Now apply this to speakers. You have a bass driver and you apply a signal to it. The current running through the coil creates a driving Force accelerating the speaker cone - (voltage is not present in formulas for force driving the cone - only current) the acceleration creates a sound wave, but when you stop the signal the cone is still moving. It does not accelerate anymore so it does not produce sound anymore right? Not quite, now you have the cone mass, surround and spider forming a resonant system that damps the excitation. This system has its own “deceleration force acting on the cone (producing sound not related to our signal) and last but not least the magnetic motor generates EMF that when run trough a load (the crossover and amplifier output ) again creates current accelerating the cone in some unpredictable direction. It is a bit like beating a drum and trying to control the sound with the sticks.
Introducing a system that measures the acceleration and velocity of the cone and comparing it to the input signal gives us the ability to create a control signal forcing the cone to start and stop as does the input signal and not as the resonant system it comprises.
As described earlier all feedback systems have latency and a number of other limitations allowing us to apply only a certain amount of correction in a limited frequency band. In other terms, the sound can never be made perfect but over a limited frequency range it can improve performance more than 10 times!!! With the implemented feedback system we are able to control (lower) the resonance of the mechanical system in the box and the total Q of the system. Taking advantage of the fact that speaker drivers operating above their resonant frequency have much lower phase shift.
To handle the 1kW of power and the high pressures and mechanical stress we built it in a all metal enclosure capable of withstanding the high sound pressures. 1kW? What for? At resonance the impedance of a bass driver can rise more than 10 times. To put this in perspective means that the power going to it is 10 times less. So your favorite 100W class A amp that can pump 30 Amps in a speaker in reality can’t deliver more than 10 watts to the bass driver!! Yet once we go to a higher frequency with very reactive part of the impedance it can pump a few hundred watts in it for no reason what so ever charging and discharging some capacitor.
Mass and its effect
A myth that large heavy cones make bass is just not true. The heavier the cone the more force and time is needed to accelerate it and to stop it. Heavier units are more robust and can take more power to compensate for the lower efficiency, so with a powerful amp you can make them sound just as loud as the lighter ones. It makes no sense but sells more speakers ;-) Anyone that studied acoustics will know that the formula for sealed speaker efficiency and extension there is a corresponding volume of the enclosure, but there is no mention about driver size, weight and shape. It is irrelevant. Only practical manufacturing reasons will define the size and weight of the driver.
Matching an active bass unit to an existing system requires removing the frequency band from the main speakers and level matching the two. We have built a crossover system in the Basus allowing for multiple interface types and level adjustments to suit every system. You always wanted that 20W SET amp to power the mid/highs and have thunderous bass at the same time, now is your chance. With it’s i/o flexibility Basus allows for balanced and unbalanced signals as well as 6 predefined crossover frequencies. amplifier damping illustrated - monkey phase shift around resonance (imaginary component illustrated).
Why no one else does and says this? Well that's not quite true. The principle we use were developed by Philips in the 60’s and 70’s and thousands of studio monitoring speakers have used it over the last 35 years. Unfortunately, most of the development effort was directed to making a small box sound like a large one and no one ever considered building commercially a big system. You can say that we have scaled, hot-rodded and turbocharged the concept, by developing a custom drive unit, drive electronics and bomb proof enclosure.. Is it that good? And, then some!
TECHNICAL SPECIFICATION: BUILT IN AMPLIFIER
DIMENSIONS: 450W x 450D x 800H mm
FREQUENCY BAND: 25~250Hz
The experience was backed by a very thorough paper written on the subject of intermodulation products of tweeters and sub harmonic distortion acting as contaminants to the background and reducing signal to noise of the speaker system. Apart from the usual break up modes there was excursion induced nonlinearities, cavity resonances, magnetic modulation, diffraction and other subjects covered.
But the proof of the pudding is in the eating. So building a speaker system as a showcase for this technology seemed the logical next step. Beware!
Max Power Handling: 250W
Dimensions: 210W x 385D x 520H mm
Finish: Black or Silver anodized aluminum
Frequency band: 34~20 000Hz
Listing all those shortcomings in a speaker would make you wonder how does it even work and yet when you are comparing 2 DACs with 100 times better specification and measured performance on the obviously imperfect speakers you can clearly hear the difference between the DACs. All arguments that speakers have the most audible artifacts of all components in the signal chain are true, but it does not make the faults of the supply chain go away. The speaker induced artifacts are of a different character. Being simple devices the computer models used to predict their behaviour are quite accurate. Very often to simplify description the more complex behaviour is generalized and many things are assumed. In those assumptions the errors start to accumulate until they prevail and the predicted result differs significantly from the measured or intended.
2-Way Stand Mounted Loudspeaker
Lyra is a unique 2 way speaker system. It features a new breed of high frequency driver loaded with a very special horn system, complimented by 2 magnesium diaphragm mid/bass drivers in an all aluminum ported enclosure.
The Basus subwoofer system consists of a bass driver with motional feedback in a sealed metal enclosure, a 1 kilowatt power amplifier, and an active crossover system with switch selectable preset frequencies. The active crossover system allows the Basus system to be used with any speaker/amplifier combination.
The Basus subwoofer project was started as a bass extension unit for the Lyra speaker that evolved in the ultimate universal woofer, for that we provide a matching stand to mount the Lyra on top of the Basus making it one system visually. The Lyra/Basus/Teres combination creates an active speaker system with unmatched synergy and visceral impact. Undistorted bass at high enough levels creates a different perception of the music. When the group delay is very low pulses and percussive instruments become solid and with well defined bodies cleaning up the murkiness in the soundstage creating a see through effect allowing one to hear the reverb and reflections in the back of the sound stage. You don’t hear more bass but more music!
Basus and the need for better bass
In Music school you are taught music has three main elements; rhythm, harmony, and melody. The bass notes lay the foundation for two of these three elements; Rhythm and Harmony. Numerous studies confirm that people react to low frequency beats and can detect timing errors in a low frequency beat more accurately than in mid and high frequency ranges. Bass is not rumbling noise associated with a passing starship, but the foundation of a musical passage. It is the lowest note that defines the harmonic structure in frequencies above it. It can make music sound Sad or Bright, or Mellow. Music contains two very different types of bass; one that is continuous and sustained, and the other pulsed and very short (percussive). Proper phase alignment in sustained bass creates the right waveform allowing you to identify the instrument and to enjoy its sound texture. The pulsed bass gives you the beat and timing of the piece. Any delay there and the sound is ever so slightly off beat making the music less enjoyable. Small ported speakers and home cinema subwoofers exhibits very large group delay giving meaning to the term “murky bass”. Large ported enclosures behave better having this problem only in the very low bass. The best overall performance is achievable with sealed enclosures and especially large sealed enclosures. In large sealed enclosures the group delay is the lowest and less obtrusive. Unfortunately, the efficiency of sealed box systems is very low. For any given cut-off frequency, the box size will have to double for each 3dB higher efficiency. Now you can understand which manufacturers "misinform" you. Below are the maximum theoretically possible efficiencies for sealed box speakers expressed as SPL per watt:
2 cu ft 30hz = 84dB
4 cu ft 30hz = 87dB
8 cu ft 30hz = 90dB
16 cu ft 30hz = 93dB
32 cu ft 30hz = 96dB
The conclusion is that to have deep bass at high levels you need large speakers and a lot of power
Cabinet’s re-radiated energy- think of a drum, vibraphone or an organ pipe. The speaker enclosure is a resonator in its own right. If you create a pulse at its opening in a bit it will respond with its own voice - like an echo in the mountains. Containing this unwanted sonic signature of the box in the box and not letting it escape the enclosure is a difficult task. Heavy boxes with thick walls still leave just a thin diaphragm between you and the inner rumblings of the box. A heavier stiffer membrane and hard surround are used extensively in the more powerful subwoofers. The box resonances, inherently creates delays, and out of time tone bursts making the bass sound murky or boxy.
Harmonic distortion in the bass region seems to be so widely accepted that on the order of 5-10% of people complain about its absence, when it is not present. Putting this in the context of audibility thresholds means that in many systems you hear the “newly created” harmonic structure of a bass note without hearing the note itself. (Bose acoustimass, laptops, tv sets).
Modulation effect of bass on rest of music
The human ear is known to produce a fair bit of harmonic distortion itself leading to the production of intermodulation products. What does it mean? Illustrated for a simple explanation if you listen to a clean tone - an opera singer and you add a low frequency signal with appropriate but still unobtrusive level, meaning you don’t notice it, you will notice in fact a change in the tone of the voice. The voice will be modulated. A clean 3k signal will sound like a few 3k signals. This is some of the Basus of music creation. A bass tone modulates a higher pitch tone giving it its beat and coloring it, so in a solo an off beat note is accentuated by having a different character as not being modulated by the bass burst. Interesting.
During my studies at the Danish Technical University in Copenhagen on the subject of acoustics, coincidence introduced me to a character called Steen Deulund, and then I found I knew nothing.
A number of books later I regained enough confidence to point at a good, or a bad design. Than I found out how little people know about good speaker design, and certainly could identify a good one.
Leap forward 20 years to an argument in Sofia about tweeters used in high end speakers and which sounds better accompanied by demonstrations and piles of marketing bla bla. Until an older gentleman comes to me and said “you should hear what Plamen has done”. Never payed much attention to this as Plamen has been doing cinemas and studios for as long as I can remember, but then again curiosity prevailed. A quick listen to a prototype set of speakers using a ring diaphragm compression driver loaded with 2” short (that is very short) horn, was a smack in the face.
The speaker system features an uncommonly high sensitivity of 90db making it usable with lower power amplifiers or in very big rooms while bass extension is generous considering the size of the speaker and it’s efficiency. It sustains severe levels of abuse without giving in. The filters are constructed with resonance free foil wound inductors and premium Polypropylene capacitors. The all aluminium body is internally damped for any internal vibration and resonance. Styled in the Thrax family of products. The value of our speakers is in the knowledge required to make them not the materials used. Time precious materials lose their mythical properties in audio. Diamonds and silver are more expensive, so they must be better is the general assumption. (I really doubt, gold teeth are still going on in dentistry). Aluminum has 2 times lower resistance per unit weight for voice coils compared to silver or copper. If we talk speed this is it.
Loudspeakers are the final component in the reproduction chain. You will hear all kinds of opinions on the importance of loudspeakers in the replay chain pitched by gurus around the globe. Most leaning to the fact that loudspeakers don’t measure very well. They all have considerably high harmonic distortion, limited bandwidth and frequency nonlinearity. Those are the parameters that are easily measured even by amateurs. Other, just as important parameters, are directivity, stored energy, time alignment, those are discussed by connoisseurs and by marketing people and require a higher level of equipment and knowledge to identify. Things like signal to noise (yes speakers have signal to noise!), break up behaviour, diffraction interference and others are discussed only among people with true experience and understanding. To measure those you need special jigs and equipment that is usually purpose built.
Noise and signal to noise
Up to now we discuss about how good it is to have bass modulating the upper tones and how it creates music, but when this is is done ad hoc without being related to the music we could classify it as noise and distortion. the level of these artifacts relative to the level of the reproduced signal will define the speaker signal to noise ratio. It varies with amplitude and spectral content and this is one of the reasons for not being able to quantify, but once experienced everyone can distinguish between various speaker systems.
One means of reducing those artifacts is to make sure they are not created in the first place. The use of feedback has been widely discussed and is the principle behind 99% of the amplifiers in use today. Why is it not applied to speakers? Not as easy and well understood or maybe too complex and with limited commercial value to be worth the effort, we won’t know for sure. Speaker drivers are linear electric motors, much like the one spinning a fan or lately the wheels of your Tesla. Those same motors are used in CNC machines and everywhere in our daily life. To make them do what we want we need to know what they do. The PC on which you are reading this has a fan mounted on the CPU that adjusts its speed according to the temperature of the CPU. This is just one example of a feedback system. You start playing a computer game and your CPU load increases dramatically, a bit later the fan stats spinning much faster trying to cool the CPU. The time it takes for the CPU to heat up so the fan speeds up and then restores the CPU temperature is called latency. Every feedback system has such a thing.
As said music is sounds and silence. Everyone tries to improve the sound and we just improve the silence.
Wasn’t Thrax an electronics company? What do you know about speakers? 28 years ago, I designed and built my first speaker. Even then with a ribbon tweeter (by Decca) and with an Alnico magnet bass unit. Needless to say it did not sound that good. Main reason was …It was designed by the book. No thinking involved. Following the rules gets you a mediocre (average) result.
Main feature of the speaker system is a solid aluminum carved front panel incorporating a horn with specific directivity and frequency response as to perfectly match the directivity of the adjacent woofers. The geometry of the front plate is such that it is time aligned between the tweeter and woofers. We use a custom designed ring diaphragm compression driver. The driver features a 118db/watt sensitivity and a very low resonance allowing us to use it effectively to below 1500Hz. This driver/horn implementation allows for very high levels and low distortion as well as very low spurious noises. The magnesium diaphragm woofers are able to match the speed and clarity of the tweeter at the expense of a very nasty break-up mode in the upper midrange, so utmost care has been taken to make sure this resonance never gets excited, so the 3rd order crossover is 3 times lower then the nasty resonance.