Surround Sound Monitoring Room Acoustics

Tomlinson Holman, in his book entitled “5.1 Surround Sound Up and Running”, discusses the room acoustic requirements for monitoring a 5.1 mix. He states,

” Multichannel affects the desired room acoustics of control rooms only in some areas. In particular, control over first reflections from each of the channels means that half-live, half-dead room acoustics are not useful. Acoustical designers concentrate on balancing diffusion and absorption in the various planes to produce a good result.” If live end/dead end is not useful as it is in two channel monitoring, what are our options with multiple channel monitoring in terms of acoustical treatment?

It appears that primary reflections off of our multichannel monitors are as much of a concern as they are in two channel. Primary reflections distort the more pure (without the room), direct sound from the monitors. The engineer wants to hear all the vocals and instruments from the speaker without the room reflections. Room reflections add the sound of the room into the mix and that is not acceptable. Near field monitoring is a process to minimize room sound by sitting closer to the speakers to hear the wanted direct sound. It is important in two channel audio and it is even more important with multiple channels that are all producing energy at the same time. No need to add room sound to 2 channels, let alone 5.

He states that acoustical designers, “concentrate on balancing diffusion and absorption in the various planes to produce a good result”. If we look at each plane or room boundary surface for two channel sound, we can get an idea on how to balance absorption and diffusion in a multiple channel presentation. The ceiling must be a balance of diffusion and absorption in two channel sound as well as multiple channel monitoring and playback. We definitely do not want ceiling reflections in our mix, just as we don’t want them in our two channel presentations.

The same will apply to all the room surfaces. A balance of diffusion and absorption will work for all the room boundary surfaces. Each surface should have the same amount and type of diffusion and absorption to provide the engineer with a uniform and consistent room sound. In two channel sound, we tend to absorb the primary reflections and use diffusion in other areas. With multiple channel monitoring consisting of multiple, mono sources, we must have a balanced acoustical field for all channels.

Low frequency issues must also be addressed, so that the low frequency effects channel can be monitored correctly and produces the necessary energy level to fill a room with explosions and other special effects. Muddy and bloated bass energy will only confuse the listener and smother the middle and high frequencies. Vocals will be lost in a low frequency muck that may prevent localization of the vocals with the image on the screen. Video movements on the screen must have a corresponding audio movement from channel to channel. Low frequency absorbers whether freestanding or built in are a must.

I hope this explanation helped. Please leave any comments below so I can get back to you. Don’t be afraid to hit those Facebook like, Google+ and Twitter buttons on the left hand side so other people can see this post. And if you want to learn more about this subject please sign up for our free room acoustic treatment videos and ebook which provide step by step instructions. Get instant access by signing up now.


How To Choose The Correct Speaker

February 22, 2012 No Comments

Working out how to choose the correct speaker for the room you are going to be using it in involves many factors. All of these factors must be considered when selecting a loudspeaker for your listening room. We are just referring to two channel sound sound with a left and right channel speaker. We need […]

What is Good Sound?

What is Good Sound?

I walk through trade show rooms and listen to the exhibitors tell me what they consider good sound. They tell me their room is kind of their idea of good sound. Some tell me that their room sounds pretty good but does not fall into “good sound”. A hotel room is a compromise and one must work around many variables to achieve a sound that demonstrates what their product could sound like in a good room some say.

Some rooms have too much bass energy. Some rooms are bright and have so much specular reflections that it is difficult to hear all the vocals in a three part harmony or hear two bass instruments each producing their own sound.These rooms are characterized by low definition and a small image. Some rooms have the listening chair up against the back wall. Some say,”Our room will have the best sound of show”. Really?

I guess everyone has a different idea of what “good sound” is. Is good sound the type of sound where their is an emotional attachment immediately to the music? Is good sound the type of sonic presentation where one can hear every instrument and vocal in a balanced presentation? Is good sound the type of sound where the speakers and amplifiers disappear and one can only hear and “see” only the music? Is good sound a combination of some of these variables and not others?

For us, it is removing the room from the sound and having the ability to hear all the instruments and vocals in a balanced presentation.To achieve this objective, all low frequencies are heard without any bass bloat. There are layers to the bass and the bass attack and decay is as tight and clean as the attack and decay of middle and high frequencies. Middle and high frequencies are layered like our bass presentation and their is a distinct separation between the instruments and vocals.Comb filtering of middle and high frequencies is under control. Their is air present and instruments and vocals float in the room all across our sound stage. No speakers are seen or heard.

How does one achieve good sound? I am sure their are many approaches as there are opinions on what constitutes “good sound”. We choose to reduce low frequency pressure in the room from all low frequency producing devices. One must first deal with low frequency pressure in order for the middle and high frequencies to come through without being smothered by excessive low frequency energy. Excessive low frequency energy can be controlled at the source or at room boundary surfaces. Middle and high frequency reflections off of room walls can be controlled through the use and application of absorption or diffusion technologies.All of this control must be applied in a way that produces a balanced sound stage with a height, width, and depth.

Headphone Sound or Room Sound

Head phone sound is different than sound in our rooms. Both have their good and bad points.

Head phones seal our ears with a small oval shaped room. Inside that “room” is a small speaker that produces sound energy and fires it directly into our our outside ear. From there, the sound travels into our ear canal and then finally into our inner ear. We hear bass energy, middle, and high frequency energy all evenly portrayed in the two channels that are wrapped around our head.

Were our ears designed to have sound that close to it and at those pressure levels produced by headphones. If they were wouldn’t they be smaller. No need for three or four inch ears if the sound we hear is generated from such a short distance away as with headphones. No, our ears were designed to hear sounds from all directions and at some distances. Men have larger ears than women. This is probably due to the way men used to hunt for food. Hearing everything from all directions when hunting for food, enabled man to bring home the dinner rather than be the dinner himself. A larger sound receiving instrument was needed to allow for selective hearing and localization of predators.

Do headphones produce a sound stage in front of our head. I have never experienced that with headphones. I have experienced both left and right channel separation, but no sound stage. Headphones do not have a sound stage and therefore do not have any height, width, or depth to their sonic presentation.

They do have definition. Headphones portray every sound in detail. One can hear all the instruments and vocals with distinct separation between them. If we can get our rooms to have that instrument and vocal separation coupled with headphone like clarity, we will have achieved our room acoustic objectives.

A room has space and the sound source is at a much farther distance from our ears than headphones allow for. We can have a small as is the case with near field listening or monitoring. We can also have a large sound stage depending on room dimensions and the correct balance in the room of acoustical treatments. A room and the sound produced in it is easier for the design of our ears to interpret. The music or sound reaches our ears in a way and manner that allows for localization and spaciousness to occur. With this spaciousness, we now can have information going into our brains that has much more data in it than just headphone sound. We have room sound and room sound is closer to free space sound which is probably how our ears evolved into the size and shape they have today.

Db Meter

A popular search term in audio is “db meter”. Sometimes people search for terms that they think go together or they have seen or heard it used somewhere. Sometimes there is a combination of words into a phrase that tries to illustrate an audio point or concept. Lets examine each word within the search term “db meter” and see if it the right word or group of words to use in this situation.

Db stands for decibels and is a unit of measure that those in the audio world use to describe intervals or amounts of energy within in a given environment. It is only that: a unit of measure. It does not have any value of its own other than to say it is a unit of measure that is calculated and formed to correspond to the human ear hearing range. A large db number can cause inner ear damage. A smaller db number may be too low to hear the difference in gain jumps. A db is part of a scientifically calculated scale or ratio for human hearing comparisons and even regulations.

What does the db unit mean when it is attached to a number? A db meter measures sound pressure levels.The sound pressure level can be assigned many different units of measurement. Therefore, using a ratio is better for human sense of hearing comparisons. A db unit is a ratio of acoustic power levels expressed in decibels that “comply” within our human hearing range. These are decibels that express a power ratio made for human hearing measurements. For example, a Saturn rocket has a sound pressure (Pa) of around 100,000 Its sound pressure level measured in db is 194. Normal conversational speech has a sound pressure of .02 while the sound level is 60.

Searching for a db meter may be confusing for the clerk at the store, sine we are really measuring sound pressure levels expressed in decibels in our room. Although, if you go to Radio Shack and ask for a sound pressure meter, they will search their product data base and will find no entries in it for “sound pressure meter” If you change your request for a db meter, they will have one for you quickly. It is funny how things work.

Building a Sound Room with a Living Roof

We have a client in Arizona who wanted us to build him a sound room with a living roof. A sound room you are all familiar with. A living roof may be an other issue. It was also a pleasant surprise for us.

A living roof is a roof designed to support 18″ of top soil and the watering and drainage system necessary to maintain this miniature ecosystem. Supporting 18″ of earth and water is no easy task, especially when the roof size is 25′ x 50′. That is 1875 cubic feet of earth at approximately 20 lbs. / cu. ft. is 37,500 pounds of earth, not to mention the piping for water and drainage. The roof must support 16 tons of earth and pipes.

Earth is an excellent barrier to external noise. Go into your basement and sit quietly. There you are surrounded on 4 sides by earth and concrete. In this project, the roof and 6′ up the 12′ side walls will also be covered with earth. So, in this project we have 1 1/2′ earth on the roof and six more feet of earth on each wall side. Now, we need concrete walls at the correct thickness to match the acoustical properties of 1 1/2′ of earth on the roof.

We determined that an 8″ poured concrete wall all around will meet all our structural issues for ceiling support and acoustical issues for sound transmission class ratings and all external noise measured calculations. The 8″ concrete shell will build a room that is 25’wide and 50′ long. The ceiling height is 12′. One could not ask for a better room size when it comes to acoustical issues that must be dealt with.

At 50′ in the length dimension, even a 20 Hz.wave, which is the lowest wave we usually work with in rooms has some room to run. No low frequency issues or any others for that matter when it comes to the 50″ length dimension.The 25′ width is also good for low frequency, but will give us a few issues. Those issues will be resolved through the use of our activated carbon technology which will be added to the inside walls. A ceiling height of 12′ only increases our room volume and is welcome for all forms of sound playback and recording.

Personal Listening Environment # 2

If you spend as much time in your personal listening room as I do, you hear many different things and you become comfortable with the sound in your room because you have worked hard to get it to sound the way you want it to. I believe most of us set up our personal listening environments in a manner that allows us to hear as much of the music as we can. This attention to sonic detail helps us develop an emotional connection with the music.

One of the many things I notice is that when I enter my personal listening environment is that the outside world does not follow me into the room. It is almost like some type of force field that will not allow the energy of the existing and outside world in. This really becomes apparent when you hit the play button on the remote. If the “force field” is strong enough to keep out the outside world by just closing its door, it completes the job when music fills the room. What a joy to not think or hear anything but music; feel anything but emotion.

Sometimes on recordings that you have played over and over, you will hear a new sound. You know the recordings I mean. They are the ones that you know every pause or breath the lead singer takes and every note the guitar player uses on a fiery break. They are your comfort and go to songs when you really need to disconnect. Somehow, someway, you bend down to pick something off the floor and just as your ears move in a vertical plane down the speaker’s vertical axis, you, for a split moment hear something new. You pause, take a breath and reach for the remote. There it is again. Thank you, room !

Sometimes one can connect so well to the music that dancing and air guitar behavior occurs. Now, this is a real connection. It is a digital cable from your ears to your heart. It can be facilitated by time shifting your stream of consciousness through the use of intoxicating beverages. I don’t know why the volume is increased in direct proportion to the amount of fluids ingested. It seems to always be the case when you check the gain control the next morning. Perhaps beverages of this nature should come out with a warning label that states: Expect 10 dB increase in SPL for every 12 ounces consumed.

Hi End Stereo

Hi end stereo is a term that has been with us since the 1950s. It probably started with the Dynaco amplifiers that people used to build at home. They were tube amplifiers that produced around 50 watts of power and sounded good. Individuals expanded upon this basic technology and began to use different techniques to create a better sounding product. I think it was this passion and concern for sound quality that created hi end stereo.

Hi end stereo is composed of amplifiers, speakers, cd players, turntables and cables. Each manufacturer tries to develop their respective technologies and create the best sound out of their products they can. An amplifier manufacturer seeks to produce the best sound they can from each watt of energy their products produce. A speaker manufacturer tries to produce sound that resembles a real instrument or vocal. Cd player and turntable manufacturers try to minimize vibrations and generate a distortion free signal. Cable companies take all of this energy and try to pass it through to each component in the cleanest way possible without adding any coloration of their own.

The most important component in the hi end stereo chain is the room in which all of these components are assembled and listened to. I want to say that that room acoustic product companies exhibit the same passion in producing their products as the amplifier, speaker, cd players, turntable, and cable manufacturers, but I can not.

Most room acoustic companies create products that are cheap to manufacture, inexpensive to purchase and when they installed in a room, they sound like no effort was put into their development. I want to say that room acoustic products are viewed as an equal quality component in the hi end stereo chain because they are. Of course, I want to say that because it is more than true. I just wish more acoustic product companies had the same passion in creating their technologies as the other members of the hi end stereo chain.

Room Music

Room music is a search phrase that 368,000 people used last month in Goggle. It is an odd blend of words to search for and I really don’t know what the search objective was for those 368,000 individuals. Were they searching for a room to play music in with a sound system? Were they looking for a room to play music in with an instrument or vocal?

At Acoustic Fields, we hope all rooms are room music. Having a room that is designed to portray music in the best manner possible is a blend of both science and art. Science and the products that science creates can help deal with the two major issues of room acoustic management: room wall reflections and low frequency pressure. If one does not control reflections from all the room boundary surfaces, there is no chance of having any quality room music. Reflected energy arriving at our ears from all room surfaces, confuses our brains and any music created will go unappreciated. Without proper low frequency, energy pressure control, there will be no room music at all. It will be smothered and blurred to the point of creating interference in all frequencies in any music type presented.

Lets have room music in every room from now on. Lets use our science to create products that make every room a music room. Forget about living in the room. Lets have a room only designed for room music. It will be a room with amplifiers, speakers, and a music source to play room music from. It will have just two live beings in the room; a man and a dog. The man will be there to feed the dog. The dog will be there to keep the man from touching the equipment.

Hi – Fi Room

Another popular search term used in Goggle in our business is the term hi – fi room. I am going to assume people are searching for information on how to create a hi – fi room. At least, I am hoping that is the case. Now, we are talking.

If someone is considering creating a hi – fi room, they have made a decision to have a dedicated space in which to put the tools of hi – fi into. They will need a set of speakers, a stereo amplifier or better yet a pair of mono amplifiers, one for each channel. A cd player or a cd transport with an external digital to analogue converter rounds out the playback equipment chain. If someone is really analogue oriented, they could use a turntable. Don’t forget the cables to connect all the components to each other.

The last part of the search term hi – fi room is the most important. One must have a room to place the sound playback equipment in. The same care and attention as one uses in choosing their equipment must also be given to the choice of room to use. Parallel walls with an 8 degree splay, rectangular shape, 20′ wide, 30′ long and 12′ high, poured concrete construction with two external walls at least 6″ apart, a direct line from the utility companies transformer outside the room to at least a 600 amp board with computer grade isolation transformers for any power line noise suppression, dedicated, 30 amp lines for each piece of equipment, and all of one’s favorite cds or albums.

Oh yes, I almost forgot about the chair. On second thought, with all of the above, who needs it.