driver engineering, materials technology

[sardonx]

Does anyone know of a good source to find design information on drivers and materials technology? I'd like to know the weight and thickness of typical metal (and carbon fiber) cones. Also something i've been trying to find out is how carbon fiber cones compare to metal (especaially magnesium) cones in strength and ridgidity. Because i know that carbon fiber is lighter but is it stronger and more ridgid? I think it can be made so.. but i'd like to know for sure. If it is.. then why do they say that metal drivers are lowest in distortion and coloration? Wouldn't carbon fiber beat any metal in those departments? Way lighter, stronger, and more ridgid... what's the deal!?!?

[LineSource]

Magnesium, due to its lightness, slow sound transportation, and natural dampening from low hardness, would seem the best metal for cones with modest physical stress. i.e. tweeters, midranges and low Xmax high efficiency woofers. A Mg bell would not ring very well.

Titanium is significantly heavier, denser, and stronger, than magnesium. This would make Titanium well suited to subwoofers.

Aluminum's physical properties are close to magnesium. Al is 1.6x heavier, but has lower tensile strength unless alloyed, and absorbs less vibrational energy. Aluminum is much cheaper than magnesium. Most Al alloys, like 6000 series, have higher tensile strength than Mg. Al cone break-up modes are slightly worst than MG due mainly to the higher mass/strength ratio.

Carbon fiber appears to be the best long term cone material for midrange and high efficiency woofers. The ideal carbon fiber cone would likely be a curve-linear profile woven from continuous fiber before thermoset in resin. When a Tiawan company invests in this technology, we could see a new plateau in cone technology. Today, most carbon fiber cones use coarse random fibers in resin, or a cut sheet glued into a linear profile.

Today, low cost Kevlar fibers are smoother and easier to weave than carbon fiber, and hence top labs like B&W have been able to bring up manufacturing lines for woven midrange cones. The weaving technology, cone profile, and resin strongly determine the break-up modes.

element ....Density.....Velocity...Young.. Rigity..Bulkmod..mineral... Brinell..Tensile Strength
Titanium ......4057...... 4140...... 116...... 44...... 110...... 6...... 716...... 345
Aluminum ......2700...... 5100...... 70....... 26....... 76.... 2.75..... 245...... 179
Magnesium .....1738 ......4602 ......45 .......17 .......45 .....2.5 .....260 ......275
Beryllium .....1848 .....13000 .....287 ......132 ......130 .....5.5 .....600 ......300

Carbon Fiber ..1780 .....3200 ......250 .......38 .......80..... 2.6 .....235 ......276



DensityKg m-3
Velocity sound m/s
Young’s modulus /GPa
Rigity modulus /GPa
Bulk modulus /GPa
Mineral hardness
Brinell hardness /MNm-2
Tensile Strength MPa

[paulspencer]

Wow, that is quite a reply and difficult to follow up something like that! A good source of info on driver materials is the LDSG:

LDSG info on driver materials

This has a general discussion on the advantages and disadvantages of each and their properties, although it doesn't have the numbers you are after.

[Pan]

"would seem the best metal for cones with modest physical stress. i.e. tweeters, midranges and low Xmax high efficiency woofers."

Seem to be a little bit of a stretch. Obviously Mg works very good for Seas, however Focal seems to favour Berylium for tweeters due to higher stiffness and sound velocity.

/Peter

[hunter audio]

very informative _ line source !

i think there are a few taiwanese company s manufacturing carbon fibres , woven too , though it has not picked up much yet

one reason may be its flat tonal balance and lack of impressiveness (this info on carbon fibres are my openion only)

as for the metal cones there are a lot of practical discussions involved speacially its commercial viability to its cost ratio

metal cones (other than titanium) require real clean sources _ high end amps _ config

and very competent enclosure and c/o designer , may be thets why there are limited mg alloy drives used

there are not many Martin Colloms around other than with Monitor Audio

suranjan

transducer design engineer

[mwmkravchenko]

Jump over to the DIY Parthenon thread. We need more people that know their stuff over there.

Mark

[SY]

As soon as you limit yourself to a single material and/or a single structure, you've greatly limited yourself.

[sardonx]

Thank you everyone for the replies

I stumbled upon a website on race bicycles that talked about different materials for frames. It mentioned that carbon fiber is still tricky to work with mainly because carbon fiber CAN be made to be extremely stong but it will only withstand stress in the direction that its fibers are aligned in. I can see how this is a problem with woofers too since the stress being put on the cone is not only bi-directional because the distance the cone flexes at the edges is greater than at the center. So a good cone shape needs to be engineered to make the most out of carbon fiber and perhaps a way to align the fibers in more directions than just one needs to be discovered. The latter is where mass R&D from those taiwanese companies will help!

Can anyone else comment on the sound of current carbon fiber cones? I've read that the audax HM170CO has a really nice midrange.

A couple of other companies that make carbon fiber speakers are Davis Acoustics and i think Illusion Audio.

[SY]

For applications like cones, the fibers are usually in a weave rather than linearly (or nearly so) aligned like those used in bicycle frames. Sort of like a picnic basket. Generalizing about properties and sound is difficult and misleading because the properties of the cone will depend on the nature of the weave, the matrix material that holds the fiber, geometry, termination...

I haven't used the Davis drivers, but I found the Audax that I tried to have a fairly nasty breakup mode in the upper midrange. Whether or not that's important depends on how you're using the driver in your design. Myself, I prefer the Aerogels.