North Creek & the W18E cone resonances - diyAudio
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Old 13th June 2006, 02:00 PM   #1
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Default North Creek & the W18E cone resonances

Obviously, while reading this stuff, you've got to keep in mind that people are trying to sell you something. But I wonder what this means, because I couldn't find any explanation of the final idea in taming the cone break-ups.

Quote:
Eventually it came to me that the problem with the W18ís upper midrange is a two edged sword. The mechanical break up of the cone is a high Q mechanical resonance. The "low pass network plus trap" approach creates a second high Q resonance. The problem, then, is that there are two high Q resonances in the electrical/mechanical/acoustic system right in the middle of the range where the ear (at least mine) is most sensitive. My goal, then, became to design a low pass network with the target acoustic response, but without using this type of filter. Finally, some progress was being made.
The whole story is here:

The idea I get from this one would be the equivalent of having an active cross-over where there's a low pass filter combined with a fixed-Q, bell curved dip to attenuate the signal enough to not excite the mechanical resonance of the driver. Which, in theory would be the equivalent of a similar L-C series filter, but apparently North Creek Music thinks it's not.

So.. What did they do? Is there any truth behind this? Does the series filter "ring" and store energy with the cone break-up? Did they simply use two different low passes (one a tad lower, one a little higher) to mimic the FRQ response of a bell-curved dip (not that it would)?

Why so many questions?
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Old 13th June 2006, 05:05 PM   #2
sreten is offline sreten  United Kingdom
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Hi, You should ignore such technowaffle. I do. /sreten.
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Old 14th June 2006, 12:11 AM   #3
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I tend to suspect that the two opposing resonant circuits analogy is an over-simplification. From the description of the breakup, a simple trap would not be able to fully compensate for the breakup.

One possibility would be an elliptical filter for the lowpass. The Josephaudio speaker company uses very steep crossover slopes,
JosephAudio Metal Cone Waterfall to also deal successfully with the same issue. The Waterfall (Cumulative Spectral Decay curve) they show indicates why a simple LC trap is inadequate.

I personally prefer a completely different approach; an Audio Technology midrange which has the same qualities of transparency and timbre, and is as easy to design with as such drivers can be. (Although to some extent this shifts the money from the xo to the driver.)

The Northcreek caveats about associated equipment and xo parts quality are very much to the point.
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