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Author Topic: Stamped baskets  (Read 13808 times)

luis Markson

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Stamped baskets
« on: April 16, 2011, 01:14:06 am »

Whats is difference in appearance between a stamped and cast basket?
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Gordon Brinton

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Re: Stamped baskets
« Reply #1 on: April 16, 2011, 06:05:39 am »

The Basket is the outer metal shell or frame of the speaker.

Stamped means that the frame is made from a flat piece of metal and stamped by a cutting machine and bent upward.

Cast means that the frame is molded from hot (liquid) metal into that shape.

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David Parker

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Re: Stamped baskets
« Reply #2 on: April 16, 2011, 08:37:47 am »

Whats is difference in appearance between a stamped and cast basket?

Stamped baskets are made out of steel, a flat piece of sheet metal is put into a die and pressed into the shape. Cast baskets are made out of aluminum, and the metal is melted and poured into a mold. Generally, cast baskets are used on more expensive speakers and stamped steel baskets are used on cheaper speakers. Cast baskets are considered to be stronger. Speaking from a machinists viewpoint, it would be easy to make the either one stronger, depending on the thickness of the metal used for the stamped steel basket and the thickness of the casting. If a speaker manufacturer wanted to make their best speakers with stamped steel baskets, they could.
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luis Markson

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Re: Stamped baskets
« Reply #3 on: April 17, 2011, 03:16:30 am »

Stamped baskets are made out of steel, a flat piece of sheet metal is put into a die and pressed into the shape. Cast baskets are made out of aluminum, and the metal is melted and poured into a mold. Generally, cast baskets are used on more expensive speakers and stamped steel baskets are used on cheaper speakers. Cast baskets are considered to be stronger. Speaking from a machinists viewpoint, it would be easy to make the either one stronger, depending on the thickness of the metal used for the stamped steel basket and the thickness of the casting. If a speaker manufacturer wanted to make their best speakers with stamped steel baskets, they could.

cheers
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Jeff Bankston

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Re: Stamped baskets
« Reply #4 on: April 17, 2011, 03:49:17 am »

was talking to a guy at jbl about why a cast basket. he said the cast basket doesnt ring like a stamped steel basket does.
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David Parker

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Re: Stamped baskets
« Reply #5 on: April 17, 2011, 06:55:27 am »

was talking to a guy at jbl about why a cast basket. he said the cast basket doesnt ring like a stamped steel basket does.

I suspected something would come up either about resonance or magnetism. The aluminum baskets are, of course, non-magnetic, and considering the size and importance of magnets on speakers, I can see how that topic might come up. Then there's the resonance thing, the ringing. Steel is much more resonant than aluminum, particularly cast aluminum. If they wanted to they could still build steel baskets that wouldn't ring, but they would be heavy. Cast iron would even be better for resonance, but that would be really heavy. We've all heard car stereo speakers and home stereo speakers with steel baskets that sound good. All things considered, including cost, and the cast aluminum is the best option, obviously, because that is what they use.
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Bob Leonard

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Re: Stamped baskets
« Reply #6 on: April 18, 2011, 12:04:48 am »

I suspected something would come up either about resonance or magnetism. The aluminum baskets are, of course, non-magnetic, and considering the size and importance of magnets on speakers, I can see how that topic might come up. Then there's the resonance thing, the ringing. Steel is much more resonant than aluminum, particularly cast aluminum. If they wanted to they could still build steel baskets that wouldn't ring, but they would be heavy. Cast iron would even be better for resonance, but that would be really heavy. We've all heard car stereo speakers and home stereo speakers with steel baskets that sound good. All things considered, including cost, and the cast aluminum is the best option, obviously, because that is what they use.

For all the reasons mentioned aluminum, cast and then machined, is the best option. Stamped baskets can not be machined and tolorence can be held to no better than .010 in most cases. This may not seem like much, however, in the scheme of things tighter tolorences equal more precise alignment of all the motor assembly components.
 
If you'll notice the majority of all JBL speakers appear to have a chrome ring around the cone when looked at through the grill of a cabinet. This is the machined face of the basket from where all height and depth dimensions are referenced to a dimension of .005 or less. Additionally aluminum conducts heat much better allowing for greater heat dissipation and far less skew of the magnetic field. A case in point would be the 2242 in the photo below where better cooling has resulted in an additional 3db gain over extended periods of time due to power compression. Also, speakers may heat to almost 300 degrees when pushed hard. Kapton, invented in 1955, has been replaced by better materials for use with todays monster drivers. The latest, but more expensive material used in forming coils is Hisco P450, invented in 1992. All of this adds up to cost which you should be willing to except if performance and longevity is the goal. The speaker below will run $650 - $750, and it's worth every penny.
 
 
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John Roberts {JR}

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Re: Stamped baskets
« Reply #7 on: April 18, 2011, 01:14:06 am »


Stamped baskets can not be machined and tolorence can be held to no better than .010 in most cases. This may not seem like much, however, in the scheme of things tighter tolorences equal more precise alignment of all the motor assembly components.
 

Not to quibble, but stamped steel baskets surely "could" be machined, but that defeats the purpose of hard tooling the stamping dies, so you don't need all the extra touches in manufacturing that add cost. 

For low volume drivers it is not worth the tooling cost to make a stamped steel basket, while cast aluminum with final machining to size results in a higher per piece price, they  cost less to tool.

Cast aluminum certainly looks and is more expensive. Stamped steel is more common on high volume drivers, for obvious cost reasons.

JR
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Jeff Bankston

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Re: Stamped baskets
« Reply #8 on: April 18, 2011, 05:14:14 am »

my Dynaudio 30W100 12" home woofers have cast magnesium baskets. they handle 300 watts rms and have a 4" voice coil.
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Bob Leonard

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Re: Stamped baskets
« Reply #9 on: April 18, 2011, 08:42:16 am »

Not to quibble, but stamped steel baskets surely "could" be machined, but that defeats the purpose of hard tooling the stamping dies, so you don't need all the extra touches in manufacturing that add cost. 

For low volume drivers it is not worth the tooling cost to make a stamped steel basket, while cast aluminum with final machining to size results in a higher per piece price, they  cost less to tool.

Cast aluminum certainly looks and is more expensive. Stamped steel is more common on high volume drivers, for obvious cost reasons.

JR

I certainly agree John, and having been a model maker / machinist for just over 20 years I also understand the process. The problem with .062 thick stamped baskets is that you become dependent on the accuracy of the 1) Punch press, 2) Dies used to form the basket.  The back of the basket and face  (not lip) become the reference point for all assembly and alignment. If the stamped basket were to be machined the start would be the face, or placing the basket on a jig/fixture, and machining the back of the basket flat where the motor assembly mounts. It's impractical to machine sheetmetal without special fixtures to eliminate flex, so maybe a Blanchard grinder and a quick pass to remove .010 at most. For a piece of sheetmetal that's only .062, that's a lot to remove. Remove the basket from the jig/fixture and it will move making all of the prior effort for naught.
 
Now it's on to machining the motor assembly and that process remains the same for all speakers, however, the magnet seat and other component surfaces for the motor assembly of an aluminum cast basket speaker are machined into the basket itself to a very high degree of precision. The pressed basket requires additional fixtures and more of the human element, and of course an assembler cost far less than a machinist or CNC operator. It can surely be done, but I venture to think it may cost the same or more to manufacture a pressed steel basket with the same precision as the cast basket. Heat is still the primary factor in my book, and a solid block of aluminum will always be a far better conductor of heat than a stamped steel shell. Just my .02.
 
Dynaudio, now defunct, never made a 100% magnesium basket. They  did however make a good product using alloy baskets. Magnesium by itself would be cost prohibitive to purchase and machine. I suspect that if you have read the basket was magnesium it was an error. I also suspect that when Dynaudio says alloy they mean aluminum alloy.
 
http://www.gattiweb.com/images/dynaudio/30w100xl_data.pdf
 
 
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Re: Stamped baskets
« Reply #9 on: April 18, 2011, 08:42:16 am »


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