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Room Sine Wave Sweep

Dennis Foley April 9, 2014 No Comments
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Anything that makes a sound in our life is usually created by something that vibrates or oscillates. All electromagnetic energy, including visible light, microwaves, radio waves, and x-rays, can be represented by a sine wave. At the lowest level, even matter oscillates like a wave, but for macroscopic objects, these oscillations are so minimal are to be impossible to measure. Sound waves can be represented as sine waves, and the up-and-down waves on an oscilloscope may be the most widely known representation of these waves.

What Is A Sine Wave?

With these vibrating sources, we can have square waves, irregular shaped waves, and a host of others. A sine wave is a waveform that more closely matches music waves and rays. A wave is classified as lower frequency energy and a ray is more of higher frequency energy. For a more detailed explanation of waves and rays, you can refer to a webinar I did for designing sound entitled waves and rays. Here is the link:

www.acousticfields.com/dennis-foley-webinar-for-designingsound-org/

When a waveform consists of only one frequency that waveform is called a sine wave. The sine wave is the most fundamental of all waveforms because all other sounds are composed of sine waves that occur simultaneously at multiple frequencies, various amplitudes and phases. We need to perform a room sine wave sweep in order to see and hear how all of this energy at different frequencies “fits” into our rooms. To accomplish this, we need what is called a sine wave generator (software) and a speaker or speakers.

Methodology

We need to connect the generator software to an amplifier which will generate the energy to move the diaphragms in our speakers, thus producing the sine wave into our room. Along with the sine wave generator it is necessary to have a real time frequency response measurement screen going in order to see the way the room handles the sine wave we are going to introduce into it. Here are links to both sine wave generators and real time analyzers that can be downloaded:

www.wavtones.com/functiongenerator.php

A sine wave generator can be set to produce each individual frequency from 20 Hz. – 20,000 Hz. It can also be set to produce this energy for certain time periods. You can adjust this time period on any of the generators. We use about 15 seconds duration in our studio when we do sweeps. If you do a sweep at say, 30 Hz. then watch the real time analyzer screen and see what happens at 30 Hz. Use a resolution of 1/12 octave band. That resolution will allow you to see the impact in your room of that 30 Hz. wavelength. You will see just how much of an impact it has and then you can put a number to it. You can do this for every frequency in your room sine wave sweep.

Start at 30 Hz. and move in 5 Hz. increments up through 100 Hz. The results of your room sine wave sweep will produce peaks and troughs in your RTA. If you inject a 30 Hz. wave into the room and you see 30 Hz. jump on your RTA and that jump is 5dB over 0 line, then you have an audible distortion. If 30 Hz. jumps +10 dB you are not only audible but now you have a real modal issue. At 15 dB, you have an acoustical nightmare that must be dealt with
immediately.

A sine wave is the closet wave we have to music. We can generate that sine wave at all frequencies using a signal generator and then take that energy and place it within our room. Once the energy is in the room, we can sustain it and measure it with an analyzer. We can see with the analyzer how that energy fits within our room or in some cases especially at lower frequencies and longer wavelengths, how it does not fit and how much it does not fit by assigning a number to it. Certain numbers represent problem areas that must be addressed with proper room acoustic technology.

In Summary
I hope this discussion has helped you. 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. In one video in particular I show you how you can use a sine wave generator to help you locate the room modes in your room and then how to deal with them.

Alternatively feel free to contact me directly at: 520 – 392 – 9486 MST or info@acousticfields.com. You can see more of my research and development story and why I started Acoustic Fields at: https://www.acousticfields.com/who-we-are/.

Thanks and speak soon
Dennis

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Dennis Foley

I am an acoustic engineer with over 30 years’ experience in the business. My technology has been used in Electric Lady Land Studios, Sony Music of New York, Cello Music and Films founded by Mark Levinson, and Saltmines Studios in Mesa, Arizona, along with hundreds of others.

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