Full range loudspeaker drivers

Back to the early years of sound reproduction, we can see that single drivers were the rule. Only when lots of power was needed, several drivers were used, all of them performing the same job.

In the 50's, with the birth of LPs and FM radio, the frequencies extended to higher values, making necessary to refine the technology.

The single driver technology for reproducing the entire sound spectrum was there, but it was costly and hard to find.

The compromising solution arrived with the introduction of a small loudspeaker called “tweeter” to cope with high frequencies.

So the two-way loudspeaker was born. With the years, boxes with three, four, five and more drivers were common.

This solution far from being ideal, carries several problems on its own:

•  Need of passive crossovers. This element introduces several electronics devices in the signal path, degrading it and making it lose some precious power dissipated in the form of heat.

•  Lack of coherence in the emitting radiators, due to the different placement of each driver. This effect translates into a vague imaging of the soundstage.

•  Phase shift on each driver. The presence of the crossover, with its capacitors and inductors, leads to the fact that each driver receives the same signal at different times. A fine receiver, like the human ear, “feels” the difference as a lesser quality sound.

Several designs of loudspeakers plagued the market, being the bass reflex and the closed box the more extended.

What happened with the full range driver over the years?

It remained in niche markets, being manufactured by few industries in the world. Japan was where these loudspeakers were most investigated and where more adepts were found. Mr. Tesou Nagaoka became the guru of single driver enclosures design.

Horns

The history of the horn loudspeaker goes back to the beginning of the recorded music reproduction.

At that time the need for speakers with very high efficiency was imposed by the lack of plentiful power in the amplification stages.

Acoustic enclosures should be constructed like a musical instrument. The sound of the loudspeaker driver must be amplified, the same way as the body and the open lid of a concert piano amplifies the sound of a vibrating chord.

In the past, engineers did a great job developing the theory and then building the speakers and acoustic enclosures of great performance. Some of these developments are milestones in the world of sound, like Altec Lansing's horns , conceived in the 40's are regarded as references until nowadays.

After the invention of the transistor, lots of power was available at low cost and minimal space, so once the restriction of power was over, the industry focused in building cheaper speakers, multiway acoustic enclosures, forgetting the good old times.

How the sound is produced. Some technical words.

The first step is to transform an electric current into movement of the cone. This is performed by the driver's motor assembly: a coil inside a magnetic field. The coil is firmly attached to the paper cone. Cones of other materials are common today, as aluminium, Kevlar® and also wood.

The cone reproduces the sound signal with its movement. The second step is to transform the cone's movement into air movement or sound waves.

This last step is the hardest for the loudspeaker. Why?

Let's put an analogy here. Imagine you want to make big waves in water in a big pool only with your hands. You may feel that the effort you put in trying to move the water is far more than the result obtained. That is because the water around your hands behaves as a soft fluid. So, much of the power you put into the water pool dissipates in heat in your muscles.

The very same happens in a loudspeaker, being the cone your hands and the air around the water in the analogy.

Lots of power delivered to the loudspeaker dissipates as heat in the driver's coil.

Now let's try to move water that is confined inside a pipe or tube. Push the water at the pipe end with a rod and it will flow in the opposite end. Here the energy is transmitted to the water in a more efficient way. This is because the water behaves as a hard fluid, uncompressible fluid in engineer's terms. This property is vastly used in hydraulic systems.

If we put a loudspeaker driver inside a small chamber, the air contained behaves more like an uncompressible fluid than in open air, so the cone can move the air to produce sound waves in a much efficient way.

Now we need to amplify these tiny sound waves for them to be listenable. This is performed by the horn portion of the loudspeaker. In the horn, the sound wave travels from the small throat to the other end, the mouth, in a channel that increases its cross section along the path.

The size and shape of this horn is subject of long studies, experimenting and listening sessions. By the use of computational calculation, this task is made possible in a way unthinkable in the 50's.

The complexity in design and construction leads to high costs in manufacturing, which make them unattractive to mass production.

Pastoral Audio approach

Pastoral Audio adheres to this tendency with its two models in the Timbó line of loudspeakers:

•  Timbó Original
•  Grand Timbó.

In them, we designed each of the enclosures using computer aided calculations and are built to very strict tolerances.

The results are loudspeakers of outrageous performance far apart from all the sound known in the market

Quotes:

1 - “ As compared to conventional dynamic or electrostatic loudspeakers, horns offer a dramatic increase in dynamic capability, image size, and presence. Harmonic distortion drops to a quarter of the value found in audiophile direct radiator systems”.... “In contrast, most direct radiators severely compress dynamic and reduce image size to the proportions of a symphony on a table-top. These are both severe distortions for which there are no measurements. More importantly, these are distortions which reduce the fun and excitement of music ”.