hz (3430 cycles/second=0.00029 seconds/cycle). If you move directly in front of the speaker, all waves reach you at the same time, so there is no cancelling at any frequency. Similarly, if you were to move your head up and down, there will still be no cancellation because the drivers will always be equidistant from your ears. That's why people usually don't put drivers side-by-side. Speakers sound better if the lobbing occurs above and below the speaker. It also explains why people usually like the drivers roughly at ear-level, and why most designers put the drivers close together. The closer together the drivers, the higher the frequency above which lobbing occurs.

Of course you're thinking "What about the waves originating from the edges of the driver, or half-way across the radius?" That complicates things beyond my understanding, but it clearly does not eliminate lobbing.

So, to answer your questions directly:
"I know the centre of a cone will vibrate at higher frequencies . . ." No. Maybe some drivers are designed this way, but in a conventional driver the center vibrates at the same frequencies as the rest of the cone surface.
" . . . do HF sound waves develop across the whole cone surface or mainly the centre?" The whole cone surface.
"So you have a main lobe and surrounding side lobe at high frequencies." Only if the drivers are side-by-side. Otherwise the lobbing occurs only above and below the drivers. Also, the higher the frequency, the more, but thinner, lobes you will have.
"I[s] it the side lobes or centre lobe that cause lobing?" I don't understand the question. The lobes are the lobbing.
"Or is it sound waves from the 2 drivers cancelling each other out?" Yes.

Here's another link in addition to GM's which probably has way more information than you want. Biro Technology

Can you tell I'm trying to put off getting yard work done?

[Bill poster]

When you say the cancellation only occurs in waves travelling at an angle relative to the plane of the driver-is that angle within a short distance or at the point of the listeners position?

[DYNABLASTERTUNERS]

Originally Posted by ByronInLawrence

In a conventional driver, all frequencies radiate equally across the whole cone surface. The beaming of drivers at high frequencies is caused by waves from one side of the driver cancelling out waves from the opposite side of the driver. The cancellation only occurs in waves traveling at an angle relative to the plane of the driver. Also, cancellation occurs only (roughly, approximately) for wavelengths equal-to or shorter-than twice the diameter of the driver. I know I'll get grilled for that last statement because it's oversimplified. It's just a "rule of thumb"

On to lobbing between two identical drivers:
First, pretend that each driver is only a point, so all waves from each driver originate from only 1 point. I say "pretend" because this is patently false, but thinking this way helps to understand lobbing. Now imagine the drivers are side-by side, 10cm apart, and you are standing off to one side of a speaker. Waves which reach you are originating from the far (relative to you) driver, 10cm behind (0.00029 seconds later than) waves originating from the near driver. If the frequency the drivers are playing is low, the wavelength will be long enough that this 0.00029 second delay will be irrelevant. As the frequency increases and approaches 0.00029 seconds/cycle, the waves will start to cancel each other out, until they completely cancel each other out at 0.00029 cycles/second or 3430Hz (3430 cycles/second=0.00029 seconds/cycle). If you move directly in front of the speaker, all waves reach you at the same time, so there is no cancelling at any frequency. Similarly, if you were to move your head up and down, there will still be no cancellation because the drivers will always be equidistant from your ears. That's why people usually don't put drivers side-by-side. Speakers sound better if the lobbing occurs above and below the speaker. It also explains why people usually like the drivers roughly at ear-level, and why most designers put the drivers close together. The closer together the drivers, the higher the frequency above which lobbing occurs.

Of course you're thinking "What about the waves originating from the edges of the driver, or half-way across the radius?" That complicates things beyond my understanding, but it clearly does not eliminate lobbing.

So, to answer your questions directly:
"I know the centre of a cone will vibrate at higher frequencies . . ." No. Maybe some drivers are designed this way, but in a conventional driver the center vibrates at the same frequencies as the rest of the cone surface.
" . . . do HF sound waves develop across the whole cone surface or mainly the centre?" The whole cone surface.
"So you have a main lobe and surrounding side lobe at high frequencies." Only if the drivers are side-by-side. Otherwise the lobbing occurs only above and below the drivers. Also, the higher the frequency, the more, but thinner, lobes you will have.
"I[s] it the side lobes or centre lobe that cause lobing?" I don't understand the question. The lobes are the lobbing.
"Or is it sound waves from the 2 drivers cancelling each other out?" Yes.

Here's another link in addition to GM's which probably has way more information than you want. Biro Technology

Can you tell I'm trying to put off getting yard work done?

If i have good understud, than a pinched Cone, like most Widerangers have, is going to beam strong, when we have a flat Cone like those new Tang Bands, there is no beaiming, just wide radiating, but then if we head a convex Cone like a tweeter, then we have a very wide dispersion Cone?

[ByronInLawrence]

Originally Posted by Bill poster

When you say the cancellation only occurs in waves travelling at an angle relative to the plane of the driver-is that angle within a short distance or at the point of the listeners position?

That angle refers to the angle of a line starting very near the driver and continuing all the way to a listener's ears.

[ByronInLawrence]

Originally Posted by DYNABLASTERTUNERS

If i have good understud, than a pinched Cone, like most Widerangers have, is going to beam strong, when we have a flat Cone like those new Tang Bands, there is no beaiming, just wide radiating, but then if we head a convex Cone like a tweeter, then we have a very wide dispersion Cone?

Not really. The shape of the driver does not effect its dispersion very much. Dispersion is mostly determined by the ratio of the driver's diameter to the wavelength of the sound it is making. A driver beams when the wavelength is twice as long as the diameter of the driver - roughly speaking.

I know some manufacturers claim to have a special driver shape which improves dispersion, like ScanSpeak's "wave guide center plug" but I am skeptical. I looked up Tang Band's flat driver, the W2-800SL, and noticed they called it a "wide dispersion driver". That's probably because it is only 2" (5cm) diameter, but goes down to 160Hz (so they say). I'm sure it has great dispersion at the lower frequencies, but I am certain that thing beams like crazy above about 3400Hz.

[dewardh]

Originally Posted by ByronInLawrence

In a conventional driver, all frequencies radiate equally across the whole cone surface.

That might be true for an "ideal" driver, and for some cone materials and geometries in real world drivers, but it is also not true by design in some real world drivers as well. Metal cones tend to move as a unit (until breakup), but poly and soft paper cones often decouple the inner part of the cone from the outer, and many large "pro" drivers have an embossed "second surround" in the middle of the cone to encourage just such decoupling. The result is high frequency radiation from the center of the cone only, and less beaming as a result. These designs have been around for a long time. The most extreme examples have separate cones (or a cone and dome), the smaller attached directly to the voice coil for high frequencies, the larger attched through an elastic coupler that passes the lower frequencies but not the highs . . . essentially a mechanical crossover. This too is a quite old design, exemplified by drivers with a "whizzer" cone in the center and a larger (typically soft, or embossed) paper cone for the mids/bass.