Speaker 101 - tweeter and cone materials

Brian Cheney at VMPS has an interesting discussion on woofer cone material at http://www.vmpsaudio.com/d-cones.htm

He is obviously very knowledgeable and entertaining, but keep in mind that his point of view is not the only valid point of view. For example, he slams metal cones in general, while many other people rave about the SEAS Excel line of magnesium drivers.

Sigfried Linkwitz also talks about driver material in his comparisons of various woofers and tweeters at http://www.linkwitzlab.com

For me, if I can see the driver, I want it to be something sexy. Metal, Kevlar, woven carbon fiber, or ceramic. Preferably with a nice pretty phase plug. If I can't see the driver, I don't care what it is made of.

Oops, the second link should be http://www.linkwitzlab.com/x-mid_dist.htm

Brian C. probably slams metal cones because I believe he generally eschews complex x-overs. With metal cones and their nasty break-up characteristics you really need x-overs with steep (real steep) slopes so that resonance and break-up nasties aren't audible. Well executed metal cones (both aluminum and magnesium) can sound quite good. You really need to hear them to decide if you like them. My preference is treated paper cones but metal cones have a certain detailed character that can sound quite interesting on good recordings.

Can you tell me what you mean by "x-overs with steep slopes"?

Well, let's be real basic - no offense. When crossing a woofer to a tweeter, a crossover is used that filters out the lows going to the tweeter, and the highs going to the woofer. Metal woofers (and all woofers) have cone break-ups at frequencies higher than they are designed to produce. Since metal cones sound particularly harsh when fed any higher frequencies near their cone break-up frequency you want to make particularly sure that they get very little input above their crossover frequency. Now, you might say how does that happen if you have a crossover. Well, a crossover is not an absolute. It has a roll-off at the crossover frequency. Let's say a woofer cone breaks up at 10k. With a 1st order rolloff, and a crossover frequency of 2.5k, the woofer is only 12db down at 10k. This will be heard easily. Now, go to a 4th order rolloff, and the woofer is 48k down at 10k. This will likely not be heard as much.

Steep slopes are created by higher order electrical crossovers. With metal cones, you'd probably want at least a 4th order "acoustical" roll-off. This can generally only be created by higher order "electrical" crossovers. In general, the higher order the crossover, the more complex the crossover becomes in terms of component count. (This is not absolute, just a generalization. Depends on how many "shaping" filters are used.) The result is a rapid roll-off of higher frequencies in the case of a woofer.

With metal cones it is more imperative because they emit some real nasty break-up noise if they receive any signal at their cone break-up frequency. In many cases, the designer will also incorporate extra "filters" to eliminate specific frequency ranges above the crossover frequency at about the cone break-up frequency. These extra filters also add to the component count. Crossover design is a complex science/art. Folks will say there are simple textbook formulas to calculate these things. They are wrong in terms of actual application and it becomes more so when you factor in things like woofer breakup and tweeter resonances, not to mention things like baffle step for small boxes designed to be used well away from room boundaries.

Joseph Audio speakers are a good example of metal cones that can sound good although again it's a matter of taste. His designs use particularly steep filters. Some designers and listeners are of the opinion that such complexity detracts from the sound. In the end, it's a matter of personal preference.

Javachip, Gmueller, Thank you for your inputs.

If there are more sites I can learn from, please let me know.

Thank you very much for explaining x-over and roll-off. Basic is good.

I like the materials but mostly the engineering to the Seas'. They seem to get the best balance, fluidness and rigitity, resulting in most musical.

There are good and bad sounding speakers using all sorts of cone material.
More important is cone suspension/surrounds.
Most modern speakers use quite thick rubber surrounds which allows for long cone excursion, which allows them to produce lots of low bass.Unfortunately it also produces a slow smeared sort of sound.This is why most modern mainstream speakers sound so bad and why so many hardenned audiophiles end up using things like Fostex,Lowther and Zu speakers that have cloth surrounds and short excursions.
Anyone who dosn't believe that modern cone surrounds are wrong needs to listen to a pair of old Goodmans Axiom 80s that have no surrounds!

JT

All your inputs are so interesting and educational. Keep them coming!

So who uses the Seas?

Jtgofish,

Good point about thick surrounds and long cone excursion....there is a lot of non linear distortion that occurs at the cone to surround interface as the rubber roll decouples from the cone - often causing a sharp change in response at higher excursions. This problem usually occurs in a range between 500 and 1000 Hz and is therefore of greatest issue in two way systems which necessarily cover that range with a single driver. Sometimes a careful manufacturer may use an intermediate material between the rubber and the cone, sometimes a damped cloth surround is used with the benefit of overall reduced coupling and smoother response. Nevertheless, more often than not, most two way systems inherently have this problem in the all important mid range...