Automotive sound systems have typically employed a plurality of speakers mounted in the instrument panels, door panels, rear package ledge or in floor consoles which permit the use of relatively large speakers of generally conventional design to allow for full range of both frequency and sound level for the reproduction of audio information. In automobiles and other motor vehicles, location becomes a particularly significant factor because of the impracticality or impossibility of moving the speakers once they have been installed and because of the limitations imposed by the physical dimensions of the interior of cars, especially with the growing popularity of smaller cars which have less interior room. The car audio speaker utilizing at least a part of a vehicle panel, such as rear parcel shelf, door inner panel or the like, as a sound-producing medium has been recently developed. Such speakers have the benefit of producing better quality audio sound, especially in the relatively low frequency range. In a passenger compartment of a motor vehicle, audio emanating from a sound system of the vehicle is directed typically from an interior panel into the passenger compartment and toward the general vicinity of the occupants of the vehicle. Speaker boxes are commonly mounted to the sports bar of sport utility vehicles to provide music and other audio entertainment for the driver and passengers. Such speaker boxes are mounted to extend across the sports bar in a fixed, horizontal position. Audio speakers are often mounted to an overhead vehicular ceiling structure, known as the headliner. The headliner may comprise a flexible molded composite of compressed, resin impregnated, fibrous materials covered by a suitable foam backed upholstery material. Speakers mounted directly to the vehicle headliner at appropriate locations and coupled to suitable sources of audio signals, such as amplifiers, delay circuits and a signal source, produces remarkable reproduction of the audio information providing dimensional sound imaging and depth not possible with speaker locations in the lower portions of the vehicle interior.

Vehicles usually include factory installed speakers that are often replaced with new speakers and/or speakers yielding higher quality sound. A multitude of different types of stereos and speakers are available from the original equipment manufacturers (OEM) of automobiles, usually tailored to the specific design of the vehicle. Factory mounted speakers are often mounted in concealed places such as behind door panels and under rear trim shelf panels. When the speakers are positioned behind or under such panels, the panels must incorporate a speaker grill that has apertures and cutouts to reduce muffling effects of the panels and to promote the efficiency of sound emanation from the concealed speakers into the interior of the motor vehicle. Many after market speakers are free standing with their own cases and speaker grills. The speaker grill is commonly used to conceal and protect the actual speaker cone against puncture or other damage. Different types of stereos and speakers are available from after-market suppliers, providing versatile stereos and speakers that can be installed in almost any vehicle by a skilled owner or after-market installer. However, the selection of available aftermarket speakers is limited to speakers that fit in the existing mounting holes in the support structure. A popular type of audio speaker is the tube speaker. The tube speaker provides enhanced perception and sound level for bass frequencies. The small acoustical environment of automobiles and trucks are particularly suited to audio tube speakers because of the small size of tube speakers and the ability of a speaker in a tube to be placed facing a corner wall of the truck or automobile at a desired distance therefrom. When tube speakers are employed in automotive vehicles, they are often merely laid on the floor of a van or on a flat panel in the rear of an automotive vehicle. However, due to their cylindrical shape, tube speakers lying on their sides on flat surfaces in an automotive vehicle will tend to roll about unless restrained. The speakers will roll due to inertia as the vehicle makes turns around corners or brakes to a stop.

Some automotive audio systems have echo systems to provide a better quality of sound, i.e. a better ambience. In typical automotive audio systems with such echo systems, the audio signals from an audio signal source, such as a radio, or a CD player, are separated into two components. One of the components is then sent to a mixer and the other is processed in an echo signal generator and then sent to the mixer. The mixer mixes the direct audio signal with the echo signal from the echo signal generator and sends the mixed signal to a main amplifier. Audio system equalization involves setting bass and treble tone controls and fade and balance controls to provide sound characteristics according to the preference of the listener. Selectable preset equalization is currently available with both a manufacturer preset and customer definable equalization settings. With these systems, the listener pushes a button on a control module to change equalization. In some vehicles, automatic equalization is available wherein inputs from sensors or system computers vary equalization according to environmental conditions. Among car speakers, the speaker apparatus for woofer or sub-woofer which deals with the voice output in a bass range is required to deal with a larger output than in a usual speaker apparatus in order that the voice in the bass range is sufficiently audible even when the running noise of the vehicle generated in the bass range is superposed on the voice.