Second Order Crossover Loudspeaker - Lab Report Example

Introduction Loudspeakers are the commonly used electrical devices that are used to increase the volume of sound. Loudspeakers are responsible for transforming the electrical signals into sound that are coming from devices such as broadcasting devices (radio), TV systems or electronic music related appliances. Loudspeakers use both electric and mechanical principles to convert an electrical signal. Mostly the speakers we use in our daily life works on the principle of audio cross-over. As the project topic suggests that we will be discussing the second order cross-over loudspeaker, loudspeakers are classified into different orders on the basis of filter order. Before discussing second order cross-over loudspeaker in detail first we get clear about basic concepts of audio cross-over , benefits , alternate designs etc .(referenced from Basic Electronics By Grob / Schultz 9th edition) Audio Cross-Over Crossovers works on the principle of dividing the audio single into several frequency parts that are transmitted to respective speakers designed to manipulate the respective frequencies. Audio cross-overs are widely used in electronics applications. We use multiple drivers or speakers in our sound systems as mostly an individual driver in not capable enough to cover and manipulate every frequency range present in sound so separate drivers are used for separate frequency ranges. What actually a cross-over circuit does is that it splits the input frequency into parts on the basis of low and high value and send it to the respective driver that will forward the signal frequency as a whole to the output load that is the speaker. Benefits of Cross-Over Circuit There are many benefits of cross-over circuits, which are as under: Two same resistance value speakers can be positioned in a parallel setting because of cross-over circuit. The resistance value speakers that are positioned in a parallel setting can be of two sorts, higher one and lower one. Because of this parallel setting, an amplifier can be there with a single valued resistance. Two varying drive units having varied efficiency values can be matched with one another with the support of cross-over circuits. With this grouping, the outcome in terms of frequency responsiveness by the drive units is not huge. The cross-over circuit permits either woofer or tweeter to equally response to the frequency due to which, the compound rejoinder is soft and smooth as compared to the unstrained curves of woofers or tweeters. Cross-Over Design Basics and Function We can make chunks of larger frequency range into minor portions to create standardized sounds. Specific drivers are there to direct the minor portions of different frequency range. Usually, it is noticed that standardized loudspeakers have a wide range of drivers and additives in order to make them more useful. The drivers and other parts include woofers, tweeters and much more in order to increase their value. In loudspeakers, the cross-over that are employed have to handle and designate a specific range of frequency to every driver. The audio signals that are received are required to be broken into varied portions of multiple frequencies, which range from high to low. There are two types of crossovers, which are active and passive. The cross-over that is employed frequently more is the passive one. The passive cross-over is not in need of peripheral power and the reason for this is that the passive cross-over gets activated because of the audio signals that go through it. Passive cross-over employs many modules present in a circuit such as inductors and capacitors. Specific circumstances are required to make the capacitors and inductors conduct. With different frequency ranges, the cross-over capacitor works varyingly. For example, when the frequency is higher, the capacitor is good at conductance, however, when frequency is low, the capacitor’s performance at conductance is poor. Unlike a cross-over capacitor, a cross-over inductor is good at conductance when frequency is low and poor when frequency is higher (International Journal of Electronics by Taylor & Francis, Volume number: 98). Fig (1) crossover passive loudspeaker (referenced from electronic circuits by Floyd 6th edition) Classification on the Basis of Filter Order The signals that are in form of audio signals pass through the speaker cable to the speaker body. While passing through the cable to the device, the signals also go through each driver that is part of the system. It passes through capacitor to flow to the tweeter. Therefore, the process of signal passing from one place to another includes the passing of signal from higher frequency level to the coil of the tweeter. Drivers in the systems usually answer back to the frequencies that are low in range. The electric current passes from one device to another as it goes through woofer, to the inductor. Varying ranges for frequency are chosen by the active cross-overs as they are the electrical instruments that choose the right kind of frequency for the signals to reach the amplifier. Every driver can have an amplifier circuit. They are better than passive crossover as we can easily adjust frequencies in active crossovers. Unlike active cross-overs, passive cross-overs make use of frequency ranges that are decided by separate constituents of the circuits. These constituents transform the signals. Capacitors and inductors that are used with passive cross-overs are newly set up. The ratio of employment of active cross-overs is not as common as passive cross-overs and the reason is that the devices employed for passive cross-overs are less expensive and less number of amplifier output for the speakers are required. The most commonly used audio crossovers have fourth order electrical filters. Higher orders filters are used in complex and costly electronic equipments. Following is the brief description about 1st, 2nd and 3rd order crossover speakers. First Order Cross-over Loudspeakers The first order cross-over loudspeakers display the Butterworth cross-over characteristic. An idealistic trait is associated with first order cross-overs. First order speakers are widely used as they are considered to be perfect for crossovers as this filter type delivers amplitude and phase equally without transforming them. It consists of lesser components and thus has fewer errors due to component internal resistances and characteristics. It is more efficient by permitting maximum signals of those frequencies that are not required to pass low pass frequency and high pass frequency sections as compared to higher order cross overs. High frequency drivers are able to be destructed because they cannot handle higher power inputs that are under the level of their frequencies. Because of this, woofers make use of first order cross-over filters. The construction and designing of first order filters is complicated because a higher amount of bandwidths are employed that are large. C1 + HIGH PASS - + L1 LOW PASS Second Order Crossover Loudspeakers The second order cross-over loudspeakers display the Bessel cross-over characteristic, Linkwitz cross-over characteristic, Butterworth cross-over characteristic or a combination of the characteristics based on the designing options and the parts that are employed. The passive cross-overs make use of second order filters frequently because a rational equilibrium is created between complication existent between this combination, rejoinder and range of frequency. C1 HIGH PASS L1 L2 C2 LOW PASS Third Order Crossover Loudspeakers These are generally the combination of first and second order filters. These crossovers usually have Butterworth filter characteristics; phase response is very good, the level sum being flat and in phase quadrature, similar to a first order crossover. Third-order acoustic crossovers are often built from first- or second-order filter circuits.( Electronic circuits By Floyd 6th Edition) C1 C2 HIGH PASS L1 L2 L3 LOW PASS C3 Detailed Description of Second Order Cross-Over Loudspeaker Passive cross-overs have second order cross-over and this combination is frequently employed. This combination is frequently employed because a rational equilibrium is created between complication existent between this combination, rejoinder and range of frequency. According to Floyd, the filters of second order have 40-db slope. There are multiple cross-overs associated with second order filters, which are Linkwitz cross-over, Butterworth cross-over and Bessel cross-over. The cross-overs already mentioned have proportioned polar rejoinder when they are related with time allocated for physical allocation. There is a common perception that a variation of one hundred and eighty degree exists between two kinds of filters having similar frequencies. The two contrasting filters are low pass filters and high pass filters. (Electronic circuits By Floyd 6th Edition). Designing a Crossover Network for Two-Way Speakers System If you are required to design a second-order filter for your crossover network, then you need two capacitors and two inductors. We construct crossover loudspeakers taking in consideration the frequency range that needs to manipulate and then we choose the inductance and capacitance value for the circuit. One capacitor should be wired in parallel with the woover, and then connected in series with the inductor. For the tweeter, you need to wire the inductor in parallel with the tweeter, then connect the capacitor in series. Circuit Diagram (Figure referenced from electronic circuits by floyd 6th edition) Circuit Description Here in a given circuit above a 25-watt power amplifier, two capacitors of 7µF each, two inductors of 900µH each are used. Power amplifier is connected across a two-way driver circuit to manipulate low and high frequency value separately. We have two capacitors and two inductors. The circuit is connected in series with the amplifier in a way that one capacitor C2 is connected in parallel with the woofer and then in series with the inductor L2. For tweeter, we have inductor L1 in parallel with tweeter and in series with the capacitor C1. There are many kinds of cross-overs such as Linkwitz-Riley cross-overs, Butterworth cross-overs and Bessel cross-overs. These cross-overs response differently on different frequencies. Linkwitz-Riley cross-overs go with reduction angles and the reason behind this is that at cross-over position, the system gives rejoinders that are quite smooth. The Butterworth cross-overs give way to a climax in terms of frequency required for the cross-over circuits. Bessel cross-overs unlike the other two create a frequency rejoinder between the other two cross-overs. The phase shift on a second-order crossover is 180 degrees (reversed polarity) (Referenced from electronic circuits by floyd 6th edition). Readings Here are the readings for certain frequency ranges for which the certain value capacitors and inductors are required. X over Frequency L(coil) C(capacitor) 1 KHz 1.8mH 13µF 2 KHz 0.9mH 7µF 3 KHz 0.6mH 4.6µF Loudspeaker Characteristics The two main characteristics associated with the speakers that affect their performance are sensitivity and impedance. Speaker Sensitivity Speaker sensitivity is a measurement of the amount of sound output derived from a speaker with one watt of power input from an amplifier. Speaker sensitivity will generally be given as a SPL (Sound Pressure Level) measurement taken at 1 meter on axis with a 2.83 volt input (1 watt @ 8 ohms). The higher the SPL, the more sensitive/efficient the speaker is generally speaking. There are many factors that affect the sensitivity / efficiency of speakers. 1 Listening environment The environment in which the speaker operates has significant impact on its efficiency or sensitivity. A significant factor in the sound of a loudspeaker system is the amount of absorption and diffusion present in the environment. The sensitivity of speakers varies with the environment features with which it interacts. They have different reflexive behavior depending upon the shape, size, volume and décor of the environment (Bogart , Theodore F. journal electric circuits, Glenco / Mcgraw-Hill , Colombus , Ohio). 2 Placement The mode spacing is critical, especially in small and medium size rooms like recording studios, home theaters and broadcast studios. The proximity of the loudspeakers to room boundaries affects how strongly the resonances are excited as well as affecting the relative strength at each frequency. The location of the listener is critical, too, as a position near a boundary can have a great effect on the perceived balance of frequencies (Bogart, Theodore F. journal electric circuits, Glenco / Mcgraw-Hill, Colombus , Ohio). 3 Directivity Directivity is an important issue because it affects the frequency balance of sound a listener hears, and also the interaction of the speaker system with the room and its contents. A speaker which is very directive (i.e., on an axis perpendicular to the speaker face) may result in a reverberant field lacking in high frequencies, giving the impression the speaker is deficient in treble even though it measures well on axis (e.g., "flat" across the entire frequency range). Speakers with very wide, or rapidly increasing directivity at high frequencies, can give the impression that there is too much treble (if the listener is on axis) or too little (if the listener is off axis). This is part of the reason why on-axis frequency response measurement is not a complete characterization of the sound of a given loudspeaker (.Electronic circuits By Floyd 6th Edition).  Speaker Impedance The term impedance refers to the resistance shown by the load to the source in accepting signal. Impedance is the internal resistance of a wire or component to the current. Impedance can be corrected in speakers by using impedance matching concept. Impedances that are similar to each other are usually not employed by solid-state amplifiers that are used in today’s era and the reason for this is that the transformers that keep the capacity of giving some output are not obtained by amplifiers that have semi-conductors. (Basic Electronics By Grob / Schultz 9th edition). Conclusion of Lab Report We discussed in detail the concept and designing of second order crossover loudspeaker and after completing this report we are well informed about the crossover concepts and other orders as well. Furthermore, we got to know about the different components used in crossover speakers and also different factors affecting the speaker performance and how to control those factors for high quality performance . References Basic Electronics By Grob / Schultz 9th edition . Electronic circuits By Floyd 6th Edition. International Journal of Electronics by Taylor & Francis , Volume number:98 . Bogart , Theodore F. journal electric circuits , Glenco / Mcgraw-Hill , Colombus , Ohio Understanding Active and Passive crossovers Author: Wayne Harris (Click Originally appeared in the January/February 1989 issue of Car Stereo Review magazine. Read More