Loudspeaker World

Understanding Loudspeaker Specifications And What They Can Tell You

Knowing how and why loudspeakers do what they do is the critical step in getting the most from any sound system.

By Kent Morris May 24, 2017

Image courtesy of Tama66/Pixabay

What’s wrong with this scenario?

A clean stream of audio, processed through state-of-the-art digital processing devices and amplified by an advanced power amplifier, is delivered to the audience through a cone of paper pulp inside a wooden box.

The weak link in this chain is the box, more commonly known as a loudspeaker. Final sound quality of any system is wholly dependent on the ability of loudspeakers to reproduce the glorious audio presented to it by the upstream components.

In the past century, commercial loudspeakers have gone through slow, steady advancement in development. In contrast, the electronic portions of systems have undergone fundamental changes in physical attributes and methodology, near the speed of light.

However, just because the transducers (loudspeakers) have not kept pace with their electronic counterparts does not mean all is lost.

Quite the contrary, amazing performance cannot be realized with today’s best designs. Knowing how and why loudspeakers do what they do is the critical step in wringing the most from any sound system.

What’s Inside?

A loudspeaker’s task is to convert the electrical signal of the audio system into acoustic energy that humans perceive as sound. In most instances, the closer this output emulates its input, the better, because a known value of input will remain true on the output (i.e. high fidelity).

It’s also important to understand that sub-standard input sources will always detract from sound quality, regardless of the excellence of any given loudspeaker.

Professional loudspeakers usually contain multiple drivers (components) in a single enclosure. The most common design is referred as “two-way,” with two components teaming up to provide output.

Two-way designs usually consist of a 15-inch or 12-inch diameter cone woofer and a smaller-format (1- to 1.5-inch) compression driver coupled to a horn offering a defined coverage pattern.

A typical two-way loudspeaker, shown as the sum of its parts: compression driver on a horn, crossover, and cone woofer, housed in an enclosure of wood, or, increasingly, poly compounds (click to enlarge)

For woofers, which reproduce the lower frequencies, the enclosure provides a plane of operation, a means of directly radiating output into the surrounding atmosphere.

In contrast, compression drivers, which handle high frequencies, would be practically inaudible if directly sent into a coverage space.

Thus the driver must be mated to a horn, to match the driver’s output with the surrounding atmosphere by unfolding the soundwave at a defined rate and dispersion pattern.

As a result, the efficiency of the horn/driver setup is raised dramatically, with only a few watts of input necessary to deliver room-filling levels.

Inside the loudspeaker enclosure, input signal is divided between the two components by a passive dividing network, commonly called a crossover, which directs the low frequencies to the woofer and the high frequencies to the compression driver.

Conventional loudspeakers work much like a car engine, with the cone action of the drivers akin to the movement of the pistons.

The back-and-forth motion of each is the source of power needed to accomplish the work – turning a drive shaft or propagating sound waves.

Auto engines use gasoline as fuel, while loudspeakers use the electrical output of a power amplifier. In both cases, matching the fuel to the motor is essential to optimizing the performance.

Loudspeakers and power amplifiers have a give and take relationship, with the amplifier pushing against the loudspeaker’s natural state of equilibrium (equal pressure inside and outside of the cabinet) and the loudspeaker pushing back against the amplifier’s varying output.

The ability of an amplifier to control the driver’s excursion is termed its damping factor and is important to overall performance. Optimizing this interface is one of the reasons for the recent surge in powered loudspeaker offerings from many major manufacturers.

Key Specifications

Given the plethora of loudspeaker brands available, finding the best unit for a given application can be akin to the proverbial needle in the haystack.

Narrowing the field is made easier by the tenacity of reputable manufacturers’ adherence to industry standard specifications. These specifications include ratings for frequency response, sensitivity, power handling, and directivity.

Frequency response is a measure of how well a loudspeaker reproduces input signals across the 10 octaves of human hearing.

The engineering obstacles that prevent a single speaker component from achieving a perfect score on the frequency charts start with the physical makeup of sound waves and the limitations imposed by the need to make the loudspeaker enclosure practical in size and weight.

Low-frequency waves can be as long as 56 feet, while highs can be as short as one-half inch. Building a device that will faithfully reproduce these extreme sizes and everything in between is nearly impossible.

Further complicating the design is the need to keep the box as small as possible and aesthetically pleasing.

When a frequency response is stated, it will have associated with it a range-defining number such as “+ or – 3 dB (decibels).” Without the range limiter in the equation, the numbers are meaningless, because any loudspeaker can reproduce almost any frequency at some level (i.e.- 45 dB).

The standard range of +/-3 dB actually grants a relatively wide window of 6 dB, and should be considered the maximum usable variance.

Read the rest of this post


Tagged with:

Subscribe to Live Sound International

Subscribe to Live Sound International magazine. Stay up-to-date, get the latest pro audio news, products and resources each month with Live Sound.