Mr. Speaker

Car Speaker Special Features

Mr Speaker

Speaker design is incredibly complex. Considering the time speakers have been allowing us to listen to electricity, it is a surprise that technologists continue to find so much that can be improved!

The internal workings of a speaker can be boiled down to a linear motor attached to a cardboard cone, all held together by a chassis. However, oversimplification is the root of misunderstanding, so we have to go a bit further to avoid giving people the wrong impression.

Let’s consider the linear motor bit first. This, in essence, is what drives the speaker cone. It converts electrical energy (the signal) into movement by passing it through a coil of wire placed within a magnetic field. The signal is presented to the coil as an alternating voltage that swings from positive to negative. Typically, when the signal turns positive, the effect moves the coil forward, while a negative swing moves it backwards. The speed of the signal swing dictates the frequency reproduced, while the amplitude of the swing dictates the volume level. Attach the moving coil to a cone of lightweight yet rigid material, and the resulting movement will move air, which we hear.

As with all products in an audio system, the quality of components and precision of the engineering is vital to the final quality of the sound. When we get to specialist level, seemingly small things make a big difference.

Each speaker’s performance can be improved by using more windings on the voice coil and bigger magnets. Some magnetic materials are more powerful than others, so size is not always the only indication of quality; however, generally, bigger magnets make better speakers.

When we get to speaker cones, we encounter many parameters that can be changed to improve performance. The purpose of this part of a speaker is to move air, so a large cone area is desirable. A lightweight cone material will make the speaker perform with more precision and agility, which needs to be considered. In a car, we are currently using quite a lot of power to provide control to the speaker’s movement. There is a danger when moving a cone against air at a great velocity that the cone could change shape or distort. This is not as desirable, so strength or rigidity is another important parameter.

There is a vehicle-specific need to provide speakers with a wide dispersion characteristic. This is due to the appalling speaker positions, which often have speakers firing at our knees. Wide dispersion gives at least some sound a chance of finding the listener’s ears.

We have spoken about motor and cone, but these both have to be housed in or supported by some kind of chassis. The chassis, in many respects, is as sonically crucial as the rest of the components we have looked at. The critical components of the chassis are the basket, spider and speaker surround. The energy from a speaker can be adversely affected by resonances. Everything has a resonant frequency, and some materials ring like a bell. This is undesirable as the resonance can rob energy from the air coming from the front of the cone. An entry-level speaker such as may be found as part of a car’s original system will probably use a pressed tin basket. A well-designed speaker will use a dense plastic or die-cast metal basket, as these will exhibit far less resonance. It is also essential that the basket is strong. The basket is often designed to move air emanating from the cone’s rear efficiently. In some sophisticated designs, this will be used to help with coil cooling along with vented base plates and other technologies.

Speaker surrounds have been subject to many reinterpretations over the years. It is safe to say that, although there are fundamentally different designs, they are all used depending on the desired result. A car speaker is often required to move further than in other applications, and this can be helped with a generous foam surround or even a “concertina” surround, as used in some Audison products.

The spider connects the skinny end of the cone to the chassis. It is designed to be quite rigid. Ideally, the speaker should rest at mechanical zero after each move to or fro. This improves accuracy and “tightness” and helps prevent distortion.

There is much more fine detail that we could describe, but this should offer the reader a decent idea of the differences between an expensive and a less expensive speaker.

It is essential always to try to get a demonstration of several speakers to help you decide on the sonic characteristics that you prefer.