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acoustic modal analysis Studio Design 2010 allows the user to enter in room dimensions of length, width, height and the reverb response for the room. It calculates all the modal frequencies for axial, tangial, oblique modes and graphs the results for easy to see modal spacing and mode buildups.

Each room dimension is calculated as wavelength (fundamental frequency) and harmonics up to the Low Cutoff Frequency for
the room. The number of modes and its color is provided in the text field next to each dimension.

This makes it easy to see which dimension(s) are causing a mode buildup. Simply change a dimension to see how it effects the modal spacing to Optimize your studio room.


User Data Entry

Enter room dimensions and desired reverb response Enter your room dimensions for a rectangular room and the desired reverb response
(RT60) you want the room to have.

Press the calculate button to see your results.

The number of modes and its color is provided in the text field next to each dimension.






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Modal Analysis Data results

Important  room calculations The room cut-off frequency (Lco) is very important to know to deal with troublesome
mode build-up. It is related to room volume and reverb response. Modes (frequencies)
above the Lco are handled by the room with a smooth response while modes below the
Lco are of concern if they cause a build-up.

Lco = 20,000 * Sqr (Reverb Time / Room Volume) in hertz

Bandwidth is the range of frequency around the fundamental frequency (and harmonics)
that is depicted as a bell curve. If one mode bandwidth is within the mode bandwidth of
another mode, it excites that mode to the extent it overlaps the mode. This extra energy
is added to the excited mode. The graph will show all excited modes in blue.

BW = 2.2 / Reverb Time

                                         Room Volume is Length x Width x Height in cubic feet.



Ratio Calculator

Convert room dimensions to ratio and upsize or downsize! The Ratio calculator converts the dimensions into a ratio where 1 equals the Height.     
This is useful when you have dimensions that provide good modal spacing and
wish to resize the room using the same ratio.

Enter a value in the ft. text field and select which wall to apply the change
to. Press either the up or down button to recalculate the dimensions by the
entered amount.

Press the Apply Ratio button to update the project with the new dimensions.




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                             Modal Frequency Distribution Graphs

Axial, Tangial, Oblique Modes

The actual modal frequencies plotted are displayed in the listbox next to each graph. The modes
for Length, Width, and Height are plotted as separate colors for easy identification when deciding
which dimension to tweak to optimize modal separation or reduce modal build-ups.

The graph is plotted up to the Low cut-off frequency for the room. These are the modes of interest.
Each dimension (fundamental and harmonic frequencies) are calculated up to the Lco.

The maximum "amplitude" is 300% which represents adding 3 modes of equal frequency which
only occurs when all three dimensions are the same.

As stated above, If one mode bandwidth is within the mode bandwidth of another mode, it excites
that mode to the extent it overlaps the mode. This extra energy is added to the excited mode.
The graph will show all excited modes in blue if their "amplitude" is over the amplitude given
for that mode.

The Axial modal frequencies are given an amplitude of 100%. Tangial modal frequencies are
given an amplitude of 50% and the Oblique modal frequencies are given an amplitude of 25%.

The All modes frequency distribution graph plots all three modes together. The graph will show
all excited modes in blue if their "amplitude" is over 100%.

Axial modes are considered primary, while tangial modes have a second order effect and oblique
modes have a third order effect. The tangial and oblique modes tend to "fill" in between the axial
modes.

The objective is to enter your room dimensions and desired reverb response then observe the graphs
for mode spacing. Start by looking at the axial graph first. The modes for length are shown in green,
width in burgendy, and height in tan.

If modes are shown too close to each other they will appear in blue. Blue is a problem and means a
mode build-up will occur at those resonant frequencies. Walls, ceilings and floors are essentially
resonating panel absorbers which have front and back panels, air space cavity, insulation, etc.
They have a resonating frequency with harmonics related to its longest dimension and will resonate
when the modes under the Lco are excited.

The goal is to get the best spacing possible while minizing modal build-ups and to identify those
problem modal frequencies. Coefficients of absorbtion are measured for materials at 125hz, 250hz,
500hz, 1000hz, 2000hz, 4000hz. Example: If your Lco is 300hz then check for build-ups at 125hz and
250hz. Other hot spots can be dealt with by designing custom helmotz resonators/absorbers for those
frequencies. Studio Design 2010 allows the user to design helmotz resonators and save them
into the acoustic materials database and then select them into the acoustic room design.

When the room dimensions are optimized, save the project and room name. Click the materials
option button to begin adding acoustic materials representing your desired construction and materials
you want to use. Click the Acoustic Materials link below to learn how Studio Design 2010
becomes an indispensible tool for your recording studio!

     

Acoustic Materials   go to top                                         



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