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Old 24th July 2006, 11:31 PM   #1
Klimon is offline Klimon  Belgium
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Default alu cone break-up

Hi there,

I'm planning to rebuild (= other tweeters, tweaked woofers + new crossover) my pair of iplacoustics transmissionlines. The original crossover is at 3khz; 3rd order filter on woofer and 2nd order on tweeter. The ideal would be to get a first order on both woofer and tweeter (new ones will be Peerless WA10 = 812978?), low crossover point 1500-2k.

The original crossover had a 3rd order on the woofer most probably to tackle break-up resonances... Can anyone tell me if it's possible to smoothen the break-up resonances of metal cone woofers (in general) to a virtual perfect roll-off or can this never be achieved with alu woofers?

I've already performed the tweaks that have proven to be so succesfull on paper midwoofers: dustcaps got removed (this could yield a big difference on these because they're quite bulky aluminium fake phase-plugs) + I'm planning to add two layers of dammar (one on each side)...

Well, this might be too specific to generate any replies but your advise is very appreciated as always

Simon
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Old 25th July 2006, 04:31 PM   #2
Colin is offline Colin  United Kingdom
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It sounds like such major surgery that you might be better starting from scratch. As you've posed the question here, you could try a fullrange driver in a TL and see how it compares to the IPL. Power handling aside, the Jordan alu fullrange driver might be a good comparison point.

Different companies have different approaches to alu drivers. Some keep them as stiff as possible and then deal with the resonances (often with the crossover), others design some flex into the cones to push the resonances out of harm's way and achieve a wider bandwidth.

Which IPLs do you have?
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Old 25th July 2006, 04:34 PM   #3
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Before you do anything to the drivers, I would actually measure them, so you know what you're working with.
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Old 25th July 2006, 06:39 PM   #4
Klimon is offline Klimon  Belgium
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Thanks for your opinions;

the reason why I asked the question here in the fullrangedriver forum was because I suspect fullrange-diyers to be more inventive with regards to tweaking drivers

The reason why I want to upgrade it is because - while performing very nicely, I had the crossover redesigned already and swapped all the caps for pios - it lacks coherence and the openness of my beyma backloaded horns. I know first order filters are the lovechild of many purists + minimum of components + good phase behaviour so this might solve the lack of 'coherence' (while the colour and refinement of the sound is excellent the ipl's tend to make the music sound more complicated, less natural when compared to the straightforward sound of the crossoverless backloaded horns. I did notice the drivers are placed a few cm more apart than acceptable with regards to the crossover frequency; dunno if the speaker placement or high order filters cause the incoherence though).

I have the S3tlm with the now discontinued ipl alu cones with fake phase-plugs. I've removed the PP's already and see that the polepiece is hollow; no hole in the magnet though so only a small cooling benefit + what's worse: an extra resonant void. I'll inspect some more but these will most probably be filled with duct-seal, I never play the speaker near their limits.

The safe alternative would be to replace the seas metaldome tweeter (I don't think I like it too much) with a low Fr like the WA10 and implement new high order filters...

I'll stick with a rebuild of these, no funds for a new fullrange project (+ many drivers already gathering dust...) + the transmissionline sounds awesome with the ipl's.

Measuring could give some information but the problem isn't really situated in uneven FR so that won't bring the solution I'm afraid.

Simon
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Old 25th July 2006, 11:24 PM   #5
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Quote:
Originally posted by Klimon
Measuring could give some information but the problem isn't really situated in uneven FR so that won't bring the solution I'm afraid.
What about distortion measurements, off axis response, or even just a waterfall plot? These will show you exactly where the breakup frequencies you worry about are, how great they are, and what you need to do with the design to sort out the problem, if it exists. I don't see how measuring will not help you towards a solution, but I can see how guesses and assumptions could fail to give you what you want.
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Old 26th July 2006, 05:16 AM   #6
Klimon is offline Klimon  Belgium
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Quote:
What about distortion measurements, off axis response, or even just a waterfall plot? These will show you exactly where the breakup frequencies you worry about are, how great they are, and what you need to do with the design to sort out the problem, if it exists. I don't see how measuring will not help you towards a solution, but I can see how guesses and assumptions could fail to give you what you want.
Point taken, guess it's time to do my first measurements --
Can you recommend any software (preferably freeware) for the measurements you mentioned? Speakerworkshop might be an option

Simon
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Old 26th January 2011, 07:43 PM   #7
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How to deal with the hard cone break general?

I found some people use the RLC paralle in series the signal path but some people use the RLC serious notch in paralle with the driver.

Are they both correct?
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Old 26th January 2011, 11:02 PM   #8
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Hello Kilmon, Kevinlin, Guys
Potentially interesting re-build projects.

Cone break up in alu woofers is less likely to be a significant issue compared to full range drivers. Woofer cones usually have higher mass and profiles that should afford more stability. These traits usually reduce breakup as the cones have greater mass/damping ratios. Full range cones are usually the opposite: low mass, wide profiles etc., all of which push designing full-range cones to very tight operational limits.

So, I don't recommend using full range drivers for any comparative work on woofers. Their cone design should be significantly different from a woofer, enough to give you the possibility of misleading results.

Much depends on what's perceive as “cone breakup”. There’s varying explanations on the issue. Kilmon, can you post pics of your Ipl's? Some close-ups of the drivers would be useful. Many woofers sadly are designed to "look nice" to the point where their operation is compromised.

Cheers

Mark.

Last edited by markaudio; 26th January 2011 at 11:29 PM. Reason: typo fix
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