Saturday, April 20, 2013

FM Acoustics 268-C

A new version of the legendary FM Acoustics 268 preamplifer is coming soon.

268-C now has a new feature - a acoustic resonance compensation (ARC).

The ARC minimizes room modes and other resonances. Room modes occur when parallel surfaces create one or more pronounced resonances (a sharp Sound Pressure Level (SPL) increase at specific frequencies).

In a typical rectangular room the 1st principal resonance is occurring at 1/2 wavelength of opposite walls (this is why it is not a good idea to listen while sitting close to walls) - in above graph this is "P1" (graph is smoothed to only show the two principal resonances). The 2nd resonance is at double this frequency ("P2").

Depending on room size the 1st and 2nd resonances can occur anywhere from around 100 Hz down to below 20 Hz. Such a resonant peak is superimposing itself on the actual music mainly resulting in boominess and poor low frequency definition.

Professional studios can ameliorate such room modes but size, construction limits and cost preclude this for home environments. Usual "hi-fi" absorbers work relatively well for middle and higher frequencies but with reasonably sized domestic absorbers such low frequencies room modes cannot be attenuated efficiently.

The ARC circuits are also ideal if there are resonances from other sources in the room, e.g. air conditioning or any other resonating surface or room component. These circuits are unique to the FM 268-C. They are pure analogue circuits and do not interfere with the music.

No A/D and D/A conversion is done. The integrity of the existing systems signal reproduction remains. The set up of the ARC needs test equipment and is performed for FM 268-C owners by FM ACOUSTICS official distributors.

The ARC circuits are located at the back of the unit.