Audio Standards for Music & Sound Reproduction

recording London Symphony Orchestra in studio by photographer 49795746 on Flikr
A proposition to give the global audio industry consistency, accuracy and noticeably better sound quality.

Lenard Audio proposes a code of Audio Standards to achieve seamless integration across all music replication platforms to, potentially, change the future of the audio industry.  Our mission, simply:  "Saving the world from bad sound".

Differing sound systems sound different

Presently, differing sound systems sound different.   No two brands of studio monitors sound the same.   It cannot be known how movies will sound until screened.   Likewise, competing brands of home Hi-Fi and live performance systems also sound dissimilar.


The purpose of the Lenard Audio Application Standards (LAAS) is to promote consistency and transparency in just how amplified sound and music are heard, with minimal adjustment to existing technology.

Standardization has not been achieved — until now...

— Lenard Audio

Audio Standards Explained

Contributions Invited

This Web site is intended to become the home for the long-awaited and needed global audio standards for music replication.   Everyone is invited to participate and contribute.   Membership and forum pages will be added.

Concept Sources

The principle ideas put forward to achieve this objective (post universal acceptance of Thiele-Small parameters) emerged in Sydney, Australia 1978, when John Burnett, Richard Priddle and Michael Dixon proposed ways to standardise sound reproduction for the audio industry.

Copyright Considerations

The Standards described on this Web Page are Copyright © 2015-2016 Lenard Audio.   Reference to these Standards requires reference to the source.   The Standards will be available for commercial application.


1   Music Reproduction — Current Practice


There is a bewildering variety of sound systems in today's world market, each with its own idiosyncratic sound.   The problem is that "no point of reference exists" as to how amplified sound/music should be heard.

"Loudspeakers are the single most important element. They influence the art as it is being created. And in that process loudspeakers need to be neutral. If they are not neutral then they become part of the art "   as stated by Dr. Floyd E. Toole (Vice President Acoustical Engineering, Harman International Industries, Inc.)   Sound Reproduction: the State of our Science.

Sound Systems
"Circle of Confusion"

Recording engineers generally master music and film sound tracks knowing that the end result will mostly be heard on small low-fidelity speakers, headphones or ear-buds.

The problem begins with recording engineer/producers selecting a monitor speaker-system as a compromise between, 1) what they assume is representative of the average speaker system in most homes, 2) and that which makes their favored recordings sound best to them.   Similarly, a consumer will choose a sound system as a compromise, often with budget restriction, that enables their favorite music to sound acceptable to them.

Recordings that are Equalization (EQ) modified and compressed to compensate for the anomalies of one speaker system will not sound the same on a different speaker system.   In each case, the outcome is often governed by the unique differences in how a given sound system modifies and colors the music.

Therefore there is little consistency between the various speaker systems in studios, and minimal association between the sound of recordings created in studios and the listening experience of consumers.

Various small monitors pics courtesy of  and
Over-compensation = Sound-degradation

Compensating for small and/or low-fidelity speaker limitations, contaminates the integrity of the recording.

Many recording engineers waste endless hours caught in a "circle of confusion" by trying to evaluate the sound quality of speaker system "A" by listening to it with a coloured recording that was created by compensating for the limitations of speaker system "B",  as defined by Toole in his book "Sound Reproduction Loudspeakers and Rooms".

"Out of control"

The lack of standards in how speaker-systems are to be defined for recording, mastering and reproducing music has resulted in other areas of the audio industry being, effectively, "out of control".

MP3 and Loudness Wars

MP3 data-compression and Hyper-dynamic-range compression (two completely separate and independent types of "compression") are major causes of confusion and contention within the audio industry.

MP3 data compression is often blamed as the primary cause of music degradation, which is argued to cause smearing of music to varying degrees.   But the supposed degradation caused by MP3 is mostly inaudible to the majority of the population, when listening to music from small or low-fidelity sound-systems.

Dynamic range compression DRC is applied as an artistic effect to individual tracks within a recording, but .... Hyper-DRC (to exaggerate loudness) has a greater effect in degrading music than all other problems combined.

Hyper-DRC problem

Hyper-DRC is used extensively (in post-production) by recording companies, radio, TV shows and advertisers competing to be heard above each other.

Hyper-dynamic compressed music sounds flat, lifeless and highly distorted.   Voice articulation can be so low that it becomes difficult to understand words in songs and dialogue in films. A link to an editorial by Hugh Robjohns  End Of The Loudness War?

The confusion between MP3 and Hyper-DRC can only be resolved after Application Standards are in place to achieve, as close as possible, neutral/transparent reproduction from sound systems.

Our Industry Needs Standards

"Unsafe at Any Speed" published in 1965, described an automobile industry that was "out of control", with no standards for performance and safety.   As a result, the global automobile industry was transformed and standards for: 1) brakes, 2) steering, 3) suspension, are now mandatory.   Cars today compete on styling, size, application and power, as a result of standards being implemented.

Every industry in the world has application standards -- except the audio industry.

Now is the time for the audio industry to adopt standards (order of precedence) for sound systems to attain being neutral/transparent  and compete (solely) on styling, size, application and power.

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2  Audio Standards — Qualification and Attributes


Almost every manufacturer of sound-systems says "Our systems are the best", irrespective of the quality of their products.   How can a purchaser ever know the true quality of any given sound system?

Attributes and Order of precedence

Below are 5 attributes by which all sound systems can be assessed when referenced to a benchmark sound-system (described in section 3).   Intelligibility is the primary attribute.   The principle being that if only one attribute can be achieved, from a sound-system, then intelligibility is selected first.   The other attributes follow suit in order of precedence, similar to Ace, King, Queen.

The 5 attributes
  1. Intelligibility and voice articulation
  2. Spectral energy balance - consistent at all power levels
  3. Harmonic detail
  4. Bass discernment - notes reproduced evenly
  5. Directivity control

Lenard Rating (LR)

The Lenard Rating for a given sound system is based on a performance-attribute rating system.   There are 5 attributes   Each of the 5 attributes is first qualified by a 5 star rating in 1/2 step increments  0.5  1  1.5  2  2.5  3  3.5  4  4.5  5.   Then each attribute is multiplied by a weighting number to create a sub-total.   The sub-totals are added to create an LR value, with the maximum being LR-100 as in the table below ↓   LR Lenard Rating.

Natural Sound
Attributes Star rating Weighting Sub total
1. Intelligibility x 6 30
2. Spectral balance x 5 25
3. Harmonic detail x 4 20
4. Bass discernment x 3 15
5. Directivity x 2 10
LR value 100

Attempting to replicate the sound-of-nature from a man-made-sound-system is an asymptotic task (that is: we can approach but never reach) therefore LR-100 is unachievable.   Therefore the reference sound-system, described in the next section, will have a theocratical limit of LR-90, but will readily achieve a value of approx LR-80 as in table below ↓

Reference system
Attributes Star rating Weighting Sub total
1. Intelligibility x 6 24
2. Spectral balance x 5 20
3. Harmonic detail x 4 16
4. Bass discernment x 3 12
5. Directivity x 2 7
LR value 79

A typical audiophile system may achieve a value of LR-30 to LR-50.   A small domestic sound system or PA sound system may achieve LR-10 to LR-30 as in table below ↓

Small home system
Attributes Star rating Weighting Sub total
1. Intelligibility x 6 12
2. Spectral balance x 5 7.5
3. Harmonic detail x 4 8
4. Bass discernment x 3 3
5. Directivity x 2 1
LR value 31.5

1. Intelligibility  is the prime objective of a sound system;   the greater the articulation, clarity and separation between voices and instruments, the greater the star rating.   Poor intelligibility causes listening fatigue.   A film may have great CGI (Computer Generated Imagery) effects, but if we have to strain to hear the dialogue, then the story's dynamic flow is severely compromised.   We may hear the words of a solo voice, or phrasing of a single instrument, but when two or more voices or multiple instruments are playing, intelligibility can be reduced to a smeared mess.   All sound systems, small and large, can achieve high intelligibility with minimal increase to manufacturing cost.

2. Spectral energy balance  refers to the bass, mid and high frequencies maintaining consistent balance at all loudness levels -   the greater the consistency, the greater the star rating.   Many small sound systems sound thin and trebly at low level - the lower frequencies only become more audible when the level is increased.   The opposite effect is often heard from cinema sound systems and large concert PAs.   A performer talking or singing at low level can sound full and rich, but when the level is increased, the sound can be shrill and harsh.

3. Harmonic detail  refers to the frequency spectrum above the voice - the greater the detail discerned within the harmonic region, the higher the star rating.   In early sound system history, adding a tweeter defined a sound system as being Hi-fidelity.   In an ideal sound system, a tweeter would be applied above the voice i.e. above 5kHz.   But most low-frequency cone-speakers tend to behave chaotically from approx. 2kHz upward.   Therefore most two-way speaker systems are crossed-over to the tweeter between 2kHz to 4kHz.   This splits the upper region of the voice between two different speaker components (where our hearing is most sensitive to capturing detail) which can cause the voice to sound distractedly unnatural.   Also tweeters crossed over at frequencies lower than they are designed for, may result in the harmonics sounding shrill and smeared.

Note:  It's not our ears that hear, it's our sense of hearing.

4. Bass discernment  refers to the ability of a sound system to evenly reproduce bass notes in the lowest 1.5 octaves - the more even and distinct the bass notes are, the higher the star rating.   Many small sound systems, speakers in laptops and small home cinema sound systems (bar speakers), may have little to zero bass.   Some larger sound systems, particularly with separate sub-bass cabinets, might appear to have an impressive bass response.   But close listening attention may identify a pronounced resonance, sounding as a single note regardless of what notes are being played in the bass scale.   This problem is most noticeable with car sub-bass systems and concert PAs, which can sound particularly annoying if the resonance peak is in the upper register of the bass scale.

5. Directivity control  refers to the physical area in which 'the stereo sweet spot' can be experienced - the greater the area, the greater the star rating.   Lower frequencies tend to be omni-directional whereas higher frequencies can be so narrow (beaming) that the stereo sweet spot can only be experienced from a single point.   A small change in listening position, left or right, can result in the closest speaker dominating.   Directivity index is a technical term referring to energy dispersion.

Frequency response

All good sound systems should already have a flat response, but may perform poorly in some of the 5 attributes - why?   A frequency response graph shows Sound Pressure Level SPL across the spectrum, but does not show of what that energy consists.   Comparing different high-end speaker systems (with identically flat responses) starkly reveals this problem.

Inter-modulation IMD is the major distortion produced by speaker-systems and is the primary reason differing sound systems sound different.   IMD is not revealed in a frequency response graph.

One of the questionable trends in the audio industry is to regard the room and speaker-system as a singular entity.   Then with the aid of DSP (Digital Signal Processing) use room reverberation as a filler to achieve a flat response or specified response.   This practice further increases IMD, reducing intelligibility.   Many audio professionals are embroiled in arguments about this approach, which is another key reason Application Standards are essential.

Professional certification

Application standards enable everyone to better appreciate sound-systems and how they can be qualified.   For this approach to have efficacy, however, requires attendance at seminars that are run as interactive workshops, where everyone can be methodically taken through the necessary steps.   Certification is based on peer achievement in attaining agreement about Standards ratings as a self-correcting process.   When audio reviewers become certified using this approach then their critique will be similar to the following examples.

Review examples

Example 1.   A renowned brand that specializes in small sound systems released a new (expensive) model marketed as having outstanding performance.   However when qualified by the 5 attributes, applied to a weighted rating system, the real performance is better understood.   The impressive bass energy was astounding for its size but highly resonant, sounding as a single note regardless of what notes were being played.   Intelligibility of voice articulation was lacking, making it difficult to understand words in songs which became inter-modulated when two or more voices were singing.   Higher harmonic frequencies were harsh and cymbals did not sound natural.   The spectral energy balance was very different between low and high power.   A stereo image was difficult to hear, as it always appeared as if the music were coming from the nearest speaker.

Example 2.   A less renowned brand, similar model to Example 1, but a lower price.   Bass energy was less by comparison, however the bass notes were even and not resonant.   Intelligibility of voice articulation was good — it was easier to hear individual words in songs.   Harmonic frequencies were minimal, not harsh, and cymbals sounded more natural.   The system was less powerful by comparison, however the spectral balance remained consistent over the limited power it had.   The stereo image was also good, the music appeared to be evenly spread between the two boxes over a reasonable listening area.

Example 3   Deliberately-introduced distortion.   Many small sound-systems try to be everything for everyone, but often perform poorly in most attributes.   An example is a video bar-speaker that has deliberately-introduced distortion to make it appear louder in comparison to other brands.   The reviews describe the bar-speaker as being delightfully bright.   The response graph shows a rise between 1kHz - 6kHz, but does not show what that energy consists of.

In this example, the introduced distortion is in the middle of the intelligibility band, which creates a psycho-acoustic effect, similar to the sound of fingernails on a school chalk-blackboard.   For someone watching sports and motor racing the added distortion might contribute to the excitement.   Whereas for someone watching a TV drama series, trying to understand the dialog can be a tiresome task.

Musical instrument amplifiers

Musical instrument amplifiers, particularly guitar amps, are intended to be highly colored, enabling characteristic types of distortion (overdrive) to be inclusive of the art.   However when the guitar amp is recorded, it is hoped that the studio-monitor and home sound-systems will faithfully reproduce the recording, which includes the artistic sound character of the guitar amp.

Market benefit

Some companies, a minority, make exceptionally high-quality sound systems.   But a large percentage of poorly performing sound systems are promoted by marketing hype and unethical reviews that describe them as being otherwise.   This makes it difficult for customers (without technical expertise) to discern what is real and what is not.

Application Standards will enable customers to identify the legitimate performing sound systems and better understand what they are purchasing.   Also, Application Standards will help those who design sound-systems to adopt an agreed discipline to achieve an ordered focus in design quality.

Choice argument

It is often argued that people have various preferences in how different sound-systems "sound".

When making this argument we should consider that no one would prefer to read a book with smeared-unintelligible text, or choose to watch a movie that is out of focus.   The same principles apply to sound.   No one would prefer listening to a sound system where the intelligibility is so low that it is difficult to understand the words in songs or the dialogue in a movie.

Consumer preference

However there are positive arguments for personal preferences in sound-system performance.

When listening to a live band playing acoustic instruments, we might prefer sitting closer to the paino, vocalist or percussionist.   These choices are associated with the artistic experience of the music and not to the quality of reproduction.   For example, a personal preference to have the bass frequencies at higher or lower energy than the recording was intended to be heard at, is a legitimate choice, providing the attribute of the bass notes is evenly reproduced and not sounding as a single resonant note.

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3  Audio Standards — Reference Sound System


Specifications for sound-systems became well defined by the 1970's;  but the methodology for arranging the components of electronics and speakers in order to achieve neutral/transparent reproduction remained elusive - why?

Traditional audio measurement

The traditional method of measurement is with a microphone in front of a sound-system.   This method is described as self-referential analysis.   But, self-referential analysis has limitations, an example is a woman trying to use a mirror to judge how beautiful she is.

Self-referential analysis is excellent for enabling us to see detail, within the response of a sound-system (similar to the woman applying makeup) but cannot provide an overall understanding of a sound-system's performance, or a woman's attractiveness.

A small video bar-speaker and a large cinema sound-system can have near identical specifications, but understandably the two sound-systems would sound completely different.   Going to a high-end audiophile shop and comparing different sound-systems, with identical specifications, reveals this problem.   Women with identical make up does not mean they are identically attractive.

Scientific method

Scientific method requires specifications to have an external reference to be valid.   An example is temperature, 0°C and 100°C are referenced to freezing and boiling points of water.   The speed of a racing-car or athlete is measured by the time traveled between two fixed external positions.   Similarly, a beauty competition has an independent panel of judges.

Therefore, specifying the attributes of a sound-system for achieving neutral/transparent reproduction requires an external reference.


"Reference" in this text does not mean absolute.   "Reference" refers to a starting point from which measurements and comparisons can be made, similar to how we use a ruler.

Common sense enables us to understand that a small sound-system with a 2 or 4-inch speaker (regardless of specifications) could not reproduce the equivalent dynamic energy of a real double-bass, violin or saxophone.   Also a bass guitarist in a rock band would not use a small amplifier with a 4-inch speaker on stage,   they would use a large instrument amplifier with one or two cabinets with 12 or 15-inch speakers.

Commercial cinemas use 15-inch speakers and large compression-driver/horns that are capable of reproducing the same, or greater, dynamic-energy as real orchestral instruments.   Therefore, such 15-inch speakers and compression-driver/horns are used in the reference system for defining the 5 attributes.

Also, a reference sound-system must be capable of replicating the performance of any sound system to which it is compared.   It is only from this reference that other standards for recording, mastering and live-productions can thus be clarified.

The System Imperatives
  •   A studio mastering system beyond the performance of ordinary studio systems
  •   A cinema sound system beyond the performance of ordinary cinema systems
  •   A home hi-fidelity system beyond the performance of ordinary audiophile systems
  •   A PA system beyond the performance of ordinary PA systems.
  •   A musician's amplifier for guitar, bass and keyboards beyond the performance of ordinary instrument amps.
Achieving progress

Four-way active sound-systems of this stature require independent assembly, utilizing currently available components.   And have the best performance achievable (as defined by the 5 attributes).   Also be at the zenith of a bell-curve where performance diminishes by being smaller or larger.

Anyone conversant with the points below can achieve this task.

The Quality Imperative

Understandably, it is essential to use appropriate, high-quality driver components.   And traditional self-referential analysis is still required to insure each driver component has minimal distortion and a linear response.

Speaker components

This reference system was originally based on JBL professional drivers.   Unfortunately only two models of these drivers are still available — 2446 Compression driver and 2226 15-inch.   The JBL 2405 slot radiator (tweeter) is no longer available.   Other driver brands, however, are available, of which some, it can be argued, are either equivalent or superior.   The parts list below is for a stereo pair.

JBL drivers
4-way Reference sound system

System calibration

Driver components vary greatly in efficiency dB/mW.   These efficiency differences need to be measured, calibrated and compensated for.   There are various approaches as to how this can be managed.   All that matters is the result.   The points below are a guide, beginning with the lower-voice 15-inch speaker.   Using two people, working together to achieve this, is a recommended approach.

Step One: Install voice range transducers (15in lower-mid + comp-driver/horn upper-mid) 90Hz to 6kHz

15-inch JBL 2226 with 2446 compression-driver/horn (or equivalents).   The 15-inch 2226 (or equivalent) can be selected as the dB efficiency reference for matching the other drivers.   The 2446 compression-driver/horn (or equivalent) is approx 12dB higher efficiency than 15-inch 2226.

Ensure correct phasing and double check.   Compression-drivers must have protection capacitors in series (approx 200µF).   These capacitors block pops, bangs, turn on/off pulses from the amp getting to the Compression-driver.

Step Two: Install the tweeters

Tweeters must be crossed over above the voice range between 5kHz to 8kHz.   Slot/Ring radiators (compression tweeters) are suited for far field, cinema or PA, and are approx 3dB to 6dB less efficient than the 2446 compression-driver/horn.

For near to mid-field listening, ribbon-tweeters might be better suited.   These can be approx 6dB to 12dB less efficient than compression-driver/horn.   Ensure correct phasing and double check.   Tweeters must have protection capacitors in series (approx 47µF).   These capacitors block pops, bangs, turn on/off pulses from the amp reaching to the tweeter.

Step Three: Install sub-bass 15-inch speakers

Thiele/Small parameters are an essential guide for bass-cabinet design.   Sub-bass must be crossed over below voice, approx 90Hz.   2 x 15-inch sub-bass speakers can be together in one large cabinet or separately, in two smaller cabinets.

Sub-bass speakers can be 6dB to 12dB less efficient than 15-inch 2226 (or equivalent).   Sealed and ported-cabinets have advantages and disadvantages, sealed-cabinets can introduce less complications.   Ensure correct phasing and double check.

Sub-bass refers to bass-speakers crossed over below the voice-range.   This ensures zero inter-modulation of the voice.   Sub-bass speakers have strong, heavy cones with extra long voice coils.   Most sub-bass speakers for cars are unsuitable for this purpose because they can be excessively inefficient, and have high Fs making them unable to reproduce deep bass.   Select sub-bass speakers with low Fs (approx 20Hz) designed for large speaker-cabinets.   Experiment as needed with the crossover points.

Certifying requirement

The certifying requirement for the Standards will require sound-engineers, audio-consultants, system-designers and reviewers to attend seminars and directly interact and experience a sound-system of this structure, so as to obtain a perspective for qualifying the 5 attributes.


Special note:   The recommendation is for the reference system to use the highest quality driver components.   However, the difference in performance of a system consisting of the highest quality drivers and another of lesser quality drivers could, possibly, be within 10%.   This is due to size and structure of the system as well as being four-way active.   Whereas, when comparing different models of small, domestic two-way passive speaker systems, that use drivers of variant quality, the auditory differences can be significantly large, despite their specifications being similar.

The reference system will give an experience of:

This system can be trollied through an average door, easily moved in a van, station wagon or pick-up truck and fit within most larger homes.   And perform perfectly as a jazz club PA.   Most of all, being fully active, it is an excellent studio mastering system, once critically aligned.

For most applications, sound systems do not need to be large-scale four-way active.   The attributes of the reference system are only used to qualify the performance of other sound systems regardless of the technology that is applied.   In the future, a new technology might be discovered that will be superior, requiring a new reference to be established.

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4  Audio Standards — Questions and Philosophy


A truly 100% transparent sound system could not actually be, because only the music would exist.   Those of us who are captured by this quest are deeply humbled.   Attempting to create something for it not to exist, is a magnificent paradox.

The audio paradox

Paradoxes are philosophical arguments that involve apparent contradictions which are valuable for promoting critical thinking.

It is often believed that a perfect sound system can be defined by "analysis".   But neutrality cannot be defined by analysis and is, therefore, a paradox in itself.   The paradox of neutrality requires us to see that a neutral sound system can only be defined by its ability to reproduce that which is not neutral.   For example - A large high-fidelity system can replicate the performance of small low-fidelity system,   but a small low-fidelity system cannot replicate the performance of a large high-fidelity system.

This approach for defining Application Standards, by measurement related to comparison of external structures (and not by self-referential measurement alone) comes under an umbrella of a discipline described as "Bayesian analysis", further explained at the end of this chapter.


An orchestra played through a sound system cannot be directly compared to an actual orchestra - why?   A sound-system may give either a poor or enhanced representation of an orchestra, but it only provides a simulation or superficial likeness, known as a simulacrum.   Sound from a real orchestra is a fractal complex multi-point and multi-directional radiated set of acoustic wavelengths;   and the perceived sound heard by an audience will be different from seat to seat.   A stereo sound-system, by comparison, simply radiates sound forward from two distinct locations.

Also, a sound-system can only replicate a representation of an orchestra from the perspective of a microphone (from a position that is quite likely unknown) including additional recording EQ effects, also indeterminate.   Therefore the performance of a sound system cannot be judged by direct AB comparison to an actual orchestral instrument.   The difficulty in understanding this logic has, for many, been the basis of confusion.

It is possible to design a sound-system that can replicate music so realistically that we can virtually feel the musicians being present.   This illusion of auditory reality is magnitudes beyond what can be achieved in the visual realm.   But no matter how close we approach the grail of neutral/transparency it will always be an elusive quest – remaining as a simulacrum.

Illusion of reality

The audio frequency spectrum is approx 10 octaves (three decades) 20Hz to 20kHz.   Our hearing is least sensitive at the ends of this spectrum and most acute in the decade from 500Hz to 5kHz, the range critical for speech intelligibility.   This is where sound systems need to be most accurate and where technical shortcomings are most apparent.

For music replication, a basic sound-system must be capable of reproducing a two decade range from 80Hz to 8kHz as a minimum requirement, and an extra octave either side is required for a sound-system to be classified as hi-fidelity.   Because the speed of sound is approx 340 metres/second, the bottom E on a double-bass is a 14-metre wavelength and efficient reproduction requires a large radiating surface.

When listening to a live band acoustically (not through a PA system) we hear the instruments separately as coming from their various locations (horizontally).   If all the instruments in the band were heard as if coming from a single point it would sound implausible much like a typical small speaker system (woofer and tweeter).

A fully active sound-system divides the frequency spectrum into 3 or 4 sectors with each sector amplified separately (vertically).   When done correctly the resultant effect is similar to the live band in that it sounds realistic.

The irony of this is that the ear equates this illusion to the separation of sectors, regardless of whether said sectors are separate instruments in the horizontal plane or separate frequency bands in the vertical plane.

With two fully active speaker-systems acting as a stereo pair, the added horizontal effect produces an equivalence of auditory enjoyment synonymous with reality, creating an illusion that the musicians are actually present.

Speaker drivers

A single given cone speaker can only accurately reproduce a maximum bandwidth of 3 octaves (1 Decade) with minimal distortion.   This being a function of cone diameter and wavelength, and therefore the reason the reference system is of a four-way active type.   Compression-driver horns follow a similar rule of 3 octaves (1 Decade).   This being a function of horn-length, flare-rate, mouth-diameter and wavelength.

The tweeter is crossed-over between 5kHz to 8kHz to ensure zero contamination of the voice.   There are many excellent compression tweeters available.   Excellent ribbon tweeters are also readily available.   This choice is discretionary.

The mid-range spectrum (approx 6 octaves) is divided into 2 sectors, lower-voice and upper-voice.   Each sector is approx 1 decade, ratio 1:10.   1 decade = 3 octaves (approx).   The crossover frequency will vary depending on the selected drivers.

The upper-voice is reproduced with a Compression driver/horn.   Compression driver/horns achieve possibly the best accuracy and highest efficiency compared to every other method known.   This is where our hearing is most acute for discerning speech articulation and intelligibility.   This is the reason compression driver/horns are applied in cinemas throughout the world.

The lower-voice is the body that gives the human voice and instruments their character.   In this lower-voice band our hearing is less acute for discerning articulation and intelligibility.   However our hearing is attentive to the averaging effect this frequency band has in acting as a carrier for the upper-voice frequencies of human voice and instruments.

A large speaker/horn could be used for the lower-voice, but it would be too large and difficult to move and fit within most rooms.   This lower-voice band, for the reference system, is best reproduced with a front loaded 12 or 15-inch speaker designed to be maximally efficient and linear in this region.

Comment:   Regardless of what opinions some audiophiles may have about disliking horns, I have found (without exception) that the sound system they heard had a poor quality horn/compression driver that indeed did sound dreadful.   Moreover, rarely did the audiophiles I spoke with mention that they were aware they were hearing a higher quality compression-driver/horn at cinemas.

The bass register is from open E 41Hz to 165Hz.   As a general rule, the cone excursion of bass speakers increases 4 times the distance for each octave decrease to maintain equal energy.   The bass speakers are crossed over below the voice range approx 90Hz, to ensure the lower bass frequencies do not inter-modulate the voice.   2 x 15-inch bass speakers for each speaker stack = 4 x 15-inch for a stereo pair, which is the minimum radiating area to achieve linear dynamic power of the bass frequencies.

1 x 18-inch speaker could be used instead of 2 x 15-inch speakers.   However, 2 x 18-inch speakers per side is ideal for extra large areas.   The technical reason is:   The diameter of the combined bass radiating area must be greater than 1/10 of the wave-length of the lowest frequency, so as to maintain equal spectral energy across all bass notes, when applied to a free field environment.   The reference system is free-field-referenced, not room-referenced.

Note: The above statement about bass radiating area does not apply to resonant bass systems.   Examples include ports within cabinets and organ pipes.

Comment:   Many bass players today have small bass amps that have 10-inch speakers.   At concerts, these small bass amps often require being amplified by the PA system to enable the bass player to be heard.   In the earlier era 1970s rock-blues, musicians often played directly to an audience and not through a PA system, a good bass player had a large speaker box 2 x 15-inch that produced real bass and often used two boxes = 4 x 15-inch speakers for a larger venue.

Inter-modulation distortion IMD

The major distortion noticeable in sound systems is IMD, which emanates from the speakers, not from electronics.   Fractal cone breakup, non linearity, nodes and cross-over anomalies all accumulating as inter-modulation within the speaker system.   Inter-modulation distortion (IMD) is caused by amplitude modulation of two or more frequencies in a system with non-linearities.   The interaction of these modulating frequencies creates additional frequencies as integer multiples of each other, which include sum and difference frequencies plus multiples of those sum and difference frequencies.

Inter-modulation creates spurious harmonic side-bands that spread out across the music spectrum.   It is these side-bands that cause the distinct coloration we hear in speaker systems, particularly passive speaker systems.   For a sound system to achieve minimal inter-modulation distortion the frequency spectrum must be divided into separate sectors and each sector amplified independently.

Digital audio-technology

Digital technology has transformed the audio industry.   Analogue Class AB amplifiers and analogue active crossovers are being replaced by Class D amplifiers and DSP Digital Signal Processing.   Some Class D amplifiers perform equally as well as Class AB amplifiers, but many do not.   Many audio DSP management systems function well but also some DSP systems use proprietary or secretive software that may have complications with unresolved bugs.

When assembling the reference sound system it is advisable to begin by using traditional Class AB amplifiers and proven analogue four-way active crossovers.   Then step by step, convert to Class D amplifiers and DSP management.

DSP enables us to obtain detailed control of sound systems that could not be achieved with previous analogue technology.   But there has been an increase in false and misleading statements in the marketing of sound systems using DSP technology.   DSP cannot fix a leaky submarine or enable a plane to fly when the wings have fallen off,   nor can DSP enable a small low fidelity sound system to perform equally as well as a large hi-fidelity sound system.   Most of all, in reference to marketing claims that DSP can resolve room reverberation problems ---

"Thou cannot equalize time with amplitude"

DSP cannot enable the performance of a sound system to be improved in an excessively reverberant environment.   The only way to solve problematic room reverberation is to fix the room.


Cinemas do not show films with lights on, nor do cinemas put mirrors on walls.   Cinemas are visually neutralized (dark).   Only the screen is seen, we are engaged in the story.   The recorded sound for a cinematic film includes the reverberation of the environment that the story is set in, which is inclusive of the art.   Therefore cinemas (already visually neutral) should be acoustically neutral as well, and not have its own reverberation that is competing with the art, contaminating the story.

The same argument applies when listening to all recorded music.   Recorded orchestral music often includes the reverberation of the auditorium, which is inclusive of the art.   Therefore the room we are listening to the recorded music, should also be as acoustical neutral as possible so as not have its own reverberation that contaminates the art.

Free field v Room reference

One of the many arguments in the audio industry is - "What is the reference by which a sound-system is designed and calibrated?"   Some argue that the room comes first, and a sound system should be designed and calibrated to comply with room measurement and acoustics.

Room acoustics on its own, without being externally referenced to free field, is non-defined.   Therefore a sound-system should be free field referenced first.   Then when applied to a room, using DSP technology, definitive measurements of difference can be made, enabling calibration of the sound-system to the room to achieve greater accuracy.

A reference for understanding sound systems in rooms is "Sound Reproduction Loudspeakers and Rooms" by Dr. Floyd E. Toole.

What is Bayesian analysis?

Bayesian analysis is an external process, as a philosophy, that when applied to the disciplines of mathematics and science, ensures theoretical concepts are grounded in reality.   Bayesian analysis is included within almost every area of science, engineering, economics and actuarial studies, but has rarely been applied to audio.

Example:   An audiophile speaker cable costing $1,000s is marketed as having magical qualities that transforms the listening experience of a sound system.   The questionable claims are supported by unethical audiophile reviews.   Any skeptic can smell snake oil and scientific analysis tells a different story.

The resistivity of copper is 1.68 x10-8 Ωm.   A quality 3m speaker cable may have a total resistance of 0.1Ω and the larger audiophile cable (for the same distance) may have a lower resistance, 0.05Ω.   This 0.05Ω difference in resistance is irrelevant, and the differences in the reactive components (capacitive and inductive) of the cable are equally irrelevant at audio frequencies.

No method of verification exists to prove that any human could detect a difference in the behaviour of a sound system (by changing speaker cables) at a distance of 6ft or 2m from a sound system.   And the same argument applies to many other questionable claims quoted in the marketing of audiophile products.

Common sense enables us to understand the difference between peeing in a tea cup compared to peeing in the ocean.   As an imagined theoretical exercise we can calculate how much the ocean will rise, which may be less than the distance equal to the diameter of 1 atom.   Obviously we see the absurdity of believing a rise in ocean level equal to the distance of an atom could be detected by human perception.

Bayesian analysis ensures theoretical concepts are verified by being detectable and measurable.   And in reference to audio, that verification is human perception, which ultimately is the only place that "sound" exists, being the product of the brain's processing of auditory signals.   This analysis is a much needed forward step towards reining in an industry that in many ways has been "out of control".

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled."   Richard Feynman

Special Note to Manufacturers of Existing Sound Systems

Audio Application Standards bring technological, economic and social benefits to the world, and help to harmonize the specifications of loudspeakers and sound systems for music replication.

As part of our Action Plan for "saving the world from bad sound" Lenard Audio is committed to developing programs to increase and strengthen our support to musicians and producers throughout the world.

In addition, the Lenard Audio Application Standards (LAAS) can improve global markets, and help define the characteristics of music production and reproduction with the intention of achieving a closer connection between the musician/producer and us, the audience as consumers.

We welcome everyone to play an active role in the (LAAS) community, promoting the Application Standards and taking part in its development.

John Lenard Burnett

John Lenard Burnett

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