Technology & Engineering

The Enhanced Ring Radiator Tweeter

Let’s start at the beginning. The tweeter: it’s the part of the speaker that reproduces the higher frequencies. This is important because your brain takes many of its directional cues from the placement and realism of detailed higher frequency audio information. Often, that higher frequency information is embedded within a wider dynamic range; tweeters work in natural lockstep with their nearby mid-range drivers. A tweeter needs to blend in, but also stand apart. Dome tweeters use a dome of silk, polymer or metal (like aluminum) attached to their voice coils. Well designed and engineered, and guided by professionally programmed crossovers, dome tweeters perform exceedingly well.

The ring radiator tweeter, on the other hand, uses a series of concentric domes (usually two) encircling a stationary “wave guide phase plug.” The ring radiator design (which has been around since the 1950s) is known for its smooth response, almost complete lack of coloration, and very detailed sound characteristics. Because of these “higher end” performance characteristics, the ring radiator became the favorite of “boutique” audio brands where expense didn’t matter; the sports cars of the audio world. (One Internet search quickly turned up ring radiator speakers costing $25,000 a pair.)

Enter Polk, whose mission has always been to design high performance loudspeakers at a reasonable price. We wanted the benefits of the ring radiator -- accuracy and detail, foremost -- without the costs. So we designed a line of high performance loudspeakers using our version of the ring radiator tweeter. Reviewers and owners were overwhelmingly positive (positively gushing) about the dynamic response and detailed you-are-there imaging capabilities of the LSi Series. Suddenly, the ring radiator tweeter had found a home in a high quality, high performance loudspeaker system that didn’t demand a second mortgage.

When it came time to up the ante for our new flagship LSiM Series, Polk engineers decided to make some nuanced improvements in the classic ring radiator design. For the new line, we wanted to reveal details in response up to 40 kHz (bats rejoice!) and to improve the tweeter’s already exceptionally smooth response and dispersion patterns.

First, Polk engineers reshaped the tweeter’s classic bullet-shaped phase plug. This allowed the tweeter to be moved farther out on the baffle, which improved dispersion and eliminated horn loading. Next, they opened up the tweeter’s solid faceplate, but covered up a portion of the diaphragm roll, to eliminate wasted energy coming off the dome and further improve dispersion characteristics. Then they enclosed this Enhanced Ring Radiator Tweeter (ERRT) in its own internal enclosure, to isolate it from performance-robbing cabinet interferences. (Then, they enclosed this new ERRT Enclosure within the LSiM Dynamic Sonic Engine. You can find out more about how that new design enhances the performance of this amazing tweeter at that link.)

On top of the already excellent, high-end performance characteristics of this style of tweeter design, these evolutionary changes put the new Enhanced Ring Radiator Tweeter completely over the top. With higher power handling, extended dynamic range with higher top-end response, better blending and improved dispersion, the Enhanced Ring Radiator takes performance to a whole new level in the surprisingly affordable LSiM Series.

This article was last modified on Mar 26, 2013

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