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The Energetic series

 

 

Summary

 

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Introduction

The ULTRASOUND brand characterizes only high quality loudspeaker systems that originate from the research and the experience of professionals in the acoustics field. All ULTRASOUND products make use of transducers designed and manufactured in our factory. They are the result of a long study and research that involve two key elements: psychoacoustics and energetics. Psychoacoustics is the discipline that studies the interpretation by the brain of the sound stimuli that reach the ears. With the term energetics we mean the study of the phenomena related to energy transformation; both these aspects are fundamental to understanding what happens during the reproduction of music in semi-reverberant rooms.

At present, ULTRASOUND offers two lines of loudspeaker: the ENERGETIC series and the MULTIPOLE series.

 

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Design philosophy

A sound can be defined as a vibration propagating in an elastic medium.

In dual mode, we can speak of sound waves, i.e. of a phenomenon of energy transport: in fact, we know that in a wave the medium particles don't move, differently from what was erroneously believed. Rather, it is the energy found in a certain point of the transmitting medium that at a given moment is transferred to the adjacent zone. Many studies have been carried out on waves propagation and some aspects (diffusion, diffraction, interference, standing waves, etc.) are well known today; however, we know very little about the mechanical and acoustical phenomena related to the production and the dissipation of acoustic energy (especially in semi-reverberant rooms like those found in our homes).

In particular, in designing a loudspeaker system - that not only transforms an electrical signal into a pressure wave, but also converts one form of energy (electrical) into another (acoustical) - nothing is done to ensure that the energetic transformation takes place in the right way. The problem becomes more serious when we consider that the efficiency of this operation is usually much less than 1% (with the usual references, a 1% efficiency means 92 dB/W on 2p str.), while in certain cases (isodynamic or electrostatic systems) it doesn't reach 0.1% or even 0.01% (70 dB/W)!

Since the conversion is so bad (more than 99% of the energy in turned in something undesirable), it is obvious that this troubled process should be controlled as strictly as possible; it is therefore necessary to take every precaution in order to transfer the information enclosed in input signal as integrally as possible to the output.

In order to achieve this, the first step is to realise that the transducer is not alone in the conversion process, as the entire system plays an important part: therefore, when we analyse the energy transfer, we must also consider the cabinet and the crossover. The best solution is to have no crossover and no box. Since, both these elements are somehow indispensable and cannot be suppressed, it is possible and useful to reduce their influence on the final result. This cannot be done by making use of low-quality transducers and designing complex crossovers; these networks seem to make systems very linear, but in reality they are disastrous from the energetic and temporal point of view. On the contrary, it is necessary to use transducers specifically designed to obtain intrinsically linear systems: this way we can reach a good behaviour both in frequency and time domains. If a transducer is energetically mediocre (heavy moving mass, small motor, etc. - that is, low efficiency) the result of the energy conversion will be mediocre as well and most musical information will be lost, independently from what we can do with sophisticated filtering. If we want to design a system able to reproduce all the musical nuances, we must do this starting with an energetically correct transducer, i.e. a high efficiency transducer.

Then we have to design an energetically correct box in order not to spoil the work so far achieved; at this stage the following considerations shouls be stressed:

the acoustic enclosure changes some of the loudspeaker's electromechanical parameters. Some of these are favourably changed, allowing a better use of the speaker, others on the contrary get worse. From a mechanical-acoustical point of view, the fundamental parameters are stiffness, mass and damping. Introducing the box, the mass is increased with respect to the speaker alone, while damping and stiffness are reduced: this is a worse situation from the dynamic point of view (the most important aspect in the musical field);
   
at low frequency, the dominant factor is stiffness;
   
at middle frequency, it's important to control damping;
   
at high frequency, the dominant factor is mass.

Since in musical signals the energy decreases with frequency increasing, the first conclusion that we can draw is that in an acoustical box stiffness is very important.

Keeping in mind that the maximum ear sensitivity is at middle frequencies, we shall look with great care to damping.

Mass, on the contrary, shall be limited as much as possible, for the following reasons: first, a high mass box resonates at low frequencies, i.e. in the area with the highest energy content; second, with high mass a lot of energy is stored in the box and subsequently released with delay respect to the musical signal.

Summarising these simple considerations, we can say that a box should have both mechanical and acoustical characteristics that vary with frequency; in reality, an optimum result could be achieved only by using an adequate box for every speaker. For practical purposes, however, it's possible to obtain an energetically correct box satisfying the following requests:

low mass;
   
high stiffness;
   
high damping.

The first two characteristics smow that the material used to build a box for high fidelity purposes (i.e. intended to reproduce music, not laboratory steady signal) must have a stiffness/mass ratio as high as possible.

Materials utilised in most cases (medium density, etc.) have on the contrary a high mass, low stiffness and poor damping; these material should be utilised only in cheap systems (by virtue of their low cost).

These considerations are well known from long time by the professionals (we could quote many works, like that of Tappan presented at the Convention of the Audio Engineering Society in 1961), and at the same time neglected by most manufacturers of so-called Hi-Fi and High-End loudspeaker systems.

 

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The ENERGETIC series

These loudspeaker systems are designed extending the designing process to the whole system rather than using commercial transducers and mounting them in an ordinary box. This "integrated design" means developing the right transducers to achieve the desired performances, modelling their transfer function so that they can work together without electric filtering, and developing a box that provides the necessary acoustic loading at low frequencies with the lowest alteration in dynamic transients. To obtain that, we have investigated the following innovative aspects:

we have carried out a careful analysis of moving masses and forces (a typical woofer has a moving mass of about ten grams with accelerations of about ten g's [the acceleration of gravity, 9.8 m/s2], while a tweeter has a moving mass of several hundred milligrams with accelerations of thousands of g's). This is particularly important because it is necessary to balance the emissions of each driver to avoid discontinuity with the frequency; on the other hand, we must take into account that a woofer can produce peak forces of 20 - 30 kg;
   
we have run an exhaustive investigation on material characteristics, both those of speakers and those utilised in acoustic enclosures, with special care to the time-domain behaviour (storage and release of the acoustic energy: this is of fundamental importance in music reproduction);
   
we have studied the enclosure's stress distribution, with respect to both the internal pressure and to speaker motion;
   
we have developed transducers optimised from the dynamic point of view (i.e. with very light moving parts, high accelerations, high damping); this means that these transducers are highly efficient.

The results of this long work suggested the use of solid walnut wood for the the enclosure; solid wood has a very favourable stiffness/mass ratio if compared with other suitable material (it is a matter of inserting the boxes in domestic rooms) and good damping. This produces enclosures with good behaviour in time domain, provided that the panels constituting the box are designed to take into account their own resonances, the internal pressure and the inertia forces; therefore, we used a computer to build a mathematical model (through electromechanical analogies), to analyse the stresses (through the finite-element technique) and to verify the vibration modes of each panel (with accelerometer and spectrum analyser).

The results have led to vented boxes without sound-absorbent material in the internal; this normally reduces standing waves, but it also greatly reduces the efficiency of the vented box. With a correctly designed enclosure we can fight the standing waves simply by avoiding their formation rather than by trying to reduce their amplitude.

The combination of high efficiency and temporal optimised transducers with rigid and light enclosures, together with the virtual elimination of crossover (only one component is needed for a two-way system) provide a much better energy conversion than more complex systems. This also means that these systems sound well even if driven with little power, with all the ensuing advantages.

All models of ENERGETIC series are available in two versions: "BASE" and "LIGHT".

LIGHT versions use transducers with moving mass 30% lower than BASE versions; so that all the dynamic parameters are improved: velocity, definition and articulation, sensitivity.

 

Ultrasound
Vicolo T. Aspetti, 18
35100 Padova (ITALY)
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Via Bachelet, 20
Busa di Vigonza (PD)
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