Is this a good buy?

[agedhorse]

8 hours ago, Dan Dare said:

 

Could you explain the physics to me? I'm always keen to learn. Thanks.

There’s the basic premise of destructive interference due to the diameter of the driver versus the mid-high frequency wavelength, but this is modified by the size/shape of the dust cap and the geometry of the cone. With the right choices, the mid polar pattern can be altered more than an octave above what the basic predictions suggest. 
 

this can be taken to an even higher level by the use of a “wizzer cone” dust cap. 

[Happy Jack]

Crossbeam's gone askew on't treddle ...

[stevie]

@Phil Starr is probably the person to explain this in a way that doesn't have you reaching for your dictionary. He'll probably be along soon. However, @Chienmortbb is right to say that the fall off in higher frequencies off axis is worse on a large diameter driver than a small one.

 

I'm fascinated to hear how you can extend the off-axis rolloff by an octave by manipulating the cone and dustcap, as I've never seen this in real life. A wizzer cone is a bit different, as it is a separate transducer attached to the voice coil.

[bremen]

5 minutes ago, stevie said:

 

 

I'm fascinated to hear how you can extend the off-axis rolloff by an octave by manipulating the cone and dustcap, as I've never seen this in real life. A wizzer cone is a bit different, as it is a separate transducer attached to the voice coil.

I always thought a whizzer was an extension to the cone, rather than a separate transducer. Used to see them on cheapo record players - the luxury ones had separate tweeters.

 

[stevie]

It depends how you want to define it, @bremen. I think of it as a supplementary cone made of lighter weight material that's attached to the cone. They've fallen out of favour nowadays, as cheap whizzers are highly resonant, and there are better alternatives, i.e. coaxial drivers.

[bremen]

Yes, they were never great.

 

+1 for coax, you can't move for Tannoy speakers here at Bremen Towers.

[agedhorse]

6 hours ago, stevie said:

@Phil Starr is probably the person to explain this in a way that doesn't have you reaching for your dictionary. He'll probably be along soon. However, @Chienmortbb is right to say that the fall off in higher frequencies off axis is worse on a large diameter driver than a small one.

 

I'm fascinated to hear how you can extend the off-axis rolloff by an octave by manipulating the cone and dustcap, as I've never seen this in real life. A wizzer cone is a bit different, as it is a separate transducer attached to the voice coil.

The simplest and most well known example of off axis extension is the Duraluminum dust cap that attaches directly to the bobbin. It radiates the HF component of the signal like a 4” driver. The Duraluminum material is the same material that jBL developed for use in high frequency compression drivers. 
 

A wizzer cone is not a separate transducer, it’s just a specialized dust cap that attaches to the top lip of the bobbin just like the JBL aluminum dust cap. How well the HF energy coupled to the secondary radiation device determines in part the effectiveness. Decoupling the dust cap from the bobbin can be used to alter the response, as does the choice of materials. 

[mikebass456]

Can you get the same overall effect by inverting the flux capacitor?  I really should have paid more attention in Physics class......🤓

[Chienmortbb]

23 minutes ago, agedhorse said:

The simplest and most well known example of off axis extension is the Duraluminum dust cap that attaches directly to the bobbin.

Aluminium dust cap was used in the late 60s by Fane on the original crescendo drivers and it did indeed extend the response considerably. 

[tauzero]

2 hours ago, mikebass456 said:

Can you get the same overall effect by inverting the flux capacitor?  I really should have paid more attention in Physics class......🤓

 

You have to reverse the polarity of the neutron flow.

[Chienmortbb]

14 minutes ago, tauzero said:

 

You have to reverse the polarity of the neutron flow.

Electrons move, Neutrons just hang around waiting for an Electron to come along🌩️

[tauzero]

1 minute ago, Chienmortbb said:

Electrons move, Neutrons just hang around waiting for an Electron to come along🌩️

 

[agedhorse]

28 minutes ago, Chienmortbb said:

Electrons move, Neutrons just hang around waiting for an Electron to come along🌩️

Things get super exciting when neutrons move...

[Phil Starr]

On 07/03/2025 at 09:59, Chienmortbb said:

You dismiss this but beaming, as the fall off in higher frequencies off axis is called, is far worse on a 15” than a 12 and a good 10 beats both. It is Physics sadly.

 
 

 

 

On 07/03/2025 at 17:55, agedhorse said:

Yet there are several mechanisms that are used to improve off axis high frequency extension. This is why some 15” designs are better than others in this regard.

 

On 09/03/2025 at 08:03, Dan Dare said:

 

Could you explain the physics to me? I'm always keen to learn. Thanks.

 

10 hours ago, stevie said:

@Phil Starr is probably the person to explain this in a way that doesn't have you reaching for your dictionary. He'll probably be along soon. However, @Chienmortbb is right to say that the fall off in higher frequencies off axis is worse on a large diameter driver than a small one.

 

I'm fascinated to hear how you can extend the off-axis rolloff by an octave by manipulating the cone and dustcap, as I've never seen this in real life. A wizzer cone is a bit different, as it is a separate transducer attached to the voice coil.

I'll have a go though I've just been reading Colloms (High Performance Loudspeakers ISBN 047197091) and I have to admit this will be a simplification.

 

The conventional theory around loudspeakers treats them as being rigid pistons The original transducers used in the classic experiments on beaming were done with very small metal discs mounted on the end of long tubes which avoided diffraction further complicating the dispersal patterns. The irregular dispersion of real world speakers at high frequencies is to a large extent due to the fact that loudspeaker cones are very far from rigid. To a large extent means that there are many other factors at play which cause frequency irregularities. but I'll keep it simple and stick to the cone..

 

So speaker cones are flexible, at low frequencies and power they are stiff enough to move as a whole and approximate to a piston. At high frequencies and powers they will start to flexand the outer parts of the cone will lag behind the movement of the coil, some parrts of the cone may be moving backwards as other parts are moving forwards and the phase difference will cause cancellation . It's fairly easy to see this with a strobe light with concenrtic rings in the cone moving independently of each other even as the cone itself moves backwards and forwards. You can also find laser interferometry pics of this which illustrate the process.This means just calculating of axis cancellation on the basis of diameter will not describe the off axis frequency cancellation by itself. This is often described as cone break up and you'll see this in the frequency response curves of just about any cone speaker. You can see this below in a typical 12" speaker The response in red is fairly flat up to just above 1kHz and then you can see a ripple in the reponse due to the cone break up and the treble response shows a rising response between 1and 4kHz because the centre of the cone is moving faster than the outside as it becomes decoupled from the heavier outside parts of the cone.  The ripple is because the cone has resonances of its own. You can also see the off axis response in Blue is falling off initially due to the off axis cancellation but then due to the resonances as the cone flexes.

Designers know about all of this and many instrument speakers take advantage of that midrange peak in the kHz area. Almost any Celestion or Eminence guitar speaker will show hage peakes in this area. So will something like the Eminence used in the Barefaced one10 or indeed the Ampeg 10" speakers. A cone can be made more or less rigid by changing the fibres in the pulp, by changing the shape of the cone, introducing ridges changing the cone surround or by using a metal cone or a plastic or even a composite . Adding a hard dust cover or a whizzer cone will also allow you to adjust the treble output of the speaker and another technique is to introduce a damping material into the cone or even treating the cone after it is formed.

 

It's worth noting that it isn't unusual to have considerable off axis output from 15" speakers and it is possible for them to exceed the off axis response from a 10" speaker. The simple explanation is that a small cone is going to be more rigid than a bigger cone made of the same material.