FRONT OF HOUSE
LOUDSPEAKERS FOR FUN AND PROFIT | Kent Morris
The only sound system component heard directly is the loudspeaker . It is the final link in the audio chain as well as its weakest link . For all the advancements in digital technology applied to consoles , power amplifiers and even microphones , the loudspeaker remains planted in decades old technology with only incremental improvements to showcase . However , despite the limitations inherent in output transduction , speakers can be highly effective converters when used correctly and creatively .
First , keep in mind the job of a loudspeaker is to convert incoming varying voltage into mechanical movement of drivers which then propagate waves into an environment we perceive as sound . Most loudspeakers are about four-percent efficient , meaning they convert one-hundred Watts of input power into four Watts of acoustic output . The other ninety-six Watts is simply converted to heat . In essence , a loudspeaker is a hair dryer with sound . As a result , heat dissipation factors considerably into loudspeaker design and maximizing the actual available power becomes of paramount importance . To that end , a loudspeaker ’ s efficiency , known as its sensitivity , determines how much output is given for a known input . In most cases , one Watt applied to the speaker input terminals will yield somewhere between 85- and 100- dB SPL on axis one meter from the front of the cabinet . Since a doubling of input power is required to achieve a 3dB increase in output , a speaker with sensitivity of 95 dB-SPL will only need half the power of a similar cabinet rated at 92 dB-SPL to deliver the same level .
The other end of the power spectrum is maximum rated output SPL and is as loud as the cabinet will go without undue distortion . It is a log application but can be thought of taking the highest acceptable input power and configuring that into a number based on the sensitivity rating . Thus , a 600-Watt input rating on a cabinet with a sensitivity of 98 dB- SPL will yield a maximum SPL of 126 dB-SPL at one meter , an acoustic gain of 28 dB-SPL . By knowing these two numbers , sensitivity , and maximum output , determination can be made as to the suitability of the speaker for a given environment .
Cabinet construction plays a significant role in loudspeaker performance , for it is the cabinet material that determines the rigidity and tone of the box . Today , plastic powered speakers dominate the market with their low price and simplicity as drawing cards . While a $ 399 speaker is not capable of providing sound for an outdoor concert , it is usable as a background speaker at a corporate event . Plastic , and its composite cousin , are inexpensive to use as a material and can be easily molded , On the downside , plastic is not rigid , is seldom used in truly flyable situations and degrades in sunlight . Wood , on the other hand , is rigid , flyable when combined with steel and holds up well in harsh environments when coated properly . However , wood is heavier and more expensive than plastic . The choice , as always , comes down to application and budget .
What is inside the box also matters greatly , for a solid cabinet with poor components will be a disappointment when heard . Usually , the incoming signal is divided between lows and highs with the lows sent to a cone woofer and
the highs to a compression driver mounted to a horn . The dividing network can be passively installed inside the cabinet or be an external device , as in an active crossover , often referred to as a “ DriveRack ” DSP device . The woofer is noted by its diameter in inches with 12 ” and 15 ” being most popular while the high driver is commonly 1 ” or 2 ” exit into the horn . For serious applications , the woofer should be a cast frame type , meaning the frame around the cone has been cast and is rigid while the cheaper pressed frame type is reserved for use only in light-duty situations . In a similar vein , the high-frequency driver ’ s diaphragm should be made from aluminum or titanium and not from Mylar or plastic . The horn will need to be designed to mate with the driver and woofer in a complementary manner to reproduce all the energy from roughly 100Hz to 15KHz .
Loudspeakers , though seemingly left behind in the technology race , are truly the most important aspect of any sound system and their selection and use should be considered thoroughly .
Kent Morris Kent is a 42-year veteran of the AVL arena driven by passion for excellence tempered by the knowledge digital is a temporary state .