ALL ABOUT THE BASS
Looking to Maximize Subwoofer Performance? Here Are 7 Bottom-End Tips For Mobile DJs
Adding bass to your sound system is a must for most DJ applications, so some explanation of how low frequencies are created and how they act in your environments will help you get the most from your system and deliver the best audio performance.
First, let’s get a few basic facts about sound out of the way. We all know that sound is a pressure disturbance in the air, and frequency measures how often these disturbances occur. Higher frequency sounds, like cymbals or female vocals, produce shorter wavelengths since they happen more often.
An Example: The sizzle of a hi-hat cymbal can be up near 10,000 Hz or cycles per second, and it will have a wavelength of slightly over one inch. At these high frequencies, two characteristics should be noted: first, these disturbances are easily absorbed by soft items in the listening area (including people, drapes and carpeting) and second, they are directional, so placement of your main speakers needs to cover your desired listening area—the dancefloor, of course!
The lower the frequency, on the other hand, the less directional the energy becomes. Consider the low E note on a bass guitar: The wavelength is a little more than 27 feet long. Clearly, a lot more energy is needed to create the sound at the same perceived level. In addition, these longer, slower pressure disturbances tend to stay in a closed listening area for a much longer time and aren’t absorbed as quickly in the same manner as higher frequency sounds.
Now that you have a basic understanding of low-frequency energy, here are seven things that DJs should consider to maximize subwoofer performance.
1. Make sure that you have the subwoofer(s) on the floor. If you use caster boards or carts for transport, remove the subwoofers and place them directly on the floor. Raising a subwoofer cabinet even a few inches off the floor will reduce its performance because they are designed to use the floor as a 90-degree waveguide to help maximize the energy produced.
2. If you are using multiple subwoofers, placement is crucial for getting the most from your system. Since the lengths of bass sound waves are so large, separating multiple subwoofers will affect the performance. While it might look better to put the subwoofers out underneath the main speakers, performance will almost certainly be improved on the dancefloor if the subwoofers are placed together near the front center of the dance floor. You might not immediately hear the improvement early in the event, but when you are really pushing the system hard in the third and fourth set, your audience will appreciate the extra acoustic output coupling the subwoofers will provide.
3. Subwoofer systems should be operated in mono. All subwoofers need the same signal to maximize their effect. A lot of manufacturers now offer stereo inputs on subwoofers. These two inputs are summed into a mono signal to feed the subwoofer. Some DJs like to have the subwoofer on a separate send apart from the stereo output so they can control levels of the subwoofer separately. If your mixer has a spare auxiliary output, or if you have a mono output, this is a great place to hook them up.
4. Phase vs. Polarity. Over the years, these two terms have been confused. Phase is a measure of both frequency and time, so it is less absolute. A switch marked Polarity on a subwoofer determines whether a positive signal applied to the subwoofer will make the speaker cone move forward, or toward the front of the cabinet. Reverse polarity will send the driver the opposite way when the same positive signal is applied. Because of acoustic abnormalities in various rooms, the ability to invert the polarity to improve dead spots, or nodes where bass response is diminished, is readily available by using this switch. If you choose to place all your subwoofers in one place near the center of the dancefloor, be aware that they operate as a single unit, so reversing polarity should be done on all subwoofers the same way.
5. Cardioid Mode. Lately, manufacturers are offering a cardioid mode on powered subwoofers. It is a method to use one subwoofer to work with another of the same type to help steer the energy forward by reducing the output of the system at its rear and increasing the output from the front of the system. Bear in mind that this treatment is more often needed for live-music reinforcement, where bass buildup can be a problem onstage. It is often used in arena concert sound systems to help reduce the “power tunnel” of bass buildup in the very front of the stage that extends forward into the audience area, but this is the exact area that most DJs require increased bass response, so the cost and complexity often rule out the need for DJs to use this feature.
6. Subwoofer Designs. Manufacturers have a lot of choices for subwoofer enclosure designs. In the early years, when amplifiers delivered relatively low power levels, a horn-loaded design helped make the most efficient use of the limited power, but horns offer a limited frequency response and the cabinets remained relatively large. As amplifiers became more powerful, manufacturers adopted the bass-reflex design, which provides a wider frequency response in a more compact, easy-to-move cabinet. Another design called bandpass incorporates the best of the other configurations mentioned above, where the woofer is mounted in a traditional bass-reflex-design cabinet with a separate compartment in front of the woofer to increase acoustic output while retaining a wider frequency response. This new design allows remarkable output from a relatively small package. (Example: Subwoofers from Yamaha’s new DXS line are bandpass designs.)
7. Make sure to use the high-pass filters on the main speakers. When using subwoofers, this is the way to maximize the main speaker’s ability to produce the full range of the music. A system that is set up this way will play at higher levels with a cleaner sound.
By gaining a better understanding of how subwoofers operate, you will be able to make a more informed choice on your next purchase and provide your audiences with all the bass response they need to feel the music on the dancefloor.
John Schauer is the longtime product manager for MI Professional Audio at Yamaha Corporation of America in Buena Park, Calif.