Hard vs. soft woofer membrane materials - diyAudio
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Old 13th September 2002, 03:02 PM   #1
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Default Hard vs. soft woofer membrane materials

Hard membranes such as aluminum, magnesium and Hexacone (Eton's Kevlar honeycomb membranes) have a much higher stiffness than polypropylene, so their movement is much more like an ideal piston than that of polyprop that can bend. However, most of these membranes exhibit strong resonances in the multi-kHz region.

One will usually hear that this is acceptable in a woofer or woofer/midrange application if a sufficiently steep low pass filter is used.

On the other hand, these membranes are like bells that can ring at certain frequencies. Imagine striking a bell with a well-padded hammer or striking it very slowly. You will probably not convey energy with spectral content at the resonance of the bell, yet you can excite the overtones.

I wonder if the same can happen with a metallic membrane even when care is taken not to drive the motor with high frequencies.

Is this why paper is still used so much in high end speakers like Scan Speak? Does anybody know what the hard paper is that they use e.g. in their 21W 8555/00? It is not the carbon or kevlar filled material that they have in some other speakers.

Eric
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Old 13th September 2002, 05:23 PM   #2
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Special virgin pulp sculpted "By beautiful women in the sunny state of California".

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Old 13th September 2002, 05:33 PM   #3
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1. paper is usually doped with resin to stiffen it.
2. al / mg / kevlar cone now employ esp. surrounds that attempt to negate some of teh resonances they exibhit. this technology came to be in the late 80s - early 90s and hence the RESURGENCE of stiff membranes since.

membranes went from paper - poly - metals - doped paper and now back to metal/kevlar/glass (aerogel, sandwiches, honeycomb etc..). not to say metal/kevlar and glass are the only way to go but todays metal membranes are far more refined than those found in the 70s.

in the end it is the sound of the driver we are after. Membranes are about 10-20% of this. the magnet circuit, coil, former, mechanical structure, etc... all play a roll

i wont name names into where and who were the first to introduce the improved surrounds and other resonance "fighting" technologies as there are many manufacturers who will lay claim to this but it suffice to say that the gist of the above is as true as I know it.
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Old 13th September 2002, 10:42 PM   #4
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"in the end it is the sound of the driver we are after. "

I couldn't agree more.
The "best" material for each job is not necessarily the newest material invented by man. Nor is there one miracle material that will meet all specifications and solve all the various driver design problems simultaniously.

And the word "paper" is really a misnomer and a disservice to drivers that use pulp based cones. There are many, many compounds invloved in a typical, high quality pulp based cone.

It's not like you could go out and chop up some newspapers, mix up some glue and water and start making your own cones.

Give the makers of high quality drivers some credit. The've been doing what they are good at a lot longer than we've been second-guessing them.
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Old 14th September 2002, 03:44 AM   #5
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Quote:
Originally posted by navin
i wont name names into where and who were the first to introduce the improved surrounds and other resonance "fighting" technologies as there are many manufacturers who will lay claim to this
Fostex has been one to turn out some new surround technology they pioneered in the NF1. A pdf of the NF-1 white paper is here - at the bottom. There is more info on the surround, the cone, and more...

Click the image to open in full size.

These also use the special "paper" formulation which includes banana pulp (i assume from the skins).

Supposed to be available early next year from a popular American distributor :^)

I'd like 4 of the 100 mm ....

dave
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Old 15th September 2002, 07:50 PM   #6
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wouldn't it be cool if they still smell like bananas? you could play all your carribean/ reggae stuff through them
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Old 16th September 2002, 05:28 AM   #7
navin is offline navin  India
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quite a few worked on this. An old man nameed Ted (ex hubby or Dorreen) worked a lot on this so as to make the Jordan metal cones more useful.

ALR-Jordan was a result of this effort (in a tie up with Karl Heinz Fink of Essen, Germany)

Before that Audax had a surround called Norosex that was effctively dead and they used it in a few speakers including a few drivers that were used by Dick Oshler's Dahlia (sterophile fame). The Audax drviers though had limited Xmax.

I can go on but I dont think this is a forum for history lessons (those 18 stone moderators might find me).
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Old 16th September 2002, 06:42 AM   #8
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An old man nameed Ted (ex hubby or Dorreen) worked a lot on this so as to make the Jordan metal cones more useful.
You mean Ted Jordan himself! He has been working on getting his cone to flex just right for over 30 years and his latest drivers prove how well he has done.

dave
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Old 17th September 2002, 06:00 AM   #9
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yup! you gussed it. I did not tell.
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Old 19th September 2002, 07:31 AM   #10
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Well, went back to look at disto plots of the 8 and 11" Eton Hexacone drivers. They tend to have a big third harmonic peak at 1/3 the resonance frequency of the membrane, which is at 2-3 kHz.

The disto peak does not really grow too much with output level, which in accordance with Nonlinear harmonic distortion vs. linear harmonics
seems to indicate that this is an overtone oscillation rather than real nonlinear harmonic disto.

Still, even if it did not sound nasty, it could be perceived as a coloration to the sound if the XO lets something pass at >600 Hz.

By the way, anybody know what NOMEX is?

Eric
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