Building an Enclosure for MM Series
Who Is Going To Build Your Subwoofer Enclosure?
Since the subwoofer enclosure is so critical to getting the best performance from your Polk/MOMO subs, you should ask yourself the following questions:
1.Do I really enjoy working with my hands?
2.Do I have good woodworking and mechanical skills?
3.Do I have, or have access to, woodworking and electrical tools?
4.Do I have a solid understanding about musical reproduction in an automobile?
•If you answered NO to any of the above questions, we recommend you choose one of these two possible alter- natives: First, there are
•If you answered YES to all of the above, let’s review some basics before you begin.
Building Your Own Enclosure
The Polk/MOMO subwoofers have been optimized to give you flat bass response in small sealed enclosures. Some lis- teners may want response other than “flat,” or may want to
Sealed Acoustic Suspension Enclosures
As the Polk/MOMO subwoofers are optimized for acoustic suspension enclosures, we suggest you use this type of design. The acoustic suspension cabinet is a sealed airtight box, and is the easiest box to build. It also is a very pre- dictable enclosure with easily calculated parameters, and it has a smooth natural sound. Properly built acoustic suspen- sion cabinets have a flat frequency response that begins rolling off at 12 dB per octave at the frequencies below its cabinet resonance. This works very well inside a car because of a natural phenomenon called “room gain” that gives you roughly a 12 dB per octave increase in bass frequencies. You can roughly calculate at what frequency this gain begins by using the equation F= 565/L. F is the frequency at which bass gain begins, and L is the longest dimension of your “room.”
If, for example, you measured the longest dimension of your car as 5.65 ft., the room gain begins at 565/5.65 or 100 Hz. If your goal was perfectly flat frequency response you would design your cabinet for this particular car to have a reso- nance frequency of 100 Hz. Since most people want more bass than a flat frequency response yields, tuning the cabi- net at a lower frequency, say 50 Hz, would give you a gain of 12 dB per octave between 100 and 50 Hz and flat resp- onse from 50 Hz down. The larger the cabinet, the lower the resonant frequency, and the lower the efficiency. Two identical systems will sound very different in a Honda vs.
a Cadillac. The bigger the car the lower the frequency at which room gain begins.
Tools You Will Need To Build Your Enclosure
If you have decided to build your own enclosure for your Polk/MOMO subwoofers, here is a list of the tools you should have available to you.
•Calculator
•Assorted Drill bits
•Screwdriver bit for drill or manual screwdriver
•Circular saw
•Tape measure
•
•Jigsaw
6 P O L K / M O M O : C H A M P I O N S H I P P E R F O R M A N C E
