Gallo's damping technique

[Few]

Does anyone know of any measurements demonstrating the effectiveness (or ineffectiveness) of Anthony Gallo's damping technique as described in this patent? I did a search but didn't come up with much.

Few

[Few]

In case having to read through the first couple of pages of the patent is putting people off, here's the bottom line: Gallo uses rolled, crumpled, or folded thin resilient plastic sheets (such as the plastic wrap used to wrap left over food in the kitchen, e.g. Saran wrap) as stuffing material.

His patent claims it is superior to the more conventional fibrous materials and provides a table to substantiate his claims that when the same woofer and enclosure are used in two systems, one stuffed with fiberglass and the other stuffed with his sheets, the one with sheets exhibits much higher output at the lowest frequencies and a resonance with reduced Q.

From the patent:

The unusually high acoustic opacity of these multilayered structures is believed to result from a combination of the high compressibility of the air pockets and the highly resilient nature of the individual layers. Accordingly, it is believed that the air pressure between the layers should not be substantially different from the atmospheric pressure during the operation of the acoustic damping material....Also, the acoustic opacity of the material is improved...when those layers are oriented substantially perpendicular to the acoustic waves being blocked.

Few

[breez]

Another method to drastically reduce the Q of the mechanical resonance is filling the enclosure with cotton cloth. I read this in "Current-driving of loudspeakers" by Esa Meriläinen. It is useful in current-driven loudspeakers, where the electrical damping disappears.

The patent claims: "improves electro-acoustic conversion efficiency, especially at low electric power levels". That may be true using traditional definition of power efficiency which assumes a constant nominal impedance (e.g. 4 ohms) across the band. Which also makes it really a voltage sensitivity figure.

However, from a real power efficiency standpoint, the reduction in Q dramatically reduces efficiency at resonance. Much higher current is required for the same output and power dissipated in voice coil is i^2 * Re.

A reduction in resonance frequency would be more useful if operation at low frequencies is needed.

Attached two graphs of a woofer under constant amplitude of current with varied box internal damping and box volume (varied Q and Fc respectively).