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Old 20th April 2009, 04:07 PM   #1
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Default Cone Materials Discussion

Good morning, all.

Consider the following application: the mid-bass driver in a 2 way system, intended for near-field, moderate SPL duty, in a small to medium sized room. The mid-bass driver shall be 6 to 7 inches in diameter.

With all other things assumed equal (for the purposes of this discussion), what are the implications of cone materials available for such a driver? The single goal of this theoretical system is transparency.
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Old 20th April 2009, 04:11 PM   #2
Henkjan is offline Henkjan  Netherlands
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talking typical behaviour, a metal cone will probably require higher order filter than a PP cone
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Old 20th April 2009, 04:46 PM   #3
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To get the ball rolling, here are some of my novice thoughts!

Polypropylene

I must admit, I am a fan of Polypropylene drivers, and strangely enough I probably carry an emotional bias toward them. My first brand-new set of drivers were Radio Shack 8" woofers, with grey-metallic Polypropylene cones, foam surrounds, and black fabric dust caps. This was back in the early 90's. What an interesting new kind of driver! So I am tempted now, to go down that path again, though I suspect that technology has been somewhat left behind. That being said, enough of the subjective, on to the meat and potatoes.

Polypropylene possesses a high degree of self-dampening. Cone break-up can be near non-existent in a well-designed example. This simplifies the crossover, as I see it, as likely no break-up controlling notch filter will be needed. Also, there might be a chance of using a more shallow crossover slope than with a stiffer cone. With the right tweeter, a 2nd order design might be do-able, at least at low volumes (which is acceptable for this application).

On the down-side, intermodulation distortion would tend to be higher than with a comparable stiff-cone driver. Energy storage would likely be higher, which would degrade transient response, would it not? I've heard of time smear, though I do not understand its meaning entirely. I would suspect this has something to do with impulse response and the delay time it takes for the cone to come to rest.


Aluminum

Stiffer cones such as this (I love the Excel Mg drivers, but sadly my goose is out of golden eggs!) seem technically attractive though I have yet to work with one. Energy storage would likely be lower (would it not?) within the usable band that is, not around break-up. Transient response would likely improve over the soft cones. From what I've seen on the net, 2 way implementations of Al cones are usually of 4th order slope or greater, which could add to phase distortions in extreme cases. Could such a stiff metal cone sound natural? It seems like the trick is to cross over below the worst harmonic multiples of the main cone break-up, and employ a notch to kill the break-up itself. Does this type of cone stand to be the most revealing? That a Mg cone is good enough for Mr. Linkwitz is a strong precedent!


Paper

The oldest material seems to be making a stand once more. Scan-Speak has certainly made a case. There are so many variations for paper, however, that it's hard to consider as a single category. I would guess that a good hard paper cone has some of the damping properties of PP, with perhaps less energy storage, and less break-up vs. a metal cone.


Feel free to jump in and destroy my assumptions: it's the only way I'll learn! Be gentle though!


I think a good set of comparison drivers for this discussion are the Seas Prestige 18 cm units. They have very similar motors, they appear to have the same frame, with different cones. I'm sure there are other differences, but they are as close to a comparison set that I can find at the moment. That and I intend on using one of them in the end!

JF

Seas P18RNX/P mmm so pretty!

Seas L18RNX/P she's been a naughty woofer!

Seas CA18RNX classic, all business, very shiney!

Seas ER18RNX quite the looker, stiffer than the coated version?
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Old 20th April 2009, 05:01 PM   #4
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Quote:
Originally posted by Henkjan
talking typical behaviour, a metal cone will probably require higher order filter than a PP cone
Hi Henkjan,

I missed this as I was writing the second part to my post! I agree, from what I understand metal cone break-up can have sonic repercussions in fractional harmonic multiples. From browsing the net it looks like the 3rd harmonic is usually the last one you have to worry about, though crossing over before the 3rd harmonic of the main break-up might push the cross-over point very low. And a shallow slope like that of a 2nd order filter will likely still allow such a harmonic to be audible.

With that in mind, do you feel a LR4 slope, for example, is much worse in terms of altering the original signal than a LR2 implementation?

JF
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Old 20th April 2009, 06:31 PM   #5
Henkjan is offline Henkjan  Netherlands
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no, don't see a generic problem. what also can work quite well is a well targeted notch filter (can be as simple as a small cap over the coil in a 2nd order filter, see this for example), it all depends on how bad the breakup shows up in the THD
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Old 23rd April 2009, 02:21 PM   #6
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Thank you for the example, Henkjan.

Hmm, it looks like I've derailed my own thread! To reform the question:

What cone materials offer the least coloration, and are as true to the original signal in reproduction as possible?

JF
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Old 23rd April 2009, 02:58 PM   #7
soongsc is offline soongsc  Taiwan
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I have found the Jordan driver family to be very good for DIY. They are the best behaved aluminum coned drivers that I have used.
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Old 23rd April 2009, 04:35 PM   #8
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Quote:
Originally posted by J.R.Freeman
Thank you for the example, Henkjan.

Hmm, it looks like I've derailed my own thread! To reform the question:

What cone materials offer the least coloration, and are as true to the original signal in reproduction as possible?

JF
There really is no such thing - one must consider the entire design of the driver, especially the motor. Scan Speak uses paper, SEAS uses magnesium, and Usher uses a carbon fiber-paper matrix. All have advantages, all have issues, but all are among the best available without a clear "winner" - it then becomes personal preference and crossover design comes into play too.

If you are trying to decide on what driver(s) to buy, it is far more helpful to know if you have a particular design/project/budget etc. as a starting point.
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Old 23rd April 2009, 05:03 PM   #9
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Quote:
Originally posted by J.R.Freeman


What cone materials offer the least coloration, and are as true to the original signal in reproduction as possible?

JF
Pistonic behaviour, so theorically the most stiff: diamond, followed by some rare metals (beryllium....), ceramics, aluminium, titanium... But the actual result does indeed depend on all the parts off the driver and how they interact...and how the driver is implemented...and on and on and on.
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Old 23rd April 2009, 06:29 PM   #10
Thawach is offline Thawach  Thailand
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Freeman Please u Try to listen the speakers(different cone materials) from anywhere. it can make u consider better because of they have the different sounds. sometime you'll know the sound that you like before u buy to build.
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