1.2 OUR BASIC PREMISE
The main goal of conventional technology is the elimination of resonances by heavy damping and flattening of the frequency curve by powerful crossover filtering. This pays surprisingly little regard for the sound itself. Unfortunately, no difference is made between undesirable and desirable resonances.
The basic acoustic principle remains: Without resonances, there cannot be lifelike sound. Music is played by instruments; hence authentic sound reproduction must also require instruments featuring harmonious resonances. While conventional loudspeakers produce illusions, they fail to sound lifelike, since all resonances have been eliminated.
Brodmann loudspeakers are instruments in themselves. Of course they don’t employ active resonators with instrument-specific sounds, as musical instruments do, but instead they use passive resonators, creating a neutral sound.
It is only through this coupling that the resonators or absorbers are brought to vibration (after Hermann Ludwig Ferdinand von Helmholtz, inventor of the “Helmholtz Resonator”). Reproduction of essential resonances is one secrets of the lifelike Brodmann Acoustics sound.
1.3 MUSICAL INSTRUMENTS AS THE BASIS FOR TRUE-TO-LIFE SOUND REPRODUCTION INSTRUMENTS
The sound produced by musical instruments can only be authentically reproduced by instruments of the same kind. The difference between musical instruments and loudspeakers is that musical instruments produce their own characteristic sound in the form of specific sound patterns, while the loudspeaker’s task is to reproduce a perfect, true-to-life copy of this characteristic sound.
Take string instruments as an example: the resonance stimulators, in this case the strings, are firmly attached either to the soundboard or the instrument’s body – stretched over the metal frame on the piano and over the bridge and tailpiece (between the ƒ-shaped sound-holes) on members of the violin family. An instrument’s soundboard, which produces its characteristic sound, is considered to be an active diaphragm.
The drivers in loudspeakers are resonance stimulators; they produce longitudinal waves thereby creating one front and one rear sound field at opposite phase locations. These two sound fields must be kept isolated from one another to prevent acoustic short-circuits as frequency decreases. Sufficiently large sound walls or cabinets must house the bass drivers; they behave like strings in string instruments – like resonance stimulators. Loudspeaker cabinets which authentically reproduce the sound characteristics of an instrument are passive diaphragms themselves.
The performance of both passive and active diaphragms depends on their composition (wall thickness, stiffness, specific weight and internal density of the material) as well as the energy level produced by the resonance stimulator.
Since Brodmann VC loudspeakers feature low-vibration bodies and tunable Acoustic Sound Boards, they represent the best solution for true-to-life sound reproduction.
1.4 THE CONFLICTING CONDITIONS REQUIRED FOR PERFECT SOUND REPRODUCTION: THE ACOUSTIC ACTIVE SYSTEM
Minimal acoustic distortion: while cabinet damping absorbs over-resonances, the damping material produces non-linear effects (the lower the frequency the less effect is achieved).
Minimal electronic distortion: while fine-tuning of the sound may be accomplished by frequency filters, the overall frequency curve must be kept as linear as possible.
Optimal bass range adaptability to the listening room: Large diaphragms reproduce delicate sounds rather imprecisely and require overly large cabinets. Reproduction of the original resonance, or the original timbre: minimal damping, yet adequate absorption of over-resonances.
Absorption of unwanted floor and room resonance (low-frequency footstep noise and standing waves)
Sound field with original radiation pattern, frequency-dependant
Faced with all these conflicting conditions, conventional technology is incapable of addressing all of them simultaneously.
Therefore HD’s comprehensive concept has found new approaches.
2.1 THE HornResonator
HD developed his patented HornResonator from the ‘Helmholtz Resonator Principle’. This principle states that a loudspeaker drives the air mass in the cabinet like a spring; this ‘springy’ air mass is attached to a resonator tube containing air equal in weight to the bass diaphragm. The disadvantages of this construction are A) that the opening created is quite small and B) that the resonance point falls on the fundamental resonance frequencies.
The HornResonator, however, has many advantages: It is horn shaped and extends from the resonator tube; there is a narrowing, ‘deep bass filter’ at the horn’s small end, which becomes proportionally larger all the way to the large end.
This allows the total bass projection area in the listening room to be increased with a minimum of sound distortion. The ‘deep bass filter’ at the beginning of the resonator tube ensures the correct frequency range, preventing sound coloration caused by the horn.
To prove that the air mass in the HornResonator truly functions as a diaphragm, and not just as an air funnel, one may simply hold a flame in front of it and observe how it waves in time to the usic. Only actively vibrating particles can cause other media to vibrate. Furthermore the angle of the HornResonator’s form enables the production of not just one fundamental resonance tone, but of many varied resonance tones spread across the entire bass spectrum.
Finally, a natural acoustic frequency division takes place at 130 Hz. Frequencies above 130 Hz are projected by the low mid-range’s front sound field, while the bass driver’s rear sound field drives the HornResonator. 130 Hz are located in the critical fundamental tone area where it is especially important for sound to be as distortion-free as possible (see 3.2 ‘The Acoustic Active Crossover’).
Minimal bass distortion is the basis for producing natural sound. No matter how well constructed a loudspeaker is, it will fail to produce a natural sound without the HornResonator’s high precision level.
2.2 THE SECOND-GENERATION HornResonator WITH Acoustic SoundBoards
The second-generation HornResonator has ushered in a new era in sound reproduction and clearly outperforms the first generation in quality as well as in bass and mid-range reproduction.
Instruments are made up of small sound stimulators (i.e. strings, mouthpieces, reeds, etc.) coupled with large resonators and projection surfaces for projecting the sound into the room. Singers make an extremely poignant example of the necessity of resonaters, for only after learning how to mplement their resonator through years of training, do they find their true voice.
Using musical instruments and human voices as models, our loudspeaker research and development has moved away from bass drivers with large diameters to significantly smaller and more powerful designs. Bösendorfer loudspeakers now employ powerful 130 mm bass drivers coupled with large Acoustic SoundBoards of the second-generation HornResonator.
SOUND PRODUCTION AND SOUND PROJECTION
The Acoustic SoundBoards feature a ‘double output’ function: Air floats between the cabinet and the board (see APPENDIX A). The boards function as active sound-producing diaphragms with no over-resonances. The normally passive Acoustic SoundBoards vibrate thanks to the defined distance from the cabinet.
The advantage of Acoustic SoundBoards compared to ‘passive radiators’ is the increase in impulse dynamics, and thereby the decrease in after-vibrations. This effect is caused by their acousticpneumatic coupling with the bass drivers.
Acoustic SoundBoards are freely vibrating diaphragms which are capable of expanding their diameter. Their amplitude can be modified by adjusting the clamp bolts, creating an effect similar to stiffening the sound board of a Bösendorfer Grand Piano. Both the natural sound field’s projection at the original performance as well as the acoustic characteristics of the listening environment are taken into consideration by the different sound projection of the tonal ranges:
Bass tones naturally form spherical waves and are projected on a large scale by the Acoustic SoundBoards, driven by the bass driver‘s rear sound field.
With midrange tones, the spherical radiation waves of the original sound can be fully taken into account. The placement of the low mid-range drivers on both sides allows mid-range frequencies to be reproduced in spherical waveform via the front sound field. In this way the sound is formed by direct sound and reflection.
High frequency tones are club-formed, which makes direct positioning of the tweeters an absolute necessity. If broader radiation patterns were used, unwanted reflections in the listening room would lead to phase errors, since in most cases the listening room is smaller than the place of the original recording, e.g. a concert hall, an opera house or a jazz club.
2.4 ARRANGEMENT OF THE LOW MID-RANGE SPEAKERS
In case the mid-range drivers are directed straight forwards, there will appeare too high sound boundels in the presence area. The consequences are:
- too direct sound
- thereby a little bit bundled hardness in the sound
- coarser undifferentiated, more unsensitive sound
(Such an effect can also appear if you use LS- and NF cables which do not open the sound enough.)
However, the optimal musicality is reached by the lateral arrangement of the low mid-range drivers - also in the reproduction.
The low mid-range drivers are arranged symmetrically for each pair of loudspeakers. Even if a loudspeaker pair is placed symmetrically in the listening room, there will be differences in the distance between each driver and the surrounding walls. Acoustically, compensating for such irregularities requires an excellent distribution of resonances. The distance between the low mid-range drivers and the tweeters is precisely defined to keep phase distortion between the two systems at an absolute minimum.
3.1 OPTIMAL CABINET DAMPING
Cabinet damping is often misunderstood. Typically cabinets are literally stuffed with damping material in order to muffle resonances. Resonances, however, may easily be brought under control by other means such as intelligent cabinet structure, angled or specially-shaped walls and use of alternative materials. In this way all non-linearity in the damping can be avoided since the effectiveness of any kind of damping material decreases at lower frequencies. This creates non-linear damping relationships (a fundamental law of acoustics).
Brodmann loudspeaker cabinets contain no additional damping material; their proportions are CADCAM-designed before being acoustically and empirically optimized. In this way, the cabinet proportions themselves are a major factor in sound reproduction. The result is a sound of unbelievable lightness and airiness.
3.2 THE ACOUSTIC ACTIVE CROSSOVER
The Acoustic Active Crossover was developed by HD in 1973. Until then, acoustic pressure as a function of frequency had been the main factor in loudspeaker and crossover design. The correlation between crossover design and resulting sound was negligible. Once phasemodulated distortion was taken into account by the design, the results were striking.
In the following years, amplitude, frequency, intermodulation and pulse-modulated distortion were additionally taken into consideration. Although these individual types of distortion may be easured separately, they actually act simultaneously, multiplying their effects. Modulation istortion greatly affects sound, its emotion and its very feeling. For example, a violin’s vibrato is itself a modulation; the lower the modulation distortion is, the more convincingly it is reproduced.
Only crossovers up to the first order produce linear distortion. When higher order filters are used, pronounced positive effects are offset by non-linear distortion. This was the beginning of the Acoustic Active Crossover, where cabinet and drivers are so perfectly matched together that minimal correction using only a purist crossover filter is required. In Bösendorfer VC loudspeakers, bass drivers operate over their entire frequency range and achieve the desired frequency on their own; the tweeter is marginally corrected.
The transition between bass and mid-range is accomplished by ‘Acoustically Active‘ control alone. Whenever possible, the bass driver is left unfiltered; if this is unavoidable, a small coil is used. The tweeter is delicately corrected at its lower end. Together, these make up the complete frequency filter system.
With the Acoustic Active Crossover a stunning three-dimensional sound is possible.
3.3 ‘The Pure Voice’-system (developed 2010)
By ‘The Pure Voice’–system (TPV) HD130 Midrange-Woofers are working nearly without mass – are swinging free in space. TPV support so the marvelous dynamics and splendour of singers and instruments in the direction of originally sound patterns. Electrically they are working in a full range manner but acoustically the effect of the acoustic short circuit lets reach a highpass filter function free of any distortions! So the system include also a phase-shifting function.
4.1 CONVENTIONAL SPEAKERS VS. BRODMANN SPEAKERS
Brodmann loudspeakers are typical two-way systems combining low and mid-range drivers and tweeters to produce as little distortion as possible. Impedance corresponds to the number of speakers used.
We use electro-dynamic speakers since these are best suited to satisfy a variety of criteria. No other system can move the air mass so homogenously through the diaphragm. Neither ion drivers, ribbons, nor electrostatic or magneto static designs can achieve such balanced results. These designs all face non-linearity in dynamics, which at lower frequencies leads to insufficient amplitude in relation to the moving surface area, causing uneven airflow.
In electro-dynamic speakers, the voice coil operates within a permanent magnetic field, converting the induced tension into mechanical vibrations. These vibrations then move through the diaphragm homogeneously and with little inertia loss, stimulating the air to vibrate.
Reproduction of the full audible spectrum
The maximum audible frequency range is 20 Hz – 20 kHz (a wave-length of 16 m to 1.6 cm). Apart from hearing loss of higher frequencies in the elderly, the human ear remains capable of distinguishing fine nuances within its hearing range for quite some time.
To reproduce the full audible spectrum with as little distortion as possible, both low mid-range and high-range drivers are required. Especially at lower frequencies, implementation of the ideal diaphragm area becomes increasingly difficult. Sound waves of 16 meters would require an equivalent 16 m diaphragm diameter! As compensation, special sound guiding is necessary.
The lower the frequency and the larger the wavelength, the more sound guiding will be required (and vice-versa).
Following this thesis, HD developed the HornResonator with Acoustic Sound Boards to act as an additional sound guide for lower frequencies, achieving inertia-free surface area enlargement for unhindered dynamics. The upper frequencies are of course unaffected, operating without the use of sound guides.
One of the Acoustic Active Principle’s fundamental goals is distortion minimization, as opposed to distortion correction by crossover filters, which actually produce new distortion. So we had to create speakers which, by correct dimensions and design, were capable of achieving all the desired frequencies.
Magnet size, voice coil power and heaviness or lightness of diaphragm alone is of little importance for optimal loudspeakers – rather a balanced combination of these variables is the primary factor for ideal loudspeaker construction. In addition, Brodmann bass drivers are extremely powerful in order to drive the Acoustic Sound Boards.
The basket must be as rigid as possible in order to adequately complement the speaker’s kinetic energy. Steel, and not magnesium as found in many speakers, is best suited to this task. Diaphragm movement creates opposing forces corresponding to kinetic energy in proportion to amplitude. These forces must be suppressed, which requires use of rigid, sturdy baskets, featuring steel joints and correspondingly strong sound walls (bass speaker mounting surfaces). That’s why our sound walls are so massive and why we don’t use ‘flexible’ cardboard or plastic inserts between the speakers and the mounting surfaces.
Air-gap focused magnets featuring smaller air gaps are clearly preferable to sintered ‘artificial magnets’ with their relatively large air gaps. This is because magnetic performance decreases with increasing air gap size at an exponential rate.
We primarily use Kevlar voice coil mounts, a material which is rigid yet linear-damped. It’s typical of our commitment to quality that we use 6-ply voice coils featuring maximum electrical conductivity as well as custom-made, flexible voice coil connecting wires.
Diaphragm and Suspension:
The paper-maché method has proven itself to be the best for bass diaphragms, with linear resonance characteristics and harmonious damping qualities. Our diaphragms are created like fine hand-made papers: they are soft inside, for optimal damping, and hard outside on the radiation surface, for optimal sound projection. These dual benefits are made possible by a sophisticated contactform technique – easily visible in the hard, structured diaphragm surface of the 130 mm low mid-range drivers.
Our diaphragms contain carbon fiber for high rigidity and Alaskan hemp for smoothness. The suspension isn’t made of rubber, but rather of UV-resistant Styrofoam, which is practically free of self-resonances. Plastic diaphragms are not used at all due to their non-linear resonances – just
imagine a plastic violin!
While consciously ignoring the recent fashion for metal, Brodmann was one of the first speaker manufacturers to use silk fibers soaked in acrylic. The advantage is a diaphragm which is rigid for fast impulses and soft against unwanted resonances. The 4-ply voice coil delivers extremely fast attacks which are required to keep pace with the HornResonator’s bass tones. The slender voice coil connecting wires are reinforced and very flexible. Both the bass drivers and the tweeters employ magnets with tiny air gaps for optimal flow. This leads to maximal conversion of energy into acoustic pressure instead of a substantial loss of energy as heat, as with conventional speakers.
4.2 OPTIMIZING CABINET FREQUENCY FOR A WELL-MODULATED SOUND
First of all the bass drivers should run at as high a frequency and the tweeters at as low a frequency as possible. In this way the ‘cut-off‘ frequencies and thereby the modulation distortion are both kept to an absolute minimum.
In practice we are confronted with certain limits: approximately 2 kHz is the ‘sound barrier’. But this isn’t feasible with conventional loudspeakers, neither with respect to frequency nor to load rating. Therefore Brodmann makes use of sophisticated diaphragm technology as well as specially-made voice coils and voice coil mounts.
5.1 FINE FINISHES ON CABINETS AND Acoustic SoundBoards
Brodmann, the manufacturer of world-famous grand pianos, treats its loudspeakers like instruments. The same premium quality is used for the cabinets, Acoustic Sound Boards, drivers and every other component.
The cabinet walls are made of high--density, specially coated wood – the same wood used for piano lids. The fine art of hand-crafted piano construction goes into their finish. The cabinet body is first sealed either in standard black or a custom color and then numerous coats of polyester-based piano varnish are applied. Finally, the surface is polished to satin finish or high-polish using a special ‘wobble’ technique.
The Acoustic SoundBoards (the side-mounted diaphragms radiating sound in the lower frequencies) are available in classic black finish or in one of the finest veneers from our grand pianos – in aged Tibetan pomele, birds-eye maple, burl walnut or burl birch, for instance. The Brodmann wood specialist carefully selects each fine veneer by hand.
Veneer application is a Brodmann speciality. Only a handful of experts are proficient at this technique. Veneer application encompasses more than precise side-by-side placement of veneer strips; the veneer’s grain creates harmonious surface ornamentation that is as natural looking as wood itself. The veneer design unites each speaker pair to create individual harmonies.
After the veneer is glued to the Brodmann Acoustic SoundBoards, the edge work egins, followed by polishing. Finally, piano varnish is applied to the veneered boards. The process is the same for the front components.
6.1 SUBJECTIVE AND OBJECTIVE HEARING
It is simply untrue that ‘everyone hears differently’. The truth is that we hear ‘digitally’ rather than ‘analog’, since from birth onwards, we have been storing acoustic signals in our ‘computer‘. We analyze these stored signals using criteria such as pitch, volume, color, pulse, etc. as well as psychological impressions such as warmth or coolness and feelings of fear or joy. All of this is accomplished by our modulation perception.
Although fingerprint and ear shape differ from person to person, our aural recognition faculty compensates for this. Otherwise it wouldn’t be possible for different people to recognize someone’s voice.
Good taste is actually objective, the prerequisites being training and a little practice. Only when errors occur do our impressions tend to be more subjective, ultimately leading to individual evaluation – what one likes or dislikes.
Therefore we can confidently claim that a good sounding loudspeaker, properly demonstrated, will please music lovers everywhere.