Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Plural or compound reproducers
Utility Patent
1999-03-02
2001-01-02
Kuntz, Curtis A. (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Plural or compound reproducers
C381S163000, C381S335000, C381S345000, C381S351000, C181S145000, C181S156000, C181S144000
Utility Patent
active
06169811
ABSTRACT:
BACKGROUND OF THE INVENTION
The Field of the Invention
This invention relates to improved bandpass loudspeaker systems.
One of the prior art configurations relevant to the invention is the multi-chamber bandpass woofer system. Historically it has been shown that for a given restricted band of frequencies an acoustical bandpass enclosure system can produce greater performance both in terms of the efficiency/bass extension/enclosure size factor and large signal output compared to non-bandpass systems such as the basic sealed or bass reflex enclosures. The basic forms of these bandpass systems are discussed in the literature. See for example ‘A bandpass loudspeaker enclosure’ by L. R. Fincham, Audio Engineering Society convention preprint #1512, May.
The earliest patent reference to a single tuned bandpass woofer system is Lang, ‘Sound Reproducing System’ U.S. Pat. No. 2,689,016. This patent reference anticipates the most common version of bandpass woofer system that is used in many systems today. This type of system includes an enclosure with two separate chambers and an active transducer mounted in the dividing panel and communicating to both chambers. One chamber is sealed and the other is ported with a passive acoustic mass communicating to the environment outside the enclosure.
The earliest patent reference to a dual tuned bandpass woofer system is shown in FIG. 1 of U.S. Pat. No. 1,969,704, D'Alton, ‘Acoustic Device’. This reference discloses an enclosure containing a two chamber bandpass woofer system with an active transducer mounted in the dividing panel and communicating to both chambers. Each chamber has a passive acoustic radiator communicating to the environment outside the enclosure. European patent 0125625 ‘Loudspeaker enclosure with integrated acoustic bandpass filter’ by Bernhard Puls and U.S. Pat. No. 4,549,631 ‘Multiple porting loudspeaker systems’ granted to Amar G. Bose are derived from the same basic structure as shown in the D'Alton reference.
An alternative arrangement of a dual tuned bandpass system is disclosed in the U.S. Pat. No. 4,875,546 ‘Loudspeaker with acoustic band-pass filter’ granted to Palo Krnan. This system includes an enclosure with two separate chambers and an active transducer mounted in the dividing panel and communicating to both chambers. One chamber is ported with a passive acoustic radiator communicating to the environment outside the enclosure. There is a second passive acoustic radiator communicating internally between the two chambers.
U.S. Pat. No. 5,092,424 ‘Electroacoustical transducing with at least three cascaded subchambers’ granted to Schreiber et al is an extension of the above listed bandpass art. It utilizes an enclosure with at least three chambers such that it is substantially equivalent to the Bose '631 patent listed above, but with an additional enclosure volume added to the outside of the main enclosure. This additional enclosure receives the two ports from the internal main chambers and an additional passive acoustic radiator communicates to the environment outside the system.
While offering certain advantages over non-bandpass prior art systems, such as the simple sealed box and the bass reflex, vented enclosure, these systems also exhibit a number of liabilities and limitations. One limitation is that the dual and triple chamber versions with multiple vent tunings, such as Bose, Scheiber, and Krnan all use much smaller chambers for their lowest frequency vent tuning. This requires a vent with greater losses than the vent in a generic bass reflex enclosure. This can cause significant overall losses in actual systems compared to the ideal theoretical lossless models of these systems. These systems also exhibit large diaphragm excursions at frequencies below the lowest vent tuning or ‘cut-off’ frequency and can have greater than normal diaphragm displacement at frequencies between the vent tunings. This can cause distortion and limit total system output. Also, the D'Alton, Puls and Bose systems are limited to narrow bandwidths if significant ripple in the frequency response is to be avoided. While reducing transducer excursion at the vent tuning frequencies, these systems can have greater transducer excursions at other frequencies in the passband which can cause distortion at high levels. They do not offer a way to reduce transducer excursion over their entire usable pass band.
Another group of prior art devices, relating to the invention, include loudspeaker systems with augmented passive radiators. The earliest of these systems is disclosed in U.S. Pat. No. 3,772,466 ‘Loud speaker system’ granted to Hossbach which teaches the use of a high frequency active transducer coupled to an augmented passive radiator. Later versions of this type of system were granted to Clarke U.S. Pat. No. 4,076,097 and Dusanek U.S. Pat. No. 4,301,332. These devices are well characterized in “Augmented Passive-Radiator Loudspeaker Systems, Parts 1 and 2” by Thomas L. Clarke, found in the June and July, 1981 issues of the Journal of the Audio Engineering Society.
These prior art devices all configure their active transducers to radiate one side of their diaphragm surface area to the external environment outside of the main enclosure and the other side coupled through a chamber to one diaphragm surface area of an augmented passive radiator which is also coupled to the outside environment. The active transducer delivers the output at the higher frequencies and it drives the augmented passive radiator only over a very narrow band of lower frequencies. An augmented passive radiator is defined as a passive dual cone radiator that has one surface area coupled through the main enclosure volume to the active transducer, a second surface area coupled to the outside environment and a third surface area enclosed in a sealed auxiliary chamber. Because of this configuration these systems cannot produce an acoustically or mechanically generated lowpass or bandpass characteristic and therefore their performance is substantially limited to that of a simple non-bandpass vented system.
These inventors also teach the reflex tuning of the augmented passive radiators being the lowest reflex tuning frequency of the system rather than having an additional low frequency capability below the tuning of the augmented passive radiators. Therefore it is characteristic of these systems that the reflex frequency of their augmented passive radiators is always the lowest tuning frequency of the system and that tuning frequency is the low frequency cut-off of the system. The systems have little useful output when operated significantly below the reflex tuning frequency of the augmented passive radiator.
It is also a limitation of these systems that the active transducer has only one side of its cone interacting with the augmented passive radiator. It is a further limitation of these systems that they achieve the augmentation provided by their augmented passive radiators only at the narrow range of frequencies near the tuning frequency. At all other frequencies in the usable passband the active transducer must provide all of the volume displacement without any augmentation from the passive radiator. Also, these systems isolate the output of one of the surface areas of their augmented passive radiators into a sealed chamber so that only one surface area can generate acoustic output. To state it differently, an augmented passive radiator is a closed architecture system with an isolated auxiliary chamber that closes off the output and coupling of one of the two smaller coupling areas of the augmented passive radiator. An augmented passive radiator system, also always requires the greater cost and complexity of an additional auxiliary chamber.
U.S. Pat. No. 4,387,275 ‘Speaker and speaker system’ granted to Shimada, et al discloses a unified transducer structure to be used in a sealed or vented enclosure. The unified transducer structure embodies a small loudspeaker cone attached to the voice coil of the transducer and this small cone is air-coupled and
American Technology Corporation
Harvey Dionne N.
Kuntz Curtis A.
Thorpe North & Western L.L.P.
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