Paper vs. Plastic (drivers)

[rskarvan]

I'd like to see an intelligent discussion regarding Polk's older coated paper cones and their newer blue cones (used in the i-series speakers). To keep comparisons on the same level - lets limit the discussion to the 6-1/2"ers.

What are the differences? Which is better? Why the change?

The old coated paper ones seemed to be pretty good and reasonably durable. Both use rubber surrounds.

THe newer ones are - well - different.
Personally, I prefer the old glossy-looking black paper cones.
I may be wrong.... but, I think the older ones just simply sounded sweeeter - imo.

I suspect the newer cones are easier to mass-produce.
Is that the reason for the change?

Likewise, is there any significant difference between the old SL3000 tri-laminate tweeter and the new tweets used in the i-series speakers (RT55i)? Its my understanding that both are tri-laminate.... but, they look/appear different. Again, which is better? Why?

Thanks for commenting (in advance).

[George Grand]

I can't pass comment on the new Polk stuff, but I do know that there are OUTSTANDING speakers, that are considered classics, that use paper drivers. I also know, that I have heard speakers that sound absolutely horrible, and they are loaded with drivers made of newer, more "exotic" materials. Exotic materials does not a great speaker make.

George Gand (of the Jersey Grand's)

[JohanK]

I haven't done any bench testing or anything to compare the old and new but I can give you some subjective impressions. I use RT55s (2 pairs) as surrounds and RTA-8TLs (with SL3000 tweets) as front mains. I also have a pair of Monitor 7Cs.

Personally, I like the coated paper better. Like you said, smoother is a good word to use as to why. The poly drivers sound a little more sterile, IMO. I like the SL3000 tweet better than the newer tweets; they are both bright but the 3000 does it w/o being obnoxious. I like the original SL2000 silver coil tweets best though I haven't heard the Peerless 810665 tweet in a Polk speaker.

...just my 2 cents.

[lycombs]

Good questions and thoughts. Let's add the question of the difference between the 6 1/2 in the RT3000s, which are NOT blue,....as compared to the RT2000 and others? Different materials,....different coatings,....different performance (obvious)???

Per the term "intelligent discussion", it would be great to get a Polk definition and terminology on this. Thx.

[RuSsMaN]

In my limited experience, I think paper sounds incredible, if done right. Even un-coated/un-treated. No scientific proof to back this up, just what my ears tell me. I do enjoy the kevlar fiber that is used today also, but I do think it produces a slightly forward, less natural midrange (due to the stiffness of the cone?).

Paper is ok in my book.

Cheers,
Russ

[rskarvan]

I think there's something to paper drivers (properly designed) having material characteristics that are superior to polymers/plastics. I think paper drivers are inherently very well dampened. The nature of paper probably also kills any resonance in the driver also. Polk's coating the old SRS paper drivers was a move that made them much more durable than paper drivers (saving them from aging issues).

I heard a similar discussion over saxaphone reeds. Nobody has improved on the original wooden reed; though, many have tried.

["Polk" Paul DiComo]

Micah is making me answer this thread even though I am VERY VERY busy and stressed out. Bad Micah. Bad.

First, for those who don't know me, I've been at Polk for over 18 years and have had more Polk speakers in my home than I could ever remember.

The paper-based cones from days past were revolutionary in their day. They were among the frst designs to use a composite structure to reduce cone resonance for flatter response. The principle is that if you combine materials with dissimilar resonance characteristics they tend to cancel each other's modal breakup modes. Think of a sheet of metal and a sheet of plastic. Alone the metal sheet "rings" when struck. The plastic sheet doesn't ring but has low frequency resonance and lacks the stiffness to be an efficient piston. But combine them together and you now get the best of both worlds. The plastic damps the ringing of the metal and the metal stiffens the plastic. The net result when you do that sort of thins in a speaker cone is flatter frequency response and reduced distortion.

The old paper cones were treated with one polymer material that stiffened the paper and a second (the sticky shiny stuff) damped the surface (acted like the soft plastic sheet in the analogy above).

In the new cones the different materials are combined together in the cone. There are both damping and stiffening elements. Yes, it is true that the new composite plastic cones are easier to produce BUT have innumerable advantages over the treated paper cones. Here are two:
1. The composite plastic cones are injection molded. That means we can (and do) vary the thickness of the cone across its cross section. The cone is thicker near the voice coil and thinner at the circumference (is that spelled right?). That makes it better in ways I am too lazy to explain. Trust me it is better.

2. The new cone is lighter, yielding higher efficiency and better transient response.

So what does this all mean in terms of sound? IMHO (well maybe not Humble), the new drivers have MUCH better detail and sound far more natural. It is an objective fact that they produce a flatter and broader frequency response with lower distortion than the old drivers.

I have a couple of pairs of older Polks with paper cones (including SDA-CRS+) and as much as love them as I do for some of their other qualities, I must recognize their weaknesses. The new models I have had at home sound more life-like with far better articulation and detail. The old models sound a bit "congested" and "thick" in the midrange.

As for the change in look to the tri-laminate tweeter - we changed the substrate material to get a little better performance and the metal coatings look a little different on the new material. There always has been noticeable color variation in the metal coatings from batch to batch but that makes absolutely no difference in measurable or subjective performance - just color.

BUT all the above having been said - you can't judge a book by its cover and you can't judge a speaker entirely by the materials used in its drivers. I have heard good very sounding paper cones and bad. I have heard LOTS of very bad sounding speakers that used exotic cone materials. A hack can screw up anything and a good designer can get the most out of the materials he has to work with.

Use your ears to judge. Use the standard of live acoustic music to set a proper frame of reference.

[Micah Cohen]

I love Paul.

:D

[Strong Bad]

A night out at Kaos to relieve some of that stress that Micah is causing you.

Come on Polk boys, bring Paul out to keep his sanity.

By the way, nice explanation on the differences in the cone materials. Now...if they would only make some SDA's with the new technology....

["Polk" Paul DiComo]

Kaos? Why, they have women there without any clothes on! I'm afraid Micah would turn purple and explode were he to be exposed to such sights.

[George Grand]

That WILL happen if his hands are tied behind his back.

George Grand (of the Jersey Grand's)

[Aaron]

Paul,
I think your assessment of the sound of the older drivers vs. the newer drivers is right on the money. That's basically what I've experienced word for word. I didn't, however, have all the technical reasons to back up my observations. Thanks!

Aaron

[rskarvan]

Paul, Thanks for answering my question.
I have a mixed HT system and I was curious as to
which was better, why, and what exactly the differences
are. You answered my question very thoroughly.

Half of the audio equipment is inside your own head.
Thats why everything is so dang subjective.
Maybe the brightness & accuracy of the blue cones
just sounds less friendly to my ears.

Thanks again.

Ron

[lycombs]

Paul,...thanks for the info. Realize you are busy but I think it makes us much better disciples for Polk by better understanding the details that you have provided.

One last question,.....with regard to the 61/2s in the RT2000s (blue) versus the 6 1/2s in the RT3000s (black), what's the basic differences there? Are the 3000 6 1/2s different still? Obviously, the power handling ratings are different, but that can be more than just cone structure, i.e. crossover design, etc,..

Thanks in advance.

[Micah Cohen]

I'm trying to get Paul to come back and pick this up. Paul takes time.

MC

["Polk" Paul DiComo]

The engineering geeks made a small tweek to the formulation of the cone material to eke a little bit flatter response out of the drivers. Frankly it is not a night and day difference. Few changes in the speaker design business are night and day. Most of the time we are inching forward a bit at a time. The effect of these little improvements are cumulative. At the end of a few years, bingo, you got something that is obviously better than what you were making a few years back. Sorta creeps up on you.

Quantum leaps in speaker pefrformance happen rarely, usually after some other technology breakthough. For example, we would not have been able to make a quantum leap in driver design about 8 years ago were it not for the development of the full field laser interferometer at Hopkins U a couple of years earlier.

That answer your question?

[lycombs]

It does,....thanks Paul.