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Harmonic Resolution Systems
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Broadband noise reduction in the audio replay environment with special reference to Harmonic Resolution Systems.

There are two simple facts that apply to the environment in which a hifi system operates. Firstly, that environment is extremely noisy. Secondly, Audiophiles show a marked reluctance to spend money on cleaning up that environment. The latter might well arise because they are unaware of quite how noisy their listening rooms are and how dramatically this noise adversely affects music reproduction. Few, if any, A/B comparisons exist for equipment support and it doesn’t help that very few Audiophiles know how resonance control devices work or what the magnitude of improvement brought about by these devices is likely to be in absolute terms. Most Audiophiles remain highly skeptical about the wisdom of making any but the most modest investment in resonance control. The first order of business therefore is to separate the science from the snake oil, mere furniture from the genuine audio components whose contribution to good sound is unmistakable.

The Beach Boys may have extolled the virtues of good vibrations but when it comes to audio playback systems, there is nothing good to be said about them; with the obvious exception of those occurring between LP groove and stylus.

It is possible to distinguish between structure-borne and air-borne vibrations and their main difference lies in the manner in which these are transmitted to the audio system. In the domestic environment, there are many sources of vibration: household appliances as well as video and audio components. The worst offenders are loudspeakers, which can literally shake the audio room. The vibrations created by the loudspeaker are fed back into the system through the room only to resurface as part of the output from the loudspeaker and so on in a vicious cycle. Worse still, given that most structural-borne vibrations in audio systems have broad frequency ranges, the prospect of exciting the natural frequencies of the rack system and audio components is very high; the result is that non-musical energy can be significantly amplified.
The greatest source of air-borne vibration is again the loudspeaker. These vibrations reach the outer skin of components, the equipment racks and floors where some of this energy is dissipated, some is reflected and the rest is transformed into mechanical vibration which is then amplified in the same way as structure-borne vibrations. All this vibration constitutes non musical information which degrades signal quality by loss or masking and the likelihood is that it will end up damaging signal quality by amplifying non musical information. An audio signal from a source component exists in a very noisy, vibrating environment and the components in the chain are themselves, to some degree, noisy as well. Non musical energy creates smearing. Musical attack and leading edge are blunted, harmonic structures inadequately resolved and decays truncated. Bass is less resolved and tuneful and overall accuracy and musicality will be reduced. Timing suffers dramatically.

Any good audio equipment rack will achieve some level of noise reduction at some frequencies. The problem, however, is that many rack systems reduce vibrations at some frequencies only to amplify them at others. The key is broadband noise reduction. This objective must be well understood; because of the way most systems behave, simple models predict only over part of the audio spectrum.  In general terms, the approach is to engineer a large mismatch between any system’s excitation frequency and its natural frequency. However, the individual components that make up the system and the compliant elements themselves have their own vibration modes that are excited by mid & high frequency energy and the entire room is energized not only one location. This means that the mathematical model for achieving broadband noise reduction in an audio system is very much more complicated than perhaps first envisioned.

 

The Harmonic Resolution Systems approach to resonance control comprises three fundamental elements. The MXR frame; the brackets which attach to the frame and on which the M3 platforms rest; and the M3 platforms or isolation bases themselves.

The MXR frame is constructed from a variety of materials (the number and type are closely guarded), but this proprietary design is then covered in a cosmetic skin that can be custom finished to match the most discriminating décor.  The external appearance is completely independent of the structural integrity and internal energy absorption system.  This means the performance of the MXR system is completely independent of the finish the customer chooses for their system.  The customer can select from standard high quality wood finishes, custom paint systems, and exotic custom wood finishes.

 

The MXR frame has a natural frequency that is significantly greater than that of the decoupled shelf system- the M3 Isolation Bases. Also crucial to the stands ability to maximize broadband noise reduction is that each of the four feet on the M3 Isolation Base contacts the frame on a custom ,ultra high frequency billet-machined, aluminium bracket.  The intersection between these custom design parts is four line elements at a near zero total surface area. This near zero contact area is also geometrically at 90 degrees to the primary mode shape of the MXR frame.  The comprehensive nature of the engineering of the MXR system means that there is virtually no path for energy to pursue from the rack frame to isolation base. It is all these innovative design features that make the HRS MRX Audio Stand unique. In addition to the performance feature, a host of adjustability is built into this design, which makes the system very flexible to future system changes.  The brackets can be moved at any time to change shelf spacing.  The number of brackets can be changed at any time to add or subtract components.  The system can also be expanded at any time to add capacity.

The shelves of each HRS audio stand are separate M3 isolation bases, which are configured for size and weight depending on each customer’s equipment dimensions. If new electronics are purchased which differ in weight, then new footers can be purchased, thereby protecting the financial investment of the customer. There are two main structural elements in each M3 isolation platform: a machined aluminium frame and a ¾” granite slab, which is decoupled from it and sits on a polymer sub-structure. The entire philosophy behind the HRS Audio stand is to ensure very little vibration gets past the primary isolation stage. Any that does penetrate the aluminium frame face a series of mechanical chokes and other energy reduction devices machined into the aluminium frame. Any mid and high frequency energy that is travelling through the frame is confronted by a barrier which is designed to reflect energy back to source and or reduce it by means of conversion to heat. In total, seven different materials are used in the aluminium frame. The decoupling polymer substructure also controls the natural resonance of the granite and the granite adds mass, durability and beauty to the overall design.

There is virtually no hope of achieving genuine broadband noise reduction through simple engineering solutions. When broadband noise reduction is achieved, one experiences clarity throughout the entire frequency range. High frequency information is naturally and fully resolved and appears part of the natural mix. This aspect of being part of a whole is particularly striking when compared to the picked out “detail” which occurs because high frequency noise, caused by poor vibration control, is being amplified and is adding itself to the signal. In a well controlled system, music playback is characterised by an ease which is also correctly dynamic. The air surrounding the musicians is recreated as it existed at the time of the original recording; because the noise floor throughout the frequency range has dropped, precipitously. One finds oneself turning up the volume control, since the elimination of “corrupting bogies”, makes each increase inject more ease and air into the performance without any corresponding increase in the size of the individual performers. Violins do not suddenly assume the size of cellos and neither do voices emerge from the mouths of giants. There is immediacy and presence as yet another layer of artifacts is removed between you and the performers.

With grateful acknowledgement to Jules Coleman for his brilliant review of the subject. The complete transcript can be found at www.avisolation.com.

 

 
Tel: 07799812271 - E-mail: glyn@amadeus-audio.co.uk
 
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