Using old physics a new way, the Thigpen Woofer is a new type of boxless monopole loudspeaker from Bruce Thigpen that improves efficiency, material use, weight, and size when compared to traditional loudspeakers. The home subwoofer is less than 3 inches thick. The subwoofer version of this technology is designed to operate next to a wall, or can be mounted on a wall and be painted any color. Multiple units project a planar low frequency wave down the listening room which is absorbed at the other end. This method of low frequency bass production, removes room modes and yields flat bass response and controls decay times.
A waveguide is a structure that guides waves, such as electromagnetic waves or sound waves, with minimal loss of energy by restricting expansion to one dimension or two.
A domestic home room wall represents a high impedance load to an acoustic wave. A high impedance load (e.g. a room wall) will cause a reflected wave in which the direction of the pressure wave is reversed but the phase of the reflected pressure remains the same.
This reflected energy causes distributed modes which result from out of phase reflected acoustic energy. These modes are a function of the wavelength and the dimensions of the room. The frequency response at the listener coming from a single small acoustic low frequency will not be flat at the listening position because of room modes.
A typical home audio system either uses full range speaker or multiple smaller speakers and a sub woofer to reproduce low frequency sound.
The woofer portion of a large loudspeaker might operate from 30Hz to 500Hz or higher, a sub woofer will typically operate from 20Hz to 100HZ.
The woofers in traditional loudspeakers are small acoustic low frequency sources (relative to the wavelength) which result in an omnidirectional radiation pattern and sets up multiple room modes.
The Thigpen Flat Woofer eschews Thiele/Small parameters and achieves excellent performance with a moving magnet and moving coil horizontally opposed motor structure, a much more favorable air mass to diaphragm mass ratio, a large diaphragm area for improved impedance match with the air and planar monopole acoustic radiation using wall loading. The prototype shown above has the active surface area of about ten 12 inch woofers!
The mass of the voice coil and magnet are each attached to horizontally opposed diaphragms in a border frame to create tuning frequencies on each side. It can be sealed with very small amount of air in the enclosed space between the diaphragms. The increase in efficiency is achieved with larger diaphragm area and the much better impedance match with the air which more than offsets the loss of box volume.
For the traditional home theater or home audio listening room, room modes are typically a big problem below about 200hz. Even though home audio woofers are very flat, in typical listening room this is far from the case. Room mode calculators and simulators will show you what the frequency response will actually look like, the swings in frequency response at the listening position can be +/-15dB. DSP " room correction" tools can reduce peaks but cannot fix the dips.
The flat horn is a new type of loudspeaker where box volume is traded for diaphragm area. This is facilitated with both a moving magnet and moving coil configuration. Diaphragm area is achieved by using parallel horizontally opposed planes (which become the speakers diaphragm or cone) of a stiff, light weight material. The motor, a voice coil and magnet span between adjacent planes, the voice coil is attached to a front plane and the magnet is attached to a rear plane, the force of the voice coil simultaneously opposes the two planes.
Parallel plane spacing might be a few millimeters to more than 20 centimeters. The area of each diaphragm plane can be a few square centimeters to more than a square meter. A frame border supports the front and rear planes.
The Thigpen Woofer:
The Thigpen Woofer is a new type of loudspeaker where box volume is traded for diaphragm area. This is facilitated with both a moving magnet and moving coil configuration. Diaphragm area is achieved by using parallel horizontally opposed planes (which become the speakers diaphragm or cone) of a stiff, light weight material. The motor, a voice coil and magnet span between adjacent planes, the voice coil is attached to a front plane and the magnet is attached to a rear plane, the force of the voice coil simultaneously opposes the two planes.
Parallel plane spacing might be a few millimeters to more than 20 centimeters. The area of each diaphragm plane can be a few square centimeters to more than a square meter. A frame border supports the front and rear planes.
The front and rear diaphragms usually have different tuning frequencies as a result of the difference in mass between the magnet attached to the back diaphragm and the voice coil attached to the front diaphragm with different stiffness designed into the diaphragms. Since the majority of the outer surface of the loudspeaker is made up of a lightweight diaphragm, the speaker ends up being about 1/3 the weight of conventional loudspeakers. There is no loudspeaker basket or speaker enclosure in a traditional sense.
Conventional home loudspeakers or subwoofers placed near side or rear walls create reflections, these reflections, depending on frequency and known as Speaker Boundary Interference response, sum with the source and cause numerous peaks and dips in the frequency response experienced by the listener. While peaks can be corrected with DSP, dips, cannot be corrected. The Thigpen woofer does improve both dips and peaks in the rooms response.
