What is the Reason For This Driver Design (Large Dust Cap)

[ZZdown]

I run across these 5" drivers in a expensive custom size speakers by Leon. What grabbed my attention is the size of the "dust cap" and I am curious if this is some sort of a hybrid between dome mid driver and woofer (e.g. is it more than a dust cap?).

I believe the driver is Morel CAW 538 or similar (customized for Leon, couldn't find OEM part#). The "radius" of the traditional cone is only about 1" and if I am calculating it correctly, the cap has larger surface area than the cone . I searched online but could not find any info about this design. As I am typing this, I see that the specs says 3" voice coil, so perhaps the cap is indeed a dust cap only?

Morel CAW 538 5" Cast Frame Woofer

Morel CAW 538 5" Cast Frame WooferThe Classic Advanced line of woofers is based on Morel's classic line - the renowned MW series. These products have high power handling due to the aerodynamic Uniflow™ open chassis and large diameter spiders. This woofer has reinforced ferrite magnets for the...

www.parts-express.com

 

[dfuller]

It has a huge (3") voice coil - you need a big cap to cover it.

 

[kyuu]

It has a huge (3") voice coil - you need a big cap to cover it.

So is it a rule that bigger dust caps mean bigger voice coil? And are bigger voice coils always advantageous?

 

[ZZdown]

At this size, the dust cap has to be producing significant part of the pressure waves and affecting performance.

 

[Chr1]

This is something I have been curious about. Would have thought that when the voice coil diameter, and consequently the dust cap, gets close to the outside diameter of the cone itself, surely it would be detrimental to the sound quality?
Though possibly not, I guess.

 

[voodooless]

So is it a rule that bigger dust caps mean bigger voice coil?

It’s more the other way around

But it’s not a mandated relationship, though in most cases it makes a lot of sense. There are drivers without a dust cap (either with a phase plug, or simply a planar driver), or you could let the cone go past the voice coil perimeter, and use a smaller dust cap. This however isn’t very common.

And are bigger voice coils always advantageous?

No, not always. Bigger also means heavier, so may impact efficiency and many other things. It’s always a trade off between various components of the driver.

 

[CptKlotz]

If I remember correctly, Morel used to manufacture drivers for Dynaudio and "inherited" some of their design features like large diameter voice coils.

A large voice coil should be able to handle more power and might drive the cone more uniformly. A downside might be higher moving mass.

You can, of course, install a dust cap that is much larger than the voice coil diameter and some manufacturers probably do

Ultimately it comes down to the application and objective parameters...

 

[CptKlotz]

This is something I have been curious about. Would have thought that when the voice coil diameter gets close to the outside diameter of the cone itself, surely it would be detrimental to the sound quality?
Though possibly not, I guess.

Those drivers are usually called "domes" and mostly used for midrange and treble

 

[Chr1]

Those drivers are usually called "domes" and mostly used for midrange and treble

No, I am not referring to midrange domes. I was meaning drivers where the voice coil and dustcap are not much smaller than the outside diameter of the cone.
Lots of smaller diameter, large excursion subwoofer drivers are like this.

 

[DVDdoug]

No, I am not referring to midrange domes. I was meaning drivers where the voice coil and dustcap

"Dome like"?

There's more than one way to do everything and there are trade-offs in speaker design as with anything else. There's rarely "one best solution". The manufacturer will always tout there decisions as "features" or advantages but the performance is what counts.

 

[Chr1]

Yes, I guess that some of the ATC woofers are examples where the dustcap is very/relatively large...

 

[CptKlotz]

No, I am not referring to midrange domes. I was meaning drivers where the voice coil and dustcap are not much smaller than the outside diameter of the cone.
Lots of smaller diameter, large excursion subwoofer drivers are like this.

I suppose my comment was half-serious

For a regular dome driver, the cone diameter is in fact equal to the voice coil diameter. Those drivers typically don't have a spider and must be centered by the surround only (exceptions exist - the large ATC dome midrange is one as far as I know). I suppose they don't handle large excursions that well and are therefore not used for bass.

Cone drivers usually have a spider *and* the surround to center the driver. If you really wanted to make the voice coil as large as the cone diameter, you would get a gargantuan voicecoil and have trouble mounting a spider unless you design a completely new kind of driver. You would probably also get different kinds of breakup modes as the cone isn't supported much in the middle.

Does anybody know any drivers like that? I wouldn't rule out that they exist, but I can't think of one.

 

[CptKlotz]

"Dome like"?

There's more than one way to do everything and there are trade-offs in speaker design as with anything else. There's rarely "one best solution". The manufacturer will always tout there decisions as "features" or advantages but the performance is what counts.

I think this is key. "Stories" about technology such as the next new cone material, operation principle or whatever don't guarantee great quality. Also, drivers that are actually great for a certain application can still be used in a poor overall design.

 

[Heinrich]

I think this is key. "Stories" about technology such as the next new cone material, operation principle or whatever don't guarantee great quality. Also, drivers that are actually great for a certain application can still be used in a poor overall design.

For starters the cone can and will flex. The dome stiffens it. In ancient times the flex was desirable, because it mitigated problems with the x/over, when targeting a most linear on-axis response. Today cones are more designed to be stiff for reasons I can't actually tell. Real improvements are rare, see the Purify surround lately.

To judge the quality of a driver from the looks or material used is an unfortunate endevour. But, as it seems, is fun to do.

 

[kyuu]

To judge the quality of a driver from the looks or material used is an unfortunate endevour. But, as it seems, is fun to do.

Wait, so you're saying I can't do this:

And conclude that this is the bestest driver ever?

 

[Chr1]

Is it the case that a big ass magnet, voice coil and consequent dustcap indicates that the driver can likely handle more power. Nothing more?

 

[Salt]

That's not about power handling but motor power.

 

[Chr1]

But midrange dome drivers are like this, yet often can't take big power...

Different excursion tho, I guess.
Apologies, I am not particularly knowledgeable about this stuff.

 

[Salt]

Power handling is the domain of voice coil geometry. Motor power is the interaction of magnet field strength and voice coil geometry.

 

[Chr1]

Okay, so next question, can a drivers motor be too strong?

Is it usually a compromise?
For subwoofer, woofer, mid/dome, dome/tweeter?