Dual range horn with acoustic crossover

A new approach has been developed to combine mid-range and high frequency sound into the throat of a horn designed for sound reinforcement. An acoustic low pass filter element is interposed between the lower frequency passage and the higher frequency passage, so that a smooth combination of the two frequency bands is achieved at the entrance to the horn bell. Thus, each frequency band has nearly identical dispersion, and the two sources have equal delay.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the design of acoustic horns for use in a speaker system.

2. Description of the Prior Art

In the design of acoustic speaker systems, typically a combination of speakers is provided to optimize the performance of the speaker system in the low frequency ranges, mid-frequency ranges, and high frequency ranges. Thus, a conventional “three-way” speaker system will have individual speaker components addressing these three frequency ranges.

Several prior art attempts have been made to create a single speaker that produces sounds in multiple frequency ranges. For example, U.S. Pat. No. 5,526,456 issued to Heinz discloses a multiple driver single horn speaker. In Heinz, the high frequency and low frequency sound take parallel paths into the horn. However, the configuration of the Heinz loud speaker produces interference between the various frequencies as well as irregularities in the sound produced from the horn.

U.S. patent application publication Ser. No. 2002/0014369 by Engebretson discloses a multiple driver sound system. The Engebretson publication also fails to cure the interference and the irregularities between the frequencies because of the failure of the frequencies to promulgate through the same horn section.

Other attempts to solve these problems have resulted in sound drivers being placed coaxially. This topology has been used in an attempt to achieve a more uniform pattern control in a more compact system. For example, U.S. Pat. Nos. 4,283,606 and 4,619,342 both issued to Buck disclose a low frequency transducer and a high frequency transducer having coaxial acoustic centers. These prior art arrangements still suffer from three basic problems. First of all, the high frequency horn shadows the mid frequency sound, causing the response irregularities. Second, the unequal time delay between the two frequencies causes frequency response problems unless there is a specific delay correction applied. Finally, the directional coverage pattern produced from these prior art devices has significant peaks and dips at and near the crossover frequency at locations off the acoustical axis.

Thus, there is a continuing need in the art for an improved speaker system which would permit higher and lower frequencies sources to utilize a common horn.

SUMMARY OF THE INVENTION

A new approach has been developed to combine mid-range and high frequency sound into the throat of a horn designed for sound reinforcement. An acoustic low pass filter element is interposed between the lower frequency passage and the higher frequency passage, so that a smooth combination of the two frequency bands is achieved at the entrance to the horn bell. Thus, each frequency band has nearly identical dispersion, and the two sources have equal delay.

In one embodiment the invention provides a horn apparatus including a horn having a bell and an entrance slot, a higher frequency source, a lower frequency source, a higher frequency throat connecting the higher frequency source to the entrance slot of the horn, a lower frequency throat connecting the lower frequency source to the entrance slot of the horn, and an acoustic cross-over filter interposed between the higher frequency throat and the lower frequency throat upstream of the entrance slot of the horn.

Accordingly, it is an object of the present invention to provide an improved dual range horn apparatus with an acoustic crossover.

Another object is the provision of a dual range horn having a very symmetrical dispersion pattern across the entire frequency range covered by both transducers.

And another object of the present invention is the provision of a low pass filter which reduces harmonic distortion generated above the pass band of the lower frequency device, thus producing better sound quality.

Other and further object features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following disclosure when taken in conjunction with the accompanied drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1shows a prior art speaker system10having a high frequency acoustic transducer12and a low frequency acoustic transducer14which sends sound energy through high and low frequency throats16and18to parallel entrance slots20and22in the bell24of a horn. The difficulty with such an arrangement is that there will be an asymmetry in the sound distribution from the two sources12and14, as they do not share a single entrance slot to the horn.

FIG. 2shows a prior art arrangement wherein there is a combining section26for the two sources12and14before a single slot28to the horn bell24. The problem with the arrangement ofFIG. 2is that if the sound sources are covering different frequency ranges, then the passage ways will not exhibit the desired exponential area increase as a function of distance, thus causing frequency response errors.

FIG. 3shows one embodiment of a horn apparatus30of the present invention. The higher and lower frequency source acoustic transducers, which may be referred to as higher and lower frequency sources, are designated by the numerals32and34, respectively. The lower frequency source34may be the “mid-range” speaker of a three-way speaker system. A horn36has a bell38which has a single entrance slot40. A higher frequency throat section42communicates the higher frequency source32with inlet slot40. An acoustic filter43, which includes a perforated sheet, is interposed between the low and high frequency throat sections44and42, just prior to joining the entrance slot40which enters the horn bell38. The acoustic filter43is a low pass (high cut) filter of 20 dB per decade slope, which constitutes an acoustic crossover network. This allows each disparate horn throat42and44to have a proper exponential flare rate, while allowing the two sound sources32and34to combine at the horn bell entrance slot40.

By way of illustration, if this perforated panel43were solid, then the higher frequency throat42would function normally, while the lower frequencies from throat44would be completely blocked. Instead, the filter43comprising the perforated plate, confines the higher frequencies to the higher frequency throat section42while allowing the lower frequencies to enter the higher frequency throat section42in a gradual manner. Thus the proper flare rates are preserved for each sound source.

The horn apparatus30of the present invention can also be called a dual range horn30. In a preferred embodiment, the horn apparatus30includes the higher frequency throat section42centrally located so that the axis of the high frequency throat section42is perpendicular to the horn flange periphery. The lower frequency source34is placed at a 90 degree angle with respect to the higher frequency source32. The low frequency throat section44is bent and arranged to engage the high frequency throat42at an angle.

The higher frequency throat42communicates openly with the entrance slot40of the horn36. The acoustic filter43provides relatively high impedance to the higher frequency sounds. As such, the higher frequency energy is confined to the higher frequency throat42. The lower frequency energy enters the higher frequency throat42from the side at an angle to the axis of the higher frequency throat42. This lower frequency energy passes through the acoustic filter43, which can also be called a low pass filter43, to blend smoothly with the high frequency sound and the high frequency throat42. The lower frequency energy encounters the entrance slot40of the horn36concurrently with the higher frequency energy. Thus each frequency band enters the horn36at nearly the same position, and the dispersing pattern is nearly identical for both frequency bands. This is due to the fact that all frequencies are directed and controlled by one bell38on a single horn36.

The result is a very symmetrical dispersion pattern across the entire frequency range covered by both transducers32and34. In addition, the low pass filter43reduces harmonic distortion generated above the passband of the lower frequency device, thus producing better sound quality. A further advantage of this arrangement is that the low and high frequency throat sections44and42are similar in length for each of the frequency sources32and34. In the preferred embodiment this length is identical for each frequency source, resulting in an equal time delay for both frequency energies.

As an example,FIG. 17shows the horizontal dispersion of a horn assembly made in accordance with the current invention using a single driver for each frequency band on a three frequency system. The crossover point is quite seamless at four (4) kHz. Thus, the invention provides evenly controlled sound dispersion across a wide range of frequencies with a virtually undetectable crossover.

By way of comparison,FIG. 18is a display of the mid and high frequency response as a function of horizontal angle for a conventionally spaced mid and high horns.FIG. 18shows a conventional system using a side by side mid and high frequency horns over the same range of input as seen inFIG. 17. Due to the non-coincident nature of the side by side arrangement, the time delay between the dual frequency sources appears in this side by side arrangement when the output is reviewed at any point not exactly on the central axis of this conventional system. As a result, conventional systems have frequency response anomalies.

The current invention also reduces the left-right asymmetry. As seen inFIG. 19the horizontal asymmetry remaining in the output from the current invention is minimal. Specifically,FIG. 19shows the remaining midrange +/−45 degree horizontal asymmetry in the dual range horn with acoustic crossover. Note the improved horizontal asymmetry in a dual range horn apparatus created according to this invention.

FIG. 4illustrates an alternative embodiment of the invention, sometimes referred to as a “quad horn”, system generally designated by the numeral50. The horn system50includes first and second lower frequency sources52and54, and two higher frequency sources such as56. A horn58includes a bell60and an entrance slot62, which as further described below will effectively have a narrower higher frequency slot width64and a wider lower frequency slot width66.

The higher frequency sound sources56are communicated with the entrance slot62, and specifically with the narrower effective entrance slot64by a higher frequency throat section68. The first and second lower frequency sound sources52and54are communicated with the entrance slot62by first and second lower frequency throat sections70and72which are disposed on opposite sides of the higher frequency throat section68.

First and second perforated plate type acoustic filters74and76are located between each of the first and second lower frequency throat sections70and72and the higher frequency throat section68. It is the two low frequency filters74and76which effective define the narrower effective entrance slot64into the horn58for the higher frequency sounds. Since the acoustic filters74and76are transparent to the lower frequency sounds, however, the lower frequency sounds have a wider effective entrance slot66.

Thus, in the embodiment ofFIG. 4, the two acoustic filters74and76essentially form an extension of the horn at the inlet slot62to the higher frequency throat section68. The advantage is that the diffraction slot62is effectively narrow such as64for the higher frequencies, and is effectively wider such as66for the lower frequencies. This is an advantage because the width of the entrance slot should be proportional to the highest frequency to be diffracted. This arrangement also leads to a more effective flare rate for each frequency range for their respective throat sections and also provides symmetrical dispersion patterns for the two frequency ranges.

In both the embodiments ofFIGS. 3 and 4, the design lends itself to equalizing the time delay from the two different range drivers, which is an advantage.

FIGS. 5-11show various assembled, cut away and exploded views of the quad horn apparatus ofFIG. 4, wherein the part numbers ofFIG. 4are utilized to identify the elements onFIGS. 5-11.

FIG. 14is an exploded view of the dual horn apparatus ofFIG. 3, wherein the part numbers ofFIG. 3are utilized.

As will be understood by those skilled in the art, in addition to the higher frequency “tweeter” speakers56, and the lower frequency “mid-range” speakers52and54of horn system50, the speaker system100will include large conventional bass or woofer speakers located behind decorative panels104and106.

FIG. 13is a right side elevation cut away view of the speaker system100ofFIG. 12. The horn assembly50ofFIGS. 5-11is shown in place therein.

FIGS. 15 and 16schematically illustrate alternative embodiments of dual and quad horns, respectively, each of which utilizes acoustic filters comprising two spaced perforated plates. InFIG. 15the two spaced perforated plates are designated as43A and43B. InFIG. 16, the first pair of plates is designated as74A and74B, and the second pair is designated as76A and76B. Such a spaced plate filter may be referred to as a “3 pole” filter. The single plate filters may be referred to as “single pole” filters.

The advantage of using two spaced perforated plates is that the filter has a sharper cutoff slope. The single pole filters ofFIGS. 3 and 4have a 20 dB per frequency decade slope above the crossover frequency, whereas the three pole filters ofFIGS. 15 and 16are 60 dB per decade.

The acoustic filter43,74, or76can be comprised of several different patterns of perforations within the plate. Calculations were performed to predict the performance of an acoustic filter. The transmission loss of a suitable acoustic filter43,74, or76is shown inFIG. 20. This transmission loss was derived from a single perforated plate 0.25 inches in thickness. This plate had 0.5 inch diameter round holes on one (1) inch, 60 degree staggered centers. Some empirical adjustments were made to obtain the desired performance. In a preferred embodiment, the spacing between holes of an acoustic filter43,74, or76is 1.25 inches.

FIGS. 21A-23Fshow three embodiments of acoustic filters43,74, or76suitable for use in the horn assembly30.FIG. 21A-21Eshow a perforated filter having four rows of openings90traversing the acoustic filter. Three of these rows have circular openings92, while the fourth row has semi-circular openings94.

FIG. 22A-22Eshow a perforated filter having three rows of openings traversing the acoustic filter. Two of these rows have circular openings92, while the third row has semi-circular openings94. The openings located after the bend can be a row of decorative circular depressions if not acoustically needed by the horn assembly30.FIG. 23A-23Fshow a perforated filter having one rows of circular openings92traversing the acoustic filter.

Other embodiments that vary the size, location, number and shape of the openings, or holes, of an acoustic filter should be readily apparent to one skilled in the art upon a reading of this disclose.