Polifemo e Phemo: the acoustic resonators variable and fine adjustments




The Helmholtz resonator is a device born to control acoustic resonance and it is very well known.

It consists of a volume of air enclosed in a cavity, coupled with the outside through one or more openings, to create a mechanical mass-spring system with its own resonance frequency at which the system is able to absorb a considerable part of energy.

The absorption of this kind of resonator is very selective about the frequency of resonance and particularly effective in the case of low-frequency booms.

However, a resonator don’t work on absorbing way only.

The principle of the resonator was used already in the past, to increase the voice volume of the actors in the open-air theatres or to amplify the sound of the strings instruments like guitar, violin and so on.

The resonator has found rare application in standard listening rooms suitable to reproduce music.

The reason is very simple.

To develop an effective resonant device to treat the acoustic problems of a specific environment, is necessary a difficult and precise instrumental design, such that the device is really effective in dealing with the critical frequency of that environment without affecting the others. Resonator works in a narrow band and NOT on broad band, such as the DAADs work.

A resonator is therefore a system stiff, fixed and dedicated only to a specific environment. It has to be very well calculated and matched between the environment and speakers. This is important if you don't want to cause an acoustic disaster.

Despite the potential of the device, up to now it has been a very difficult use in the home environment and thus has been little used.

Polifemo and Phemo are the modern answer of the principle of Helmholtz, giving the possibility to use their features free of usual problems, having an effective use of the resonator in the home environment and other positive further effects.

Polifemo and Phemo can be adapted to each specific acoustic problem of the listening rooms.

By some exclusive and effective technical solutions, they change their resonance frequency to match that required in a certain environment. Their possibilities are almost limitless.

Starting from 26 Hz up to about 60 Hz, Polifemo and Phemo give the opportunity to work on any frequencies in a clean and well-defined way.

Changing the environment or replacing the speakers, Polifemo and Phemo will be fully exploited again in all their powerful.

Polyphemo and Phemo have a cylindrical shape.

At the base, which is appropriately elevated from the ground, there is a port that can be gradually opened or closed, by a rotating plexiglass disk, to set the correct frequency resonance of the device for a certain room.

While Phemo is a "Pure" resonator and its regulation is simply performed by the correct tuning of the port in the base, Polifemo exalts the performances of an Helmoltz resonator by the exhibit of further two exclusive regulations. The first is the "Eye" of Polifemo, a sophisticated iris diaphragm, whose aperture can be gradually and finely changed; the second is the internal paddle membrane that changes the speed of the internal air flow.

Since it can be considered as a “passive speaker”, the orientation of the “Eye”, which is obtained by rotating the entire device, influences the distribution of the sound into the listening room, as more is convenient in terms of space representation, tonality, dynamics of the reproduced sound.

The positioning and set-up aren’t random. Double click on the button “Positioning and Set-up of Polifemo and Phemo”: it opens a text where are described all the suggestions and methods about the correct and infallible positioning and adjustments of the devices.

All these adjustments of Polifemo and Phemo can be performed by instrumental way and/or by “ears”.

The results are striking both to the ear and during the instrumental analysis phases. In addition to a precise control and articulation of low frequencies, the result is that Polifemo and Phemo give a clear enlargement of the soundstage space due a better resolution at low frequencies and an improvement of how the medium and high frequencies "float" on the low.

When the system is properly tuned, Polifemo and Phemo give the best possible performances about dynamic, which increases of realism, gaining in terms of micro-information.

In a listening room of standard size (160/270 sq.feets) one or two devices are necessary. These can be tuned in different ways to correct asymmetry of the soundstage and to solve various problems. In some cases, to obtain the best results, 3 or 4 can be used.

Generally, the suggested positions are along the walls or, in specific cases, in the corners.

Polifemo and Phemo can be used with other acoustic treatment systems such DAAD or Eco DAAD.


















Acustica Applicata - Tel. +39 0583 730322 - Cell. +39 340 7565285
Fax +39 0583 730914 - info@acusticaapplicata.com - P.I. 01441820469
2009 Michele Lucchina