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Electronics Design in a Passive Speaker System

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Electronics Design in a Passive Speaker System Teemu Jortikka Electronics Design in a Passive Speaker System Metropolia University of Applied Sciences Bachelor of Engineering Electronics Bachelor’s Thesis 15 May 2021 Abstract Author Teemu Jortikka Title Electronics Design in a Passive Speaker System Number of Pages 57 pages Date 15 May 2021 Degree Bachelor of Engineering Degree Programme Electrical and Automation Engineering Professional Major Electronics Instructors Hannes Nieminen, Project Manager Heikki Valmu, Senior Lecturer The goal of this thesis project was to start the research and development of the electronics of a passive loudspeaker system. The project being started from scratch, many of the topics included in speaker design are not limited to electronics engineering. The project was not ordered by any company but is rather a passion project of two audio engineers. The project started with the research of the proper speaker drivers. Once the drivers were chosen, the enclosure was next in line for the design. Once the drivers and enclosure were brought to physical reality, the frequency responses from different combinations of elements were measured. From these measurements, with the help of a little DSP, the requirements for the passive circuitry of the speaker were discovered. The circuit was to consist of a simple crossover circuit and a delay. The crossover is simple due to it just being a high pass filter and a low pass filter, but the delay is a much more tricky subject. The delay was chosen to be implemented using an all-pass filter topology. All the circuitry was simulated, but due to the limitations of the software and the nature of sound design in general, most decisions and opinions had to be made by ear. After the circuit was simulated, numerous PCB:s were designed. These consisted of two versions of the crossover circuit, and one PCB containing one order of the all-pass filter. These orders were to be stacked in order to find the optimal amount of delay. The end results of this project are a little inconclusive. The delay was found to be too costly and large for the benefit it brought to the sound of the speaker. The crossover worked well, and further development of the speaker continues outside the limits of this thesis project. Keywords Loudspeaker, passive circuitry, audio, PA speakers Tiivistelmä Tekijä Teemu Jortikka Otsikko Electronics design in a passive speaker system Sivumäärä 57 sivua Päivämäärä 15 Toukokuu 2021 Tutkinto Insinööri (AMK) Tutkinto-ohjelma Sähkö- ja Automaatiotekniikka Ammatillinen päänimike Elektroniikka Ohjaajat Hannes Nieminen, projektipäällikkö Heikki Valmu, yliopettaja Tämän insinöörityön tarkoitus ja päämäärä oli aloittaa kaiuttimen tutkimus- ja kehitystyö. Koska kyseessä on tyhjästä aloitettu projekti, monet käsitellyt aiheet eivät rajoitu pelkästään elektroniikkasuunnitteluun. Insinöörityötä ei ole tilattu minkään firman toimesta, vaan on enemmänkin luonteeltaan kahden äänisuunnittelijan mieltymyksiin perustuva projekti. Projekti alkoi tarkoitukseen sopivien kaiutinelementtien tutkimuksella. Kun elementit olivat valittu, oli seuraavana vuorossa kotelosuunnittelu. Kun elementit ja kotelo olivat tuotu fyysi- seen todellisuuteen, erilaisten elementti- ja koteloyhdistelmien taajuusvasteet mitattiin. Näi- den mittaustilausten pohjalta,pienen DSP:n avustuksella, passiivipiirien vaatimukset saatiin selville. Piiri koostuu yksinkertaisesta jakosuodattimesta ja viiveestä. Jakosuodin on yksinkertainen, sillä se on vain yksi ylipäästö- ja yksi alipäästösuodin. Viive on paljon mutkikkaampi asia suunnitella. Viiveen toteutustavaksi valittiin kaikkipäästösuodin. Kaikki piirit simuloitiin, mutta simulointiohjelman ja äänisuunnittelun luonteen vuoksi suurin osa päätöksistä piti tehdä kor- vakuuloon perustuen. Sen jälkeen kun piiri simuloitiin, lukuisia piirilevyjä suunniteltiin. Nämä koostuivat kahdesta eri versiosta jakosuotimesta ja yhdestä piirilevystä ensimmäisen asteen kaikkipäästösuoti- melle. Asteita on tarkoitus kasata, ja lopullinen ratkaisu asteiden määrästä tullaan tekemään korvakuuloon perustuen. Projektin lopputulema oli vähän tulokseton. Viive todettiin liian kalliiksi ja suurikokoiseksi suhteessa sen tuomaan sointihyötyyn. Jakosuodin toimi hyvin, ja projektin kehitystä tullaan jatkamaan tämän insinöörityön ulkopuolella. Avainsanat Kaiutinsuunnittelu, kaiuttimet, PA, passiivielektroniikka Contents List of Abbreviations 1 Introduction 1 2 Loudspeaker Operation 2 2.1 The driver 3 2.2 The enclosure 5 3 PA Systems In General 7 3.1 Point source vs line array 7 3.2 Active speaker design 9 3.3 Passive speaker design 11 4 n-Array Design 13 4.1 Small size and the drivers of choice 13 4.2 Enclosure design 17 4.3 Passive electronics 20 4.4 One channel per unit 21 5 Acoustic Measurements 22 5.1 Mark 1 SMAART measurements 23 5.1.1 PTMini-6 measurement 24 5.1.2 PT816-8 measurements 25 5.2 Mark 2 SMAART measurements 29 5.3 Crossover, delay and EQ requirements 31 6 Electronics Design 32 6.1 Parallel or series connection 32 6.2 Crossover design 34 6.2.1 The Butterworth filters 35 6.2.2 Component choices 37 6.3 Delay design 38 6.3.1 All-pass filter design 39 6.4 Circuit simulation 40 7 PCB Design 44 7.1 Logic 45 7.2 Layout 47 8 Assembly & Measurements 50 8.1 Crossover 51 8.2 Delay 52 9 Conclusions 54 References 56 List of Abbreviations AC Alternating current. AV Audiovisual. A blanket term compassing all media consisting of visual and audio components. dBFS Decibel Full Scale. A digital audio measurement scale, from -¥ to 0. Any- thing above 0 leads to digital distortion of the signal. DSP Digital signal processing. EQ Equalization. A term used in audio production referring to applying different filters to affect the spectrum of a signal. PA Public address system. SMD Surface mount devices. SPL Sound pressure level. 1 1 Introduction Ever since the first loudspeaker was installed in a telephone by a scientist by the name of Johann Philipp Reis in 1861 [1], engineers have been coming up with different imple- mentations and installation locations for them. In our modern era the most familiar appli- cations for loudspeakers include (but are not limited to) the speakers on smartphones, televisions, reference monitors and the big sound systems at live music venues. While speakers are a very familiar sight for most, not many are aware that they do not come “one size fits all”. For example, a terrific speaker for replicating the sound of one’s favorite song with authenticity and excitement may be a horrendous choice for replicating the sound of minimally processed human speech. The idea for this bachelor’s thesis came from years of combined experience in the field of audio engineering. Multiple live shows, conferences, studio sessions and lately streamed webinars combined with the experience of an AV integrator gave rise to a need for a specifically tailored speaker for a specific purpose. Many venues where speakers are installed are increasingly conscious of their visual ap- pearance. With the rise of globalism and the internet the world has become an increas- ingly smaller place, and people are generally more aware of different kinds of products and implementations on the market. This has led to the gradual decline of the traditional speaker, a wooden box suspended from a ceiling or mounted on a wall and given rise to a need for innovation. One famous Finnish company manufactures very aesthetically pleasing speakers, which sound phenomenal. However, the average customer is not aware, that these said speakers are designed to be reference studio monitors with an optimal listening distance measured in meters (depending on the model). This may not be a huge issue when finished music products (mastered to be close to 0dBFS, which means a very compressed and loud signal), but when these speakers are assigned the task of reproducing the waveform of human speech things become more difficult. There simply is not enough strength in the dispersion of the high frequencies at longer dis- tances than for example three meters. Add to this problem the tendency of amateur speakers to talk too quietly to the microphone and the habit of holding the microphone at a bad place (too far from the sound source, this time being the mouth of the speaker) and the sound technician has a big problem on his hands. 2 All this had led us to the desire to design and produce a speaker, which is pleasant to look at, very small and thus easy to conceal, powerful at reproducing sound in the speech spectrum and easy to install. The project name for this speaker is n-Array. 2 Loudspeaker Operation It is beneficial to know the basics of the operation of loudspeakers before diving any deeper into the design of the n-Array. Loudspeakers can be classified into many different categories depending either on the frequency bandwidth of operation, the speakers tar- geted application, the speaker’s operational functionalities or the design of the frequency dispersion inside the speaker. Generally, one is familiar with the classification of active-and passive speakers, the for- mer being powered by its own power source and the latter requiring a separate amplifier in order to function. Both methods of powering a speaker are used widely on both pro- fessional and consumer applications. Things become a bit more complicated when the frequency dispersion is added to the mix, resulting in the categorization of one-way, two- way and three-way speakers. One-way speakers are speakers which have only one speaker element responsible for the whole sound output of the speaker. Usually this type of speakers are specialized on the low end of the sound spectrum and are called sub- woofers. Two-way speakers are speakers with internal filters (known as crossover filters) which divide the audio signal from the input into two different speaker elements, one being responsible for the lower end of the sound spectrum and the other for the higher end. These speaker elements are called the woofer and the tweeter. A three-way speaker is logically very similar to the two-way speaker with an added woofer responsible for the mid-range sound reproduction.
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