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Multi-Way Conventional loudspeakers with crossovers

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Old 8th May 2008, 03:06 AM   #3511
SamL is offline SamL  New Zealand
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From an old post on alnico and ferrite magnet by JBL.

"Here is an interesting document written by John Eargle that compares various magnet structures and what performance can be expected from them. A horn provides 10dB to 15dB gain and a similar reduction in distortion. But the geometry of the driver's magnetic flux can do that much or more where distortion is concerned.

Three magnetic structures are compared, each having physical symmetry, but each made with a different material or technology. One is an alnico magnet, the other a ferrite and the third is a ferrite magnet with a flux stabilization ring........."

Oh yes! Good to hear from you again Nick.
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Old 8th May 2008, 02:02 PM   #3512
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Take that JBL structure, extend the pole outward about an inch, then cover it with a thick layer of copper so that no matter where the voice coil is located the copper is right next to it. Then you have a TD motor. The JBL ring is a good low cost design, but it doesn't address the inductance and phase response of the driver, nor does it help with heat sinking and power compression.
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Old 8th May 2008, 03:28 PM   #3513
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Regarding magnet materials, Englishman John Watkinson has written on the subject in Electronics World magazine and in a more abreviated form at www.celticaudio.com/ Go to "technical articles" and read the last two paragraphs of the PDF called "putting the science back into loudspeakers" Mr Watkinson is no fool, being a fellow of the AES, the author of several books on digital audio and television and runs a company offering training in these and other subjects.

He seems to make a basic destinction between magnetic materials that are conductors and those that are insulators (ferrite) He suggests that in ferrites the magnetic domains move around when they are interacting with the coil flux and its attached load. This movement is not a linear process but rather is granular or noise like. The assumption seems to be that a ferrite magnet speaker is going to have noise sidebands associated with everything it reproduces. In the EW article he invited disbelievers to wrap some turns of wire around the ferrite magnet of a speaker being driven and look at/listen to the noise signal.

Keith
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Old 8th May 2008, 04:21 PM   #3514
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Quote:
Originally posted by Keith Taylor
Regarding magnet materials, Englishman John Watkinson has written on the subject in Electronics World magazine and in a more abreviated form at www.celticaudio.com/ Go to "technical articles" and read the last two paragraphs of the PDF called "putting the science back into loudspeakers" Mr Watkinson is no fool, being a fellow of the AES, the author of several books on digital audio and television and runs a company offering training in these and other subjects.

He seems to make a basic destinction between magnetic materials that are conductors and those that are insulators (ferrite) He suggests that in ferrites the magnetic domains move around when they are interacting with the coil flux and its attached load. This movement is not a linear process but rather is granular or noise like. The assumption seems to be that a ferrite magnet speaker is going to have noise sidebands associated with everything it reproduces. In the EW article he invited disbelievers to wrap some turns of wire around the ferrite magnet of a speaker being driven and look at/listen to the noise signal.

Keith

Thats why you need a giant piece of solid copper intersecting as much of the flux field as possible.
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Old 8th May 2008, 05:24 PM   #3515
badman is offline badman  United States
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Indeed!

Or just to use quality AlNiCo drivers

The 12" Aquaplas JBLs had a lot going for them- some had very wide bandwidth and they all had monster motors to drive those heavy cones.
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Old 8th May 2008, 06:13 PM   #3516
SunRa is offline SunRa  Romania
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Quote:
Take that JBL structure, extend the pole outward about an inch, then cover it with a thick layer of copper so that no matter where the voice coil is located the copper is right next to it. Then you have a TD motor. The JBL ring is a good low cost design, but it doesn't address the inductance and phase response of the driver, nor does it help with heat sinking and power compression.
Quote:
He seems to make a basic destinction between magnetic materials that are conductors and those that are insulators (ferrite) He suggests that in ferrites the magnetic domains move around when they are interacting with the coil flux and its attached load. This movement is not a linear process but rather is granular or noise like. The assumption seems to be that a ferrite magnet speaker is going to have noise sidebands associated with everything it reproduces. In the EW article he invited disbelievers to wrap some turns of wire around the ferrite magnet of a speaker being driven and look at/listen to the noise signal.

Thanks for your comments. Most interesting! Where would you place neodymium magnets in this discussion?
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Old 8th May 2008, 07:23 PM   #3517
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Default Welcome Back Nick

We missed you, and your talent.
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Old 8th May 2008, 08:13 PM   #3518
mige0 is offline mige0  Austria
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Maybe one should put together a HowTo - as simple as it gets - for DIY CSD measurement.

Why do we need that CSD at all?

CSD is not just an other way to interpret a FR plot. CSD makes available additional information about what's happening when you want that driver to shut up.
This important piece of cake is not enclosed and cannot be derived mathematically from a FR measurement plot (though with some experience you may develop a subjectively "good guess" to extrapolate from FR to CSD).

Good thing is - CSD's are easy and intuitively to "read" and nowadays - thanks to the Hungarian guys of ARTA headache free to catch.






Click the image to open in full size.

To get 90% of what CSD can tell you, the requirements in terms of time, investment and specialised knowledge are amazingly low.
In the context of this thread its even easier, as we really don't need CSD examination beyond around 300Hz.






Click the image to open in full size.

This roughly 300Hz cut off is one hard limitation to allow measurement even in relatively small rooms.
Easy to accept for OB designs - where 99,9% of all speakers show the same and easy predictable behaviour of piston movement and no box decay has to be chased.


An other hard limitation you have to accept is, that this CSD's are ONLY good to tell you about the decay time behaviour of a speaker.
Its way more difficult to get a 90% informative frequency response measurement than a 90% informative CSD measurement

If you are that kind of measurement perfectionist that wants to show around brilliant, academic level graphs stay away buy sunglasses of RayBan or Boss - invest a smaller or bigger fortune on equippment, a looooot of time to wrap your head around and come back once you realise that you got a brilliant 93% of what's in the pot.







Click the image to open in full size.

Of course a CSD measurement shows the frequency response as well. This is basically the Z-direction (height at the very beginning of the decay-timeline) but this is not what we are interested in here nor do we make any effort to get that aspect somewhere close to perfect.







Click the image to open in full size.

The main focus of CSD is what's happening along the Y-direction, the decay-timeline over the frequency band.
Frequency response and CSD are not that closely bound to each other than FR and phase for example is.



To stay correct both FR and CSD measurements have its roots in the impulse response. Unfortunately impulse response graphs don't make sense to most of us they are really hard to decipher in detail - though it basically contains ALL the data we can extract from a speaker (well, obviously you wont get the spider diameter nor the smell of the cone material ).



to be continued....
Michael

PS :
to correct a gross mistake at my last posting:
one more excellent - page about CSD is from the '"owner" of this thread.
http://www.nutshellhifi.com/MLS/index.html

PPS :
an other page that I came across some time ago and forgot about - with lots of CSD data I'd like to make available, is from the French guys. Its focused on Audax speakers only, but almost the complete range from way back.
http://www.hautparleur.fr/

PPPS :
a page I recommended earlier is from the Czech guys at ProDance with some of the newer PRO-speakers having CSD graphs
http://www.prodance.cz/protokoly.php?AnchorID=49&Lng=CZ
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Old 8th May 2008, 08:30 PM   #3519
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Neo magnet material is some of the best man has ever invented. Its only problem is that it doesn't like to be any thicker than about a 1/4" which sucks for woofer duty unless you place it sideways like the Aura stuff did. Its other problem is that you need one hell of a magnet charger..............
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Old 8th May 2008, 09:24 PM   #3520
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Lynn I tried finding a post you had made about an $80 or so autoformer you had found. Do you still have the link to that?
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