The Black Box

An innovative amplifier for the classical guitar on the stage

by Vincenzo Landi

The BlackBox is an amplifier for classical or acoustic guitar designed to amplify the sound of the instrument just enough to help the performer to reproduce all the nuances of the piece when he is playing in unfavorable conditions, for instance outdoors, or in a large and crowded hall, and when he plays together with the orchestra or in ensemble.
Furthermore it has two main pros: it weighs few and its overall dimensions are very limited, so that the box is quite invisible; consequently when it is correctly used it becomes very difficult for public to be aware that the sound of the guitar is amplified.

The idea of this project came to my mind in summertime 1992, when the Maestro Michelangelo Severi asked me, more joking than speaking seriously, if I might make an amplifier that could be kept under the chair of the guitarist, in order to prevent any disturbance to the performer during the execution.
I answered that something could be done. The outcome was the system that was illustrated on the pages of the Italian quarterly Il "Fronimo" no. 84, July 1993. The device was not made to be put under a chair but on one side of it. It was built in fact as two separate boxes: the speaker and the amplifier. The former was contained in a cube of 15" of edge equipped with a professional 12" driver; the latter into a standard box with the same width as the speaker and placed above it. That contained all the necessary electronics, namely the microphone preamplifier, the line one, the power amplifier and the supply section.
The amplifier has only one input for a microphone that must be positioned in front of the performer, close to the guitar, one output to the loudspeaker, the power switch and the master volume control. The central project "philosophy" was in fact that the system had to pick up as more possible of the sound emitted from the guitar, amplify a little but carefully and return the listener a sonorous feeling virtually indistinguishable from that given from the acoustic guitar, without modifying nothing if not the power of the sound itself.

The amplifier was therefore the simplest and linear possible, deprived of all the accessory circuits that usually characterize audio equipment, relying the success of its operation exclusively on the quality of the realization; that came to the overall advantage of the reliability, besides the other goods.
The conceived system had some pros and cons. It was strong and reliable, easy to use and it had a quite natural sound. It allowed, after having put it in the neighbor of the guitarist, to behave so that the public in the concert hall perceive in fact only a sound source, the sum of emissions of the instrument and of the loudspeaker; without echoes, delays or any kind of timber alterations.

For the cons it was rather delicate to position it because the microphone and loudspeaker were close between each other, making easy to bait the so-called "Larsen effect," a characteristic and very annoying whistle that is produced when microphone and loudspeaker are put one in front of the other and the volume is get up high, too.
In addition also the weight was not light, being of around seventeen kilos. The system was not therefore exactly portable, but rather transportable.

It is worth however to remember that at that time nothing else did exist of good (or at least: to my knowledge: I remember that the Maestro Ernesto Bitetti, after the reading of my article on Il "Fronimo" wrote me from the United States, telling that he had a compact amplifier, of the weight of twenty kilos, buildt at the Indiana State University !) and that however it has always been working perfectly, both outdoor and indoor. It was used with satisfaction by many guitarists, among which Michelangelo Severi, Emanuele Segre and Stefano Cardi.

The amplification of the classical guitar was not a real new, of course: many different guitarists had before then electrified their own live performance and they still do it; often in a way, to my advice, really unsatisfactory.
They usually employ to this purpose the P.A. amplification equipment of the theater in which they perform; this solution is comfortable for the musician because it avoids him the expense of the acquisition of the amplifier and the undeniable bother of his transport, but it almost never furnishes I to the listen to a correct sound results. In fact the P.A. equipments are born for a completely different task, and they often have a poor sound and affected by leading noise, resulting absolutely unsuitables for the amplification of a delicate instrument like the guitar. Besides that, the loudspeakers are always positioned at the two sides of the stage, in order to "cover" all the public.
In such way it often happens that the people placed at the extreme right or left perceives only the emission of the box nearer to him, experiencing a sparely natural sound due to the fact that he sees the sound source (the guitarist) at the center of the stage but he listens the music originate from another direction.

A clarely better feeling is for whoever is placed in the first central seats of the stalls, because they from those places can enjoy the real sound of the guitar very well; while in central but behind positions the emission of both the loudspeakers prevail on that of the instrument, giving the listener the feeling that is playing a ten-meters-guitar.

If today the things are changing, to the point that happens not rarely of being present to concerts of guitar in which we one uses of a correct amplification, some worth goes surely attributed to that "glorious" equipment presented on Il "Fronimo" and to its successor.

In 1994 I have buildt a new version of the amplifier, identical to the first in the principles but deeply different in the substance.

The new amplifier is a right-angled box of the frontal dimensions of cm 24x26 and width 30 cm, made of multilayer wood painted with black varnishes (from which bearing its name) containing inside all the electronics and a high efficiency 8" loudspeaker; the weight goes from 6 to 9 kilograms according to the maximum output power that the amplifier has to furnish, and a folding handle set on the top easily allows its carriage.

The Black Box has allowed to satisfy the initial demand that was to the base of all the plan: a power amplifier of so much reduced dimensions, to be put under the chair of the performer.

I must tell, to be true, that I initially gave few credit to this particular, considering him the mincing ways of the musicians, but I definitely had to reconsider in front of the evidence of the facts.

The new amplifier has three decisive advantages on the old one: first of all its weigh is minor in the range from half to two third less and its overall dimensions are a fifth, therefore it can be really easily transported (by plane it can be considered like hand luggage); in second place it can be hidden under the chair allowing to the musician to behave in the most natural way, and for the public is almost impossible to see it.

This is very important because if the public is not distracted from the "electronic objects" it can better enjoy the music. And then, knowing that the amplification is there, it works well and it is not warned, it is very gratifying for the designer: it tells that he hit his goal, and that the initial idea was indeed good: to help the guitarist having more output power, also giving to the public the impression to listen to a purely acoustic event.

Finally there is a third advantage: the new employed loudspeaker, having smaller dimensions than the predecessor, it reduces greatly the risk the so much feared Larsen effect; it achieves the fact of it, only in paradoxical appearance, that this amplifier, also having smaller electric power than of the precedent, it is able in fact to provide an acoustic power output equal or straight better because, other conditions being the same, it allows to keep higher, when needed, the sound volume.

The Black Box, like its predecessor, it is a reliable equipment that has given good proof of itself always in all situations. It was particularly been employed since its debut by Maestro Stefano Cardi, who can by considered its official beta-tester. Among his many performances I like to remember some particularly meaningful: in the June 1995 at the Festival of contemporary music of the biennial exhibition of Venice, Teatro "La Fenice"; April 1th 1996 to the Academy of France at Villa Medici, in Rome; in the June 1996 to the Roman Aquarius for "Progetto Musica '96" and in February 97 to the national Italian radio on RAI Radio Tre.

In these and in all other occasions the small amplifier has proven indeed easy to use, comfortable to transport, discreet in appearance and well-balanced in sound. Concerning this, please let me remember an anecdote.

The first version of the Black Box weighed nine kilograms. In occasion of the above mentioned concert in Venice, Maestro Cardi kindly asked my presence as sound-engineer, being the so much prestigious event as technically unknown: a concert for harpsichord, harp and guitar, all amplified, orchestra and an ensemble of instruments outstage, in a first absolute performance.

The amplifier behaved perfectly and everything went for the best; however at the end of the evening I had to carry the amplifier from La Fenice to the railway station. By foot, of course.

Nobody pays attention to the fact that the Canal Grande has crossed by only three bridges: Venetians are used to this, and the tourists don't mind it, while they are walking for the "calli" of the most beautiful city in the world.

At that time I forgot that after nine o'clock p.m. the ferry-gondolas, as characteristics as useful, stop the service, so Maestro Cardi and I had to leave the short cut by now useless, returning on our footsteps and reaching the railway station making a broad turn and spending for the Ponte di Rialto.

You must consider that 9 kilos for an amplifier of such building are indeed few and that the Black Box was, with all probability, then unique in the world for quality and performances; aniway I can assure you that carry it was a hard work.

Venice is naturally an extreme case, but I promised to Maestro Cardi that if he would have still played at La Fenice I would have brought a lighter equipment.

I maintained my promise making a new amplifier in very few time, less powerful but able to assure the same quality and good sounding of the other one, but weighing the 30% in less.

La Fenice, unfortunately, was not any more.

First of all we have to choose the microphone, among many types existing, some of wich specifically thought for the guitar. We do two preliminary considerations: 1) the sound that reaches the listener raise both from the vibrations of the harmonic table and the air; 2) the reproduction the amplifier can offer could be considered hi-fi only if it is able to give birth to sound as close as possible to the original one.

That means that we need to pick up sound of the guitar with an external microphone, able to gather, like the human ear, both types of vibrations. Instead we must exclude the contact microphones, that are settled down directly on the table or on the bridge: they are undoubtedly very comfortable, and they allow to amplify without risk of Larsen Effect up to high levels; unfortunately they amplify only the vibrations of the table, returning a very unnatural sound. They suit very well in jazz and rock music and in all the applications in which the sound will suffer effects and treatments of various types; they don't suit in our case.

The austrian company AKG shows in its catalogue a couple of microphones for guitar wich allow both compact dimensions and good quality; one settles down on the guitar table and the other on the hole, and is used with a suited preamplifier: their action results complementary, and it should assure a good result. I wrote "it should" because I never did used them.

Concerneing external microphones we say that they can be divided in two great categories: dynamic and condenser microphones. The firsts are strong, easy to use and they don't require cares nor feeding: just stick to the amplifier and start working. Condenser microphones are more expensive and require a supply voltage, that could be furnished from a battery or directly through the cable of connection (the so-called "Phantom" supply); besides their output signal is so weak to require absolutely a special preamplifier. On the other hand their fidelity is often excellent. In case one decides to use them, the preamplifier can be suited inside the Black Box, as already stated, too. One microphone is enough, because having the amplifier an only loudspeaker, its operation is evidently monophonic, and such must also be the recording.

Among the commercial models we need to choose a directive one, namely able to privilege the sounds deriving in front as regards those from other directions, for avoid the resumption of near instruments, noises and other sound sources; our preference will go the cardioide and ipercardioide models. These latter has an interesting property: if used from very near they emphasize the lower frequencies.

The microphone must be positioned close to the guitar, regulating distance and angling according to the experience and the type of desired sound. Small dimensions and light weight are useful, in order to assure poor visibility and allow to fix it on an adequate support, i.e. a music stand. The traditional poles work well but are inadvisable because they are cumbersome and to much visibles. Very proper,instead, the flexible supports, also said "goose-neck", provided that of sufficient length.

I can tell you, for instance, that I use a Shoeps Colette with cardioide capsule, a professional recording microphone;its quality is State-of-the-Art, and its price, unfortunately, too. A less expensive microphone but also providing good results is the model AKG 747 comb, a light and very thin ipercardioide that can be furnished with two goose-necks of different lenghts and joinables when needed, and a folding tripod.

Whatever model of condenser model you choose, you must be shure that the amplifier will be able to provide it with the correct Phantom supply voltage. In other words: before spending your money make sure that microphone and amplifier are compatible.

About the amplifier, there is little to say. It has three cascading stages; the first is the microphone preamplifier, and it is long far the most delicate because it must amplify much, say 30 dB, and at the same time be noiseless, two requisites that are difficulty to reach at one time. in order to reduce weight and overall dimensions it is constructed by means of integrated circuits, and the same is true for the second stage too, namely the line amplifier. The master volume controlis is usually set between these two.

Finally we have the power amplifier; it must be little bulky, light, it can work very hard for a long time heating little, and its sound quality is no less then hi-fi.

I had to put a particular care in selecting the loudspeaker among the models that can guarantee a high sensitivity, compact dimensions and good behaviour in power handing. The box will be designed considering its electro-acoustics parameters.

In conclusion I can say that this amplifier meets all the goals I had established in advance and that it easily satisy the most demanding on-stage applications.

By the way: it also works well with cellos, violas, violins and so on.

How much is the cost of a complete system? Certainly less then a fair concert guitar.