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How much impact does driver material actually make?

Killingbeans

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But if the weight of the cone is different due to a different material then the motor and surround will also be different so you're now changing three variables.
Impossible to compare cone 'signaures' in my view unless nothing else changes but the cone itself...

The spider too. Case in point, the material is just a single piece of the puzzle. It can help achieve a design goal, but does not guarantee a specific result.
 

fineMen

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But I think we don’t need a definition of esoteric either to have a meaningful conversations among engineers we just refer to the materials in question directly. What do you think?

Esoteric, maybe a more suitable term would be alchimistic? Not all of us understand the compromises with designing a driver. The stiffness measured on a rod of a specific material doesn't tell it all--to us. But for the engineer the specific use case combined with such data would be sufficient to estimate the feasibility of a scientifically accompanied trial.

What is the contribution of the surround which for obvious reasons shouldn't be that stiff?

The cone's diameter is 27cm, the surround's width is 1cm, thus the relative surface areas are 572cm^2 versus 660cm^2 or 1:1,15. The surround takes 15% of the surface area of the driver's moving parts. It has a stiffness of virtually zero. What is it worth to get into extremes with the cone's stiffness? Actually even some otherwise tremendously well designed JBL pro drivers suffer from, as they call it, cone edge resonances. It is the surround's resonance, not the break-up, that easily raises intermodulation from the cone's movement alone (not motor related!) to 30%.

Only Purify addressed the issue successfully with that odd shaped solution. Other dampen and broaden the issue, it's complicated. Are we due to discuss that topic on the basis of cone stiffness? Wishful thinking me thinks.
 

MattHooper

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QUESTION:
(Which I'll get to...)


As I indicated earlier in the thread, I'm skeptical about the idea that particular drivers have a "sound." Ideally if a driver is well implemented it shouldn't really have a "sound" that is different from another driver material. Paper drivers shouldn't sound "more organic" than well implemented metal drivers etc.

My single hesitation here is just my anecdotal experience owning two different speakers that use similar SEAS midrange drivers:
My old Hales Transcendence 5 speakers (and current set of Hales transcendence L/C/R speakers) and my current Joseph Audio Perspective speakers.

Years ago when I first encountered the Hales Transcendence speakers, in comparison with many other speakers I'd heard, the thing that stuck out to me was the combination of clarity and smoothness through which the timbral characteristics of different instruments and voices seemed to be particularly varied and convincing. To use a visual analogy: Imagine taking a very detailed photo of the instruments in a symphony orchestra - you see all the brassy colors separated from the woody tones of strings, black shiny clarinets, wood finish of a piano etc. Now take a spray bottle with white paint and spritz a very fine mist of white particles over the photo so you can still see the photo. So now the overall color is slightly whitened and this cast over everything slightly de-saturates and homogenizes the details and precise color of the instruments in the photo. Take away the white particles and the instrumental images again become richer in color and more differentiated.

The Hales speakers sounded to me like they had "wiped away" this fine scrim of homogenizing distortion so timbral "colors" became that much more differentiated and vivid and clear. As a nut about instrumental timbre, I hear just those kind of differences between some speakers (and also playing with room reflections).

And that is exactly the quality that attracted me to the Joseph speakers when I compared them to tons of other speakers. It was a "jump out at me" character in both the Hales and Joseph speakers. It's not simply "clarity" and "vividness" which plenty of speakers do. It's a particular smoothness or "lack of grit/grain" making for a less mechanical sound to my ears. I also hear this characteristic in the L/C/R Hales Transcendence speakers I own which use the SEAS drivers.

So it's hard not to look at those SEAS midrange drivers they share (even though different models over time) and wonder if there is something about those drivers, properly implemented (both Hales and Joseph use high order crossovers) that provide this impression.

Even if I presume for sake of argument my impressions are accurate, I am in no position to answer this question so I'm wondering if there might be something to this. But one thing in the measurements at least seem to indicate low distortion from both speakers (?). I'm thinking of the cumulative spectral-decay or waterfall plot for both speakers:



They seem pretty clean. Could that explain what I might be hearing to some degree?
 
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JustJones

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Here's a company using something different from anything I've seen in their woofer , basalt. A lot of market speak on their part, not sure it's any better than other material.

 

Inner Space

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I'm skeptical about the idea that particular drivers have a "sound."
Me too. But I have an in-principle question I have long been curious about, from research on something unrelated.

Years ago I was looking into tuned-mass bass absorbers. These are made from rigid sheet material loosely hung. To determine resonant frequency, you need to know mass, which you work out from size times density. It turned out that while sheet materials obviously had an overall bulk density, they tended to vary their density throughout their thickness, having denser surfaces and less dense centers, presumably for handling durability.

This became important, because some theories required controlled HF reflection along with max LF absorption, to preserve in-room liveliness. Some sheets proved very reflective at their surfaces, and some were slightly absorptive. I pictured sound waves impacting, in some cases with every air molecule bouncing off again, and in other cases with some air molecules driven into the material, never to return.

Then I pictured the process in reverse - a loudspeaker cone accelerating forward, punching into a mass of air and accelerating it hard. In such a case, what is the physics of a cone material that drives all air molecules -vs- a material that absorbs some at its surface?
 

Killingbeans

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fineMen

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I pictured sound waves impacting, in some cases with every air molecule bouncing off again, and in other cases with some air molecules driven into the material, never to return.

Then I pictured the process in reverse - a loudspeaker cone accelerating forward, punching into a mass of air and accelerating it hard. In such a case, what is the physics of a cone material that drives all air molecules -vs- a material that absorbs some at its surface?

Did you try to coat the surface, e/g with some polymer, vulgo paint? You suggest that some material wasn't air tight at the micro Pascal pressure level, but I'm pretty much sure that mdf at some tens of PSI is. I don't want to pick on you, but speculation from singled out, uncertain observation is just the point where things get unnecessarily complicated.

Wasn't it comfortable to just speak of measureable things? I personally published intermodulation data from highly respected driver chassis. Nobody was interested. Actually I understand that it may be even more comfortable to speak of the unknown ...
 

Frank Dernie

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It is actually not difficult to understand why different cone/dome materials may sound different as long as you do not use static thinking to try to understand dynamic behaviour.
There are other things radiating sound too, like the surround, in ways not exactly the same as the excitation signal sent to the driver, anyway.

There is an excitation signal sent to the speaker which causes the driver to move, ideally in an exact motion copy of the electrical input.
At low frequencies the accuracy of driver movement is more dependant on linearity of the magnetic and electrical circuit and the linearity of the suspension (surround and spider) once the displacement is small enough for these to be working in a reasonably linear part of their range the cone/dome will follow the signal accurately up to the point where structural resonances in it start producing inaccuracies. This is the point where the cone/dome material must be influencing the sound it is no longer a question of whether it is or not but by how much.

There are two principle ways of dealing with this inevitable product of physics, one is to damp the resonant peaks to an "acceptable" level, the other is to only use the driver in its non-resonant range then cross it over to a smaller driver with its first resonance at a higher frequency.

In the frequency range before any resonance I can't think of any reason why one cone material could sound any different to any other, maybe somebody else can?

Once in a frequency range where resonant effects are influencing output I can't think of any reason one cone material would sound the same as another, it is pretty well not credible.

So what effects the resonances and their amplitude? Cone/dome shape and the mass, material stiffness and internal (and external if applied) damping.

For most of my lifetime there have been no practical and affordable materials with mechanical properties allowing operation with entirely resonance free radiation.

There are other interesting effects, one is to use the fact that thigs resonate by cleverly exciting a lot of the higher modes so there are far more but much smaller peaks. NXT and BMR drivers exploit this.

I suspect things like ribbon, AMT and Lineaum tweeters actually radiate in ways nothing like the "static thinking" explanations we have all seen!

As an aside, I have often seen it mentioned that objects in different materials sound different when struck as an explanation of why they would sound different in speaker drivers but, of course, when you strike an object it resonates and that is the frequency region loudspeaker material choice is trying to avoid, so is a false argument as long as used below any resonance, but true in the resonant radiation range, depending on damping.
 

fineMen

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I suspect things like ribbon, AMT and Lineaum tweeters actually radiate in ways nothing like the "static thinking" explanations we have all seen!
Exactly; especially the often praised electrostatic is more of an DML than any other.

There is a quite simple solution to the problem, following the analysis above: three-(4?!)-way! It reduces intermodulation by factors of 10..50 (!!) and it easily replaces diamond by paper with virtually the same result in regard to a consistent cone movement.
 
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Frank Dernie

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easily replaces diamond by paper with virtually the same result in regard to a consistent cone movement.
Not for a tweeter.
I don’t know what the characteristics of the diamond being used but no paper or fabric tweeter will bea able to radiate the top octave without resonance.
Anodised aluminium or magnesium can do it maybe titanium and definitely beryllium, but it obviously depends on the mechanical design too.
The ally domes made by Monitor Audio for decades and those by Vivid and others are probably good enough not to be bettered in the audio band by the Beryllium or diamond ones, though again, detail design dependant.
 

fpitas

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This isn't a personal attack just adding some engineering facts to burst the bubble of some marketing implications I have seen about materials in speaker cone/domes.

I hadn't heard of Textreme, so I looked it up.

It is a trade name of one of the carbon fibre vendors.

The actual performance of any carbon fibre part is every bit as much dependant on weave, fibre orientation and resin content as it is on the fibre mechanical properties themselves.
It is often just the fibre properties which are quoted when talking about carbon fibre and the actual performance of a complete woven component will actually be nowhere near that because of non homogeneous structure, non straight fibres due to weaving and the resin mass. Using unidirectional fibres gets rid of the non-straight fibre problem but is much harder to lay up into 3D curves like a speaker driver.

I would think a tweeter would actually be the driver least suited to having good performance if made from carbon fibre, it could be good but very expensive for mid and bass drivers if properly designed and excecuted.

Carbon fibre is a brilliant material, I have been using it in Formula 1 car parts since 1977 but the name is used nowadays almost as an implication of magic properties it doesn't have and it has even become fashionable in shiny resin rich panels for embelishment :( - which is a dreadful waste of a good engineering material IMHO.

Next, it is incorrect imply any equivalence between Titanium and Berillium.
Titanium has about the same specific stiffness as aluminium and magnesium (and steel fwiw) so a titanium part the same weight as an aluminium part will not be any stiffer, less so probably because the Ti part will have to be thinner since it is denser than either.
Berillium OTOH has a much higher specific stiffness than these other metals so a piece the same weight will be stiffer or a piece the same stiffness will be lighter. Take your pick.

From its mechanical properties I actually would expect titanium to have the worst breakup characteristics of any metal being used for tweeters.

The only other material with competitive mechanical properties to Berillium is Boron and realistically no Boron manufacturing process could make a speaker driver moving part, fibres are about it - hence its use in cartridge cantilevers.
I know from experience, I hate titanium diaphragms for anything but rock. Beryllium on the other hand works for anything without any flaws I can hear.
 

fpitas

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Since the pistonic range and almost inevitably the crossover varies between drivers with different cone materials, the thread question may not be answerable in any meaningful way.
 

Frank Dernie

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Since the pistonic range and almost inevitably the crossover varies between drivers with different cone materials, the thread question may not be answerable in any meaningful way.
It is because the pistonic range varies that the crossover must vary, so it is inextricably linked to driver material.
Two drivers isn’t enough though for any drivers of any material remaining pistonic for the whole audio band.
 

fpitas

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It is because the pistonic range varies that the crossover must vary, so it is inextricably linked to driver material.
Two drivers isn’t enough though for any drivers of any material remaining pistonic for the whole audio band.
Careful. Most guys here have 2-way speakers they love ;)
 

fpitas

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Why? what most people have, and whether they like them has nothing to do with it.
True. I just like to restrict the operation to where the driver is pistonic, and isn't straining to reach the crossover.
 

Hayabusa

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Why wouldn't the material make a difference?

When we see smooth FR charts, they're smooth because we have digitally applied smoothing. In reality, there are thousands of peaks/dips that I imagine are a function of the driver itself, including the diaphragm material (i.e not a function of the room). For instance, take a simple swept sine wave starting at 500H (TOP), with 1/12-octave smoothing. This is what we're used to analyzing:
View attachment 91236

But in reality, this is what the actual swept sine wave FR "curve" looks like (same as above, but without smoothing):
View attachment 91235

Or perhaps someone is aware of evidence that the unsmoothed response doesn't matter?
looks like the room has some involvement in this graph?
 

fpitas

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fineMen

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Careful. Most guys here have 2-way speakers they love ;)
A fallacy introduced by BBC research in the late 1960s ignoring off axis radiation and intermodulation urging for cost savings and not the least for innovation as such as to justify the expenses ... .

Not for a tweeter.
I don’t know what the characteristics of the diamond being used but no paper or fabric tweeter will bea able to radiate the top octave without resonance.

... but if one uses membranes of 5mm diameter ... ;)
 

fpitas

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A fallacy introduced by BBC research in the late 1960s ignoring off axis radiation and intermodulation urging for cost savings and not the least for innovation as such as to justify the expenses ... .
Well, if you have a very small listening space, a large 3-way may not be appropriate, too ;)
 
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