Free Space Listening
If we want to hear sound in our two channel and home theater systems the best way possible, we need to move our stereos and home theaters outside in the mountains somewhere away from civilization. An ideal setting would be a grass land area surrounded on four sides by mountains to shield our sound presentation from the wind. No babbling brook close by just a nice flat area covered by grass at least 6″ thick. We want to keep ambient noise levels as low as possible.
Free Space Sound
This idealistic setting would be termed free space listening. Free space because we are just that, we are in a space that is free from any room boundaries. The only surface we will have to deal with is the earth. We will not have four walls and a ceiling to increase middle and high reflections and cause low frequency pressure build ups which produce resonances or standing waves. We will have just our speakers and a chair. Now all we need is a quiet and steady power source.
Our four walls and ceiling in our listening rooms, home theaters, and professional recording studios produce a sound of their own. It is termed “room sound”. Every room has its own sonic signature. It is not as unique as a fingerprint, but it is close. The size or dimensions of the room contribute to the overall room sound by defining the volume of the room and how that volume or capacity reacts with low frequency energy that is placed inside it by our speakers. The dimension that spans from our left side wall to the right side wall produces a certain set of resonances that are the most powerful and can present the most difficulty in dealing with acoustically. These are axial modes which represent two opposite, parallel surfaces. Tangential modes represent four surfaces and oblique modes involve all six room surfaces. We have distortion everywhere.
Room sound is also influenced by the room materials used to build it. Sound or rather the sounds produced inside of our rooms take on the color or characteristics of the surfaces that they strike. If sound strikes glass, we have “glass sound”. It is a bright and harsh sound that destroys middle and high frequency clarity. A room made mostly of wood will have a far different sound than a room made from drywall. Wood has a warm, harmonic, and richer sound that is very welcome to our ears. Drywall, well drywall, sounds exactly as the name implies. No need to say more.
Our rooms produce a sound of their own because of dimensions, volume, and materials they are constructed with. Each wall contributes its own set of ingredients to our acoustical room soup. Most of our room boundary surfaces effects have an impact on our sound stage. A sound stage is the distance between our speakers, above our speakers, to the left and right of our speakers and even above our speakers. It is the stage in which our electronics portray the music stored inside them. It is our speakers and amplifiers job to portray each and every vocal and instrument on our sound stage. With a properly designed and created sound stage, our speakers sonically disappear and our replaced by the music. If it is done properly, you are brought up out of the audience on to the stage. Don’t forget to bring your instrument.
Walls and Ceiling – 83%
Our room boundary surfaces or walls and ceiling produce 83% of the room sound we hear. The walls deal with many rays and waves of energy striking their four surfaces. Some of this energy is absorbed by the wall, some is not and is reflected back into the room. Energy from our speakers strikes the side wall and we immediately start this acoustical chain reaction which bombards the listening position with wall surface reflections and these reflections are then laced with the wanted direct energy from our speakers.
Direct Sound Please
The wanted, direct energy is the energy that travels the shortest distance to your ears directly without reflection off of any wall surface from our speakers. Draw a a straight line from your speaker cone to your ears. That is the pathway direct sound travels. A properly set up two channel room will have all side wall reflections delayed below 15ms.from the direct sound. This will allow for the correct balance between direct and reflected sound at the listening position to produce a full and balanced sound stage. This can be accomplished using the correct diffusion and absorption technologies.
Side Wall Reflections
Side wall reflections uncontrolled, confuse our hearing mechanism and distort the direct wanted sound. We do not want all direct sound from our speakers in a play back, listening mode. We want approximately 70% direct and 30% reflected or “room sound”. So, reflections must be controlled not eliminated. This is not the case with professional monitoring of recorded music for edit. We want no room in the mix. This is the very reason behind near field monitoring. Side wall reflections properly controlled, can add more width to our sound stage. We can actually create a sound stage that extends more right of the right channel speaker and more left of the left channel speaker with a greater height and depth, by minimizing and balancing reflections at the listening position.
Front And Rear Walls
Front and rear walls can be acoustically extended. With a balance of diffusion and absorption on both the front and rear wall, we can have a sound stage that has more depth that extends from the front of the stage to the rear of our sound stage. With diffusion on the front and rear wall surfaces, we can also realize more separation in our vocals and instruments which provides us with more definition and focus. We must use two dimensions of diffusion on the front and rear wall surfaces to allow for the front and rear walls to acoustically disappear. A series of vertical and horizontally placed quadratic diffusors will accomplish this. One must make sure the listening position is far enough away from the front and rear wall diffusors, so that the diffused wave form has time to develop fully before reaching the listening position.
Our ceiling must be treated with three types of acoustical treatment. We must first have both horizontal and vertical diffusors and with those a proper balance of middle and high frequency absorption. We want our ceiling to acoustically open up or as some say disappear and add more height to our presentation, so that our sound stage sounds much larger. Just as with controlling side wall reflections we widened the sound stage, we can raise the height of our own sound stage by diffusing and absorbing all ceiling reflections at the listening position in a controlled, balance, and measured manner.
Our walls and ceilings contribute to the sound we hear in our rooms. Every room has a sonic signature (room sound) that it imparts onto and into our music playback and recording sources. Understanding what each surface contributes to the total room sound and then applying the proper room acoustic treatment goes hand in hand. You can not successfully have one without the other.
If you would like to learn more about room acoustics please sign up for my free videos and ebook by joining the mailing list here. I send room tuning tips and things for you to test in your room every Wednesday. They are easy to follow and will really help you enjoy more of your music.
Alternatively feel free to contact me directly at: 520 – 392 – 9486 MST or email@example.com. You can see more of my research and development story and why I started Acoustic Fields at: https://acousticfields.com/who-we-are/.
Thanks and speak soon
Very few people attend to define what is ideal listening environment so I am pleased to see that in your case you consider it as being grass with mountains in far distance. The problem is that some might argue that such open space arrangement with zero background noise would arguably not be as pleasant as for example another extreme (and yes this is more artificial definition) where you would still have grass but you would find yourself in the forest and garden which would produce perfect theoretical diffusion sound.
In this case you would have no idea where the sound comes from but you would be exposed to 100% perfectly diffused sound across all frequencies between 20Hz and 20kHz.
Some audiophiles try to present that the main objective is to listen to sound precisely as recorded = authentic. Than they often complain about recording qualities because lets face it recordings quality differs a lot!
So at the end of the day and arguably the real definition of ideal sound environment would possibly be such where listener understands what they LOVE and because they understand principles and they know how to get there without spending large sums they can suit themselves maximising pleasure and enjoyment of listening to music.
A room has its own “sound”. This sound is composed of the room dimensions, volume, energy levels, surface materials and wall construction methods. Modal pressures and reverberation times are also factors. With all of these variables to balance and maintain, it is better not to have a room. If you look at all the motivations, both subjective and objective behind acoustical treatments, you quickly realize that the room should just go away which is what we try to accomplish with diffusion and absorption technologies.
It is always an uphill battle as one tries to overcome the room sound at every turn during the room tuning process. With unwanted, low frequency pressure issues and the need for proper reflection time signature management for direct versus reflected energy, the room is always in the way and quickly becomes its own sound source and source of many issues that must be dealt with in a systematic and hierarchy of order of importance because all sound energy that is heard is a factor of so many of these variables that are all bi products of each other and each one’s acoustic contribution is directly impacted by each of the other variables. A single sound can have many room contributors.
Your room can be made to disappear acoustically but the space requirements to accomplish this actually make the room smaller. It is a bit counter intuitive but surface areas must be covered with either absorption or diffusion technologies and this reduces the physical area within the room. Low frequency pressure issues demand depths of up to 15″ in some cases to correct. How much, what type, and where to place everything must be addressed and calculated based upon room usage. I would rather just set up my system outside and yes, a grass floor would be welcome, especially around nap time. Unfortunately, finding such a place is no easy task with all the crazy humans running around.