US 20120213386A1 (19) United States (12) Patent Application Publication (10) Pub. N0.2 US 2012/0213386 A1 Knight et al. (43) Pub. Date: Aug. 23, 2012

(54) AUDIO CROSSOVER SYSTEM AND METHOD Publication Classi?cation (76) Inventors: Ian Howard Knight, Leicester (51) Int‘ Cl‘ (GB); Anthony Richard Milat, H03G 5/0” (2006-01) Sarasota, FL (US); Kym Martineni, Sarasota’ FL (Us); (52) US. Cl...... 381/99 Giles GarWell Smith, Leicester (GB) (57) ABSTRACT (21) APP1- NO-3 13/ 462,276 An audio crossover system and method is disclosed. An audio _ system includes tWo driver circuits, one for each of tWo audio (22) Flled: May 2’ 2012 frequency ranges, e.g., high and loW frequency ranges. The Related U‘s‘ Application Data driver circuits are des1gned to provide a combined frequency response curve that has a pronounced mldrange attenuatlon (62) Division of application No, 11/539,210, ?led on Oct dip, in contrast to prior art designs that attempt to provide a 6, 2006, noW Pat. NO. 8,194,886. ?at response over all frequency ranges. 18

14 12 AMP Patent Application Publication Aug. 23, 2012 Sheet 1 0f 2 US 2012/0213386 A1

20 200 1 k 20 k’

FIG - 1 (115 A Phon 130 /__,-130./\ 110 110--/\A 90 / 9o/\/\ 70 /_70./\/\ 50 /_50/\/~ 3O10 /-3O'/\/\/;10-/\ A b 20 200 1 k 20 k

FIG - 2

18 _| 16

12 AMP c T | 1 f Patent Application Publication Aug. 23, 2012 Sheet 2 of2 US 2012/0213386 A1

105.0 100.0 95.0 90.0 85.0 80.0 75.0 70.0 65.0 60.0 55.0 overplot 20.0 100.0 1000.0 10000.0 FIG-3

850Hz 13.6 KHz /><\ 20 50 100 200 500 1k 2k 5k 10k 20k FIG-5 US 2012/0213386 A1 Aug. 23, 2012

AUDIO CROSSOVER SYSTEM AND METHOD coloration caused by interaction of drivers, often attributed to box design, is minimiZed such that reproduction is both more RELATED APPLICATIONS natural and life-like. [0014] The subject invention has a Wider dynamic range. [0001] This application is a divisional application Which Due to several bene?cial design properties, Which become claims priority to US. patent application Ser. No. 11/539, evident as a result of the application of the design, system 210, ?led Oct. 6, 2006, and to US. Provisional Application performance as a Whole is increased and alloWs the system to Ser. No. 60/724,828, ?led Oct. 7, 2005, the entire disclosure experience a fuller and more dynamic signal range. of these applications being considered part of the disclosure [0015] The subject invention alloWs for very loW listener of this application and hereby incorporated by reference. fatigue due to loWer . Due to the lack of distortion inherent in the design, the brain does not need to ?lter unnec BACKGROUND OF THE INVENTION essary noise and information present in most speaker sys [0002] 1. Field of the Invention tems. The brain only has to process a faithful reproduction of [0003] The subject invention provides an audio crossover the original signal, Which ultimately causes less listening system and method. fatigue for the listener. [0004] 2. Description of the PriorArt [0016] The subject invention provides increased signal to [0005] The Way humans hear sounds is complex. The audi noise ratio. Trying to process distortion along With the signal tory canal Within the human ear is a long tube and it possesses causes the hearing system to produce its oWn noise; this resonances and peaks at certain frequencies. The loWest reso manifests itself as a Hash Distortion Within the ear. As a result nance is broadly peaked around 3 kHZ and appreciable gains of the distortion not being present, the signal to noise ratio is are incident from about 2 kHZ to 6 kHZ. perceived as Wider to the listener. [0006] This frequency range that is accentuated by human [0017] The subject invention improves ampli?er perfor hearing coincides With the frequency range in Which impor mance. The ampli?er is able to exert more control over the tant lingual sounds have their major spectral contents. Sounds drivers due to the relationship betWeen the speaker and the like “p” and “t” have very important parts of their spectral ampli?er When used With the design. This results in an overall energy Within the “accentuated” range, making them easier to loWering of system artifacts and maximiZes the potential and discriminate betWeen. To hear sounds in the accentuated performance of even an entry level ampli?er. range is vital for speech communication. [0018] The subject invention provides rock solid stereo [0007] When exposed to an incident directional sound ?eld images and sound staging. Speakers disappear and provide a and including diffractive effects of the head, the maximum more complete stereo illusion, With excellent sound-staging sound pressure level (SPL) at the eardrum can be approxi depth resolution and precision image accuracy to a level not mately 7 dB to 20 dB higher than in the incident ?eld, depend previously de?nable by the average listener. ing on the direction of the sound. In effect this gives humans [0019] The subject invention improves dispersion charac a sensitivity increase Within the range from around 2 kHZ to 6 teristics. Regardless of cabinet siZe, the speakers provide a kHZ of betWeen 7 dB and 20 dB. presentation that portrays the scale of the recording more [0008] Because of this sensitivity, a ?at frequency response faithfully than traditional designs, such that large recordings in the 2 kHZ to 6 kHZ area, Which is directly Within the Will retain their siZe even on small cabinets. midrange crossover area, is not required. This sensitivity is [0020] The subject invention provides a universal design illustrated in the Fletcher Munson curves as shoWn in FIGS. applicable to all standard multi-driver designs. Designs can 1 and 2. If the curves of FIG. 1 are turned upside doWn, as in be applied to 2-Way, 3-Way, 4-Way, 5-Way and other designs FIG. 2, they provide an indication of hoW the human hearing of speakers in any con?guration regardless of driver type. attenuates and accentuates parts of the audible frequency [0021] The subject invention Will loWer manufacturing range. costs. No additional special tooling or processes are required [0009] Typical industry standard crossover designs do not to implement the designs and no exotic or precision compo take this human hearing sensitivity into consideration and, nents are needed With the subject invention, Which results in therefore, attempt to provide a ?at response Within this area. signi?cantly loWer manufacturing costs than With traditional The subject invention, in contrast to the typical industry stan crossover designs. dard ?at response design, provides a response that is inversely [0022] The subject invention loWers R&D costs. The proportional to the increased sensitivity. This inversely pro designs can be implemented into existing speaker designs and portional design Will indicate a dip in response Within the con?gurations With minimal R&D expense and R&D can be critical area When measured on a spectrum analyZer. focused on very speci?c areas for future development. [0010] SUMMARY OF THE INVENTION AND [0023] Furthermore, the subject invention folloWs a unique ADVANTAGES methodology and have applications in home hi-?, profes [0011] The crossover system and method of the present sional monitors, cinema systems, live sound, commercial invention provides numerous advantages over the prior art. sound and car audio. The process can provide fresh neW [0012] The subject invention signi?cantly loWers audible concepts in an established market that, to date, has provided distortion in the midrange frequency area. The most evident feW true innovations. distortion in multi-Way speaker designs is predominantly [0024] Although the designs of the subject invention Were located in the midrange area. The system of the present inven primarily developed for passive speakers, the principles can tion interacts With drivers to provide superior midrange clar be applied to active con?gurations. Active systems can be ity and a more natural reproduction With minimal distortion. in?nitely tuned and are variable by nature to achieve any [0013] The subject invention provides signi?cantly less desired result. HoWever, utiliZing our design principles, coloration of signal. Due to the properties of the design, signal active systems may be tuned With phenomenal results, results US 2012/0213386 A1 Aug. 23, 2012

Which have not been seen or heard by anyone else in the [0042] General convention dictates that because of the sloW industry in systems tuned in this manner. 6 dB/octave slope and also because designers feel obliged to “butt up” the frequencies of each individual driver and con BRIEF DESCRIPTION OF THE DRAWINGS sequently the drivers are in a situation Where they are being [0025] Other advantages of the present invention Will be used or pushed in Well into the breakup Zone. This in turn readily appreciated, as the same becomes better understood negates any of the bene?ts of using ?rst order slopes. by reference to the following detailed description When con [0043] First orderusage should expose the inherent bene?ts sidered in connection With the accompanying draWings of the design, clearly revealing the best transient behavior Wherein: from both the speaker and the ampli?er. This results in giving [0026] FIG. 1 is a graph shoWing Fletcher-Munson loud maximum control over to the ampli?er, Which increases ness curves, poWer handling due to cleaner absolute control of the ampli [0027] FIG. 2 is a graph shoWing inverted Fletcher-Munson ?er over the driver. loudness curves, [0044] Using conventional thinking and methods, the [0028] FIG. 3 is a graph shoWing frequency response of a crossover frequency applied to the bass/midrange drivers in a typical , tWo-Way design is too high. This crossover point is typically [0029] FIG. 4 is a schematic diagram of a crossover system around 2 kHZ to 6 kHZ. With the crossover point so high for of the subject invention, and the bass driver, the bass driver is excited in the less-than-ideal [0030] FIG. 5 is a graph shoWing frequency response of a region near its mechanical limits and exhibits roughness/ and Woofer as implemented by the crossover system breakup, Which in turn prevents optimal integration With the and method of the subject invention. tWeeter. DETAILED DESCRIPTION OF THE INVENTION [0045] When this (breakup) area is being excited, the driver passes back (feeds) the ampli?er this energy/distortion on [0031] Referring to the Figures, Wherein like numerals return. Then the ampli?er attempts to control it and grip it. indicate corresponding parts throughout the several vieWs, an The result is the energy Within the system (ampli?er and audio crossover system and method is described herein. speakers) is in oscillation, more commonly referred to as [0032] All drivers have extreme mechanical distortion. limitations in their operation. Once these limits are reached, [0046] As the crossover frequency is loWered and the use the driver Will exhibit some form of mechanical breakup. able area is moved aWay from the mechanical limits of the When this mechanical breakup occurs, the movement of the driver, the roughness disappears and the bas s/midrange driver driver becomes distorted, i.e., the driver no longer moves in an starts to be more linear in its behavior and response to the ideal pistonic motion. signal applied to it. [0033] When drivers are used close to their mechanical [0047] This smooth response occurs because of a combi limits, they excite the inherent mechanical break-up proper nation of several factors: ties, Which are present in all drivers. Thus, there Will be no [0048] l. the bass/midrange is behaving more like a pis chance of integrating it Well With other drivers. The driver Will ton; produce distortion, and the energy present Will not give the driver a chance to faithfully or accurately reproduce the audio [0049] 2. the ampli?er is being fed less distortion back signal given to it. from the speaker; and [0034] The crossover system of the subject invention is a [0050] 3. because of the above, the ampli?er is producing true ?rst order crossover in its operation and has the folloWing less distortion and this occurrence alloWs a beating With characteristics: the signal to begin. This beating is in phase and harmony [0035] l. CORRECT PHASE AND AMPLITUDE With the signal and not ?ghting it. [0036] 2. MAXIMUM CONTROL OF AMPLIFIER [0051] The high frequency driver (tWeeter) is dealt With in OVER DRIVE UNIT quite the same Way as the mid/bass driver. The only difference [0037] 3. LOWEST DISTORTION POSSIBLEiEI is that the loWer end of its frequency response is limited. The THER PASSIVE OR ACTIVE breakup frequencies With Which a designer should be con [0038] 4. PISTONIC BEHAVIOR OF DRIVE UNITS cerned start as the signal approaches the driver’s resonance [0039] Unlike many commercial designs, the system of the frequency, or Fs. Again, general convention and industry subject invention needs no Zobel impedance correction or standard suggests that crossover frequency points should be other types of correction circuits such as Notch Filters, Reso approximately one octave above Fs. Unfortunately, operating nant Traps, etc. the tWeeter that close to Fs With any order slope causes prob [0040] The smoothness of frequency response and integra lems and excites the tWeeter, similar to that With the mid/bass. tion is achieved by the novel design, the correct usage of the [0052] Once good smooth frequency response has been drive units employed, and the correct implementation of ?rst achieved With the tWeeter, good integration With the mid/ bass order crossover slopes. can be realiZed and the combined frequency response curve of [0041] Conventional thinking and industry standard appli the crossover system Will operate such that the drivers Will cation in conjunction With accepted trade-offs using ?rst begin to beat together smoothly. The Wide frequency gap, or order crossovers actually prevent the mo st effective use of the attenuation dip, betWeen the drivers is being “psychoacous ?rst order crossovers. The usual and commonly accepted tically plugged” and is draWing open the curtains of the mid practice of the “butting up” of drivers (in terms of frequency range. response) actually prevents ?rst order crossovers being used [0053] Due to the fact that tWo drivers are smooth and under effectively, and thus getting the desired bene?ts from their control of the ampli?er, they are “beating together”. With the use. Basilar Membrane of the human ear not having to deal With US 2012/0213386 Al Aug. 23, 2012

the tWo-tone noise generation, distortion and unwanted noise impedance curve shoWn on the graph, We can see a drastic is drastically reduced and We are in fact creating a “Virtual increase in impedance of the driver due to voice coil induc Mid Range Driver”. tance rise. [0054] When tWo tones of nearly identical pitch are played [0068] As can also be seen from the graph in FIG. 3, the together, We get an audible modulation or pulsing (‘Beating’) area from 550 HZ to 850 HZ is relatively ?at and free from any at the rate of the difference betWeen the tWo frequencies. If the negative effects. Typically a driver of this type used With tones are nearly in time With each other (meaning the fre traditional crossover methods uses a frequency equivalent to quency difference is small) the beating Will be sloW. If the the actual crossover point of approximately 2 kHZ to 4 kHZ, pitches (tones) are further apart the beating Will be faster. Which is Well into the problematic area of the driver response. Beating occurs because the tWo sound Waves reinforce each [0069] The designs of the subject invention rely on the fact other When their peaks align and they cancel each other When that drivers are used Within their individual pistonic range. they are out of phase (or step) With each other. Whether tWeeter, midrange, or Woofer, the idea is to prefer [0055] This occurs in every multi-driver speaker system ably use drivers Where their frequency response is ideal, ?at, Within the midrange crossover area. When the speakers/cross and even. This alloWs the driver to provide optimum perfor over/ system is beating correctly: mance With negligible distortion. This also ensures that other [0056] l. Harmonics are restored and dynamic range artifacts, problems and issues With driver performance and becomes Wider, response that are common When using drivers in a Wider band [0057] 2. Distortion (hash, fuZZ, grittiness) is loWer, of frequency and closer to the maximum of their ideal limits, Will not need extra compensation or need to be resolved [0058] 3. Processing of the sounds becomes easier for the through additional design and components. The driver listener, behaves and exhibits tremendous control as it is not required [0059] 4. Images become solid, to perform anyWhere near any of the mechanical breakup that [0060] 5. Sound staging becomes realistic and has depth, exists on the outer limits of its response curve. and [0070] Referring to FIG. 4, the passive component value [0061] 6. Listener fatigue is loWer. used in the crossover system 10 for the Woofer 12 is an [0062] Any crossover order higher than ?rst order (6 dB/oc 14 and its value is determined based on the standard tave) causes time smear, and loses harmonic detail to com ButterWor‘th ?rst order formula by using the frequency deter plete the signal Within the pass band. The so called disadvan mined above from the response and impedance of the Woofer. tage of ?rst order crossovers is that, When implemented, the This frequency, as previously stated Will ideally be betWeen drivers have to accept a frequency range that is too Wide and, 550 HZ and 850 HZ depending on driver characteristics. consequently, are operated up to tWo octaves outside their [0071] An example folloWs beloW using a driver impedance useful range. This causes the common misconception that of 8 ohms and a comer frequency point of 850 HZ: they exhibit poor poWer handling characteristics. [0072] LIinductance value in millihenrys (mH) [0063] By using higher and loWer frequency points, instead [0073] Zlqvoofer impedance in ohms of the actual crossover point as is traditionally used, the [0074] Pi (n):mathematical numerical constant (3.1416 Harmonic Structure of the Signal is preserved. In effect, the system operates similar to a “Band Reject Filter.” [0075] f1:corner frequency for the loW frequency driver [0064] When used Within the critical mid range frequencies (Woofer) of the 2 kHZ through to 6 kHZ area, the amplitude of the L:Zl/[(pi><2)>

[0078] Therefore using our example above, the capacitor a second driver circuit, and value of the capacitor 18 for our high frequency driver a second speaker operably coupled to said second driver (tWeeter) 16 based on our Woofer comer frequency is calcu circuit, Wherein said ?rst and second driver circuits com lated as folloWs: bine to create a combined frequency response curve of [0079] CIcapacitance value in microfarads (uF) said audio crossover system that comprises an attenua [0080] Zh?weeter impedance in ohms tion dip proximate an actual crossover point of a ?rst [0081] f1:corner frequency for the loW frequency driver frequency response curve of said ?rst driver circuit and (Woofer) a second frequency response curve of said second driver [0082] cm:crossover multiplier (in this example, circuit. cm:l 6) 2. The audio crossover system of claim 1, Wherein said ?rst speaker comprises a Woofer. 3. The audio crossover system of claim 1, Wherein said second speaker comprises a tWeeter. 4. The audio crossover system of claim 1, Wherein said [0083] lnversely, the comer frequencies can also be calcu attenuation dip is present substantially betWeen a ?rst and lated opposite from our description above by calculating the second comer frequency. tWeeter frequency ?rst and then applying the formulas in 5. The audio crossover system of claim 4, Wherein said ?rst reverse so as to determine the Woofer comer frequency. corner frequency comprises a point at Which said ?rst fre [0084] This attenuation dip or crossover gap betWeen the quency response curve of said ?rst driver circuit is attenuated tWo comer frequencies can occur at any point Within the approximately 3 dB. audible frequency band, and can slide up or doWn the band 6. The audio crossover system of claim 4, Wherein said from 20 HZ to 20 kHZ based on driver characteristics and second comer frequency comprises a point at Which said desired results. second frequency response curve of said second driver circuit [0085] Although the example above is calculated based on is attenuated approximately 3 dB. a ?rst order design, Which is considered optimal, the desired 7. The audio crossover system of claim 4, Wherein second results can be achieved With other variations and orders of corner frequency is approximately 16 times said ?rst comer crossover When the frequency gap is calculated correctly. frequency. This “gaping” method is unique to the method of the subject 8. The audio crossover system of claim 7, Wherein said invention of providing tWo separate comer frequencies for a actual crossover point of said combined frequency response tWo Way design, three separate corner frequencies for a three curve of said audio crossover system is approximately 4 times Way design, etc. said ?rst corner frequency. [0086] When using the ButterWorth ?rst order method as a 9. The audio crossover system of claim 4, Wherein said ?rst basis for calculating the comer frequencies in the method of driver circuit comprises an inductor, said inductor having an the subject invention, it becomes apparent from FIG. 5, that inductance (“L”) determined by the equation: the sloW 6 dB/ octave slope When used With the ideal cm (crossover multiplier) value of 16 (four octaves) becomes a symmetrical con?guration, Where the tWo frequency Where: response curves cross at —l2 dB and then at —24 dB are Z1:?rst speaker impedance in ohms, symmetrically aligned With the comer frequencies. This J'EIPi, mathematical numerical constant (~3. 141 6 . . . ), and “beating Zone” Where these parameters align is considered f1:said ?rst corner frequency. the “ideal” con?guration. HoWever, the crossover multiplier 10. The audio crossover system of claim 4, Wherein said can be of varying value depending on the desired character second driver circuit comprises a capacitor, said capacitor istic required from the system. having a capacitance (“C”) determined by the equation: [0087] The subject invention shoWs that the traditional and commonly accepted practice of “tuning” or adjusting speaker systems to have a typical 20 HZ to 20 kHZ frequency response Where: as close to ?at as possible is, in fact, not optimal, and the ideal ZhIsecond speaker impedance in ohms, response should have a noticeable attenuation dip in the f1:said ?rst corner frequency, and response curve betWeen the tWo comer frequencies. cm:a crossover multiplier. [0088] The tWeeter and midrange point in a three-Way sys 11. A method for providing crossover in an audio system, tem is calculated exactly as With a tWo-Way system With tWo comprising the steps of: separate Widely spaced comer frequencies. In addition a providing a ?rst driver circuit, Wherein said ?rst driver negative band-pass ?lter based on the loWer frequency of the circuit ?lters an output of said audio system to obtain a midrange is calculated and the Woofer Will alWays share the ?rst speaker output, same inductor as is used on the loWer portion of the midrange providing a second driver circuit, Wherein said second driver. driver circuit ?lters said output of said audio system to [0089] Obviously, many modi?cations and variations of the obtain a second speaker output, present invention are possible in light of the above teachings. providing said ?rst speaker output to a ?rst speaker, and The invention may be practiced otherWise than as speci?cally providing said second speaker output to a second speaker, described Within the scope of the appended claims. Wherein said ?rst and second speaker outputs combine to create a combined frequency response curve of said audio What is claimed is: system that comprises an attenuation dip proximate an actual 1. An audio crossover system, comprising: crossoverpoint of a ?rst frequency response curve of said ?rst a ?rst driver circuit, driver circuit and a second frequency response curve of said a ?rst speaker operably coupled to said ?rst driver circuit, second driver circuit. US 2012/0213386 A1 Aug. 23, 2012

12. The method of claim 1, wherein said ?rst speaker 19. The method of claim 14, Wherein said ?rst driver circuit comprises a Woofer. comprises an inductor, said inductor having an inductance 13. The method of claim 1, Wherein said second speaker (“L”) determined by the equation: comprises a tweeter. 14. The method of claim 1, Wherein said attenuation dip is present substantially betWeen a ?rst and second corner fre Where: quency. Z1:?rst speaker impedance in ohms, 15. The method of claim 14, Wherein said ?rst corner frequency comprises a point at Which said ?rst frequency J'EIPi, mathematical numerical constant (~3. 141 6 . . . ), and response curve of said ?rst driver circuit is attenuated f1:said ?rst corner frequency. approximately 3 dB. 20. The method of claim 14, Wherein said second driver 16. The method of claim 14, Wherein said second corner circuit comprises a capacitor, said capacitor having a capaci frequency comprises a point at Which said second frequency tance (“C”) determined by the equation: response curve of said second driver circuit is attenuated approximately 3 dB. 17. The method of claim 14, Wherein second comer fre Where: quency is approximately 16 times said ?rst corner frequency. ZhIsecond speaker impedance in ohms, 18. The method of claim 17, Wherein said actual crossover f1:said ?rst corner frequency, and point of said combined frequency response curve of said cm:a crossover multiplier. audio system is approximately 4 times said ?rst comer fre quency. * * * * *