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Room Acoustics: Science and Art

MikeSorensen May 16, 2012 No Comments
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Room Sound

It is amazing to me that each room we go into has a different “sound” to it. Some rooms (most) have a lot of bass energy. Some have low reverberation times, some high. Sound stage presence ranges from small to not so small. Individual vocals and instruments can be heard or smothered in a comb filtered bath. Room sound seems to vary with the personality of the room user, the personality of the room, and the room’s use objective. We must use science to assist us with low frequency resonances and their associated harmonics within our rooms.

Bass Energy

Bass energy or low frequency control in our rooms is a constant and predictable sonic threat unless we have at least a single room dimension of 30′. Two room dimensions of 30′ is even better. No one has that. Therefore, we are all faced with managing low frequency issues within our rooms. We must manage because low frequency energy issues in our rooms is like having a chronic disease. You will never be completely cured, but science can help you manage it and keep it under control, so it does not interfere with the chosen room use. Low frequencies blurring and smearing our mixes in the recording process are as unwanted as “bass boom” in our home theater and listening room environments.

Bass Control

How to control bass energy issues is another story. First, a clear and concise definition of low frequency is required. A lot of companies who build acoustical products use the label low frequency or bass absorber too freely. Most room “bass absorbers” do not really absorb bass, at least bass in terms of the frequencies that cause real acoustical issues in small rooms. In fact, the term “bass absorber” is a misnomer all by itself. Absorbers do not really absorb bass in the total sense the name implies. They absorb at different rates and levels depending on the low frequency targeted and some do way better than others at this task. Lets use a definition that says bass energy and the room problems it creates is any energy below 100 cycles. This is a good frequency break point since frequency issues above 100 Hz. can be easily managed with current available absorption technology that is consistent and predictable. Frequencies below 100 Hz. are much more difficult and require specific design criteria to accomplish.

Individuals using most of the rooms we have been in have resigned themselves to the “fact” that this is the way bass sounds in every room. Bass is always bad and we just should get used to it because that is the way it is in smaller rooms. This has been their experience and their experience tells them that bass in a room is always like what they now hear with all the resonances accompanied by the blurring and smearing of vocals and instruments. It is not good but we just have to live with it, work around it, or try to ignore it. This is the thinking.

Make The Room Smaller

Most rooms are bass heavy and the individuals who are listening or working in the room have accepted that small rooms are bad for bass. They are but one can reduce resonance enough, not eliminate, so that there is a more clear and defined bass energy presentation to the room. You do not do this by making the room larger (wish), but rather, by making it smaller. You must make it smaller using that proven and time tested method of real, low frequency absorption, namely diaphragmatic absorption. It must be built with using as low of a resonant frequency for the absorber as the room exhibits resonances and having at least 14″ – 16″ of space to work with. It will be heavy, but it will provide a rate and level of absorption that will let other energy come through uninhibited. Bass can be managed, so that it gets out of its own way.

Mids and Highs

Middle and high frequencies within our rooms are another facet of this science / art blend lacing itself through room acoustic science. You can go into a professional recording studio and listen, please listen at same pressure level, and hear one type of room sound. Lets just call room sound the sound from the speakers and the room all mixed together. Go to another recording studio down the street, different sound completely, not even close no matter what listened to pressure level.

Best Sound At Show

Home theater or listening rooms are the same. Go to a audio trade show where they have different speaker and amplifiers set up in basically the same size rooms because they are really all hotel rooms with furniture removed. Well, not all furniture has been removed. Listen to the same equipment type. Listen to just tube amplifiers and solid state amplifiers. Listen to how different each room sounds with basically the same equipment in it from same size room to same size room. Listen to the same size speakers in each room. Most exhibitors will tell you that they are going to win best sound at show.

Both professional and consumers think their art sounds good to them and I am glad it does because you want to work and play in an environment that sounds good to you, not the other way around. However, better sound is there in your room. One can have it and stay in the same room. It just takes a little acoustical effort especially with the low frequency energy in the room. Diaphragmatic absorption will manage excess low frequency pressure issues. Middle and high frequency absorption is available for those problematic frequencies above 100 Hz. We even have diffusion which can be spread out in both horizontal and vertical planes to provide us with two dimensions of diffusion in our rooms. Use diaphragmatic absorption to cover the resonances in the room and then use absorption/diffusion to inject “air” into your sonic presentation.

MikeSorensen

I am a structural engineer as well as a master furniture maker. I design cabinets for low frequency, activated carbon absorbers. Connect with me on Google+

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