Passive Room Correction
started on December 10  ^st ,2012

INTRODUCTION

After the experience with high-resolution PCM tracks I began a series of tests with DSD files, downloaded as free samples from sites like Blue Coast Records or found as SACD ISO ripped with PS3.
Listening a DSD track is certainly exciting because it looks like an analog sound without noise and with much more dynamic.
The difference between a high-resolution PCM and DSD file is much larger than that between a high-resolution PCM and a CD.
I have develop with Quanghao and Amanero technologies a true Hi-end DAC enabled  to play also DSD tracks at a relative low cost, see Here.
The major disadvantage of the DSD is the inability to use digital filters and equalizers such as the DRC (Digital Room Correction).
Not using the DRC have been forced to take action in the listening environment to improve the performance by reducing reflections.

PHASE 0

PHASE 1

Obviously my goal was to spend a little and get the most out also because I was not convinced that small changes would make a big difference.
My initial idea was to use panels of rock wool because it costs very little and you get good results from the 250-500Hz.
The panels to be used for this purpose are from 75 Kg / m³ and a thickness of 5 cm.
Rock wool is a material made of fibers from a mixture of stone materials that are abundant in nature: volcanic rocks, limestone, dolomite and bauxite. 

The rock wool releases spores and dust so to be safe human health is necessary to cover the panels with acoustically transparent polyester filter.
Making a wooden frame and then cover it with the filter is not a simple and quick operation, so I looked for something that could be applied directly to the wall.
I was also looking for a more broad-spectrum absorber panel so I chose the 3D model Diffusion got on online shop Isol Centro.

The Diffusor 3D (Abffusor) creates a wide absorption band with a combined circulation of the waves are not absorbed, resulting from the different 
thicknesses of polyurethane, which follow a mathematical "square to rest, " or other schemes acoustically effective.
Diffusor 3D drawing is the result of precise mathematical calculations to size and shape. 
The openings are the same width but the depth is based on mathematical sequences in quadratic remainder. 
The wavefront of the reflected sound from the bottom of any opening propagates toward the front of each channel of varying depth. 
The depths range from zero to about half the wavelength, in agreement with the mathematical sequence used. 
The result of this complex set of interference is that the sound is spread with an angle of 180 ° with respect incident sound wave. 
Diffusor 3D sound-absorbing polyurethane foam is made with charcoal gray color, unique, and it spreads the sound absorbent is the correcting.

This type of panel is not very elegant in a normal domestic environment but from the point of view of the technical characteristics is 
much higher than the normal pyramid shaped panels and rock wood.
For better visual impact of the panels on the walls I decided to paint the room in red, I think that light affects listening then a color more hot can improve the result.
I had thought to take measurements to verify the results but the change obtained with only 8 panels of 1x1 meters is so radical that just listen to the human voice.

PHASE 2

Solved the problem on medium and high frequency now I need a good low frequency range so I have build this subwoofer with integrated DSP.

see details on: Extreme Hi-End Audio subwoofer