Pressed steel speaker chassis vs cast or plastic

[rdenney]

It is about the materials a lot of the time too.
Anything that touches corrosion, space, the ocean, heat, or strength and stiffness limits.

I agree for a bicycle or a bridge it is more about shape.

I said it was about how the shape accommodated the material properties. I didn't exclude one over the other, which was my point. People make assertions about the material without understanding the overall structure, or they make assertions about the overall structure without understanding the material.

Rick "true for speaker frames as much as for bicycles, both of which are shape-constrained in important ways" Denney

 

[uwotm8]

The old driver is in red and the new in blue.
Fortunately, the new driver shows considerably less distortion. The levels in the bass are not quite the same, but I suspect that the new driver would still considerably outperform the old driver.

Can I dare to ask you how do current drivers of similar size - cast and steel chassis - compare?

 

[AOR]

Can I dare to ask you how do current drivers of similar size - cast and steel chassis - compare?

Unfortunately, I can't think of a directly applicable comparison. If there exists a driver with a steel chassis, we wouldn't really make a cast version. The closest off the top of my head is the Q950 UniQ and the Ci200RR-THX. They are basically the same apart from the chassis. However, the Ci200RR-THX has a/some demodulation ring(s), so it's not a fair comparison.

 

[uwotm8]

My 2 cents
Wait, disclaimer first: talking abroad and philosophically, this is no user's business how and with which drivers, crossovers etc good (or not so good) sounding speaker was engineered; result is all that matters. You like how it sousnd for the price, you buy it, done.
At the same time, in most cases result is not that irrelevant to price and components used.

Keeping said in mind, "chassis question" looks pretty simple to me, here's a few points:
- Сast chassis may be only a formal advantage if this is the only difference and it's arguable if that will ever be noticeable to ear. But as far as I can tell, it is extremely rare that it's is the only difference. The improvements in more expensive drivers are complex, which means that if a certain brand produces an entry-level line on a stamped chassis, and a more advanced one on a cast one, the advanced one will be better not only because of the chassis itself.
- Nowadays a "decent enough" 5"-6" woofer with a cast chassis retails for around $30-70 (rough estimate of wide range from Dayton to Seas). And you can get a 10%+ discount if you buy just 5-10 pcs at a retail e-store. I suspect that unit price might be a few times less in a big amounts in direct sells for a big manufacturers.
- Same "dicount" for another parts and manufacturing (especially!) is reachable for, again, big amounts.
So, I expect a 2-way bookshelf speaker costing more than $500/pcs or $1000/pair to have "advanced basic" units at least, not the cheapest. That includes cast chassis and tweeters with a rear chamber, not the shamefully looking soft domes with coin-size magnet. Dynaudio (!) manages to do that in LYDs, all basic checkboxes marked including decent and dense case.
Wharfedale, Elac and other manage to produce $200-300/pair (!) speakers with a cast chassis drivers. Some are plastic, some are "normal" Alu alloy.
Seeing Peerless SDS in a $500-$1000/pcs studio monitor is kinda meh. Yes, they are enough, especially cooked with a DSP, but their better siblings are not that pricier (and must be better - maybe much, maybe not). Using them would also eliminate such talks, so there's a psychologicall aspect as well.
If we're talikng about something really budget, say, Adam T/JBL 3/Kali LP - well, for these manufacturers had to cut sosts as agressively as possible. I can't imagine anything but the cheapest chassis and amps. Yet Adam still managed to make a decent MDF fron baffle (covered with plactic) while other went "full economy" and decided thin plactic is enough (you can check that "enough" on distortion graphs). Seeing "only plastic" face on a 8" 3-way "coincidental" however, even keping in mind its $400-450 price, is a total no-go to me.

 

[Holmz]

I said it was about how the shape accommodated the material properties. I didn't exclude one over the other, which was my point. People make assertions about the material without understanding the overall structure, or they make assertions about the overall structure without understanding the material.

Rick "true for speaker frames as much as for bicycles, both of which are shape-constrained in important ways" Denney

I’d like to believe it, but if the main force is in-n-out, then most of the basket force is tension and compression… So the stiffness is a finction of cross sectional area.
Now diffraction around the basket would be shape dependent, but ignoring that… we have whatever the stiffness is, and that likely creates a high Q resonance at a specific frequency.
So I am not sure whether it helps or not??

 

[uwotm8]

Q950 UniQ and the Ci200RR-THX. They are basically the same apart from the chassis. However, the Ci200RR-THX has a/some demodulation ring(s), so it's not a fair comparison

But maybe Q150 and LS50 (or Q1 Meta and LS50 Meta) Uni-Qs can be compared? Woofers only, I mean

 

[AOR]

But maybe Q150 and LS50 (or Q1 Meta and LS50 Meta) Uni-Qs can be compared? Woofers only, I mean

Unfortunately not. Those motors are quite different. Different demod rings, different pole geometries. Both of those have a reasonable effect on current distortion.
LS50: Top
LS50 Meta: Middle
Q1 Meta: Bottom

 

[rdenney]

I’d like to believe it, but if the main force is in-n-out, then most of the basket force is tension and compression… So the stiffness is a finction of cross sectional area.
Now diffraction around the basket would be shape dependent, but ignoring that… we have whatever the stiffness is, and that likely creates a high Q resonance at a specific frequency.
So I am not sure whether it helps or not??

But changing the cross sectional area is of course a response to the material properties.

I suspect, though, that casting has more to do with the shape of a cast basket. Casting metal requires sufficient section to allow the molten metal to flow without being slowed down by the drag and cope sand (or whatever it used for the mold), so that the metal won't freeze before it reaches the vent. The shape also requires substantial draft so that the pattern can be pulled from the mold without bringing the mold material with it.

Looking at the fabricated basket in the AR speaker pictured upthread makes me think that was made that way because in small quantities it was the most feasible option. It looked to be made of standard sections cut and welded together and then epoxied into the baffle, which is easy in a small shop. Stamping is more difficult, and requires a substantial batch to minimize the unit cost of creating the stamping patterns. Casting is more costly still in medium quantities, though can be cheaper in higher volumes (and in onesies and twosies).

If a steel basket is stamped and has a spider arm that is, say, two inches wide and is stamped from 14-guage plate, that has a cross sectional area of 0.15 square inches, with a strength of maybe 5000 pounds. An aluminum spider arm that is an H-section that is 3/4" square with, say, 1/8"-thick material, has a cross section of 0.28". It will have about two-thirds the strength and stiffness of the steel arm. Of course, those shapes are imagined from pictures in this very thread, and could be much different in any given pair of examples.

Note that the discussion of mechanical properties avoid what seems to be an important discussion of electrical properties in how the basket material affects the em field around the magnet and voice coil.

Rick "stiffness is always a function of section and material properties" Denney

 

[Heinrich]

I said it was about how the shape accommodated the material properties. I didn't exclude one over the other, which was my point. People make assertions about the material without understanding the overall structure, or they make assertions about the overall structure without understanding the material.

Rick "true for speaker frames as much as for bicycles, both of which are shape-constrained in important ways" Denney

To press a steel sheet results in a deformed sheet, but it is still a sheet. Peerless uses a collar bend around the edges to stiffen the sheet. With cast material the rods, as to say, have nearly arbitrary cross section. This allows for having more open windows for the sound to travel outside the basket. Being at that, ventilation of the motor's gap becomes more straightforward.

The deformation of a more simple steel basket when mounted may be another factor. Thinking of the notorious first generation KEF chassis with their floppy 'ears'. Not countersunk, have fun, and we had fun back in those days!

 

[uwotm8]

Unfortunately not. Those motors are quite different. Different demod rings, different pole geometries. Both of those have a reasonable effect on current distortion.
LS50: Top
LS50 Meta: Middle
Q1 Meta: Bottom

Thanks again!
Well, quite unsurpising that chassis improvements come along with other.
Even more reasons to prefer cast chassis versions of "visually almost the same" woofers... like I said earlier

 

[JDS]

This is not true.
Aluminium and steel are available in a plethora of alloys, some very much more malleable than others.
Pure aluminium is neither stiff nor strong and all the alloys have a specific modulus around ⅓ that of steel alloys. It is pretty soft and malleable when pure but the alloying elements change its properties a lot.
Alloys which cast easily can be pretty brittle but they are not stiff, the alloys have close to the same modulus - what varies is the stress strain curve and the load before plastic deformation and failure.

It is true aluminium alloys have no load below which fatigue failure won't happen, whereas steels do.

The way I explain this property of aluminum to people (usually whoever is sitting next to me on a long flight) is that if you stood on the end of the wing of a jet liner and jumped up and down enough times, the wing would eventually fall off.

Once upon a time I had friends.

 

[mhardy6647]

Hi DanielT,

Your question of new vs. old KEF drivers intrigued me.

I didn't manage to find any B200, at least not without dismantling any of our lab standards, but I did find something older. I found a B110 (SP1003). I believe that this is the first driver that we have in our current documentation. Production started on SP1003 on 20th November 1969, so the design is quite old...

Here it is compared to a modern small bass driver, which also has a steel chassis.

View attachment 433258

As I didn't have a suitable box, I performed nearfield measurements of both units. Both drivers have a nominal impedance of 8 ohms, and were driven with a 1Vrms signal.
View attachment 433260
The old driver is in red and the new in blue.
Fortunately, the new driver shows considerably less distortion. The levels in the bass are not quite the same, but I suspect that the new driver would still considerably outperform the old driver.

This is really interesting to see. I see differences, no doubt.

 

[Holmz]

The way I explain this property of aluminum to people (usually whoever is sitting next to me on a long flight) is that if you stood on the end of the wing of a jet liner and jumped up and down enough times, the wing would eventually fall off.

Once upon a time I had friends.

The airlines will not let you stand out on the wing anymore.

They’ve also changed the wings, making them with composite materials.
Game, Set and match!

 

[Penelinfi]

The way I explain this property of aluminum to people (usually whoever is sitting next to me on a long flight) is that if you stood on the end of the wing of a jet liner and jumped up and down enough times, the wing would eventually fall off.

Once upon a time I had friends.

Don't tell them that when flying, the wing is "jumping up and down" for the entire flight ;-)

 

[mhardy6647]

The airlines will not let you stand out on the wing anymore.

View attachment 438330

They’ve also changed the wings, making them with composite materials.
Game, Set and match!

There's some physics goin' on in the shenanigans recorded in that photo!

 

[Holmz]

Don't tell them that when flying, the wing is "jumping up and down" for the entire flight ;-)

The damned streaming even has pops-n-clicks.