Here is a small collection of basic and useful tips that can be used in all aspects of audio and sound. They are in no specific order, or subject, we will put things up here from time to time as they come to our attention. In most cases we find in conversations with colleagues and customers that there is a wealth of information, sometimes controversial, sometimes we think "everybody knows that", but information that can be used to improve our understanding and the way we work.
The back of most equipment is just as much a part of the user interface as the front. Most items of equipment have connections, controls, or indicators on both sides. All equipment housings should consider this when being designed.
For the safety and comfort of the operator the back of equipment in a recording environment should be safely accessible, free from obstruction, and most definitely away from any live exposed electrical equipment. Electrical terminal blocks, exposed terminals, or cables without strain relief should never, ever, be used in an audio equipment rack.
The rear of any rack should be accessible for configuration, reconnection, and inspection by the operator at any time. It is an important part of the equipment operation that it may be essential to verify the state of controls and connections on the rear of an item if it is not performing as expected.
Part 2. Electro acoustic advice.
Useful Tips and Advice
Part 1. Safety and Conditions.
A safe and comfortable workspace is an essential part of a good recording, or show. When people are able to feel that they are in a well controlled professional environment where others care about their well-being, and where there are proper facilities that are clean comfortable and well-maintained, they often feel better able to perform to their optimum. Where there is someone who seems professionally in control of that environment, who has a good line of communication, and who seems to take care of them, they can feel even more comfortable with their working conditions and so perform to their optimum.
When designing and building a recording space it is essential to take into consideration all aspect of occupant and user welfare, from the essential fire alarm and emergency evacuation systems right down to temperature and mood lighting, everything has to be addressed properly to create a safe and comfortable work environment for all who use our products. There are, however, quite a few things that a user can do to make sure this degree of safety and comfort is maintained.
If you are going to work with sound gear, live shows, or large-scale recording set-ups, then go and invest in some form of rigging or safety education courses. It is your professional duty to do so.
Most audio schools are horribly negligent in this aspect, they just assume that you will be pushing faders about or telling the artist to play louder, faster quieter, slower more, more, more, or similar.
The reality of our work is that we often, as recording staff, end up contriving some form of pseudo-mechanical, physical, contraption to achieve our aims. This can vary from a conglomeration of microphone stands and cables to get a microphone to a required position, all the way up to being the person responsible for hanging 3 tons of loudspeakers above “the president’s head”.
In a responsible world we have a duty to those around us to ensure that we are competent in this task. Most sound engineers are not very competent in this aspect, and even more so, those fresh out of “sound school” are, sadly, not in any way trained to be competent in such aspects.
Even laying out the stands, chairs, and cables in a studio with an orchestra should be properly planned and competently managed.
The sound engineer is often responsible for deciding where to put microphones and speakers and has influence over what others do. Without proper knowledge and training of such things it is common to see inappropriately rigged systems that are sometimes dangerous and often hazardous done so at the say of the sound engineer.
We have a professional duty to all those around us to properly understand the consequences of our actions and to mitigate the risks to others, we really must be properly trained and competent in this aspect.
Think about the recording space as a work site. Consider the musician’s needs and safety as an integral part of your work. Sit down, think, and plan the “user interface” of your workspace and take into account all the risks and potential circumstances that can arise. When you have more than one or two people in a recording space somebody needs to take responsibility for managing the safety of these people and the responsibility for providing a safe place of work for these people, most of them are at work and therefore are legally entitled to the correct conditions. Create a plan, asses the risks, nominate someone to take care of this, and above all assess your own competence in this area.
What happens when the lights go out? When working in any recording space, be it permanent or temporary we must consider the unexpected. When working in confined spaces with large numbers of people we are obliged to consider how we can cope with an unexpected event. In a live show it should be the production management in conjunction with technical staff, in a recording environment often the only responsible person is the recording engineer. Are you competent in this aspect? Do you have training? Are you practiced in dealing with large numbers of musicians (sometimes superstars) in the event of an unforeseen circumstance? How do you control your studio or recording space layout? Are cables, stands, chairs, and any platforms or steps all well managed to reduce the risk of slips, trips, and falls? Is the emergency lighting adequate to safely evacuate a room without damage to persons or irreplaceable instruments? Really, every large-scale session should be quickly and competently assessed in this manner.
What about the risk of death from faulty electrical equipment?
Are you competent to control and eliminate such things? Do you know how to manage electrical systems in audio?
Plenty of musicians have been killed by electrocution from the equipment around them, are you confident that this will never happen “on your watch”? Have a think, do you periodically check all your gear in a competent manner?
This does not mean asking an electrician, it means getting a “competent person” who understands the equipment and all possible risks, both electrical and operational, to check things over. Do you have a fail-safe means of removing unsafe equipment from use immediately that it is found to be unsafe, and ensuring it only returns to use when repaired or replaced?
Do you have adequate methods and authority to stop work when a dangerous condition is identified, or would you carry on and let a high pressure producer or client put people’s lives at risk, because “the show must go on”?
When considering designing a recording space it is essential, and in some jurisdictions a legal requirement (UK CDM), to consider how it will be used, how the user will interface with it, and how every expected interaction with the facility will ensure that the safety of the user will not in any way be compromised by the design of the facility. This not only relates to all of the usual obvious aspects like fire protection, escape routes, entrance routes and so, but more in-depth use like access to cable runs, ease of removal of cosmetic covers, access to service areas, and the size and weight of any moving parts or user interface objects. In all cases we must consider that any confined access space must allow for the easy removal of an incapacitated worker, and any service or storage area must allow for safe entrance and exit of workers with all the expected equipment they will carry with them. Racks and cabinets should be easily accessible from both sides, and where required, have adequate cable to allow for the racks to be moved on wheels to an accessible space for servicing and maintenance. Adequate lighting in all service areas must be provided. There is plenty to consider when designing the layout of any recording space.
In all circumstances, without fail, all studio structure, surfaces, and materials must be able to withstand a fire, without spreading that fire, or generating toxic fumes for an adequate duration to ensure safe and orderly evacuation of the premises. This should be irrespective of the regulatory need for such measures.
No "acoustic materials" should be used that are not adequately fire resistant, and care should be taken to ensure that no materials that can generate toxic fumes (Such as foam rubber, synthetic sponge, or some lightweight insulation boards) should be used. If you don't have proof of fire resistance on any material, don't use it.
No materials that support other materials should be used in a way that fire would compromise the support of those other materials in a way that would cause them to fall and obstruct escape within a reasonable expected escape time.
Cable ways and ventilation systems should be adequately protected to prevent the spread of fire from room to room.
It can be incredibly tempting when building a studio oneself to use the cheaper option material, but first one must check in every way that the material will not support combustion and will not emit toxic fumes before using it in place of a more expensive safe option.
Recording studios and their associated acoustic treatment can be immensely heavy. They have to be in order to function.
Before considering anything it is wise to consider and get advice on structural weight loadings. Something as benign as a small audio for TV editing suite, when sound isolated, can weigh as much as five tons, bigger rooms can be up to a hundred tons, in some cases light-weight floors may not have adequate strength. The consequences of a floated room crashing through a weak floor into an office below are instant death of all those below. It is essential that in any circumstances no work on any room begins before a professional comprehensive survey of any proposed space for a studio is carried out, and we have confirmation that there is adequate structural strength to support all intended weight, equipment, and occupants.
The speed of sound is.......
Well actually, it isn't.
The speed of sound can vary with the media it travels through, the temperature, and the humidity of air. It is an important thing to know as you could otherwise be looking for problems that don't exist.
In normal atmospheric conditions where one could expect to find a human listener there can be significant variations in the "reference" speed of sound.
The speed of sound is an immensely complex variable to pin down, a bit like trying to catch a fly. The atmosphere we are in is in a state of constant change, in many ways, including temperature, humidity, density, and other movement currents. some of these will affect the propagation of the sound-wave, others the speed. They are all changing as we work or listen to something. Air, in itself, as a medium is non-linear in many ways.
The speed of sound increases with increased humidity and this effect increases with an increase in temperature.
Large amounts of Carbon Dioxide in the air such as in an unventilated room can lower the speed of sound.
There are also minor effects that may cause up to a 0.1ms drop in the speed of sound below 100Hz down to 10Hz.
So.... Using the speed of sound for accurate fine measurements is rather like using a rubber tape measure. Take care, get a reference before you make any fine adjustment, you can be as far as 10% away from what you may expect, or have previously set, and in many circumstances 10% is a significant variation that can change a perfect summation into a total cancellation.
But this means that "modal effects" in a room which are dependent upon the speed of sound through air can also vary as much as 10% (in extremes) from one day to another. (although such environmental differences my be a little uncomfortable a 5% shift is possible in more benign situations.) - That's rather inconvenient isn't it, especially for modelling and "tuning" such issues.
Phase is not polarity.
Or should we say, Polarity is not phase. (Stop saying "phase reverse" it's wrong)
Yeah, but it's out of phase ins't it? Well, No it isn't, not in that context.
Phase is a relative difference in time from one signal to another, a phase shift is a time shift. We use phase (measured in degrees) as a convenient way of describing a time difference of one amplitude / time signal to another as a measure of the relative cycle of a waveform, but in a linear time delayed signal that measure is only relative to one infinitely small frequency point.
If we delay a signal by 0.5ms we introduce a 180 degree phase shift at 1,000Hz, but at 500Hz we have introduced a 90 degree shift, and at 2,000Hz we have a 360 degree shift. Conversely, if we introduce a 180 degree phase shift to a full bandwidth signal at 1000Hz, we introduce a 90 degree phase shift at 500Hz, (which is twice as long, therefore half the rotational difference) and so on. There are complex phase relationships in non-linear circuits which we shan’t go into here, but suffice to say none of this relates to polarity.
Polarity on the other hand does nothing to time, there is no time domain effect at all from a polarity inversion.
Look at it this way, if you wave your arm from left to right a video camera with a video delay can invert this movement in a delayed replayed image, it has lag, it is slow to respond by one half cycle. When you look at the monitor the image will behave like a mirrored response of your movement. This is a phase shift. If you move your arm faster the delay will alter the relative position to your real arm, and the mirrored movement will be lost, just as a phase shift delay changes relative to frequency.
A mirror on the other hand has no delay, it will seem to equally laterally invert the movement of your arm relative to what you would see if you were at the mirror's perspective, however, no matter how fast you move your arm you will always see the inverse of what others would see, and this relates to a polarity inversion.
Take care, applying a 180 degree phase shift to correct a polarity problem is wrong, just as applying a polarity inversion to correct a 180 degree phase shift is wrong.
The correct place for a critical motoring loudspeaker is either in a wall, or in totally free space.
But wait, I hear the cry, "users don't listen like that". True, very true, but two different and not inverse wrongs never make a right.
If a monitoring loudspeaker were to be totally directional, throwing all of its radiated energy forwards within a tight nominal coverage area it would be fine to place this loudspeaker "free standing" close to boundaries outside the directivity pattern. As it happens we have not seen any monitoring loudspeaker with such a directivity response, and are not likely to see for some time.
In all circumstances when free-standing a vast quantity of energy in the lower frequency region, depending on the geometry of the source loudspeaker, is propagated in all directions at the same time. Some of that energy, a minority, goes towards the listener, the rest of it, the majority, goes off in other directions until it hits something, at which point it reflects and heads back at various angles. Some of this eventually reaches the listener, now late, and out of time with the initial first "true" arrival, it reacts with the pressure of the true arrival and modifies that pressure to create a "false" response. In higher frequencies we are able to easily differentiate between a source and a reflection, not so in lower frequencies where wavelengths are long and reflections are often well within the cycle of the direct arrival. What happens is a modification of the direct arrival in the time domain, and we get a series of peaks and dips in the bass response frequency-amplitude domain that can totally colour the direct sound in a way that means the loudspeaker can never reproduce the input signal truthfully. The loudspeaker-room combination is then said to have a very strong character that will impose itself on all program played.
Mounting a loudspeaker in a wall very simply and totally effectively removes all the problems related with rearward propagation. There is no acoustic compromise to this, it is wholly effective. All energy is radiated forwards so long as the integrity of the wall is adequate.
Mounting a loudspeaker in a wholly absorbent space is also as effective, but exactly what constitutes a wholly absorbent space at 25Hz is very debatable, and very expensive to do. In addition, a wholly absorbent space is a horrid environment for human listeners, especially when we can see the space but not hear that space. This is not a viable option for anything except a laboratory environment.
A loudspeaker wall cannot be "seen" by the sound propagating from the loudspeaker, it cannot reflect from that wall, and therefore the wall can be bright and reflective to give a comfortable space for the user. The only walls requiring acoustic treatment being the ones the sound will be directed towards.
A loudspeaker mounted in a wall will exhibit the flattest response it can, far flatter than a free standing loudspeaker which is always subject to a bass roll-off as the bass propagation begins to expand into a greater omnidirectional space.
Bass from a flush mounted loudspeaker will exhibit more impact and detail, and be a far truer representation of the electronic signal.
Well, what about the listener at home?
Well as the bass response of any free standing loudspeaker is totally dependent upon the precise geometric position in the room, virtually every listener will have their own different problems in their bass response. It is impossible to pre-empt this situation in the production environment. If their problems are not too bad they may even be able to hear through them slightly. Whatever the case the only professional solution is to make the music correct in the first place and leave the problem solving to the user in their unique surroundings.
Where should I place my loudspeakers for best stereo image?
Hmm. Maybe we could say "at the end of the rainbow".
No, seriously? where?
Well, that is a serious answer to this question.
That and most definitely, sometimes, occasionally the universal answer "42"!
The audio world, and the internet is awash with theories and equations for such questions, but really devoid of any single "correct" answer.
"It depends" is probably the best professional expert answer we can give in this circumstance.
Again, the internet is awash with pictures of professional recording studios, many with vastly varying Left-Right loudspeaker geometry. Some of those pictures show absolutely ludicrous positioning that really wouldn't work well at all, but the fact that they exist in the first place, and the fact that the studios are not laughed out of business is testament to the vagueness of the answer to our question.
So what is the long answer?
Well. The biggest issue is the room, if you have a good room and a good set-up then you are probably not even asking this question, maybe 42 was the answer, but, of course, you knew the question.
The room can greatly affect where you would place a loudspeaker for least compromise, where you would listen from, and what will reflect and create phantom images and a collapse of stereo imaging. Go too wide and we get a "hole in the middle" or "sound in our head" effect, too narrow and the stereo sound field collapses to almost mono. In a more "live" listening environment we sometimes need to spread the speakers a little to create a wide enough soundfield as reflections can be masking the image. In a very controlled environment we can close in the speakers a little without losing the image and get a better centre phantom image, if pushing the loudspeaker out to a great stereo position ends up pushing them into a reflective corner, then often the stereo advantage is outweighed by the reflective disadvantage.
If the loudspeaker is a poor point source with poor time response you will find that the stereo image is poor and the speaker has to be pushed out wider to exaggerate the soundfield.
Strongly reflective surfaces behind the head can make almost any geometry useless.
Stereo is a psychoacoustic effect, we create virtual sources in our brain based on what we hear binaurally, the only way to verify any psychoacoustic effect is to run it for real and use the human ears and brain for verification. When the listening environment includes distracting influences we have to do test runs to see if we can make things work.
At a design stage we can't go around waving our speakers in the air to find a sweet-spot, we have to nail down our positions, especially when they are wall-mounted flush, in our case it is based on an intimate knowledge of our rooms, years of adjustments, and great control over the loudspeakers we use. Thee is no substitute here for experience and decades of customer feedback on which geometry was deemed to be best.
So what about "42"?
Well, actually, 42 degrees off the centre line is actually not too bad a starting point for a beginner.
Nothing is exactly what it seems in this game.
One of the most common totally correct, absolute, answer we find ourselves giving is "it all depends on.....(insert infinite parameters here)"
This doesn't mean we don't know. The more we know the more we know that we don't know, and the more we know that other factors beyond our immediate control are huge modifiers of our work causing our answers to be vague.
We have already ascertained that even the speed of sound "depends", that where we put our speakers "depends", and how our speakers sound "depends". Even how to build a recording studio always "depends", just as how to cable a studio "depends".
In a world of people who want absolutes, black and white answers, this or that solutions, this vague incalculable tendency to come back and say "maybe" is deeply dissatisfying to many.
It can be hard to teach a subject to eager students when all we can say is "maybe that is ------- but it depends on so much you don't know yet". That is deeply dissatisfying to the student, especially when they are being sold knowledge.
In the absence of black-and-white answers we see endless opportunist merchants preying upon those seeking certainty, folks purveying "the absolute answer" to "the ultimate question", folks saying, if you do this, or buy that then you will have that answer you seek.
Snake-oil sometimes has a very bitter after taste that burns, despite being so sweet and soothing initially.
In many things we can, as yet, only ever "ball-park" our predictions, and results. We can get things there, or thereabouts with a reasonable degree of certainty within the variation, but that often leaves room for unscrupulous operators to move in and be critical of our lack of precision. Even where they have no better (often worse) results they find benefit to their position in claiming certainty that they do not have, and cannot prove (but do not need to) to those who do not know.
The problem here lies with the human trait that is a desire for absolute answers, black-and-white binary logic, something that I can do that is simple and absolute to resolve my problem. Something I can just buy with my money and not take any responsibility for if it doesn't work.
Audio and acoustics often don't work like that. We're incredibly grateful that they don't too. This is an industry of almost infinite probabilities, a space where we know precious little in the bigger picture and where we have great scope to improve upon things. It should not be a disappointment that we are not in full control, but a great point of excitement for what is left to do, how we can embark upon great journeys of enlightenment, how there is so much to master. Maybe we should stop seeking to have control, and better learn to navigate this vast complex electro-acoustic universe in a more imprecise enlightened way to better achieve the essence of what we strive to achieve.
I am struck by the number of lifelong experts in our industry who in face-to-face conversations reply with "We don't fully know that yet" "Ah, yes, in that situation it is all different" or "It all depends on so may unknown factors" to seemingly simple questions that lesser knowledgeable folk claim to have the answer to, and how their eyes light up with any suggestions of new results, new approaches, or new methods.
Many lifelong experts rely equally on a lifetime of experience of empirical results, educated intuition, putting together of different experiences in different situations, and a knowledge of what we yet do not know, just as much as they rely on a library of calculations and learned texts (which we should always hold a shred of doubt over) . When working in such a vague subject it can be as useful to know and observe what is actually happening and search for an understanding of why it is happening, as it is to know what should have theoretically happened and figure out what to blame for why it did not.
In may ways, professionally, at a high level, to say "it may probably do that if all is as expected" is an incredibly precise answer, and to say "Oh, that's easy, it always does this" is a very dangerous assumption to make.
It is a point of great amusement that as an industry, we are an industry of so-called experts, who often insist on micro-measuring immensely vague and variable circumstances to fractions of units with immensely expensive finely calibrated equipment, only to finally report that the immensely precise fractional number to the nth degree they come up with is actually only able to be qualified as a vague approximation to 5% or 10% certainty due to uncontrollable environmental factors and inadequacies in the measurement concept itself.
There is something almost dishonest in the very process presented to the layperson that implies immense precision in the measurement of imprecise often moving targets to achieve approximate answers.
If there was only one piece of advice I could give to any student in this subject it would be to be suspicious of certainty and to embrace and understand the concept of uncertainty in all we refer to.
Beware those who pedal certainty, and trust those who express their qualified uncertainty openly.
Julius Newell Acoustic Engineering (Unip)Lda
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