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Acoustical Science

In the science of room acoustics, we have many variables that we can measure. We can measure resonances, reverberation, and frequency response not to mention a host of others. Each variable has an associated acoustic sound in our room. We measure these variables using science to assist us with certain starting points. That is all science can do for us is give us a starting point and for that we are thankful. The real “science” occurs when we take our personal perception of what good sound actually is to us and use this perception to voice the room.

Science and Art

Voicing a room is a blend of science and art. The science comes from measurements and numbers. The art comes from taking those numbers and fitting them or parts of them into our sonic perception of how much,for example, reverberation should we have? We know the numbers, but where on each side of those numbers does it lie for us. Which ones and how many of the resonances should we tame to allow us to be comfortable with the low end of our room? Is the attack and decay rate what we want? How much absorption do we use to minimize reflections? We must balance science and art.

Easy Science

It is easy to “get the numbers” to any variable. We can measure for it or look it up in a book. We can do this using very little time or energy. However, we must ask,”How does it sound to me”? Do I like it? Can I and do I become emotionally involved with the music. Does the room help me with my emotional connection with the music? What little things can I do to make it sound the way I want it to. This is the voicing part of the equation. This part takes much longer and is way more fun. It is a journey that must be taken slowly and done over longer periods of time.

Low Frequency Resonances

There are three parts to voicing a room. The first part is getting all resonances or most of them managed. Low frequency issues are present in almost any room. Room resonances at lower frequencies, especially those below 100 cycles, can ruin any quality sonic presentation. Low frequency resonances are like bulls in a china shop. They charge into everything and bump into everything else. They trample over our middle frequencies and can even have an impact on higher frequencies.

Attack And Decay

Low frequency resonances can impact attack and decay times with individual bass notes or chords. Excess resonant energy at lower frequencies can exaggerate some bass notes and completely eliminate others if our listening or monitoring position falls within a room mode. If we can’t hear where one bass note begins and ends in its entirety, we are missing too much music. There is a lot of music below 60 cycles. Don’t let the room get in the way of the music. Proper low frequency resonance control is a must have. There is no art needed on this one.

Middle Frequencies

Middle frequency ranges are plagued by reflections from our room boundary surfaces. All of these reflections add up to a certain reverberation time in our room. If we are listening to music and not recording instruments or vocals, we want a certain amount of reverberation in our room. Reverberation assists us in feeling the music all around us. It is different with a microphone. The microphone normally does not like reflections and will tell you so in the mix.

Vocals Are Emotion

Our vocals lie in this range of frequencies. Vocals are our primary source and link to the emotional content of the music. We must have a balance of the direct sound from our speakers and the reflected energy from our room. In a professional monitoring studio room, we want no reflections, so the engineer does not have to contend with room sound in the mix. In our listening or home theater rooms, we want the music to be part of the room and we want the room sound in our musical presentation for more emotional involvement and realism. We want to hear room sound and mix sound.

Time After Time

Achieving this balance between science and emotion takes time. It takes time because no one set of measurements will ever produce emotion or feelings. It is the sum of many variables with the personality and sonic preferences of the listener and room user thrown in. This emotional drive can be taken every time in a room where one has spent a great deal of time listening to music from many different genres.

Thunder And Lightening

We want the thunder from a bass kettle drum in our classical music. We want the attack and decay of every note to be heard and felt in our room. Only numerous playing and listening sessions will reveal the true color of the room. Once we have found out over time and patience what we like about the room and what we don’t, we can try and voice for the likes and try to eliminate or manage the dislikes.

Resonant Hunting

With low frequency resonances, we must find their locations within the room and place large low frequency sponges in those locations. Please, no foam. Low frequency resonances must be identified and the proper low frequency absorption technology applied. Please, once again, no foam. If you are serious and you must be when dealing with low frequency resonances, you must employ diaphragmatic absorption or a Helmholtz resonator that is frequency tuned. Resonances don’t play around. There only mission is destruction.

Check The Corners

Start in the corners first, going floor to ceiling. Next, look at all room boundary intersections. Treat the ceiling to wall intersection and the floor to side wall intersection. These are the areas of greatest pressure within our rooms. Do not forget the area behind the speakers; the area between the front wall and speaker back. This is a high pressure area where resonances like to get together and party. Please, no foam.

No Foam

Alright, I will stop saying, no foam. We have to get away from the myth that foam can absorb low frequency energy. It can not. I do not know how this myth officially got started but I have a good idea. For years, acoustic products companies have been distorting the term low frequency absorber. Some companies even call them “bass traps”. Most “bass traps” do nothing to absorb any energy below 100 cycles. They definitely do not “trap” any bass.

Definition Alert

Acoustic products companies have been raising the sound absorption bar when it comes to promoting their “low frequency” absorbers. If you examine some companies definition of bass absorber, you will see that it will not be low enough in frequency to absorb below 100 cycles. One company claims that 400 Hz. is even a low frequency. Lets stop this nonsense. Make sure you obtain the performance numbers on any bass absorber first and foremost from a manufacturer prior to purchase, if you can find them.

Reflection Control

One can control reflections through absorption. Once we have our primary and secondary side wall reflections managed correctly, so our sound stage has width, depth, and height, we are free to add or subtract absorption technology over time and many different listening sessions. We can add or subtract materials from different places in the room to find that correct balance between direct and reflected or room sound that brings us closer to the music. It takes time and many efforts, but the destination is worth the journey.

Voicing our rooms is an art form that we personally get to exert upon our room. We get to add or subtract different acoustical technologies over time to help us better emotionally connect to the music by emotionally connecting to our rooms. We develop this working relationship with our rooms by first knowing how the room sounds with all types of music and then listening to the changes our voicing makes in the existing room sound. This knowing our room and what we need to do to help it help us emotionally better connect to our music is what voicing is all about. I am connected to my room but my connection to my room transcends even feelings.

MikeSorensen

Author 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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