Isolation/damping mounting system for loudspeaker crossover network

A long post but interesting reading if you're DIY inclined, taken from the US patent office.


Isolation/damping mounting system for loudspeaker crossover network

Abstract

A mechanical mounting system and extensional damping technique for loudspeaker crossover networks. This system decouples the crossover network from the loudspeaker enclosure (cabinet), isolating it from any vibrational energy in the cabinet walls. In addition, an extensional damping material is applied to the crossover network to damp any vibrational energy which may be coupled from the surrounding air into the network. The mounting system can be used for mounting any sensitive electronic components within an enclosure to provide isolation from the walls of the enclosure and from surrounding or environmentally induced vibrational energy.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to mechanical mounting arrangements and, in particular, to a mechanical mounting system and extensional damping technique for loudspeaker crossover networks.

2. Description of the Relevant Art

Loudspeaker crossover networks (the electrical filtering and equalization circuitry of a loudspeaker) are very prone to low level intermodulation distortion effects when exposed to vibrational energy. This often becomes critical when the crossover networks are mounted within the loudspeaker cabinet where vibrational energy may be propagating freely though the cabinet walls and the interior air. Since most crossover networks are rigidly mounted to the cabinet walls, vibrational energy is directly coupled into the network. Energy coupled from the cabinet usually will travel though the network mounting screws, pc board or mounting board (if hard-wired) and into the electrical components themselves. It is also possible for vibrational energy in the internal air of the cabinet to be coupled either directly into the electrical components or through the pc board or mounting board into the components. The effects of this vibrational energy, when coupled into the electrical components, are typically manifested as a masking of low level detail and a subtle, but perceivable, intermodulation of the desired audio signal.

Manufacturers have attempted to address this problem in several different ways, including: (1) mounting the crossover networks outside of the loudspeaker cabinet; (2) encasing the crossover network in a highly damped potting compound; and (3) isolating the crossover networks within the cabinet by hanging them from wires or springs.

Mounting the loudspeaker networks outside of the cabinet offers improved performance since the cabinet walls and interior air of the loudspeaker can no longer couple vibrational energy into the networks. Unfortunately, vibrational energy can be coupled from the air in the listening environment (i.e., the loudspeaker's output energy) into the networks. Therefore, the networks still must be isolated in some manner from vibrational energy in the air. Mounting the networks outside of the cabinet usually will require an additional enclosure and its associated external wiring complications and additional electrical connections, as well as significant added cost.

Encasing the crossover networks in a highly damped potting compound can offer improved performance provided the damping characteristics of the potting compound are sufficient. However, this method has the disadvantages of poor heat dissipation from the network components, lack of repairability and high cost.

Other methods of isolation, such as hanging the networks, are usually either ineffective or overly complex. The effectiveness of hanging the networks is completely dependent upon the transmissibility characteristics of the hanging system (e.g., the wires or springs). The hanging system may not isolate adequately at all frequencies. In particular, if the hanging system resonance is too high, amplification of vibrational energy will occur, making the problem worse. A hanging system also does nothing about airborne vibrational energy within the cabinet. Hanging systems are also prone to shipping damage if the cabinet encounters rough handling.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mounting system and extensional damping technique for loudspeaker crossover networks that overcomes the problems associated with the existing mounting systems described above.

More specifically, it is an object of the present invention to provide a mounting system that isolates electrical components from vibrations in the walls of an enclosure and from surrounding or environmentally induced vibrational energy, that does not interfere with heat dissipation from or repair of the electrical components, that is inexpensive and not overly complex, that is not prone to shipping damage, and that will isolate adequately at all frequencies encountered.

Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

The present invention provides an isolation grommet/ferrule mounting system for damping and acoustically isolating crossover components of a loudspeaker from the speaker cabinet and from airborne vibrations within the cabinet. The elimination and damping of all cabinet, driver, and crossover resonance, allows the natural resonance of music to be conveyed in a more revealing and realistic way with minimum distortion.

In order to achieve the objects set forth above, the present invention comprises a mounting system for mounting an electronic component within an enclosure. The mounting system comprises a board on which the electronic component is secured, the board comprising at least one mounting slot, an extensional damping material disposed between the board and a surface of the enclosure, a grommet inserted into the mounting slot, the grommet having surfaces which sandwich the board about a periphery of the mounting slot, a ferrule inserted into the grommet, the ferrule having an enlarged head which engages a surface of the grommet and a shank which extends through the grommet and engages the surface of the enclosure, and a mounting screw inserted through the ferrule and anchored into the surface of the enclosure, the mounting screw having a screw head in engagement with the enlarged head of the ferrule.

In a preferred embodiment, the extensional damping material covers at least 50% of the surface area of a side of the board facing the surface of the enclosure and is bonded to the board. The grommet may comprise an internally ribbed grommet or a shear grommet, depending on the particular application.

In a further aspect of the present invention, the objects set forth above are achieved by a method for mounting an electronic component within an enclosure. The method comprises the steps of securing the electronic component to a board, attaching at least one grommet to the board, inserting a ferrule into the at least one grommet, placing an extensional damping material between the board and a surface of the enclosure, and inserting a screw through the ferrule and anchoring the screw to the enclosure.

The method preferably comprises attaching the extensional damping material to the board before anchoring the screw to the enclosure. The method also preferably comprises providing a plurality of mounting slots in the board, and attaching a plurality of grommets to the board such that portions of the board adjacent the mounting slots are sandwiched between two surfaces of each grommet. The screw is preferably tightened to a specified torque and a preload is applied to the extensional damping material and to the grommet as the screw is anchored.

In accordance with yet another aspect of the present invention, the objects set forth above are achieved in a loudspeaker having an improved mounting system for isolating vibrational energy from a crossover network. The loudspeaker comprises a speaker cabinet, at least one crossover network, and a mounting system for mounting the crossover network to the speaker cabinet. The mounting system comprises a board on which the crossover network is supported, the board comprising a plurality of mounting slots spaced about a periphery thereof, an extensional damping material disposed between the board and a surface of the speaker cabinet, a grommet inserted into each of the mounting slots, the grommets each having surfaces which sandwich portions of the board adjacent the mounting slots, a ferrule inserted into each of the grommets, the ferrules each having an enlarged head which engages a surface of a respective grommet and a shank which extends through the respective grommet and engages the surface of the speaker cabinet, and a mounting screw inserted through each of the ferrules and anchored into the surface of the loudspeaker cabinet, the mounting screws each having a screw head in engagement with the enlarged head of a respective ferrule.

The extensional damping material used in the present invention preferably comprises a thermoset, polyether-based polyurethane with high energy absorption and pliability. The mounting system is preferably constructed to have a natural resonance frequency which is less than a lowest frequency reproduced by the crossover network by a factor of 0.707 or less.

FULL ARTICLE
http://www.patentstorm.us/patents/6173064.html

 

I'm sometimes surprised by what's patentable...

Is there any evidence that this technique solves a real problem? (of course, an invention - if this really is an invention - doesn't have to be useful to be patentable).

If I reduce the verbiage to its essentials - "put the crossover on something soft" - it scarcely seems believable that this is new (even in 1997 when the application was lodged). But then I'm not a patent lawyer.

 

As far as I understand Dick a patent confers intellectual property rights irrespective of whether the invention would work as claimed or not. Similarly I don't have a full understanding of patent laws in the US or UK.

I chanced upon this patent because I was looking for techniques used for crossover isolation. Subjectively I've noticed a consistent improvement with a variety of different loudspeakers after removing the crossover from the loudspeaker enclosure – particularly in terms of high frequency detail. However this requires an additional 'box' and at least three separate runs of loudspeaker cable per side; this isn't as neat an arrangement as I'd like.

What I'd prefer to do is to structurally isolate the crossover from the loudspeaker enclosure while in situ. Bitumen damping, Deflex, Sorbothane and other lossy polymers are the obvious contenders to do this.

 

I think I'd go for a separate section within the main box - and probably be more concerned about possible overheating of crossover components than if they were in the main enclosure.

It often seems to me that one of the pleasures of DIY as opposed to commercial construction is that practicalities of transportation need be less of a concern for the DIYer. I'm sure one of the reasons commercial speakers mostly have the crossover in the box is that it makes things easier to put on trucks.

Anothe thing to think about regarding changes to performance with crossovers inside/outside the box - compensating for component volume. It's also good to be sure that inductors are way outside the influence of driver magnetic fields.