CA1148091A - Speaker crossover networks - Google Patents
Speaker crossover networksInfo
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- CA1148091A CA1148091A CA000405871A CA405871A CA1148091A CA 1148091 A CA1148091 A CA 1148091A CA 000405871 A CA000405871 A CA 000405871A CA 405871 A CA405871 A CA 405871A CA 1148091 A CA1148091 A CA 1148091A
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Abstract
SPEAKER CROSSOVER NETWORKS
ABSTRACT OF THE DISCLOSURE
The invention comprises improved electroacoustic audio speaker cross-over networks. The improvements comprise both the addition of various passive elements and a novel inductively coupled circuit configuration. The improvements are applied to low pass and nigh pass networks and combinations thereof. In the preferred embodiments a separate electrical circuit is inductively coupled to the filter network. The physical configuration of the separate circuit can be easily adjusted to counter variations in individual speaker performance parameters Thus, production variations in speakers from the same manufacturer or among the products of different manufacturers can be overcome and a better matching of speakers provided.
In the simplest embodiment the separate inductively coupled circuit comprises a copper ring placed within an inductive coil of the filter. Adjust-ment is accomplished by adjusting the physical location within the coil or by small changes in the physical dimensions of the ring.
ABSTRACT OF THE DISCLOSURE
The invention comprises improved electroacoustic audio speaker cross-over networks. The improvements comprise both the addition of various passive elements and a novel inductively coupled circuit configuration. The improvements are applied to low pass and nigh pass networks and combinations thereof. In the preferred embodiments a separate electrical circuit is inductively coupled to the filter network. The physical configuration of the separate circuit can be easily adjusted to counter variations in individual speaker performance parameters Thus, production variations in speakers from the same manufacturer or among the products of different manufacturers can be overcome and a better matching of speakers provided.
In the simplest embodiment the separate inductively coupled circuit comprises a copper ring placed within an inductive coil of the filter. Adjust-ment is accomplished by adjusting the physical location within the coil or by small changes in the physical dimensions of the ring.
Description
SPEAKER CROSSOVER NETWORKS
BACKGROUND OF THE INVENTION
The field of the invention pertains to electroacoustic audio reproduc tion systems, the most com n examples of which are monophonic and stereophonic speaker systems. Best indivitual speaker or triver performance is severely llmitet within the normal range of hearing (about 20 - 20,000 Hz). Acoustic output ant efficiency become severely limitet outsite of the frequency range of best performance. This may be at the upper or lower end of the frequency range depending on the particular driver.
One approach to the problem is U.S. Pat. No. 3,497,621 wherein a low frequency compensation circuit for a single speaker is disclosed. A second com-pensating circuit for a single speaker is discloset in U.S. Pat. No. 3,838,216.
A more contemporary approach is to provide multiple separate speakers or drivers to cover the entire range of frequencies. Electronic crossover or filter networks are utilizet to feed low frequencies to low frequency drivers ("woofers") and hlgh frequencies to high frequency drivers (i'tweeters"). U.S.
Pat. No. 2,802,054 discloses the use of a crossover network and compensating network for separate low ant high freqoency speakers. Disclosed in U.S. Pat. No.
3,727,004 is an electronic crossover or filter network for a multiple speaker ¦system sold co~mercially. Crossover or filter circuits incorporating additional ¦passive electronic elements for both two and three speaker systems are disclosed ¦in U.S. Pat. No. 3,838,215. However, despite extensive speaker circuit develop-¦ment, the quest for better speaker performance continues in the attempt to meet ¦the public desire for a more perfect reproduction of sound and in particular I music.
¦S~nlARY OF THE INVENTION
The invention comprises improvements in electroacoustic audio speaker crossover or filter networks. The improvements comprise both the addition of various passive elements and a novel inductively coupled circuit configuration.
¦A separate electrical circuit is inductively coupled to the filter ne~,work and 1l~ 1148~91 s conveDien~1y adjsutab1e dur1Lg assemb1y to vary the ~u31ity factor (Q - fac-tor) of the filter. The inductively coupled circuits may be used with either the high pass, low pass or both filter networks of the crossover. The physical con-¦figuration of the separate circuit can be easily adjusted to counter variations¦
¦in individual speaker or driver performance parameters. Thus, protuction varia-¦tions in drivers from the same manufacturer although within specifications or ¦among the products of different manufacturers can be compensated and a better matching of speakers in a system accomplishet.
In the simplest embotiment the separate intuctively couplet circuit ¦comprises a copper ring placet within an inductivelcoil of the filter. Atjust-¦ment is accomplished by atjusting the physical location within the coil or by ¦small changes in the physical dimensions of the ring. As an alternative, the ¦separate circuit can be a secontary coil with a suitable cross section ant ¦number of turns. This alternative allows a switch or disconnect to be incorpora-¦ted in the intuctively coupled circuit to switch in the inductively couplet ¦ circuit when tesiret.
DESCRIPTION OF T~E DRAWINGS
¦ FIG. l is a schematic of a typical low pass filter network and dual ¦ low frequency trivers;
FIG. 2 is a schematic of a modified low pass filter network and dual i low frequency drivers;
FIG. 3 is a plot of frequency versus acoustic output for a l~w fre-quency driver;
FIG. 4 is a side view of the inductively coupled circuit;
1 FIG. 5 is a schematic of an alternative form of the inductively coupled ¦ circuit;
FIG. 6 is a schematic of a typical high pass filter network and dual high frequency trivers;
FIG. 7 is a schematic of a motifiet high pass filter network and dual¦
high frequency drivers;
1 ~4t~091 FIG. ~ is a schematic of a crossover network incorporating one inductively coupled circuit and a high pass resonant filter;
FIG, 9 is a plot of frequency versus acoustic output for a high frequency driver;
FIG. 10 is a schematic of a further modified high pass filter network and dual frequency drivers;
FIG. 11 is a schematic of a crossover network incorporating triple inductively coupled circuits; and, FIG. 12 is a plot of frequency versus acoustic output for a complete loutspeaker combination.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 a typical low pass filter network and drivers are shown schematically. An inductance 20 and resistance 22 are in series with parallel coils 24 of trivers 26. A capacitance 28 ~nt secont resistance 30 are in parall~ 1 with the driver coils. The resistance may be the inherent resistance of the inductance and capacitance or adtitional resistive elements. To accommotate the indivitual electroacoustic characteristics of a single triver or the tual drive~ s shown, the inductance 20, capacitance i8 ant resistances 22 and 30 are selected to compensate for large scale performance inadequacies. Such selection is tone at the design stage or ~ust before the assembly stage of the network - driver combination.
In FIG. 2 the network retains the capacitance 28 ant resistance 30. A
second capacitance 32 and resistance 34 are atted in parallel to the inductance 20 and resistance 22 to increase the impedance of the network above the upper cutoff frequency of the trivers. Again the resistance 34 may be inherent in the capacitance 32 or also inclute a separate discrete resistance. Magnetically coupled to the intuctance 20 is a secont circuit generally denoted by 36. The inductively coupled circuit 36 comprises an inductance 38 and resistance 40, however, in one preferred embotiment the resistance 40 comprises the inherent resistance of the coil forming the intuctance 38. Thus, the inductively coupled circult 36 c rl6es a shorteù coil.
1~48Q9l The effect of the shorted coil 36 on the performance of the drivers 2 in terms of acoustic output versus frequency is illustrated in FIG. 3. Curve 42 illustrates the response of typical low frequency drivers without the filter network of FIG. 1. Curve 44 illustrates the typical response of the same driver with the filter network of FIG. 1. Curve 46 illustrates the effect of the inductively coupled circuit 36 of FIG. 2.
In a network assembled according to the schematic of FIG. 2 for a pai~
of Heppner (Heppner Manufacturing Co., PØ Box Q, Round Lake, Illinois) 6 1/2 ¦
inch prototype low frequency drivers, the hump 48 on curve 44 was cut 1/4 to 1 db at 300 Hz and the dip 50 was raised 1 to 4 tb between 1 and 4 kHz. By properly choosing the inductance of the shorted coil 36 the response of the drivers is effectively leveled over the portion of the curve between the upper 51 (4 kHz) and lower 49 (50 Hz) cutoff frequencies of the drivers.
FIG. 4 illustrates a particularly effective configuration for the shorted coil 36 and inductance 20. The inductance 20 comprises a multiple turn coil of insulated coil wire 52 surrounding a copper ring 54. The copper ring comprises the shorted coil or inductively coupled circuit 36. The ring is about two inches in dia~eter with a thickness of about 1/16 inch and depth of 1/2 inch .
Rings may be conveniently formed by taking slices of copper pipe. By either adjusting the depth of the ring when cutting from the pipe or the depth of placl-ment of the ring within the coil 52, the reactance and Q-factor of the filter can be adjusted to suit an individual driver or several essentially identical drivers. In practice drivers are carefully tested and the ring positioned withi¦
the coil during assembly to correct for variations in driver or speaker parame-ters. A s~illed technician utilizing the combination of a noise generator, microphone and spectrum analyzer or the combination of an impulse excitation signal, microphone and oscilloscope can finely adjust the response of the filter driver network.
The ring alternatively can surround the coil 52 or be tilted with respect to the coil 52, the important factor being the proper magnetic couplingl of the inductance 20 to the ring 54. The selection of the final relative positijn l ll 11481~91 of the coil 52 to the ring 54, once made, may be retained by cementing the part to an insulated support in the same relative position. Alternatively, the ring ~ay be mounted on an adjustable fixture so that the magnetic coupling may be varied subsequent to assembly. The post assembly adjustable ring has been found very effective as a mid range (between driver lower and upper cutoff frequencie ) tonal balance adjustment control. The size and geometric position of the ring 5 relative to the coil 52 determine the shift of the curve 44 to the curve 46 in FIG. 3.
An alternative form of the inductively coupled circuit 36 is shown schematically in FIG. 5. The inductance 20 again may comprise a multiturn coil of insulated wire. The inductively coupled circuit 36, however, comprises a coi 56 of one or more turns and a disconnect or shorting switch 58 in the circuit.
The inductively coupled shorted circuit may thereby be selectably added or dele ted from the filter network as desired. The inductively coupled circuit 36 is not limited to the shorted coil, the inductance and separate resistance or the inductance ant sliorting switch disclosed above but may incorporate additional passive elements.
In FIG. 6 a typical high pass filter network and driver is shown , schematically. The network comprises a capacitance 60 and resistance 62 in seri s with the driver coils 64 of high frequency drivers 66 and an inductance 68, secont resistance 70 and secon~ capacitance 72 in parallel with the driver coils 64. As above the resistance may be the inherent resistance of the inductance or capacitance or additional discrete resistive elements. To accommodate the electroacoustic characteristics of the drivers, the values of inductance, capa-citance and resistance are selected to compensate for large scale driver perfor mance inadequacies. Such selection is done at the design stage or just befo~re the assembly stage of the network - driver combination.
In FIG. 7 a modified form of the high frequency filter network retainll the capacitance 60 and resistance 62 as well as the inductance 68, resistance 70 and capacitance 72. Inductively coupled to the inductance 68 is a second circuil generally denoted by 74 comprising an inductance 76 and resistance 78. Again in¦
the preferred e~bodiment the second circuit comprises a shorted coil wherein the resistance 78 is that inherent in the inductance 76. A copper ring as disclosed above provides a particularly effective shorted coil for the high pass filter network. For best performance the resistance 70 should be as low as possible, preferably no more than that inherent in the inductance 68, capacitance 72 and connecting wires, In FIG. 9 the efect of various passive elements in the high pass filter network is shown. The peak of curve 80 occurs at approximately the lower resonant cutoff frequency of the driver. In the case of curve 80 for a driver ¦with a lower cutoff frequency of 1000 Hz, the filter consisted of the series ¦capacitance 60 and resistance 62. Such a filter is conventionally modified by adding the inductance 68 resulting in curve 82 and possibly the capacitance 72 ¦resulting in curve 84. The combination of inductance 68 and capacitance 72 are ¦normally selected for resonance at the triver resonant frequency and to modify Ithe input impedance of the filter to complement the electromechanical impedance ¦of the driver at the resonant frequency.
Although obtaining a fairly flat frequency response (curve 84) the associated phase angle response and frequency roll-off can be further improved by adding the inductively coupled circuit 74 shown in FIG. 7 or the plural reso ¦nant circuits 86 and 88 and inductively coupled circuits 90 and 92 shown in FIG
10. The latter network provides the smooth roll-off of curve 94 in FIG. 9 and a ¦¦very flat phase response. Capacitance 96 is selected for resonance at the reso-nant frequency of the pair of drivers 9~ and capacitance 100 is selected for resonance at a frequency above the driver resonant frequency. Typically, capaci tance 100 is selected to be 7/10 ths of capacitance 96. Alternatively, the inductance 104 is selected to be 7/10 ths the inductance of inductor 102. The inductively coupled circuits 90 and 92 may very satisfactorily consist of a pai~
of copper ring shunts as described above and properly positioned with respect tq the respective coils 102 and 104.
The actual values chosen for the elements of the high pass filter net jwork of FIG. 7 or FIG. 10 are obeained by the empirical analysis of the step !1 - 6 -il ¦response or impulse response of the high frequency drivers. The frequency and phase response are derived from a Fourier analysis of the impulse or step response. The importance of a flat phase response appears in the superior effic-iency of the dual low frequency and high frequency driver and crossover network combinations shown in FIGS. 8 and ll.
In FIGS. 8 and ll the inductively coupled circuits are applied to crossover networks. The network of FIG. 8 consists of a low frequency filter driving a pair of low frequency drivers on the left and a high frequency filter driving a pair of high frequency drivers on the right. The low pass filter includes an inductively coupled shunt circuit 36 and is basically the circuit o FIG. 2. The high pass filter includes parallel resonant circuits 106 and 108 ¦with intuctances llO and 112 and capacitances 114 and 116 selected for resonanc at the high frequency driver cutoff frequency and a suitable second frequency thereabove.
As in the description for FIG. lO above the capacitance 116 is 7/lO t s the capacitance 114 or the inductance 112 is 7/10 ths the inductance 110, the other eLements being equal. This ratlo has been determined empirically to best flatten the phase curve. The dual resonant circuits increase the damping of the high frequency driver above the resonant driver frequency thus producing the very smooth roll-off of curve 94 and the flat phase response. As noted above th resistance 70 in FIG. 7 is as low as possible and therefore deleted from circui~s 106 and 108 of FIG. 8. The crossover of FIG. ll is basically the combination of¦
the crossover of FIG. 8 and the high pass filter of FIG. lC. The parallel resonant circuits 106 and 108 are combined with inductively coupled shunt cir- !
cuits 90 and 92 to fine tune the improved roll-off characteristics of curve 94 !
in FIG. 9.
In practice the precise frequency and phase response adjustments abovq allow a coupling effect to be utilized for superior efficiency. Ideally the highl frequency and low frequency drivers should be coincident in space, however, if j optimally located within a fraction of a wavelength and where the low frequen~
- 7 - , ` ~ 1148091 and high fsequency signal are closely in phase at the crossover frequency the coupling effect is effective. Additionally, the phase response of the combinatic n of drivers and filters must remain substantially linear outside f the pass band s of the filters for the greatest radiating efficiency through the crossover range between the high pass and low pass bands.
In practice a high frequency and a low frequency driver are spaced les s than one half wavelength apart and the desired attenuation of each filter - dri ver combination is adjusted to -6 db at the actual crossover frequency as shown at 118 in FIG. 12. The coupling effect levels the acoustic output through the crossover frequency as shown at 120. This is distinguished from the conventiona placement of speakers more than one wavelength apart with a -3 db attenuation a the crosso~er frequency. An additional result is a substantial doubling of the radiating efficiency of applicant's speaker systems over what would be expected from the drivers and a conventionai crossover network.
The shorted coil inductively coupled circuits disclosed above have proven to be particularly effective means of adjusting the filter circuits to compensate for deviations in driver performance among drivers from the same manufacturer or differing manufacturers although the drivers meet overall speci-fications. For best performance the acoustic output for each channel of a sterec _ phonic or quadraphonic high fidelity system should be identical. Thus, the crosq-over network for each channel should exactly compensate for the electroacoustic mis-match of the corresponding drivers connected thereto. The shorted coii inductively coupled circ~its disclosed above allow the drivers for each channel to be carefuliy matched during assembly to obtain the results disclosed above. ¦
The filter and crossover circuits disclosed above are shown directly connected to the electroacoustic driver~, however, other passive or active elements may be interposed between a filter and a corresponding driver or within a filter. As an example, a power amplifier can be interposed between the filter¦
and driver.
~ flat or linear phtie respo~s in ~his application 1 a time delay I 1~48~9~
¦compensated phase response that is substantially independent of frequency. On a plot of phase angle versus frequency a flat or ii~ear phase response is a hori-zontal line. The procedures for carefully adjusting the phase response outside of the pass bands to a substantially flat or linear response while re~aining th~
linear phase response within t'ne pass bands allows a carerul matching at the crossover frequency. Combined with an equal phase response at the crossover frequency the coupling effect of the high and low frequency drivers is most effective.
BACKGROUND OF THE INVENTION
The field of the invention pertains to electroacoustic audio reproduc tion systems, the most com n examples of which are monophonic and stereophonic speaker systems. Best indivitual speaker or triver performance is severely llmitet within the normal range of hearing (about 20 - 20,000 Hz). Acoustic output ant efficiency become severely limitet outsite of the frequency range of best performance. This may be at the upper or lower end of the frequency range depending on the particular driver.
One approach to the problem is U.S. Pat. No. 3,497,621 wherein a low frequency compensation circuit for a single speaker is disclosed. A second com-pensating circuit for a single speaker is discloset in U.S. Pat. No. 3,838,216.
A more contemporary approach is to provide multiple separate speakers or drivers to cover the entire range of frequencies. Electronic crossover or filter networks are utilizet to feed low frequencies to low frequency drivers ("woofers") and hlgh frequencies to high frequency drivers (i'tweeters"). U.S.
Pat. No. 2,802,054 discloses the use of a crossover network and compensating network for separate low ant high freqoency speakers. Disclosed in U.S. Pat. No.
3,727,004 is an electronic crossover or filter network for a multiple speaker ¦system sold co~mercially. Crossover or filter circuits incorporating additional ¦passive electronic elements for both two and three speaker systems are disclosed ¦in U.S. Pat. No. 3,838,215. However, despite extensive speaker circuit develop-¦ment, the quest for better speaker performance continues in the attempt to meet ¦the public desire for a more perfect reproduction of sound and in particular I music.
¦S~nlARY OF THE INVENTION
The invention comprises improvements in electroacoustic audio speaker crossover or filter networks. The improvements comprise both the addition of various passive elements and a novel inductively coupled circuit configuration.
¦A separate electrical circuit is inductively coupled to the filter ne~,work and 1l~ 1148~91 s conveDien~1y adjsutab1e dur1Lg assemb1y to vary the ~u31ity factor (Q - fac-tor) of the filter. The inductively coupled circuits may be used with either the high pass, low pass or both filter networks of the crossover. The physical con-¦figuration of the separate circuit can be easily adjusted to counter variations¦
¦in individual speaker or driver performance parameters. Thus, protuction varia-¦tions in drivers from the same manufacturer although within specifications or ¦among the products of different manufacturers can be compensated and a better matching of speakers in a system accomplishet.
In the simplest embotiment the separate intuctively couplet circuit ¦comprises a copper ring placet within an inductivelcoil of the filter. Atjust-¦ment is accomplished by atjusting the physical location within the coil or by ¦small changes in the physical dimensions of the ring. As an alternative, the ¦separate circuit can be a secontary coil with a suitable cross section ant ¦number of turns. This alternative allows a switch or disconnect to be incorpora-¦ted in the intuctively coupled circuit to switch in the inductively couplet ¦ circuit when tesiret.
DESCRIPTION OF T~E DRAWINGS
¦ FIG. l is a schematic of a typical low pass filter network and dual ¦ low frequency trivers;
FIG. 2 is a schematic of a modified low pass filter network and dual i low frequency drivers;
FIG. 3 is a plot of frequency versus acoustic output for a l~w fre-quency driver;
FIG. 4 is a side view of the inductively coupled circuit;
1 FIG. 5 is a schematic of an alternative form of the inductively coupled ¦ circuit;
FIG. 6 is a schematic of a typical high pass filter network and dual high frequency trivers;
FIG. 7 is a schematic of a motifiet high pass filter network and dual¦
high frequency drivers;
1 ~4t~091 FIG. ~ is a schematic of a crossover network incorporating one inductively coupled circuit and a high pass resonant filter;
FIG, 9 is a plot of frequency versus acoustic output for a high frequency driver;
FIG. 10 is a schematic of a further modified high pass filter network and dual frequency drivers;
FIG. 11 is a schematic of a crossover network incorporating triple inductively coupled circuits; and, FIG. 12 is a plot of frequency versus acoustic output for a complete loutspeaker combination.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIG. 1 a typical low pass filter network and drivers are shown schematically. An inductance 20 and resistance 22 are in series with parallel coils 24 of trivers 26. A capacitance 28 ~nt secont resistance 30 are in parall~ 1 with the driver coils. The resistance may be the inherent resistance of the inductance and capacitance or adtitional resistive elements. To accommotate the indivitual electroacoustic characteristics of a single triver or the tual drive~ s shown, the inductance 20, capacitance i8 ant resistances 22 and 30 are selected to compensate for large scale performance inadequacies. Such selection is tone at the design stage or ~ust before the assembly stage of the network - driver combination.
In FIG. 2 the network retains the capacitance 28 ant resistance 30. A
second capacitance 32 and resistance 34 are atted in parallel to the inductance 20 and resistance 22 to increase the impedance of the network above the upper cutoff frequency of the trivers. Again the resistance 34 may be inherent in the capacitance 32 or also inclute a separate discrete resistance. Magnetically coupled to the intuctance 20 is a secont circuit generally denoted by 36. The inductively coupled circuit 36 comprises an inductance 38 and resistance 40, however, in one preferred embotiment the resistance 40 comprises the inherent resistance of the coil forming the intuctance 38. Thus, the inductively coupled circult 36 c rl6es a shorteù coil.
1~48Q9l The effect of the shorted coil 36 on the performance of the drivers 2 in terms of acoustic output versus frequency is illustrated in FIG. 3. Curve 42 illustrates the response of typical low frequency drivers without the filter network of FIG. 1. Curve 44 illustrates the typical response of the same driver with the filter network of FIG. 1. Curve 46 illustrates the effect of the inductively coupled circuit 36 of FIG. 2.
In a network assembled according to the schematic of FIG. 2 for a pai~
of Heppner (Heppner Manufacturing Co., PØ Box Q, Round Lake, Illinois) 6 1/2 ¦
inch prototype low frequency drivers, the hump 48 on curve 44 was cut 1/4 to 1 db at 300 Hz and the dip 50 was raised 1 to 4 tb between 1 and 4 kHz. By properly choosing the inductance of the shorted coil 36 the response of the drivers is effectively leveled over the portion of the curve between the upper 51 (4 kHz) and lower 49 (50 Hz) cutoff frequencies of the drivers.
FIG. 4 illustrates a particularly effective configuration for the shorted coil 36 and inductance 20. The inductance 20 comprises a multiple turn coil of insulated coil wire 52 surrounding a copper ring 54. The copper ring comprises the shorted coil or inductively coupled circuit 36. The ring is about two inches in dia~eter with a thickness of about 1/16 inch and depth of 1/2 inch .
Rings may be conveniently formed by taking slices of copper pipe. By either adjusting the depth of the ring when cutting from the pipe or the depth of placl-ment of the ring within the coil 52, the reactance and Q-factor of the filter can be adjusted to suit an individual driver or several essentially identical drivers. In practice drivers are carefully tested and the ring positioned withi¦
the coil during assembly to correct for variations in driver or speaker parame-ters. A s~illed technician utilizing the combination of a noise generator, microphone and spectrum analyzer or the combination of an impulse excitation signal, microphone and oscilloscope can finely adjust the response of the filter driver network.
The ring alternatively can surround the coil 52 or be tilted with respect to the coil 52, the important factor being the proper magnetic couplingl of the inductance 20 to the ring 54. The selection of the final relative positijn l ll 11481~91 of the coil 52 to the ring 54, once made, may be retained by cementing the part to an insulated support in the same relative position. Alternatively, the ring ~ay be mounted on an adjustable fixture so that the magnetic coupling may be varied subsequent to assembly. The post assembly adjustable ring has been found very effective as a mid range (between driver lower and upper cutoff frequencie ) tonal balance adjustment control. The size and geometric position of the ring 5 relative to the coil 52 determine the shift of the curve 44 to the curve 46 in FIG. 3.
An alternative form of the inductively coupled circuit 36 is shown schematically in FIG. 5. The inductance 20 again may comprise a multiturn coil of insulated wire. The inductively coupled circuit 36, however, comprises a coi 56 of one or more turns and a disconnect or shorting switch 58 in the circuit.
The inductively coupled shorted circuit may thereby be selectably added or dele ted from the filter network as desired. The inductively coupled circuit 36 is not limited to the shorted coil, the inductance and separate resistance or the inductance ant sliorting switch disclosed above but may incorporate additional passive elements.
In FIG. 6 a typical high pass filter network and driver is shown , schematically. The network comprises a capacitance 60 and resistance 62 in seri s with the driver coils 64 of high frequency drivers 66 and an inductance 68, secont resistance 70 and secon~ capacitance 72 in parallel with the driver coils 64. As above the resistance may be the inherent resistance of the inductance or capacitance or additional discrete resistive elements. To accommodate the electroacoustic characteristics of the drivers, the values of inductance, capa-citance and resistance are selected to compensate for large scale driver perfor mance inadequacies. Such selection is done at the design stage or just befo~re the assembly stage of the network - driver combination.
In FIG. 7 a modified form of the high frequency filter network retainll the capacitance 60 and resistance 62 as well as the inductance 68, resistance 70 and capacitance 72. Inductively coupled to the inductance 68 is a second circuil generally denoted by 74 comprising an inductance 76 and resistance 78. Again in¦
the preferred e~bodiment the second circuit comprises a shorted coil wherein the resistance 78 is that inherent in the inductance 76. A copper ring as disclosed above provides a particularly effective shorted coil for the high pass filter network. For best performance the resistance 70 should be as low as possible, preferably no more than that inherent in the inductance 68, capacitance 72 and connecting wires, In FIG. 9 the efect of various passive elements in the high pass filter network is shown. The peak of curve 80 occurs at approximately the lower resonant cutoff frequency of the driver. In the case of curve 80 for a driver ¦with a lower cutoff frequency of 1000 Hz, the filter consisted of the series ¦capacitance 60 and resistance 62. Such a filter is conventionally modified by adding the inductance 68 resulting in curve 82 and possibly the capacitance 72 ¦resulting in curve 84. The combination of inductance 68 and capacitance 72 are ¦normally selected for resonance at the triver resonant frequency and to modify Ithe input impedance of the filter to complement the electromechanical impedance ¦of the driver at the resonant frequency.
Although obtaining a fairly flat frequency response (curve 84) the associated phase angle response and frequency roll-off can be further improved by adding the inductively coupled circuit 74 shown in FIG. 7 or the plural reso ¦nant circuits 86 and 88 and inductively coupled circuits 90 and 92 shown in FIG
10. The latter network provides the smooth roll-off of curve 94 in FIG. 9 and a ¦¦very flat phase response. Capacitance 96 is selected for resonance at the reso-nant frequency of the pair of drivers 9~ and capacitance 100 is selected for resonance at a frequency above the driver resonant frequency. Typically, capaci tance 100 is selected to be 7/10 ths of capacitance 96. Alternatively, the inductance 104 is selected to be 7/10 ths the inductance of inductor 102. The inductively coupled circuits 90 and 92 may very satisfactorily consist of a pai~
of copper ring shunts as described above and properly positioned with respect tq the respective coils 102 and 104.
The actual values chosen for the elements of the high pass filter net jwork of FIG. 7 or FIG. 10 are obeained by the empirical analysis of the step !1 - 6 -il ¦response or impulse response of the high frequency drivers. The frequency and phase response are derived from a Fourier analysis of the impulse or step response. The importance of a flat phase response appears in the superior effic-iency of the dual low frequency and high frequency driver and crossover network combinations shown in FIGS. 8 and ll.
In FIGS. 8 and ll the inductively coupled circuits are applied to crossover networks. The network of FIG. 8 consists of a low frequency filter driving a pair of low frequency drivers on the left and a high frequency filter driving a pair of high frequency drivers on the right. The low pass filter includes an inductively coupled shunt circuit 36 and is basically the circuit o FIG. 2. The high pass filter includes parallel resonant circuits 106 and 108 ¦with intuctances llO and 112 and capacitances 114 and 116 selected for resonanc at the high frequency driver cutoff frequency and a suitable second frequency thereabove.
As in the description for FIG. lO above the capacitance 116 is 7/lO t s the capacitance 114 or the inductance 112 is 7/10 ths the inductance 110, the other eLements being equal. This ratlo has been determined empirically to best flatten the phase curve. The dual resonant circuits increase the damping of the high frequency driver above the resonant driver frequency thus producing the very smooth roll-off of curve 94 and the flat phase response. As noted above th resistance 70 in FIG. 7 is as low as possible and therefore deleted from circui~s 106 and 108 of FIG. 8. The crossover of FIG. ll is basically the combination of¦
the crossover of FIG. 8 and the high pass filter of FIG. lC. The parallel resonant circuits 106 and 108 are combined with inductively coupled shunt cir- !
cuits 90 and 92 to fine tune the improved roll-off characteristics of curve 94 !
in FIG. 9.
In practice the precise frequency and phase response adjustments abovq allow a coupling effect to be utilized for superior efficiency. Ideally the highl frequency and low frequency drivers should be coincident in space, however, if j optimally located within a fraction of a wavelength and where the low frequen~
- 7 - , ` ~ 1148091 and high fsequency signal are closely in phase at the crossover frequency the coupling effect is effective. Additionally, the phase response of the combinatic n of drivers and filters must remain substantially linear outside f the pass band s of the filters for the greatest radiating efficiency through the crossover range between the high pass and low pass bands.
In practice a high frequency and a low frequency driver are spaced les s than one half wavelength apart and the desired attenuation of each filter - dri ver combination is adjusted to -6 db at the actual crossover frequency as shown at 118 in FIG. 12. The coupling effect levels the acoustic output through the crossover frequency as shown at 120. This is distinguished from the conventiona placement of speakers more than one wavelength apart with a -3 db attenuation a the crosso~er frequency. An additional result is a substantial doubling of the radiating efficiency of applicant's speaker systems over what would be expected from the drivers and a conventionai crossover network.
The shorted coil inductively coupled circuits disclosed above have proven to be particularly effective means of adjusting the filter circuits to compensate for deviations in driver performance among drivers from the same manufacturer or differing manufacturers although the drivers meet overall speci-fications. For best performance the acoustic output for each channel of a sterec _ phonic or quadraphonic high fidelity system should be identical. Thus, the crosq-over network for each channel should exactly compensate for the electroacoustic mis-match of the corresponding drivers connected thereto. The shorted coii inductively coupled circ~its disclosed above allow the drivers for each channel to be carefuliy matched during assembly to obtain the results disclosed above. ¦
The filter and crossover circuits disclosed above are shown directly connected to the electroacoustic driver~, however, other passive or active elements may be interposed between a filter and a corresponding driver or within a filter. As an example, a power amplifier can be interposed between the filter¦
and driver.
~ flat or linear phtie respo~s in ~his application 1 a time delay I 1~48~9~
¦compensated phase response that is substantially independent of frequency. On a plot of phase angle versus frequency a flat or ii~ear phase response is a hori-zontal line. The procedures for carefully adjusting the phase response outside of the pass bands to a substantially flat or linear response while re~aining th~
linear phase response within t'ne pass bands allows a carerul matching at the crossover frequency. Combined with an equal phase response at the crossover frequency the coupling effect of the high and low frequency drivers is most effective.
Claims (5)
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In an electric loudspeaker circuit comprising at least one electro-acoustic driver, an acoustic frequency filter connected to said driver, said filter including a resistance and a capacitance in series with the driver and in series with each other, the improvement characterized by, a plurality of separate series resonant circuits in parallel with the electroacoustic driver and in parallel with each other, said series resonant circuits located between at least a portion of said filter and said driver, and, said separate series resonant circuits being selected and adjusted to produce a smooth rolloff of amplitude response and a flat phase response within and beyond the pass band of the filter.
2. The electric circuit of claim 1 wherein the resistance of at least one of the resonant circuits is substantially limited to that inherent in the capacitance and inductance.
3. The electric circuit of claim 1 wherein the inductance of a first series resonant circuit is substantially 0.7 ths of the inductance of a second series resonant circuit in parallel with the first resonant circuit.
4. The electric circuit of claim 1 wherein the capacitance of a first series resonant circuit is substantially 0.7 ths of the capacitance of a second series resonant circuit in parallel with the first resonant circuit.
5. The electric circuit of claim 1 including at least one second cir-cuit, said second circuit including an inductance and being inductively coupled to one of said series resonant circuits.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000405871A CA1148091A (en) | 1980-03-26 | 1982-06-23 | Speaker crossover networks |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000348460A CA1148090A (en) | 1980-03-26 | 1980-03-26 | Speaker crossover networks |
| CA000405871A CA1148091A (en) | 1980-03-26 | 1982-06-23 | Speaker crossover networks |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1148091A true CA1148091A (en) | 1983-06-14 |
Family
ID=25669062
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000405871A Expired CA1148091A (en) | 1980-03-26 | 1982-06-23 | Speaker crossover networks |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1148091A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4885772A (en) * | 1986-02-19 | 1989-12-05 | Telefonaktiebolaget L M Ericsson | Apparatus for obtaining a high sound level and good sound reproduction from a loudspeaking telephone |
| US5568560A (en) * | 1995-05-11 | 1996-10-22 | Multi Service Corporation | Audio crossover circuit |
| US5937072A (en) * | 1997-03-03 | 1999-08-10 | Multi Service Corporation | Audio crossover circuit |
| US6707919B2 (en) | 2000-12-20 | 2004-03-16 | Multi Service Corporation | Driver control circuit |
-
1982
- 1982-06-23 CA CA000405871A patent/CA1148091A/en not_active Expired
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4885772A (en) * | 1986-02-19 | 1989-12-05 | Telefonaktiebolaget L M Ericsson | Apparatus for obtaining a high sound level and good sound reproduction from a loudspeaking telephone |
| US5568560A (en) * | 1995-05-11 | 1996-10-22 | Multi Service Corporation | Audio crossover circuit |
| US5937072A (en) * | 1997-03-03 | 1999-08-10 | Multi Service Corporation | Audio crossover circuit |
| US6707919B2 (en) | 2000-12-20 | 2004-03-16 | Multi Service Corporation | Driver control circuit |
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