NSC15 Subwoofer Design and Build Study

Natural Selection Compact 15” Subwoofer 1,000 Watts RMS, 4” Voice Coil, 8 Ohms


I remember coming across the webpage of a speaker aficionado’s personal mission, to expose the frequency fraud of a high end manufacturer’s Acoustimass home theater system. He proved that the subwoofer in the system wouldn’t produce frequencies below 40Hz. That was definitely not low enough for home theater, but the system still sounded loud, even with its small 6″ woofers, and compact enclosure.

The NSC15 started with the concept of a small, but loud system. To maximize the loudness from the sub amp’s power, it would be high-passed at 40 Hz. A Dayton Audio 15″ woofer, with the above specs, was selected. There would be two NSC15 wired parallel to an amp that provides 2,000 Watts in bridged mono, to 4 Ohms.


• A vented enclosure was chosen to maximize loudness.
• The vent needs to be tuned at a certain frequency, and the lower that frequency, the bigger the enclosure needs to be.
• The lower the frequency of a sound, the more energy is required to reproduce it from an amplifier. The human ear’s lowest audible frequency is 30 Hz.
• A relatively high frequency of 37 Hz was chosen to keep the enclosure smaller, not surpass the mechanical limits of the chosen woofer, and put more of the amplifier’s energy into loudness.
• Freeware WinISD was used to calculate the volume, and port dimensions, based on the Dayton woofer’s specs.

Calculating the required volume of the enclosure, 3.16 ft3, based on the tuning frequency of the port, 37 Hz. Then
calculating the dimensions of the vent, and its distortion.


The above 3d model was made to visualize the enclosure that would satisfy the calculated volume, have the correct vent dimensions, and be compact. For speaker design and building expertise, I turned to Shaun of Chico, CA’s Get Down Sound. He made sure to add bracing, and utilized his experience to make the design a reality.