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Stamped Steel vs. Cast Aluminum Baskets

jdmccall

jdmccall

Super Member
I suppose there is not much dispute as to which is better, but how audible are the differences and how much is the difference worth?

I've been surf shopping speakers for a while now (even though I really like the sound of what I have) and it seems once you move to speakers with cast baskets and real wood finishes, the cost goes up dramatically. And it pretty much appears those two upgrades go hand in hand with a lot of speakers. There are exceptions, of course: Klipsch Heritage speakers have nice wood finished but use stamped steel baskets, while my JBL Studio 5's have vinyl wraps but use very nice cast-basket LF drivers.

Specifically, I've been eyeing a couple of Polk models: the R700 and the L600. The L600 uses cast-basket 7" woofers while the R700 uses, as far as I can tell, stamped steel 8" units. The Legend model has a nice wood veneer (mostly) while the Reserve speaker uses a vinyl wrap...although I rather do like the black, textured look of the vinyl on the R700. The R700 is getting universal rave reviews while reviews on the the L700 are a bit mixed.

Then there's JBL. The HDI-3800 is well-built but pricey (even with the current sale they are still $3850/pr.). They have very nice drivers and finishes. But the new Studio 6 line is waiting in the wings. They look very similar to the HDI line but are much, much cheaper...and you guessed it -vinyl wraps and stamped steel LF drivers (apparently). I don't know that the Studio 6's are much if any upgrade over the Studio 5's, sound-wise. The TotL 698 is a 3-way so maybe that's an improvement but maybe not. My 590's sound darn good!

So how important is driver basket material? Steel, aluminum, magnesium, plastic(!)...what does it matter as long as they are properly designed?
 
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This is just MHO, but I don't think that basket material counts for much more than bragging rights, at least at the consumer level. I think a well-engineered driver can go a long way of addressing any deficiencies in the material used for manufacture. I notice that stamped frames are not uncommon even from some higher end brands.

As an example, I have owned Infinity Kappa 8s and the newer Kappa 8.1. The Kappa 8 (and 9) used a cast basket woofer while the woofer for the 8.1/8.2 and 9.2 is stamped. The later speakers hadn't gone downmarket, it's just that Infinity determined that they could get similar performance with a less expensive manufacturing process.
 
I tend to agree but I do think they (cast) can be better in terms of less resonance and less reflectivity back to the cone. Whether it’s audible to human ears is questionable though.
 
Been rebuilding a set of damaged Konzert speakers, they got banged up bad coming back from the Philippines. One of the 12" woofers was completely torn loose, just hanging there in the box. Anyway, I cut the ridiculous 1/2" thick particle board baffles out and replaced them with 3/4mdf.

I sprayed the inside of the lower part of the cabinet with 3M Super 77 spray adhesive to apply damping material. Whilst doing this, I was wondering what kind of damping properties the rubber cement spray adhesive itself might have? Any thoughts?

BTW, one might wonder why I would bother hauling a set of speakers sporting a 1/2" thick baffle (and back) all the way from the Philippines back to America? Well, in spite of the poorly constructed cabinets, the drivers sound quite good. I intended to build new cabinets for them even before I bought them, the price was right.

I didn't however plan on the Qatar Airways employees destroying the original cabinets, which I planned on using this weekend for my daughter's birthday party, thus the quick repair.

Getting back to damping, I can't help but wonder if applying a coat of rubber cement to the baskets would give favorable damping? Obviously one would have to protect the driver and other components before applying. Yes there's always the 'try it and see' angle but I don't have any drivers that I am willing to commit to experimentation just now
 
I like to apply Dynamat Xtreme to stamped steel baskets as it eliminates any ringing. You don't need to cover every square inch, just enough to cover the spokes. Of course, if the basket is cast then there's no need.
 
Doesn't your car drive better after you've washed and waxed it? Your speakers will sound better if you feel better about them, and there's nothing prettier than a JBL cast-frame speaker. I've owned them for over 60-years and never tire of seeing the quality when I go inside the box—especially when it's visible from the outside!
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Cast baskets can be machined with a high degree of accuracy as far as symmetry is concerned. All machining will also be concentric, extremely important for proper speaker operation. It also dissipates heat away from the voice coil, raising its operating range. Steel is not very good at dissipating heat, that is why they make wood burning stoves out of steel.
 
Cast baskets tend to be stronger and less resonant than stamped steel. Also less likely to allow "magnet shift" and tend to dissipate heat better in high power applications.

Cast baskets are more expensive to manufacture and machine hence their typically higher price.
 
Speaker temperature is something I haven’t considered. Do they really get hot enough to need heat sinks to dissipate heat? Is SQ degraded by not having a temperature controlled room? At what temperature does a driver start suffering from heat?
 
Speakers are a form of resistance, resistance = heat. Feed enough power into a resistor and you generate heat, sometimes lots of heat.

Imagine a speaker at a concert playing at very high levels with lots of power applied for an extended period of time.

Excessive heat can cause voice coil formers to deteriorate and warp, sometimes the voice coils themselves can overheat and short out. Not as much of an issue today with the advent of aluminum, kapton and other materials used.

Cast baskets are also stronger allowing them to support the huge magnets used, especially important when you start bouncing all that mass down the road. They also tend not to flex under extreme conditions keeping the voice coil in alignment within its gap.
 
Yeah I get the potential for heat if overdriven for extended periods but the more a cone driver moves the more air it moves, in effect being a fan running across it. I am still curious if heat has ever been a design concern.
 
Not necessarily overdriven but driven hard for extended periods of time. Imagine driving on a flat highway at 60mph your engine runs at a certain temperature, increase the load with a trailer or a long incline and the temperature will rise, not over driven but workning harder.

The vented pole piece is a perfect example of using the drivers motion to aid with cooling but in many instances that is just part of the thermal management scheme. Most home audio applications dont have the potential to generate that kind of heat but Pro and even car audio applications certainly can. Situations where the drivers are fed substantial amounts of power over extended periods of time.

As the cone moves, it does move air but the back of the speaker is inside a cabinet, usually not much airflow inside there. Even a vented enclosure still has "stagnant" air as the air moves but does not necessarily circulate exchanging cool air for hot air.
 
wmgwizard said:
as the air moves but does not necessarily circulate exchanging cool air for hot air.
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True but moving air is still absorbing heat. A fan in a hot room still feels better on you as the hot air still has a cooling effect do to velocity.

I usually listen at high levels and my the whole cabinet will warm up and you can feel the warmth from the port.

Admittingly I am probably not in the norm to generate that much heat.
 
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grillebilly said:
Yeah I get the potential for heat if overdriven for extended periods but the more a cone driver moves the more air it moves, in effect being a fan running across it. I am still curious if heat has ever been a design concern.
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Yes, thermal compression is a very real thing and is one reason that I use big, efficient speakers. Thermal compression can start to manifest itself at <10% of the rated power.

As for more cone movement moving more air, this only really cools the voice coil if the speaker's architectecture allows for it. If the voice coil is not vented, as many aren't, the air doesn't really circulate around the windings.

https://jblpro.com/en-US/site_elements/2241h-data-sheet
 
Aluminum is going to dissipate heat better than steel. Both aluminum and steel are going to ring. Damping a basket can eliminate or at least minimize that. Every speaker has to fall under a budget so that’s why a certain manufacturer may have aluminum basket drivers while they cut cost on the cabinet by finishing it with vinyl laminate instead of real wood veneer. Sometimes the cost cutting is in the crossover. Or maybe the input terminals. Most of the time there is going to be a compromise somewhere in the design.
 
grillebilly said:
I am still curious if heat has ever been a design concern.
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It's always been a design/engineering concern.

Before permanent magnets there was a field coil continuously energized with DC that produces heat.

How much heat? depends on the design.

grillebilly said:
At what temperature does a driver start suffering from heat?
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That depends entirely on the design and materials used.

Consider why vented dust caps appeared in the 1930's/40's, and why high temperature adhesives and dielectrics for loudspeakers have been in more or less continuous development since that time. ;)

A very quick patent search reveals a loudspeaker patent awarded to Hugh Knowles at Jensen in 1934 which in part deals with a heat dissipating device.
 
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NH-MAN said:
I would think I am pretty awesome if I could hear what my woofer frame is made of. :dunno:
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That's hysterical !
Now you have me picturing audiophiles listening to speakers like a sommelier tasting wine:

Listen to a passage of music, stare off into the distance for a little while, then remark
"Original Large Advent, 1971, utility cabinet, masonite drivers, new foam, original caps, grills on but badges missing".

Apologies for the diversion, carry on....
 
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