Bass Radiator Technology
Explanation of bass radiators used on DSW Micro Pro and VM Series
Bass Radiator Technology is found on our new DSW MicroPro subwoofers and VM Series slim-line speakers. Simply put a bass radiator reinforces the ultra lows of the subwoofers and is a much more sophisticated version of a port. DSW MicroPro series use a Quadrilateral Fluid Coupled Bass Radiator, while VM Series uses multiple Planar Bass Radiators. Polk is no stranger to Bass Radiator Technology; we used them extensively on our legendary SDA and SRS Series speakers.
To understand what purpose a port serves and how a Bass Radiator is better we have to understand how a port works. A port will reinforce the lowest notes of a particular speaker or subwoofer. When a speaker driver makes sound, it moves back and forth. Half of the sound produced comes out the front while the other half comes out the back. The “back sound” is usually trapped inside the box. The port allows this back sound of the driver to reinforce the lower notes. The port is tuned by varying its length and diameter. Quite similar to blowing air on a bottle, a longer bottle will have a deeper tone then a shorter bottle. To tune the port lower, it must become longer.
So why not just use a conventional port on the DSW MicroPro and VM like other designs? Conventional ports have some limitations. One main difference is they cannot be tuned to an extremely low frequency without being quite deep and large. Both the DSW MicroPro and VM were designed to play loud and low but in a compact enclosure. A conventional port would have required a much larger enclosure in order to fit the port. Here a Bass Radiator is a clear advantage.
Further, a high performance speaker or subwoofer is capable of displacing a huge quantity of air. This will cause air to rush in and out of the port. A rather large port is needed to deliver the rushing air, otherwise air turbulence will be heard. The term for this is “chuffing.” Though our PowerPort technology helps to minimize chuffing, it still cannot address the issues of long port length. Because no air is actually rushing through the radiator like a traditional port, Bass Radiators eliminate the possibility of any air turbulence or chuffing. Chuffing is disruptive and can make a speaker sound blown.
Another advantage of a Bass Radiator is mechanical control. A port is either a simple tube or a slot with no moving parts. The Bass Radiator has characteristics similar to that of an active driver- without a voice coil, wires or magnet assembly. We can tune the bass radiator by adjusting its mass, size, shape and suspension.
Disadvantages of Bass Radiators:
Bass Radiators are much more complex and harder to design then conventional ports. More time and effort goes into the design, because the radiator has its own suspension. Second, instead of a traditional port which is either a tube or a slot, a Bass Radiator is its own component with moving parts. The extra parts increase a speaker’s complexity, so Bass Radiators are reserved for top of the line performance.
Bass Radiators also require a surface area at least the same size as their “active” drivers to work properly. What this means is usually a rather large cabinet and the need for place to mount the Bass Radiator. To address this issue, we take a different approach for each series. VM Series uses multiple Planar Bass Radiators per speaker. VM20 has 2, VM30 has 4! On the DSW MicroPro, we position the Fluid Coupled Bass Radiator at the bottom of the enclosure. Not only does this protect the radiator, it also keeps it out of site. Also, instead of a traditional round radiator, we use a Quadrilateral surface which maximizes the Bass Radiator’s surface area in what would otherwise be wasted space. DSW MicroPro Bass Radiators also use unique suspension features, including a butyl rubber surround and dual spiders just like the active driver. This design ensures uniform stiffness throughout its travel range. The surround is affixed to the radiator surface with both adhesives and stitching. It will hold together even under the most demanding conditions.
Overall, Bass Radiator Technology allows the speaker or subwoofer to keep its small compact enclosure, while still providing deep bass performance.
