One of the main tasks in choosing a good sound system is the acquisition of a set of speakers. In the end, the loudspeaker is one of the most labor-intensive components in converting an electrical signal into a three-dimensional sound wave.
And this goal must be achieved by maximizing fidelity within the contour condition we all have: cost. The objective of this article is to guide the beginning audiophile in relation to some technical specifications, and to expose the impact of the materials of the components to obtain a sound without colorations and with good handling of power. Once a speaker goes through this small list of desirable characteristics, the ear should be the primary judge in this choice.
Initial Considerations. In general terms, the speakers made by companies solely dedicated to these are superior to speakers manufactured by companies that manufacture the entire audio portfolio (although in rare cases there are exceptions).
The speakers have a combination of transducers of different sizes, according to electronicsencyclopedia. The low frequencies are generated by a cone-shaped transducer (known as a “Woofer”), while the high frequencies are generated by a dome of smaller diameter (known as “Tweeter”). In general, for a given price, there is an inversely proportional relationship between sound quality and number of transducers (or tracks). Thus, a 2-way speaker (1 woofer and 1 tweeter) will probably sound better than a 3-way speaker (2 woofer and 1 tweeter) if both have the same price. However, the general public tends to believe in the perceived value of “more for the same cost”, believing that the larger a speaker and the more ways this has, the better. In short, this is not necessarily so.
Main Specifications: Frequency Response, Maximum Power, Sensitivity and Impedance.
An important point is to assimilate the main specifications. Performed correctly can help to understand some advantages and limitations.
The frequency response. The first specification that is usually mentioned is the so-called “frequency response”, which indicates the relative volume (measured in decibels) with which a speaker reproduces the full frequency range of the audio (between 20 Hz and 20 kHz).
Leaving aside durability issues, the transducer must be rigid for proper reproduction of the sound. For example, in woofer (or cone) type transducers, sound is generated by creating movement from the inside diameter (see figure above). Alternatively an excellent interactive graphics can be seen at the following link:).
If the cone is of a material that is not rigid or very flexible, it will tend to bend at the initial pressure points, which will produce distortions in the generation of the sound wave. In contrast, if the material chosen is rigid but very heavy, the transducer will not be able to move, inertia, quickly enough to generate sound. Thus, researchers have worked for decades to replace traditional materials (formerly, woofers were simple cardboard cones) by others that are rigid and light at the same time. The best manufacturers use proprietary plastic derivatives, such as Kevlar, and the Magnesium Silicate Polymer, which meet the requirements of durability, rigidity and weight for optimal reproduction. Another material used is polypropylene, although the latter is less rigid than Kevlar, which generally handles a lower power level (both Kevlar and Polymer handle 20% more power than polypropylene transducers).
In addition, the tweeter material is very important in the correct reproduction of high frequencies. The current trend in high-end manufacturers is soft materials (derived from plastic or silk), which replace titanium. Which is traditionally used. Silk tweeters and soft materials have a less abrasive and more natural reproduction than those made with Titanium.
The construction materials of the transducers and their impact on sound.
If there is one factor in which the speaker evolved in the last decades is in the choice of materials in the transducers. The great challenge that every designer has is to choose a material that has rigidity and is light at the same time.
The Importance of the Cabinet and its materials.
One of the ironies of making a speaker is that the average consumer perceives less value in their cabinet (in the end, it is considered that it does not “produce” sound). However, it has a huge impact on the final sound by generating vibrations that affect the sound. Therefore, one of the factors in which high-end speakers differ is that their manufacturers have spared no resources to minimize these vibrations.
A frequent question is: why does a speaker need a cabinet? The reason is simple: as shown in the previous figure, the cone of the transducer, which exerts pressure on the air with its movement, actually generates two sound waves: one front and one rear. These waves have reverse air pressures (when one is positive, the other is negative) and if they are mixed they would cancel each other (and therefore there would be no sound). One way to prevent these waves from mixing would be to place a panel, of infinite dimensions, separating the front and rear side of the transducer. This is not possible in practice and the intermediate solution is to place a cabinet “trapping” the back wave and if possible, cancel it with internal attenuation.
However, low frequency sound waves have the ability to deviate from small objects and this is one of the reasons why small speakers have difficulty reproducing basses. For this reason, some engineers have designed “internal paths” (known as waveforms) that cause the back wave to diffuse back and rebound to have characteristics similar to the front wave, thereby reinforcing the sound. So small speakers can generate sound waves whose length is very large (for example, at 50Hz the sound has a wavelength of almost 7 meters, which is reproduced by speakers whose dimensions are less than 30 centimeters!).
Finally, internal resonances must be minimized by choosing special materials or by using non-parallel surfaces.
Conclusions. While the final judge in choosing a speaker should be the ear, these recommendations based on physics and engineering principles can be used as a starting point, or first filter, in that choice.