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Old 16th April 2008, 07:01 PM   #3401
Anglo is offline Anglo  Canada
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Quote:
Originally posted by Magnetar


Why would you recommend crossing a narrow radiation ( ihave plenty of Altec 15 curvalinear cones here - they work best no higher than 1.2K with a wide radiation horn) 15" driver to a wide radiation ribbon tweeter? To me that would be a disaster. IE I found a 6" driver to be much more appropriate with a ribbon.., even when use a big ribbon as low as 1K with a 8th order network a ten inch was pushing it.
O.K. now Batman would like to know why this is a very bad approach. This in regards to what exactly? IOWs I run a 15" wideband driver (wizzer) fullrange; I have to this a ribbon tweeter at 5.6Khz- so this is obviously really bad.

Thanks in advance!
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Old 16th April 2008, 08:04 PM   #3402
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Quote:
Originally posted by Anglo
O.K. now Batman would like to know why this is a very bad approach. This in regards to what exactly? IOWs I run a 15" wideband driver (wizzer) fullrange; I have to this a ribbon tweeter at 5.6Khz- so this is obviously really bad.
If you read carefully Magnetar's post (and also scroll back a couple of pages and read his comments on the LeCleah profile) his main objection is radiation pattern, with larger drives (resp. horn) beaming where the ribbon has its wides lateral dispersion (Magnetar, pls. correctly if I'm wrong).

Now, the _real_ question is: Besides the subjective objections of a small sweet spot (i.e. "having 2m tall headphones") are there any _other_ drawbacks of this compromise ?

Again, both larger drivers and horns+CDs have "suffer" this in mating with the RAAL (again, when attempting to cover same/similar freq. range).

Wrt direct radiatiors Lynn mentioned somewhere in this thread (IIRC) the possibility of bringing in different drivers (of the 6ND410 quad he already purchased two months ago) at different freq. Not sure what was the followup on that...
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Old 16th April 2008, 08:27 PM   #3403
Anglo is offline Anglo  Canada
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Thanks for the response. I have been following the thread and once again this beaming thing comes up again. For me the beaming isn't that much of an issue. Now, does that make me ignorant to better sound? Maybe... What, other than head in a vice does beaming do to the sound? When it becomes really directional, is it also breaking up? Is it changing tone? My ribbon tweeter "overdisperses" but isn't cutoff where the wideband begins its beaming.

If I understand this correctly, I should, to avoid beaming, cut my wideband at 1Khz and integrate my ribbon; right? Then all my loove for my wideband went out the door and I have replaced the tone density of wideband for a light weight metallic mid range that, however, doesn't beam.

I'd love to know the main reason for avoiding beaming in my case, consider weight in the mid from my wideband, impact, SPL slam, agility and tone density.

I am very open minded on hearing the +'s and -'s of a different approach.
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Old 16th April 2008, 09:01 PM   #3404
mige0 is offline mige0  Austria
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Quote:
Originally posted by John_E_Janowitz


The driver is an overhung although different from most overhung drivers. It has a 3/4" gap plate with 1" long coil so the overhang is very short. The BL curve however is very broad. You can see the details on the motor design here:
http://www.aespeakers.com/Lambda001-1.php

John

Obviously great effort has been made to avoid motor induced IM as far as possible with this design.

The main difference between this and Doppler induced intermodulation is that it occurs at different points of the SPL pressure curve.

Picture a simple two sine wave mix and taking the lower frequency as the reference - motor induced IM has its maximum at the maximum excursion = at the minimal pressure points whereas Doppler induced IM has its maximum IM where VC speed is maximum e.g. at the points of peak pressure of the low frequency sine wave.

Motor induced IM - at the very first - is of the same type as produced by non linear circuits (VC heating effects not taken into account ), whereas Doppler induced IM isn't .

Might be that our ear brain system distinguishes between this two completely different forms of IM distortion easily – don't know.

Greetings
Michael
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Old 17th April 2008, 03:40 AM   #3405
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mige0,

One experiment of interest done in the past lead to the lengthening of the phase plugs on the 15" drivers. Paul Butterfield found that when playing a 1Khz tone simultaneously with a 10Hz tone at high excursions, you could audibly hear the 1KHz tone being modulated. This was found to be due to the "loading" of the cone being different as the coil got closer to the end of the phase plug. The solution was to lengthen the phase plug by nearly 1.5". The same test could be performed again with the same driver and longer phase plug, but now this modulation of the 1KHz frequency was no longer audible.

John
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Old 17th April 2008, 06:36 PM   #3406
mige0 is offline mige0  Austria
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Well that sounds interesting

– do you have any kind of measurement protocol about the test conditions like Xp-p-linear of the driver / Xp-p for F-low & F-high independently?
– if Butterfield's solution was to lengthen the phase plug to as it is now, does this mean that what we can see as a silver phase plug is much more than just an eye catcher and for the ventilation of the VC? Is it made of iron plated with copper and actually part of the magnet system?

Greetings
Michael
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Old 17th April 2008, 08:26 PM   #3407
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Quote:
Originally posted by mige0
Well that sounds interesting

– do you have any kind of measurement protocol about the test conditions like Xp-p-linear of the driver / Xp-p for F-low & F-high independently?
– if Butterfield's solution was to lengthen the phase plug to as it is now, does this mean that what we can see as a silver phase plug is much more than just an eye catcher and for the ventilation of the VC? Is it made of iron plated with copper and actually part of the magnet system?

Greetings
Michael

The experiment was originally done playing a 10Hz tone at near peak-peak linear excursion, approximately 14mm one direction. 10Hz was chosen because it was not an audible tone in itself so the 1KHz tone being modulated was easy to hear. I'm not sure what the level on the 1KHz tone was and there were not technical measurements on the modulation. From my understanding it was a clearly audible modulation that was completely inaudible after the lengthening of the phase plug.

The phase plug is a solid piece of polished aluminum weighing just over 1lb. The copper sleeve on the pole helps to pull heat from the VC where the heat is then transfered more effectively to the steel pole. The phase plug then is attached by a threaded set screw to the top of the pole and heat sink grease is placed to help transfer heat to the phase plug where it can then be dissipated better into the air. You can heat the phase plug to the point where you can burn your finger if touching it, but the VC stays quite cool with little measurable increase in DCR.

John
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Old 17th April 2008, 09:27 PM   #3408
mige0 is offline mige0  Austria
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thanks!
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Old 18th April 2008, 04:06 AM   #3409
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"I'd love to know the main reason for avoiding beaming in my case, consider weight in the mid from my wideband, impact, SPL slam, agility and tone density."

Hello Anglo

Me I like CD type waveguide presentation. I like to be able to move around and not have the frequency balance change. I also like using CD waveguides for HT because the coverage in the setting area is very uniform and you get the same frequency balance over the entire listening area. Can't do that with a beamy set-up as your balance changes too much as you go off axis.

If you are solo and you have a small sweet spot I doesn't matter as much providing you can get them set-up to work well in your listening space. With a driver set-up that are highly directional they tend to limit your placement options and also define your toe in and seating height.

As far as weight, impact, SPL and slam and the rest there are lots of ways to get there. I like multidriver limited bandwidth systems. 4 ways for the most part. I would never run a 15" woofer up that high. In my set-ups they are crossed over at 300 hz to 10" midranges but that's my preference. I have a coax center that takes a 15' up to 800-900hz and that's limit for me. Depending on the driver compliment you can get beaming in those systems just as easilly as with a larger fullrange driver. That doesn't mean they can't sound good when you are in the "zone"


Rob
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Old 18th April 2008, 05:35 AM   #3410
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Default Re: Very Brief History of Compression Drivers

Hi Lynn,

There are a few points that you've repeated in this thread that I heartily agree with and also some that I take exception to.

Quote:
Originally posted by Lynn Olson
Not surprisingly, the large format drivers were intended for high output. However, there was a tradeoff in high frequency extension. Due to the higher mass of its large diaphragm, its response was limited to 10khz. The small format drivers, with their lighter diaphragms could extend response up to 15khz, but could not match the output levels of their larger counterparts.
Absolutely. This makes perfect sense and is just a question of tradeoffs. Of course, for this project we are trying to minimize the tradeoffs (which usually involves increasing the costs).

Quote:
Originally posted by Lynn Olson
The first significant innovation to these designs occurred in 1979 with JBL’s introduction of the diamond surround. These surrounds take advantage of a phenomenon called “parasitic resonance”. The aluminum surrounds have a natural resonant frequency. Forming the surround into a diamond pattern pushes the second resonance out in frequency to result in a broad band response. This allowed the large format drivers to match the frequency extension of the small drivers.
Yes, of course. Using resonances to extend the "working range" of *any* reproducer is nothing new. That's what happens in virtually any non-metallic cone or dome (eg, paper, cloth, polypropylene, et cetera). Not to mention things like whizzer cones, or even dust caps, for that matter. So nothing new here.

That's not to say that it's a *good* thing. In my estimation, *any* resonances are bad things that color the sound. But to pick on this particular one seems to be overlooking the sins of the many....

Quote:
Originally posted by Lynn Olson
However, it was soon discovered that the diamond surrounds limited power handling. The diamond peaks are more susceptible to stress concentration and failure. This led JBL to pioneer the use of titanium as a diaphragm material in 1982. Titanium is an order of magnitude more resistant to fatigue failures than aluminum. With this new diaphragm, JBL now had compression drivers with exceptional output and extension.
Again, absolutely true. All metals lose strength as the flex. This is known as fatigue. Nearly all metals will lose about half of their initial strength over time EXCEPT ALUMINUM.

Aluminum is peculiar, because it loses strength *without* limit! In other words, if you flex it lightly, eventually it will *always* fail no matter how lightly it is loaded. It is just a question of how long you want it to last.

Quote:
Originally posted by Lynn Olson
However, it was recognized that there were compromises with the new diaphragms. Titanium does not have the internal damping of aluminum and thus has marginally higher distortion levels. The diamond surrounds, while extending frequency response, do so at the expense of transient response. Further, due to its lower stiffness, titanium goes into breakup at a lower frequency.
Now this is where I have to part ways with you. I have never seen *any* studies that show any meaningful differences between the internal damping of titanium and aluminum. I just don't buy off on this one. I could give dozens of counter-examples, but don't even see the point.

Similarly, the claim for a lower breakup frequency for titanium is completely unsubstantiated. Titanium is actually stiffer than aluminum. It is also denser, so the breakup frequencies end up being quite similar. Probably within 5% or closer. I have no idea why someone told you this stuff, but it is simply untrue. Either they were making stuff up or they simply misremembered the facts.

Quote:
Originally posted by Lynn Olson
So what titanium has going for it is fatigue resistance and ability to withstand abuse, not anything to do with audio quality - in fact, it is worse, with more distortion, and goes into breakup at a lower frequency (4 kHz instead of 7 kHz). Combined with heavy equalization that is standard practice in theaters, now you know why the sound is so harsh. (Very few theaters are using beryllium diaphragms - Ti has become the industry standard, thanks to JBL's dominance of the theater market.)
Again, completely untrue. This apparently comes from a summary of an interview with Doug Button. And either he misspoke or is being intentionally misleading. Titanium will last longer due to its greater fatigue strength, but the breakup frequencies are virtually identical to aluminum.

Thanks for the interesting thread.

Best regards,
Charles Hansen
Founder of Avalon Acoustics, and (to the best of my knowledge) first US manufacturer to use metal dome tweeters.
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