Technology & Engineering

Bass Radiator Technology

Advanced Bass Radiator Technology goes where no port has gone before.

At Polk, we love deep, musical, floor vibrating, rafter shaking bass. Our subwoofers really do go to eleven. Over the years, we’ve designed and engineered innovative ways to improve bass response in our subwoofers and traditional loudspeakers. Our solutions have helped us keep our speakers small and efficient, and we never sacrifice smooth dynamic musical response to boomy, distorted low end.

Bass Radiator Technology, in which a radiator that mimics a speaker cone works to reinforce a speaker’s ultra low end bass frequencies, is one way we’ve found to efficiently provide deep bass in a speaker with a compact enclosure. Polk made headlines back in the day by using bass radiator technology in our legendary SDA and SRS Series Speakers. Today, we use advanced bass radiator technology in our new DSWmicroPRO Subwoofer Series, and in the VM Series Slim-Line Speakers.

How is a Bass Radiator Better than a Traditional Port?

When a speaker driver makes sound, it moves back and forth. As it does this, half the sound comes out the front of the driver and the other half comes out the back. The part that comes out of the back of the speaker driver, the back sound, is usually trapped inside the box of the speaker enclosure. We can use that back sound energy to reinforce the low frequency response of the speaker by allowing the back sound to escape the enclosure in a controlled way. To do this, we can tune a port for the enclosure.

The port, which looks to you and me like a hole in the enclosure, is really the opening for a sophisticated acoustic tube. This tube is engineered to the exact length and width to enhance the low frequencies of its enclosure. Blow air across the small hole at the top of a glass bottle. A longer bottle will have a deeper tone then a shorter bottle. Longer port tubes work the same way. Sometimes, the port tube you need to do the job right is too long to fit in your enclosure. This is one of the limitations of port technology. And that’s when you need to find another solution.

In small enclosures that demand deep bass, Bass Radiator Technology has a clear advantage, since it takes up no interior tube space but still generates an enhanced deep bass response. Both the compact DSWmicroPRO subwoofers and the VM Slim-Line Series Speakers are designed to play loud and low. A conventional port would have required a much larger enclosure, making these compact designs sort of irrelevant.

Another advantage of our Bass Radiator Technology is the actual mechanical control it gives us to tune its frequency enhancements perfectly. A traditional port is tuned only by varying the length or width of its tube. But even though a bass radiator lacks the motor (voice coil, wires, magnet) assembly of an active speaker driver, it retains many of the characteristics of that speaker driver. This allows us to perfectly tune the passive bass radiator by adjusting its mass, size, shape and suspension!

Big Bass, Small Space

Passive bass radiators require a surface area that is at least the same size as the other active drivers in their enclosures. Because of this, you need a cabinet design large enough to allow for the mounting of both active and passive drivers. This could be a deal killer when you’re designing compact enclosures!

Have no fear! We’ve engineered some unique ways to get around this limitation; to have our bass and be compact, too.

In the VM Slim-Line Speaker Series, we’ve designed multiple planar bass radiators that, combined, equal the required surface area needed to successfully enhance the low end frequencies of the speaker. (The VM20 has two planar bass radiators; the VM30 has four!)

DSWmicroPRO Subwoofers feature a bottom mounted fluid coupled bass radiator with a quadrilateral surface design. In this downward firing position, we’ve accomplished four things simultaneously: We’ve hidden the radiator from view (protecting it as well), maximized the surface area of the driver through quadrilateral surface design, and successfully used otherwise wasted enclosure space to boost the deep, musical bass response of this compact subwoofer. This special bass radiator position also allowed us to add additional elements to this particular radiator to give us even more performance than we imagined. A unique suspension hangs the radiator in place, with a butyl rubber surround, affixed with special adhesive as well as stitching, and dual spiders. For the DSWmicroPRO, we’ve engineered a passive bass radiator with the uniform stiffness and durable toughness of a heavy duty active driver!

Deep, Musical, Audiophile Bass; the Kind We Love

It goes without saying that Bass Radiator Technology, with its intimate relationship to a speaker’s active drivers and its capacity for fine tuning, is more complex than that of conventional ports. You can see why bass radiators are usually reserved for flagship performance loudspeakers.

You’ll feel the deep, radiating bass when you listen to the DSWmicroPRO Series Subwoofers or VM Slim-Line Series Speakers.

This article was last modified on Jul 10, 2012

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