Efficiency analyse
Graph presented on below gallery show efficiency of damping the wave reflected from the hard concrete wall by use of GRAND-11 panel.
Sound source generating MLS sequence was directed into the wall under the angle of 45deg. Microphone was installed under opposite angle to measure reflected wave coming from the wall surface. Total distance from source to the mic was 100cm.
Between the microphone and the sound source it was located insulation baffle to prevent disturbance of direct wave on reflected one. On that graph we present 3 plots:
- Red - wave reflected directly from the plain wall – no damping at all
- Grey – reflected wave damped by the 5 cm foam
- Green – reflected wave damped by GRAND panel
Conclusions:
From the plots we can conclude that Grand panel is starting to damp even from 100Hz. Very clear effect (damping more than 3dB) is visible already from 200Hz. It means twice less sound of being reflected from the panel than from the plain wall
We see that foam up to around 1,2kHz is not giving any effect! Efficiency of foam is increasing slowly and in very not linear manner to equalize with the panels at 12kHz.
In reverse to the foam panels are working in linear way starting almost from the beginning.
Actually foamy panels can do much more mess by cutting out the trebles from the whole music information
Spectrograms and waterfall:
Spectrograms and overlaid waterfall graph are showing how two GRAND-6 panels change the acoustics in rectangular room. Dimensions of this room are 4x6m. Typical height – 2,7m. Measurements were taken for frequency range 100…1000hz. We can observe that reverberation in this range stops in about 100ms earlier when we use panels. Panels were installed in 1st reflections point behind the speakers. Microphone positioned at height of 90cm, around 2,5m from the speakers where is the listener’s location for that room. On waterfall green plot was taken with panels and red plot without them.