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

[kemmler3D]

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

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

It can, if it's overpowered for its intended use. More power generally requires more coils which means more mass. I'm not good with t/s parameters but I don't think that's always helpful. AFAIK it's usually a good thing for woofers and subs but for true mids and tweeters I think other factors tend to be more important.

 

[CptKlotz]

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

Different excursion tho, I guess.
Apologies, I am not particularly know

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

Is it usually a compromise?

Everything with speakers is a compromise. Midrange and tweeter domes need to be somewhat lightweight for efficiency and a reasonable upper frequency extension. Therefore you can't use a huge coil with large diameter wire.

A bass driver's motor along with other parameters like moving mass and compliance of the suspension determines the Thiele/Small parameters. These in turn determine whether a driver is useable at all and whether it's best suited to open baffle, sealed, transmission line, bass reflex or horn applications.

 

[Chr1]

Ah. So presumably, ideally you want everything except the frame/basket to be as light as possible, but with the strongest magnetic field and greatest heat dissipation plus cone stiffness possible? The compromises made being due to max SPL/power required.

Presumably like basket stiffness, magnet strength/size can never be too high? Or no?

 

[Heinrich]

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

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

Fun question, as somebody's notion went like "big magnet is the most expensive means to hinder bass reproduction". Ha, ha, no. Today' speaker design follows very different paradigms. See, for instance, JBL's 2020H driver. Oversaturated air gaps were used to reduce distortion, nowadys substituted by copper caps, and so forth.
Are you going to become a driver expert? Trust the measurements of the finished speakers instead, in case not. It's a rabbit hole, with many detours ...

... Thiele/Small parameters. These in turn determine whether a driver is useable at all and whether it's best suited to open baffle, sealed, transmission line, bass reflex or horn applications.

As I said, the rabbit hole. No, the T/S parameters determine nothing, actually. We have (DSP) equalizing today. Switch of paradigm! Many tinkerers need decades to get there ...

 

[Chr1]

Indeed. No delusions about becoming an expert here for sure.
Just curious about optimal designs for the various types of drivers and how they have evolved, inherent compromises etc. I am aware that measurements are pretty much everything here and compromise is usually to do with frequencies and volumes required. Plus cost obviously.

 

[Arindal]

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

No, there are some dust cap designs which are glued to the main cone, so not indicative of a big voicemail.

An important aspect for different driver geometry is stability and production issues of the diaphragm and voicecoil former unit. Gluing a dustcap onto the voicemail former, is much easier and will result in just a little tolerance over the production run, compared to glueing it onto the cone.

And are bigger voice coils always advantageous?

No. For woofers and subwoofers, bigger voice coils are advantageous in most cases, but it very much depends on the motor design. For midrange drivers reaching a bit higher, or particularly for tweeters, bigger voicecoils come with a lots of problems, as the whole driver will merely behave like a ring radiator instead of a cone or dome. The Manger transducer is a prominent example reaching 35K Hz with a 3" (76mm) voicecoil. As the wavelength is much smaller at 20K already, actually pretty funny things can happen dispersion-wise.

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

There are ATC midwoofers which have a soft dome-shaped dustcap which in fact is similar to their midrange dome. It is as large as the voicecoil itself.

Some companies prefer to make cone and dustcap from one piece. Dynaudio´s MSP cones are a prominent example. If you look closer, you notice little gaps exactly there where they are glued to the voicecoil former. If I am not mistaken, the main purpose is to get the cone into magnet gap with as little tolerance as possible.

 

[CptKlotz]

I think Dynaudio said this and they are not entirely wrong in this case
(Big magnets being the most expensive way to prevent bass reproduction).

I suppose it might help to look at bass drivers with different Thiele/Small parameter sets in a software like WinISD, AJHorn or something like that. Or read up on the influence of parameters such as fs, mms, Q factors, especially qts etc....

 

[Salt]

Ah. So presumably, ideally you want everything except the frame/basket to be as light as possible, but with the strongest magnetic field and greatest heat dissipation plus stiffness possible? The compromises made being due to max SPL/power required.

Presumably like basket stiffness, magnet strength/size can never be too high? Or no?

At the end every parameter interacts with the others of TS-Parameters.
With light membranes and coils (low Mms, Moving Mass), it will be more than difficult to get sufficient bass with vented or closed box. With mids and highs it would be fine, otoh.

 

[Arindal]

Lots of smaller diameter, large excursion subwoofer drivers are like this.

My assumption would be that this is mainly a measure to achieve rigidity. Small, powerful, high xmax subwoofers are prone to tumbling and diaphragm bending, so a big cap ensures rigidity just like a 2-layered sandwich cone of different geometry (often steep cone plus inverted dome, glued together at both the surround and voicecoil former area).

Example:

Speaker Database

4" woofer with xmax of 8.9mm linear.

I found an example of a 5.25" woofer being labelled as ´dome woofer´.

looks interesting, do not know where they are sourced from.

 

[Heinrich]

I think Dynaudio said this and they are not entirely wrong in this case
(Big magnets being the most expensive way to prevent bass reproduction).

I suppose it might help to look at bass drivers with different Thiele/Small parameter sets in a software like WinISD, AJHorn or something like that. Or read up on the influence of parameters such as fs, mms, Q factors, especially qts etc....

Nope

T/S parameters are descriptive of the driver, parts of it. But they do not determine the use of a certain model, pushing it into vented, sealed, what have you.

Just an example, and as that leaving it to you and the DIY community, the bass reflex port is, today, a very crucial part in the overall design. You cannot tinker it, a plain good ol' tube would allways limit contemporary drivers in output due to "chuffing" noises and other. To get hands on insofar competent specimen of, just, a port is impossible.

And then we see stand mount speakers that deliberately tune to 90Hz, meant to be fullrange, and still people pay 10 thousend a pair and are happy. Why should a consumer ask what the bestest dustcap should look like? Use a grille instead ;-)

 

[Chr1]

My assumption would be that this is mainly a measure to achieve rigidity. Small, powerful, high xmax subwoofers are prone to tumbling and diaphragm bending, so a big cap ensures rigidity just like a 2-layered sandwich cone of different geometry (often steep cone plus inverted dome, glued together at both the surround and voicecoil former area).

Example:

Speaker Database

4" woofer with xmax of 8.9mm linear.

Kind of what I thought. And sub drivers are obviously having to deal with comparatively high power and hence heat. Presumably they are more likely to benefit from a bigger voicecoil for this reason also.

 

[Arindal]

So presumably, ideally you want everything except the frame/basket to be as light as possible,

For dedicated compact subwoofers, this is not the case. One important aspect of TSP is achieving a low resonance frequency, and more moving mass actually helps here. But it usually comes at a cost of lower efficiency. As we live in the age of powerful compact amps, developers are willing to accept this compromise.

 

[Arindal]

a very crucial part in the overall design. You cannot tinker it, a plain good ol' tube would allways limit contemporary drivers in output due to "chuffing" noises and other.

That is why the lord, or someone else, has invented the passive radiator. It is really astonishing what is possible in terms of bass with the latest generation of 3"...4" units.

 

[Arindal]

And sub drivers are obviously having to deal with comparatively high power and hence heat. Presumably they are more likely to benefit from a bigger voicecoil for this reason.

I guess it is rather a matter of heat dissipation and heat resistance. With modern materials, voicecoil diameter is seemingly not the limiting factor when it comes to getting the heat outside.

Example by Hertz:

Speaker Database Hertz Mille 10"

500 Watts of nominal and 1000 Watts of peak power gone to the air through a 1.5" (38mm) voicecoil. Another example of very large dustcap presumably for rigidity reasons as this is a 10" polypropylene. Linear xmax of 16.8mm equates to 1.2l of air being displaced within linear operation. Not so bad.

 

[Timcognito]

There were these in the late '70s

 

[Chr1]

That is why the lord, or someone else, has invented the passive radiator. It is really astonishing what is possible in terms of bass with the latest generation of 3"...4" units.

I picked up a pair of 80s 10" Tannoy T-185s with passive radiators for £25 about 20 years ago. They were the speakers that put me onto the speaker/hifi path as a youth.

Now using pro audio Tannoy V12s from ~2000, with the 3142 driver, which are ported and infinitely superior to me. What I find curious personally, is the reverence (and prices) of the vintage Tannoys. And speakers, in general. I doubt very much that they perform as well as the modern equivalents.
The V12s are made for use with subwoofers, but for some reason this is deemed to be detrimental by some. I just don't get some of the logic. Kind of outdated surely.

With a bit of DSP I actually like the sound of them as much as my Neumann KH310s and am just trying to figure out why...
Hence all the questions here.

 

[Heinrich]

There were these in the late '70s

Sure, go and try it out. As said, I leave it at that, as the DIY related topic it is. Looks don't decide if a speaker is competent.

 

[Timcognito]

Sure, go and try it out. As said, I leave it at that, as the DIY related topic it is. Looks don't decide if a speaker is competent.

Well KEF and Thiel both successfully built and sold thousands of speakers with it.

 

[Chr1]

---

Again, apologies for my lack of knowledge, but is a passive radiator essentially a middle ground/compromise between a sealed box and one with ports?

 

[Arindal]

is a passive radiator essentially a compromise between a sealed box and one with ports?

No, it is based on the same principle as a vented enclosure and has similar properties. The port and the air inside the tube (which is the mass of this resonator), are replaced by a conventional stiff diaphragm. As this one has a suspension with a quality factor of its own, calculating it is a bit different from a classic vented design with a port, but it does something similar: using the air displacement behind the active diaphragm via resonator to create more SPL outside the box, lower in frequency than what the active driver would reasonably produce.

Main advantages of passive radiators are no loss of volume for internal tubes/ports, and no chuffing/diffraction noise at higher SPL. Disadvantages are higher costs and much more area on the speaker walls which are eaten up by the radiator(s). In very very compact subwoofer designs like battery-powered bluetooth speakers, they are mainly chosen for the fact that a port for such a low tuning frequency would not fit into the enclosure no matter what.