WO2004071129A2

WO2004071129A2 - Multimedia loudspeaker

Info

Publication number: WO2004071129A2
Application number: PCT/MK2004/000001
Authority: WO
Inventors: Vladimir Filevski
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-02-07
Filing date: 2004-02-05
Publication date: 2004-08-19
Anticipated expiration: 2005-08-07
Also published as: WO2004071129B1; WO2004071129A3

Abstract

The present invention is a two-way loudspeaker that has the following three features: - a horn tweeter (2) with a narrow sound dispersion in a vertical plane so mounted that its reference axis of radiation is angled at between 10 and 40 degrees respective to the horizontal surface; - a bass/midrange unit (3) mounted close to the bottom surface of the loudspeaker so that its acoustic center is less than 63 mm off this bottom surface; - a crossover circuit with a crossover frequency lower than the first minimum in the resultant frequency response of the bass/midrange loudspeaker that comes as a result of the interference between the direct sound wave and the sound wave reflected from a surface on which the loudspeaker is placed. This loudspeaker exhibits a flat frequency response both when standing on a desk or when located in free space. All other known multimedia loudspeakers (intended to stand on a desk) suffer from interference between the direct sound wave and the sound wave reflected from the surface on which the loudspeakers are located, interference which results in an uneven frequency response.

Description

MULTIMEDIA LOUDSPEAKER Technical Field

MULTIMEDIA LOUDSPEAKER belongs to the field of loudspeakers. According to^' the

International classification of patents the invention subject is classified and marked by the following symbol: The technical problem can be described as follows: as multimedia loudspeakers usually stand on a desk facing the listener, both the direct sound from the loudspeaker and the sound reflected from the desk surface reach the ears of the listener - Fig. la as a result of which an interference takes place. The interference is a result of the direct sound from the loudspeaker and the sound reflected from the desk surface passing different distances on their way to the ear of the listener due to which appears a certain phase difference between them.

At certain frequencies the direct and the reflected sound waves are going to be in a phase which leads to a sound amplifying while at other frequencies they are going to be in an opposite phase which leads to a sound annul. Result of this is an uneven frequency response (that is, unnatural, bad sound quality) even in cases when the loudspeaker has a perfectly flat frequency response (measured in free space, clear of reflections). The frequency of the maximums and the minimums in the resultant frequency response as well as their amplitude depend on the following: the distance between the loudspeaker and the listener, the position of the acoustic center of the loudspeaker (respective to the desk surface) and the position of the ear of the listener (respective to the desk surface). The invention MULTIMEDIA LOUDSPEAKER resolves the above mentioned problems by providing a flat frequency response regardless of the distance to the listener and regardless of the distance between both the loudspeaker and the ear of the listener from the desk surface.

Background Art Multimedia loudspeakers intended to stand on a desk usually have angled front baffle on which the loudspeaker unit (or loudspeaker units) is mounted - Fig. lb. The front baffle is usually angled at 60 to 80 degrees (that is, the referent axis of the loudspeaker is angled at angle α of 10 to 30 degrees) respective to the desk surface in order to lower the amplitude of the reflected sound wave - especially at higher frequencies. The lower amplitude of the reflected sound wave comes as a result of the narrow dispersion (that is, lower amplitude) of the higher tones out of the referent axis of the loudspeaker - Fig. 1 c. Still, the measured resultant frequency response (along with the sound wave reflected from the desk surface) of this type of multimedia loudspeakers - Fig. Id compared to the response of the same loudspeaker (measured in a free space, clear from reflections) - Fig. le shows clearly that angling of the front baffle itself is not enough to achieve good results. If the used. loudspeaker has a peak in its own frequency response at exactly those frequencies that have minimums as shown at Fig. If and if at the same time it has dips at exactly those frequencies where the maximums are, then what we get is a flatter resultant frequency response. But, this flatter resultant frequency response comes only at exactly determined distance between the loudspeaker and the listener and exactly determined positions of both the ear of the listener and the acoustic center of the loudspeaker respective to the desk surface. If the listener (or the loudspeaker for that matter) moves from the most favorable position for only a couple of centimeters the resultant frequency response will show worse results than the one shown at Fig. If. The market offers this type of multimedia loudspeakers that have the said disadvantages, The Fig. le shows measured frequency response of a multimedia loudspeaker with a built-in single fullrange loudspeaker. If a classical two-way loudspeaker is used (bass/midrange and a small tweeter divided by a crossover in two frequency bands) then the result will be an even worse frequency response, especially at higher frequencies - this is because the tweeters by rule ^•have better dispersion at higher frequencies than a fullrange loudspeaker. Dispersion of high tones can be narrowed by a horn-type of a tweeter especially constructed for narrow dispersion of high tones but this is not sufficient if we want to achieve a flat frequency response. Other conditions are necessary to be fulfilled as well in order to get a flat frequency response. The market offers multimedia loudspeakers with a horn tweeter that gives a wide dispersion of high tones, a crossover of a too high crossing frequency and a bass/midrange loudspeaker placed too high from the desk surface. Due to the mentioned disadvantages these multimedia loudspeakers also do not have flat frequency response.

Disclosure of Invention

The invention MULTIMEDIA LOUDSPEAKER is a two-way loudspeaker with the following characteristics necessary for its proper functioning:

- horn-tweeter with a narrow sound dispersion in a vertical plane, so mounted that its referent axis of radiation is angled at 10 to 40 degrees respective to the horizontal desk surface.

- bass/midrange loudspeaker positioned as closer to the desk surface as possible, so that its acoustic center is less than 63 mm off the horizontal desk surface. - crossover with a crossing frequency lower than first minimum (the one with the lowest frequency) in the resultant frequency response of the bass/midrange loudspeaker which comes as a result of interference between the direct-sound wave and the sound wave reflected from the desk surface. The constructive solution of the invention is shown at Fig. 2a. According to Fig. 2a the tweeter (2) and the bass/midrange unit (3) are both built in the loudspeaker box (1). The referent axis of the tweeter is angled at angle α respective to the .horizontal desk surface. Fig. 2a shows a loudspeaker box (1) as closed type but it can also be a bass reflex or any other type. The tweeter (2) is a horn-type so designed and constructed that it has a narrow sound dispersion in a vertical plane. Thus, the amplitude of the sound wave reaching the desk surface and reflecting from it becomes smaller. The amplitude of the reflected sound wave can be additionally lowered by mounting the tweeter on the loudspeaker box so that its referent axis of radiation is angled at angle α of 10 to 40 degrees respective to the desk surface. Bass/midrange unit (3) is mounted at position as close to the desk surface as possible so that its acoustic center will also be as close to the desk surface as possible. The acoustic center of the bass/midrange unit should be less than 63 mm off the horizontal desk surface in order to achieve good results. This way is achieved the highest possible frequency of the first minimum in the resultant frequency response. Bass/midrange units that are built in the multimedia loudspeakers in most of the cases are small so that it is easy to get the first minimum in the resultant frequency response at frequency higher than 3 kHz which gives easier way regarding the construction of the tweeter and the parameters it should meet.

The crossover that divides the audio signal into two frequency bands must have a crossing frequency lower than the frequency of the first minimum in the resultant frequency response of the bass/midrange unit. Fig. 2b shows measured resultant frequency response of the multimedia loudspeaker (standing on a desk) constructed in accordance with the described invention. Fig. 2c shows measurements of the same multimedia loudspeaker made in a free space without the influence of the reflected sound waves. Comparison of Fig.2b and Fig. 2c shows that the invention MULTIMEDIA LOUDSPEAKER gives flat frequency response both standing on a desk and in a free space.

Claims

MULTIMEDIA LOUDSPEAKER is a two-way loudspeaker intended to stand on a desk, characterized by a horn tweeter with a narrow sound dispersion in a vertical plane, so mounted that its referent axis of radiation is angled between 10 and 40 degrees respective to the horizontal desk surface; bass/midrange unit placed close to the desk surface so that its acoustic center is located at height less than 63 mm from the horizontal desk surface; and a crossover with a crossing frequency lower than the frequency of the first minimum in the resultant frequency response of the- bass/midrange loudspeaker, which minimum is a result of the interference between the direct sound wave and the sound wave reflected from the desk surface.