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Room Acoustics: The Listening Environment -Our First Post!

Note from Choice Audio:  Special Thanks to Dale Pitcher for allowing us to publish this article for our first blog.  We have known Dale for almost thirteen years and I have personally been using his products since 1992.  They are very few people that have the skills and know how to design and build the products that he makes.  To this day his speakers, (Denalis, Summits, Super Gems and Amethyst 10A) are still some of the best that I have ever heard at any price.   The fortunate few that are lucky enough to have a listening room designed by Dale Pitcher know how good they have it.  I’m one of the fortunate few and I’m also lucky enough to have a friend that’s not too far away that has a “Dale Room” as well.  What follows is an interesting read about Dale’s journey and discovery of what makes a room sound good or not so good.  Some of what he writes about may be contradictory to some of the acoustic experts in the field.  What ever your opinion, I hope you enjoy this thread.

 

Room Acoustics:  The Listening Environment

Copyright 2014,  Dale Pitcher

Overview

The purpose of this thread is to open up new avenues of thought on how acoustical issues may be addressed.  The higher value for many forum users, however, may be the posts on real-world application of these concepts.  An overview of these upcoming posts is below in Section D.

There are many ways to see things.  Sometimes it is useful to step back and look at things from an entirely different perspective.  Not only does it allow you to clarify your own understanding, but sometimes you can pick up new facets.  Combining these with your previous knowledge may provide you with some unexpectedly powerful tools.

For example, about  ?? years ago, there was a scientific battle over whether light was a particle or a wave.  Scientists lined up entrenched on both sides with their measurements and documentation.  It finally became apparent that both camps were absolutely correct, and a whole new understanding was reached on the nature of light.

There are many gifted – even brilliant – people in the acoustical field.  There are excellent books on the subject, and highly sophisticated programs and test equipment are now within reach of many serious audiophiles.

Yet, there is a continuing struggle for audiophiles to achieve good room acoustics.  I have heard $5000 systems sound simply extraordinary in rooms that had excellent acoustics.  I have also heard $300,000 systems, vastly superior in every way, sound completely lackluster in beautiful rooms with poor acoustics.

I’ve been in this industry since 1972; when I opened up a high end audio store selling IMF, Stax, Tannoy, Thorens, Transcriptors, Decca and a number of other good lines.  Since then, I have been the Director of Engineering for a number of companies, designing loudspeakers, amplifiers, preamplifiers and audio interface cabling.  I have also done a great deal of recording over the years in a wide variety of acoustical spaces, mostly with my Studer A-80 and various ribbon microphones.

Over the years I have overseen many installations – some quite costly.  Often clients would ask me to design both the acoustics and the aesthetics for the listening environment.   Many of these people were fairly affluent, and gave me free rein to take their rooms as far as I could.

I’ve had the opportunity to observe both ends of the acoustical spectrum – from very poor listening environments – to exceptional.  I observed what made the poor rooms sound the way they did.  But when I encountered a room with exceptional acoustics, I would spend a great deal of time trying to discern the underlying secrets.  I started incorporating what I observed, and began to have far better success in my own efforts.

I’ll give you an illustration of how difficult challenges can often be disguised learning experiences.
I was given the go ahead to build a completely non-compromise, cost no object room about 25 years ago.  I felt that I had been able to get everything right.  Then I got to the ceiling construction, which was a constrained layer assembly which weighed over 1600 pounds.  This was pressed against a 1” thick wool damping layer with mounting assemblies that utilized thick Sorbothane washers.

Until we put this secondary ceiling in, the room sounded great.  Afterwards, it had a very noticeable “overhang” from the upper bass through the entire mid-band. We were almost positive that the actual ceiling assembly itself was not at fault.  We removed the ceiling assembly twice, and made a few seemingly minor changes in the mounting assemblies.  The heavy “overhang” anomaly completely vanished. The room sounded “right”.  I’ll tell you why I believe this change came about in the next post.  It’s in the section “Acoustical Laws” under the heading “Use of Elastomers”.

This example illustrates how I have been able to develop concepts and methodologies over the years.  I suppose if I were to develop a slogan for my years working with acoustics, it might be this:

Few things are more useful than a properly executed mistake.

This combination of opportunities and challenges has given me the chance to experiment extensively over the years.  I feel that I have been able to come up with some unique ways of seeing acoustical issues.  I believe that there are underlying concepts not often explored, and effective methodologies rarely utilized.

At times, I’ve run into acoustical issues that seemed to defy resolution. This was often in the area of strong secondary bass modes.  My first impression was to “damp” everything down like crazy.  This would diminish the targeted problem, but would also significantly compromise other acoustical issues.  I was able to come up with an innovation that I have since used for over 25 years, with a large degree of success.  This will be covered more completely in Post 3, but there is a “proof of concept” for it in Section F, below.

Summarizing:

The first two posts provide a brief overview of my basic core concepts and, along with some technical expansion.   Future posts will elucidate these concepts a bit more fully, but the primary focus will be to outline cost effective ways to implement these things in your room environment.

 

So posts after #2 will be structured as follows:  1) Acoustical issue, 2) Definition of how the problem is manifested in the listening environment, 3) Methods for dealing with the problem, and things to avoid,  4)  Construction plans for devices,  5)  Material list and vendors,  6)  Notes on use of devices (placement, orientation, etc.).

These concepts, along with material sources that will be provided, will allow you to build devices that should make tangible improvements in your room acoustics.  If you room is basically of sound construction, some of them will cost you less than $200 to implement.  Many of them cost no more than $600 to implement, unless you put a lot into aesthetic considerations.  The different areas that will be addressed in these posts are shown below in “D”.
You will also need basic set-up tools – a good tape measure, a laser level that will provide 1/32” accuracy at 20 feet,  and a digital angle finder (.l degree accuracy at all angles).  A very reasonable version is the Johnson 1186-0200 – about $45 from www.zoro.com or www.grainger.com. There will be notes along the way on how to measure different things, if you have the test equipment, but the posts will be structured with ways to figure things out without test equipment.

 
First, a couple business matters:

Section A)  All of my posts are copyrighted.  Please e-mail me for permission before you copy and paste this anywhere.  Providing a link to the WBF post is fine, since this allows one to read things in context.

Section B)  Disclosure of Industry Involvement:

I am a partner in two audio related companies; Mosaic Audio – Audio interface cables, and Mosaic Acoustics – Hybrid dynamic loudspeakers (transmission line, horn and aperiodic loads incorporated in the same cast housing).  I have initiated patents on this enclosure topology.

I own these two companies;  Theorem Science – Power Conditioners;  and Solution Acoustics – Acoustical treatment systems, and listening environment design and fabrication.  I currently have several patents in process on acoustical  treatment systems.

Many of the concepts and construction notes that I will post are Solution Acoustics technology that is one or two generations back from current thought.  So it is yours for free.

This will be the last post that will mention any company that I am associated with.  But if you wish information on these products, you may e-mail me directly through the Whats Best Forum or at mosaicaudio@yahoo.com.

Section C)  Core Concepts

There are six primary core concepts that underlie much of my work with room acoustics. I will address four of them in progressive posts.  I briefly list these out here (a), along with a more detailed expansion (A) to place the information in a more technically expanded context.

The technical expansion will have terminology with wording that will be unfamiliar or words that may be used in a different way than one might think.  This is because I pull much of this from my technical documentation, where I have developed a bit of a language.  You will see words and phrases such as “contributive effects”, “expositive effects”, “transforms”, “loads”, etc.  The first time there is usage of these, it will be accompanied by a full definition of the word or phrase.  A glossary of this terminology will be at the end of this section on Core Concepts, and an expanded glossary will be at the end of the second post.

The importance of various issues is illustrated here utilizing acoustical events.  An expansion in the second post will show that this is just as important for studio-derived recordings.
The information on Core Concepts shown in this first post is the groundwork for the conclusions drawn in the expansion of Core Concepts in the second post.
1)  Listening Environment Characteristics

1a)   The listening environment should allow you to hear every aspect of what the original performance was like, including the acoustical signature of the original environment.  It must do this without changing anything.

 

1A)  The listening environment should provide a platform for the progressive and precise inverse                   reflection and projection of the “Original Event / Recording” process.  It must not exhibit any characteristics that will alter the projection of energy from the loudspeaker in such a way as to provide a secondary signature.

This is a deceptively simple concept. Number 2 will show you some of the reasons why this is so.  As above, first I’ll give the overview (a); then the technical support copy (A) – which places the information in a more technically expanded format.

2)  Contributive and Expositive Effects

Visualize yourself in a stone cathedral listening to a string ensemble.  There is an “aliveness” to the music, a total immersion in the event.  Now think of the same musicians, playing the same music in a gymnasium with poor acoustics.  For most people it would not be nearly as involving.  The sound coming directly from the musicians is largely the same.  So what makes it so different?

2a)  The differences between these two venues is in what I term “Contributive Effects”.  This is essentially the signature acoustics of the environment that is heard after we hear the initial sound from the musicians.
2A)  The boundaries in the “Original Event/Recording” process have “Contributive Effects”.  I refer to  these as “transforms” (a contributive effect that modifies an acoustical event with the addition of time-derived information that contains: changes in the frequency envelope, and resonance-derived information).   The nature of the delayed near and far field information that is received at the microphone is different in significant ways.  It is delayed in time that corresponds to the distance from the musicians to the surfaces encountered.  These surfaces have absorption / reflection properties that “decode” the nature of this structure.  Some of the frequencies may pass through this boundary, some are largely reflected and some create resonances in the boundary that contribute to the reflected wave.

2b)  A good sound engineer may spend hours setting up microphones in just the right way to capture   the direct sound along with the signature of the room in a natural way.  If he or she is really good, the recording can provide a startling sense of the original performance.  This is what we seek to re-create in our home.
2B)  A good engineer can discern the locations in the original acoustical space that will give playback characteristics of the proper instrument size and spatial characteristics of the musicians, as well as the delayed signature information of the acoustical space.  This delayed information is a variant from the direct musician to microphone path, not only in arrival times from the various locations, but also in the acoustic signatures (absorption/reflection co-efficient) of all surfaces encountered.  A well-executed recording will allow for an uncanny reflection of the original event with proper playback.

 
Here’s where it gets a little complicated..

2c)  In the original recorded event the characteristics of the acoustical environment contributes a desirable signature .  This signature is an extension of the musical instruments themselves, and provides the “cues” that separate an involving performance from one that is less so.

The Listening Environment must behave very differently, however.  It must present the performance just the way it was recorded, or it will detract from the sense of realism.  I refer to this as an “Expositive Event”.  If the end goals correspond to that of #1 above, the room should provide for the exact reproduction of the original performance, with no compression of dynamics.
2C)  The acoustics of the original recording environment provide a “contributive effect”.  The delayed information received at the microphone was that of the original instruments, overlaid with the characteristics of the recording environment:  time-delayed information that contains changes in the frequency envelope and resonance-derived information.

The characteristics of the Listening Environment, however, must exhibit a special set of parameters, unlike that of any other type of space.  It must provide no signature of its own, but rather, provide for the characteristics of the original event to be propagated in a completely neutral manner.  This is an “Expositive Effect”; the ability of a space to provide the goals outlined in #1, while allowing the full linear expansion of dynamic fields, with no compression of micro or macro dynamics.
2d)  While the acoustical signature of a good original acoustical space is very desirable, a signature in the listening room will color the music unnaturally.  If possible, these listening room signatures should be removed, if it can be done without creating other acoustical problems.

2D)  While a “transform” in the original event provides a signature stamp, a transform in the listening environment demonstrates an artifact.    These artifacts should be removed or neutralized, if it is possible to do so without creating other anomalies.
2e)  But methods for removing this signature can be difficult to come by.  Sometimes it is hard to fix one problem without creating other problems.  The primary objective, then, is to find methods of removing signatures in the listening environment without creating other unwanted effects.  Sometimes you have to think “well outside of the box” to find an appropriate solution.
2E)  Many devices for addressing acoustical issues in listening environments are available.  While some of these are effective in addressing specific issues, it is important to note the full characteristics of any device placed within the listening environment.  Does the specific device deal with the entire acoustical issue in a linear fashion?  Does the device exhibit secondary characteristics – such as re-radiated energy at different frequencies?  If so, the device itself creates “transforms”, which must be addressed.

Because the listening environment itself contains “transforms”, measures must be taken to bring the  listening environment into a neutral state in regard to these acoustical signatures.

Once the locations of room acoustical transforms are noted, suitable “loads” must be placed in such a way that the transform is neutralized to the highest degree possible.  My description of a load is “a device that is specifically designed to neutralize the properties of specific transforms without creating secondary properties of their own (especially in the areas of compression and re-radiation of nonlinear energy)”.
Expansion and Summary of 2 – Contributive and Expositive Effects

A pair of microphones will retrieve spatial information first from the direct path to the musicians, and then from all acoustical boundaries in the original performance environment in a time-correct fashion. This time-derived data contains information regarding all surfaces encountered.  At the points of interface, acoustical energy will do various things; some energy will pass through the boundary, some energy will be reflected, and some energy will create a resonance in the boundary surface.  The reflection of this acoustical information from every surface encountered is received at the microphones in a spatially accurate time delayed fashion that elaborates the size and dimensions of the acoustical space, and the nature (reflection / absorption parameters) of all surfaces encountered.

 

The information presented in 1 and 2 bring me to a place where I am willing to state what I believe to be the FIRST Priority to address in listening environment setup.  There will be further information on this in the second post.  So here is my:

 

A)     FIRST CONCLUSION: 

There is a sequence to follow in addressing room acoustics.  The FIRST of these is the ability to replicate spatial properties accurately.  Many listening environment anomalies can be addressed to a reasonable level of efficacy.   However, there is NO acoustical treatment system (to my knowledge) that can restore a distorted spatial field or the loss of time-derived information.

 

If the recording is achieved in a spatially accurate way, and the playback system up to the loudspeakers maintains this time-derived information with integrity, the first goal is achieved.  Now it is up to the listening environment and the loudspeakers to provide a neutral framework that will allow this information to emerge intact.   This will provide a three dimensional shell of information, which includes a spatial field that spreads far beyond the boundaries of the listening environment.  Placing loudspeakers to fully retrieve this three dimensional shell is the FIRST priority.

The “even lighting” of this shell is provided by frequency linearity characteristics in both the loudspeaker and the room.  The even “filling of” – and projection of energy from – this shell is based in the speaker/listening rooms ability to maintain linear energy projection and expansion modes.  If, after proper placement of the loudspeaker,  “even lighting” or “even filling/linear energy projection” present acoustical issues within the listening environment, then these issues should be addressed with appropriate “loads” in the listening environment, rather than movement of the speakers.

Unless absolutely necessary, speakers should never be moved out of the spaces where spatial information retrieval is best.  Information on addressing room issues with “loads” will be coming in the upcoming posts, as well as ways to set up loudspeaker alignments for maximum signal integrity.
3)   Convergence Patterns

An understanding of convergence patterns provides key insight into the many factors that affect room  acoustics.  Ideally, like the Lamborghini Egoista, the perfect listening room (from an acoustical standpoint) should only be designed for use by one person at a time.

If further listener seating were required, it would be provided front to back, rather than side to side. This would still allow for the symmetrical projection of energy to each listener’s ears.  As this is generally not plausible, the level of compromise for the “sweet spot” must be factored in for a multiple seating environment.

Convergence patterns play into the design and placement of acoustical room treatment devices for specific types of loudspeakers.  If one expects to change the primary loudspeakers at a point in the future, then flexibility in the acoustical treatment systems should be designed into the room from the start.  This is especially true if one anticipates moving to a speaker that is based on an entirely different operating topology and methodology.
4)   Differences in Auditory Sensitivities

People have very different sensitivities to various auditory parameters; phase integrity, impulse  response,  spatial cues, transparency, micro-dynamics,  linearity , etc.  Just as this will be reflected in the type of speakers they choose to purchase, it may also reflect which room parameters to address first, and to what degree.  For example, the fourth post will show why the ceiling in front of the speakers is the most critical area to address for multi-driver speakers that emulate a point source.

Section D)   Next Five Posts

The next post will fill in more on the Core concepts, and touch on several acoustical “Laws”;  things that in my experience are somewhat fixed.  I will pick up more of the technical aspects of the first two posts in post 7 (if there is interest), where I will begin outlining basic issues relating to room design.

Acoustical Room Fixes:

My 3rd through 6th posts will address simply-executed and inexpensive “fixes” for primary acoustical room anomalies.   In 3 to 4 weekends of work in your garage, and at a total material cost of $600 to $2000, I would project that you can address 80% of the primary acoustical issues, at an efficacy of 75 to 85%.  You may even be able to do better than that.  Here’s an upside; it is possible that the room treatment systems that you remove may sell for a higher price than the cost of these “repairs”.

Post 3)  Secondary Support Modes:  This addresses non-linear bass modes – which correspond to  peaks, suck-outs and overhang.  The primary cause is usually either room dimensional issues or room boundary anomalies.  Depending on the gravity of the issue, correcting 60% to 70% of this is usually a very inexpensive fix;  $150 if you do not care  what it looks like, $500 and some time for it to look good, and $1000 and up, if you want it to look  aesthetically pleasing.

Post 4)  Time Staggered Ceiling Reflections:  This seems to be one of the most overlooked areas in room treatments, yet it is often the most crucial, especially if you have lower ceiling height or dynamic speakers.  Everything you gain from having invested in a speaker that emulates a point source is markedly compromised by the ceiling.  Its’ easily fixed though.  Depending on the degree of the issue and the level of aesthetic finish, this will cost anywhere from $200 to $800.

Post 5)  Isolated Mechanical Speaker Grounds:  This can be done for as little as $100, but costs about $500 to implement fully.  This provides for greater inner-space silence, lower frequencies floated in  space – rather being centered in the loudspeaker, markedly improved inner dynamics and a removal of many overhang characteristics.  I’ve been doing this in almost every installation for the last 30 years.

Post 6)  Symmetrical Energy Projection/Speaker Alignment:   The symmetry of acoustical energy projection modes is very important to address if you have a  dedicated listening room. Even an irresolvable acoustical anomaly on one side, should be mirrored on the other side, if possible.  I know that this may seem totally counter-intuitive, but I’ll explain why in this upcoming post.

The first thing to address is bringing your speakers into perfect symmetry in relationship to each other and to the room boundaries.  You would be surprised to know just how far out of alignment your expensive speakers might be.  Correcting just a 1/4 degree offset of speakers on all axis will gain you a great deal more than you might think.

In every aspect of the work illustrated in the upcoming posts, a minimalist approach is key.

Section E)   Answering Questions

I can usually spend ½ hour each day on answering posts – at most an hour.  However, the development of my primary posts will involve a great deal of time, things like going back to construction notes, notes on the rational of the approach, measurements, efficacy of treatment,  etc.  I expect to be able to post a new topic every month to six weeks.

If you have a technical question of importance on room acoustics, you may e-mail me directly through the forum or at: mosaicaudio@yahoo.com.  If I can‘t answer the question quickly, I’ll reply with an estimated time frame of when I’ll be able to respond.  If it is of a complex, time consuming nature, I’ll have to give you a quote on cost.  I can’t give substantial blocks of time away without compensation.

Section F)  Quick Proof of Concept
First read “A)  FIRST CONCLUSION” at the end of section 2.  You may wish to re-examine your primary speaker placement before you take on the following.  Before you move your speakers, mark out masking tape around the footprints so that you can return them back to the exact original position, if you wish.
After the first two posts that lay some of the theoretical groundwork, we’ll turn to the fun “proof of concept” part in posts 3 to 6.  Since these will probably be out six weeks or so, I’ll give you something to work with in the meantime.  Its’ based on the 3rd post (which is far more comprehensive), and if it does not work, your total outlay will be one roll of masking tape and a piece of paper (just return the bags of sand to Home Depot for a refund).

If you have a bass resonance / suck-out in your listening room that’s been hard to get rid of, try the following steps.  The methodology is to seek out locations of strong resonant modes, and place something directly on them that contains a highly reactive mass.  The premise is that this mass will interface in such a way that the acoustical resonance will be dissipated into the mechanical movement of the aggregate.

First, select low frequency source material that you are familiar with that has both percussive (such as a Kettle drum or Kodo drum) and more steady state (such as organ or bowed bass).  Listen to you system set up as it currently is – all room treatment included.  Very carefully notate the levels on each track.  You will want to replicate these levels exactly at each phase.

Now get a roll of masking tape and eight 50 pound bags of sand at Home Depot.  Empty two gallon buckets (6 or 8) are useful for fine tuning.

Carefully mark out the locations and orientations of room treatment systems for bass frequencies before removing them from the listening room.  You want to be able to return them to the exact location at a later time, if necessary.  It is important to expose the bass modes at their full level.

Now listen to the system again – same tracks, same levels.  Readjust to what the room is now doing.

Lay out a grid of one foot squares with masking tape on the floor behind your speakers.  If you have the appropriate test equipment, map out the peaks and dips along the grid (with the microphone set at 40“  from the floor) – a waterfall plot is even better.  Notate these also on a sheet of paper with grid lines that correspond to the masking tape grid on the floor.

If you don’t have the test equipment, here is a way to get a reasonable plot of resonances (even if you have plotted this out with test equipment, the following may help you hone things in).

Find a friend with a deep voice.  Sit in your listening position and have your friend walk this grid while he speaks at a uniform level.  To start, have him cup his hands over his mouth slightly.  This is the type of resonance that you are listening for.

Mark out the areas where the voice becomes resonant-laden and cloudy.  There are usually 2 to 3 of them behind each speaker.  If your room is symmetrical, these modes should be symmetrical side to side.  Mark them out with tape on the floor as to the level of severity.  Also map out these locations on a paper grid.  Also note where the voice becomes clearer as well.

[ [ NOTE:  If have taken these steps this far, and have any problems with latter steps, I will be glad to help you.  In order to do that, I must have the following;  A PDF that accurately shows from a top view the placement of speakers, room furnishings and your listening position in the room  (along with ear to floor distance in your listening position), accurate room dimensions and three photographs of the listening environment.  Send these to me at: mosaicaudio@yahoo.com ] ]

Now, taking the worst resonance area, place one sand bag on each side behind the speakers, centered on top of this location with the bag length front to back, rather than side to side.  Now repeat listening to the same tracks.  There should be a tightening up of the bass, with less overhang, though at this point it may be subtle.

Now place a pair of sand bags on the second worst mode in the same fashion.  Do repeat listening. There should be another reduction, though this time it will probably be more directed to the overhang characteristics, rather than the room peak.  If there is a suck-out in the mid-bass, the amount of sand will have to be smaller.

Now place a second bag on top of the first set of bags you put in place.  This should result in a noticeable reduction in the room peak.  The combined effect of just six sandbags should reduce your bass peak by at least 20%, and overhang by as much as a third.

But you can take this much further.  Experiment with additional sandbags.  Keep in mind that the worst location is usually associated with the magnitude of the peak, and the second worst often affects the overhang characteristics.  You will rarely have more than two bags (in fact, its’ better to use the 2 gallon buckets to progressively tune this area) on the secondary location – more can create a suck-out.  But you might end up with five bags on each primary location if you have a very bad bass peak.

Here are some things to note as you listen.  As the room resonance diminishes, the bass will get tighter and go deeper, but it may not seem as loud as to what you‘ve become accustomed to. You will probably have to do a mental reset for these new bass levels.

As you get closer to eliminating this bass mode, you should start sensing far more clarity, authority and projection of energy not just in the lower frequencies, but across the whole band.

Here is how to know you’ve overdone it.  The lower bass will start to dynamically compress and get too lean.  Remove one set of sand bags from the primary location if this occurs.

At this point in time, you may choose to address the third resonant mode, if one was noted.  This will rarely get more than one 2 gallon bucket of sand.

Note that this is just something to try out until I get post three up in a few weeks.  But if the sandbags work for you, keep the sand.  You’ll want to put it in cylinders made out of 8” and 10” Sonotube (also at Home Depot).  Post three will be far more comprehensive in how to make this system work.

Summary:  I will complete the overview in the next post.  This post will also flesh out the Core Concepts and “laws of acoustics”.  The first two posts lay out the primary technology that is the basis of future posts. The 3rd post onward will be much easier reading.