Velodyne SPL-800 Build Quality and Design
Subwoofers have been conventionally known for their deep bass extension and wow factor, essential for today's home theater systems, usually requiring a big heavy box loaded with large woofers to achieve ultimate impact and performance. Until my experience with the Velodyne SPL-800, I was happy with this stereotype about subwoofers as until that point, I haven't heard a small subwoofer that could do both music and movies justice. Enter the SPL-800. Occupying less than one cubic foot, this little giant weighed in more than many other subwoofers over twice its size. It wasn't until I pulled the woofer out of the box that I discovered why. The motor structure (12.7lbs magnet) of the single 8" woofer of the SPL-800 was nearly as large as the woofer basket itself. It was obvious by the powerful motor structure, large voice coil (2 ½"), and, heavy duty butyl rubber surround and extremely stiff cone material, that this subwoofer had one hell of an excursion ability that many 10" and 12" lesser designed woofers could only dream about. I was very impressed with the look and feel of the SPL-800. It had an unusually good build quality that I felt was not typical in most subwoofers of this price range. I found the little blue light on top of the cabinet both intoxicating and useful as it served me well as a nightlight. Moving on to the amplifier that powered this monstrous little woofer, it was apparent that Velodyne was after a powerful, yet efficient design, thus their reasoning behind choosing a 600 watt Class D amplifier.
Class D Amplifiers Explained
A class-D amplifier has an efficiency degree of normally more than 90%. That means that more than 90% of the power which is delivered into the amp from the power supply is transferred to the load, and less than 10% is transformed into heat as opposed to conventional Class AB designs that rarely achieve efficiencies beyond 60%. This means that cost and size may be reduced for needed cooling (less heatsink area), power supply and output transistors. Class D amplifiers convert the audio signal into high-frequency pulses that vary in width with the audio signal's amplitude. The varying-width pulses switch the power-output transistors at a fixed frequency.
A lowpass filter converts the pulses back into an amplified audio signal that drives the subwoofer. The added efficiency of Class D amplifiers usually comes at the expense of linearity and distortion. However, for low frequency applications, such as powering subwoofers, this is much less problematic, and thus the added efficiency, cost and size reduction versus the increased distortion and compromise in linearity represents a good design trade off.
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