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Sound diffusers and adaptation♔

Long time ago I wrote diploma about material for fight against high decibel sound pressures. Also I wrote some articles about soundproofing the home studio, home cinema rooms for sound adaptation. 

But I have forgotten about third effect of sound waves - diffusion. Difusion in home adaptation of walls is using a barriers, panels, balls, piramids 3d skyscrapper mosaics, binar plates etc. Everything is for diffuse impact of front of sound wave and take the energy of sound to different, random or almost directions. 

It is urgent for good guitar, percussion, speech recognization, realisation of home speaker systems such as Hi-Fi, HomeCInema, recording testing. 



Room full of sound proof materials, no echo at all

Our ears do not like no echo effect in rooms. Anechoic chambers are really torture for human. It is weird sensation. Our sensoric integration cannot find the source of sound for example speaker, guitar. No echo or almost zero echo it is weird for recognization as band member. If you have 4 persons playing in room full of isolations you cannot hear tones. Your sensoric integration between feeling vibrations, visualisation vector of sound wave by eyes. THe position of musicians are not visible for human brain in phisiologic. Situation causes put extra gain and volume of every guitar, bass, keyboard, speaker, vocal microphone loudspeaker, amplifier, mixer console up to maximum before noise, and give negative impct of ears and musical logic. 

In that weird room you feel only sound directly from speakers and mirrored from band members, instruments and wood parts from instruments. In that position you cannot even proper position of speakers in that room. 

Tonotopic maps are a striking feature of the mammalian auditory cortex and underlie the representation of complex sounds, such as speech. This spatial separation of frequencies originates in the inner ear, where high frequencies are processed in the base of the cochlea and low frequencies in the apex.



Cochlea


Full reflective room

Ideal echo in room sometimes is better than full soundproof
It is depend on sound pressure level. Resistance of air is -3dB each 1 meter from speaker or different sound source. 


If the sound pressure is bigger we got similar situation like in well acoustic proof room. 

Our brain hears sounds from nature from grass, from trees, from stones. In normal houses we got lamps, paints, mirrors, carpets, plaster on walls, curtains and tables, beds, shelves with books. All of these are good examples of not bad sound adaptation materials. 

Sounds of guitar, bass, acoustic, electric, ukulele is in term of acoustics types of behavior


1. SOUND ABSORPTION IN MATERIAL
enery of wave going through border material-air and change inside material to heat, left inside material,

2. SOUND REFLECTION
energy of wave reflects from border material-air and come back to source. 

3. SOUND DISPERSION, DIFRACTION, DIFFUSION

sound difracts on shape of materia, wave front change direction in function of shape. Change angles, vectors, directions, bend on edges of material,.some part of energy enters to material like in absorption. 


Corect set of diffusors on walls and/or ceiling could do extra clarity of tones. Give better balans, than rooms with lot of absorption and reflection. It is better to good understanding between musicians, speakers. 

All dimensions and shape causes different transmission of sound in room. 


Diffusers shortcut presentation






Diffusor Skyline - with random mosaics of heights

Schroeder diffusor



1-dimensional diffusor schroeder type. Dimension consist of frequency characteristic and squre residuum function


Useful type case as sound difuser

2-dimensional difuser, square residuum in 2-axis X and Y

All special dimensions you can calculate in QrDude program. 

you can download it from: : https://www.subwoofer-builder.com/qrdude.htm

For example grid 7:7 dimensions:

==========================

Report from program:


QRDude report for 2D QRD diffuser
===================================

STANDARD PANEL is based on a modulated series of STANDARD 1D QRD panels
Panel does have fins

Panel order =  7
Design frequency  1304 Hz
Number of wells =  49
Panel is shifted 4 wells to the left and pulled 4 rows towards the front

One depth unit is equivalent to 18.9 mm
Build depth is 113 mm

Panel width including additional end fin is 415 mm

Period width is larger than design wavelength - good!


Block Heights in mm
-----------------------------------

Row 6 (Back) ... equivalent to 1D panel N7+2,4
38,   0,   57,   75,   57,   0,   38

Row 5 ... equivalent to 1D panel N7+4,4
0,   94,   19,   38,   19,   94,   0

Row 4 ... equivalent to 1D panel N7+1,4
57,   19,   75,   94,   75,   19,   57

Row 3 ... equivalent to 1D panel N7+0,4
75,   38,   94,   113,   94,   38,   75

Row 2 ... equivalent to 1D panel N7+1,4
57,   19,   75,   94,   75,   19,   57

Row 1 ... equivalent to 1D panel N7+4,4
0,   94,   19,   38,   19,   94,   0

Row 0 (Front) ... equivalent to 1D panel N7+2,4
38,   0,   57,   75,   57,   0,   38



Block Heights in depth units (w przeliczeniu na jednostkę głębokości 1Unit = 18,9mm)
-----------------------------------

Row 6 (Back) ... equivalent to 1D panel N7+2,4
2,   0,   3,   4,   3,   0,   2

Row 5 ... equivalent to 1D panel N7+4,4
0,   5,   1,   2,   1,   5,   0

Row 4 ... equivalent to 1D panel N7+1,4
3,   1,   4,   5,   4,   1,   3

Row 3 ... equivalent to 1D panel N7+0,4
4,   2,   5,   6,   5,   2,   4

Row 2 ... equivalent to 1D panel N7+1,4
3,   1,   4,   5,   4,   1,   3

Row 1 ... equivalent to 1D panel N7+4,4
0,   5,   1,   2,   1,   5,   0

Row 0 (Front) ... equivalent to 1D panel N7+2,4
2,   0,   3,   4,   3,   0,   2



Well depths in mm (głębokości - lub pomiar odwrotnej siatki)
-----------------------------------

Row 6 (Back) ... equivalent to 1D panel N7+2,4
75,   113,   57,   38,   57,   113,   75

Row 5 ... equivalent to 1D panel N7+4,4
113,   19,   94,   75,   94,   19,   113

Row 4 ... equivalent to 1D panel N7+1,4
57,   94,   38,   19,   38,   94,   57

Row 3 ... equivalent to 1D panel N7+0,4
38,   75,   19,   0,   19,   75,   38

Row 2 ... equivalent to 1D panel N7+1,4
57,   94,   38,   19,   38,   94,   57

Row 1 ... equivalent to 1D panel N7+4,4
113,   19,   94,   75,   94,   19,   113

Row 0 (Front) ... equivalent to 1D panel N7+2,4
75,   113,   57,   38,   57,   113,   75



Well depths in depth units
-----------------------------------

Row 6 (Back) ... equivalent to 1D panel N7+2,4
4,   6,   3,   2,   3,   6,   4

Row 5 ... equivalent to 1D panel N7+4,4
6,   1,   5,   4,   5,   1,   6

Row 4 ... equivalent to 1D panel N7+1,4
3,   5,   2,   1,   2,   5,   3

Row 3 ... equivalent to 1D panel N7+0,4
2,   4,   1,   0,   1,   4,   2

Row 2 ... equivalent to 1D panel N7+1,4
3,   5,   2,   1,   2,   5,   3

Row 1 ... equivalent to 1D panel N7+4,4
6,   1,   5,   4,   5,   1,   6

Row 0 (Front) ... equivalent to 1D panel N7+2,4
4,   6,   3,   2,   3,   6,   4



Block details - program podaje jakie trzeba zrobić klocki - pisze że trzeba 2,38metra materiału.
=============
Block width 25 mm

Number of empty wells 8
8 blocks of height 1 depth units, or 19 mm
8 blocks of height 2 depth units, or 38 mm
8 blocks of height 3 depth units, or 57 mm
8 blocks of height 4 depth units, or 75 mm
8 blocks of height 5 depth units, or 94 mm
1 blocks of height 6 depth units, or 113 mm
----------------------------------------
Total block length 2.38 metres


Fin details
===========
Fin thickness 30 mm
Fin height 113 mm

Number of fins slotted to form cross-matrix =  12    cut to length = 355 mm  plus any allowance to rebate into sides
Side fins (not slotted) = 2    cut to length = 355 mm
Front and back fins (not slotted) = 2    cut to length = 415 mm  .. plus any allowance for flush-trimming with router
---------------------------------------------------
Total fin length 5.8 metres  .. plus any allowances


Volume based on hollow build using fins plus well bottoms made of same material as fins (no backboard)
---------------------------------------------------
Volume =  .0197 cubic metres


Estimated weight using various materials
---------------------------------------------------
Hoop pine ply  10.8 kg
MDF  13.8 kg
Cedar  7.5 kg
Styrofoam  1.9 kg
Balsa  2.3 kg
Cork  4.9 kg
Oregon (Douglas Fir)  9.8 kg
Normal Plywood  11.3 kg
Birch ply  13.8 kg
Oak  14.8 kg
Hardwood  15.8 kg
Plaster  16.8 kg
Red Gum  17.8 kg
Glass  49.4 kg
Granite  53.2 kg
Aluminium  53.4 kg
Steel  155.3 kg


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