I have a confession I feel I should make before you read any more of this article. I design products for a factory in China. We build great products for home and car audio, a few of which you see gracing the pages of CA&E. That's not what I am confessing though. My confession is that I tried to get Polk to build the SR6500 in the factory that I work with. In fact I made a special trip to China to meet with them, went through their qualification program and jumped through more hoops to get their business than I have ever gone through. In the end though, they decided to use a factory that they had more experience with (sigh).
Seeing these speakers brought up very mixed feelings: a little disappointment because I really wanted to work with Polk and I wasn't afforded the opportunity; a little curiosity because I thought the design was great from the specs and drawings I saw; and finally, a little jealousy that there are engineers in the business that are this good.
If you are short on time and don't want to read all the details, here is what I am going to say at the end of all of this: "The Polk Audio SR6500 component sets are the best component sets and coaxes I have tested. The best performance, the best cosmetics, the best engineered and so far the only thing I have seriously considered putting in my own car," and I hate to install. If you want to know why, keep on reading, it's pretty interesting...
I know a good bit about what it takes to build a product for Polk. It's documented in a few hundred pages of testing standards, product description statements, production standards, internal quality control standards, even standards, standards. These are all written by some of the best engineers, product managers, purchasing managers and manager managers in the business. If you think this is the way most big companies in the audio business work, especially the car audio business, it's not. Polk may have products built in Asia, but they control every part of the process as if it were being done next door. Their system pretty much guarantees that a product is going to exactly meet a consumer need, is going to perform according to the specification, and that every product shipped to a dealer and put in a customer's car is going to meet the specification. In a world of mostly amateurs, these guys are the real deal.
"The Polk Audio Signature Reference SR6500 is the ultimate expression of Polk's 22-year experience of developing superior performance mobile speakers. We drew upon several exclusive Polk technologies to produce a speaker system with the best performance, flexibility and fit in Polk's history of mobile loudspeaker design. It is designed with the serious listener in mind-a listener who is serious about the accurate reproduction of music and movie soundtracks in a mobile environment." This is from their white paper and was the first paragraph in the "Product Description" that they gave out to potential vendors like me. Talk about a mission statement!
Like the product, the white paper is the best I have seen-go to their site and download it even if you don't buy the speakers. Its one of the best no-BS articles on speaker technology one could read.
The woofer is a combination of very cool materials and great engineering. The cone is made of "aerated polypropylene" which is essentially standard mica-filled PP (polypropylene) that has been puffed up with air to make a honeycomb-like structure. It's light, stiff and very well damped. It's also not a lot more expensive than a conventional PP cone, just a lot better. Because it is convertible, the woofer uses a phase plug when the coax post is not in place. If this is done well (and it is), the response can actually be better than a conventional woofer with a dust cap. The basket is cast aluminum with a spider that is almost as large as the cone. This gives a very long linear compliance range (more on this later). The basket serves as a heatsink for the neodymium motor structure. The coil, at 30mm, is larger than most component woofers, which gives it a higher power handling and ultimately a better coax response (more on this later too). The woofer is also easy to install. It's shallow and has 19 mounting holes that will fit virtually every Euro, Asian and American mounting system in the last 15 years. With two supplied spacer rings it will even fit shallow door panels like Subaru Imprezas and Honda Civics.
For the tweeter, Polk decided to use what is considered one of the best tweeters in the world. Made by Vifa, this tweeter is actually used in high-end home systems that cost over $35,000-no kidding. Polk's position is that it's tough to build really good tweeters, especially in China, and a product of this quality should use the best. Vifa has a factory in China that sells OEM, so it was probably an easy call.
The tweeter is pretty remarkable. It uses a very unusual (and patented) design called a ring radiator. It's basically two concentric donuts connected to a bullet in the center, and a voice coil where they join (pictures are worth a thousand words, so check out www.polkaudio.com for a good look at the tweeter). The tweeters have low resonance, great high-frequency range and are ruler flat. Maybe even more important, is that "golden ears" everywhere all agree: This is one of the best-sounding tweeters ever made, period!
Polk of course has added their magic to the tweeter as well. A few little tweaks here and there, a very slick mounting system, the best convertible coax mechanism I have ever seen and a cool rubberized paint coating on the plastic parts that give it a very high-end feel.
The crossover is every bit as cool as the woofer and tweeter-a beautiful mix of cast and injection molded parts make up the housing. All of the crossover parts are the high quality you would expect, without resorting to the ridiculously expensive and highly questionable.
This last sentence is the core of what impressed me the most about this product. It's uncompromising in every place that matters without spending too much to get there.
On to the testing...
Parameter Testing
My testing setup has changed dramatically with the addition of the Klippel Distortion Analyzer. I still use the ACO Pacific 1/4" microphone, lab amplifier and IEC baffle, however all of the testing is done through the Klippel now. It is the "be all-end all" analysis tool for the loudspeaker engineer. The Klippel is revolutionizing loudspeaker design in virtually every application. Check it out at www.klippel.de.
In fact Polk was one of the first companies to purchase a Klippel system and they have made great use of it in the design of this product. Their white paper goes into great detail about how they use it and how most other speakers on the market that don't are inferior. They actually show tests they have done on their competition and the Klippel makes it really easy to see the difference.
My testing starts with "Small Signal Parameters" for the woofer. If you have been following the last year's reviews, you know that I actually measure "Small Signal" at a more realistic level than traditional tests. Small signal for the Klippel system can be measured as the highest voltage before the speaker starts to become nonlinear. For the Polk Audio woofer this was at 2 watts, which is a pretty good starting point considering the very high efficiency of the speaker. The key parameters are listed in the chart below.
Parameter
Small signal 2 watts
Re (Ohms)
3.59
Qms
12.68
Qes
0.86
Qts
0.8
Fs (Hz.)
62.6
Vas (l)
10.65
Cms (mm/N)
0.41
Efficiency at 2.83 volts (dB)
90.23