ECE Sound Reinforcement System Design Spring Loudspeaker Active Spectral Divider Design Project

Transcription

1 Loudspeaker Active Spectral Divider Design Project

2 Project Report Evaluation Team ID: 4 Derek Devin Zack Team Member App Tech * TOTAL Maximum Points Possible * technical content, writing style, professionalism, clarity, completeness Instructor comments: 2

3 TABLE OF CONTENTS Abstract i 1.0 Introduction Design Narrative? 3.0 Results? 4.0 References? Appendix A: Activity Logs? Appendix B: Schematic (Analog) or Tuning Parameters (DSP)? Appendix C: Frequency Response Measurement? Appendix D: Subwoofer Design Documentation? Abstract The objective of this project is to design an active, DSP-based 3-way spectral divider (crossover network) for a 3-way (tri-amplified) labyrinth loudspeaker system. The DSP board ( loudspeaker enclosure, amplifier modules (4 x 100 W), and power supply will be provided. Primary goals including optimizing frequency response (target ±3 db over the range of 40 Hz to 16,000 Hz), optimizing signal arrival from each driver, and minimizing THD (total harmonic distortion). For bonus credit an (add-on) subwoofer can be designed and constructed, which will require a 4-way spectral divider. 3

4 1.0 Introduction Zack Bennett: My motivation for taking this course centers around my work in sound for the performing arts. As a Sound Designer for theatre and events, I am interested in learning more about the tools I work with and how to use them to their full capabilities. I found the process of choosing and researching drivers especially informative as I have primarily purchased pre-built speaker units, not individual components. The process of determining the range for each speaker s filter was also educational. I expected the results to be more clear audibly and be more sharply defined. My career goal after completing my masters is to sound design in regional theatres and in the corporate sector before becoming a professor. Derek Tenny: I took this class because I always have had a passion for audio and music. I loved music at a young age and as I got older I loved seeing how to make sound, sound its best. I was looking through ECE classes I could take going into my senior year and saw a class with a focus on audio and instantly got excited. I had listened to Professor Meyer s online lectures in 270, and was looking forward to learning from him in person. I learned a ton about how big of a different tuning can make, and the importance of spending time on the cross-overs. I also had never worked on a speaker/sub enclosure before, and it definitely got me comfortable with the process. In the future I hope to work with audio in the form of signal processing for a microphone or speaker company. Combining my EE background with my passion. Devin Clausen: The reason I took this course was because I believed it would fit in well with my curriculum. I have always had a passion for audio and music and recently have been more fascinated with the area of Acoustic Consulting and AV Design. My current career goals center around Acoustic Consulting and both this project and the upcoming EASE project will absolutely help me to learn more about what I can expect in that path. Specifically regarding this project, I was fascinated with how the different drivers interacted with each other and how we were able to adjust that interaction with the design of the crossover. I also definitely hope to build my own custom system now because of this project. 4

5 2.0 Design Narrative Physical Characteristics of Main Cab: Originally our 3-way labyrinth had a titanium bullet tweeter. While there are many applications where this would work fine, we all agreed we wanted a soft dome tweeter. The main reason was we felt the titanium would be to bright and harsh want wanted something that would blend better sonically with the rest of our system. We felt the the 4 inch and 10 inch drivers were exactly what we were looking for. We sweeped each frequency to compair it s listed range to its actual functioning range. We then sweeped again taking note of any resonance frequencies or frequencies that would cause rattle. The most time was spent picking the crossovers for the 10inch on the 3-way to the sub more on this later. Once we were comfortable with the cutoffs on paper we adjusted the levels using the spectral analyzer working to create a flat frequency response. After experimenting we decided against using any delays. One of the main issues we ran into was in regards to the tuning of the low end spectrum. The subwoofer had a similar frequency crossover to the 10inch driver on the 3-way system. It became a choice then where to crossover as the subwoofer would produce a warmer sound while the the driver on the 3-way had better transient response. Different songs would then differ based on how low or how much bass they had. We decided sonically we wanted the kick of the drum on the 3-way and bass to be primarily on the sub and tuned it to this criterium. Subwoofer: The enclosure we decided to use for the subwoofer was a bass reflex (or vented) enclosure. We chose this design over the sealed enclosure mainly due to the increase in output that a vented design can bring. A vented enclosure can have a larger run-off than a sealed box design, but we determined to sacrifice the small difference for the loudness of the lower frequencies before the run-off. When choosing the subwoofer s components, we were stuck in between two different drivers: GRS 10SW-4 and GRS 12SW-4. Our reasoning for choosing GRS was that they had very good reviews and the specifications were exactly what we were looking for with a very reasonable price. In the end, we chose the 10 GRS 10SW-4 because we did find that the similar 12 had a very high total Q value of For our vented enclosure, we chose the Super Forth-Order Boom Box (or SBB₄). The reasoning being that we desired the better transient response that it provides over the SC₄ and QB₃ alignments. The tuning frequency is higher than it would have been in a QB₃ aligned enclosure, but we made up for that by having a larger port diameter of 10 cm (~4 ). The dimensions given by the AJDesigner software were for a x x cm enclosure (Appendix D). For the finalized design, we stayed as close as possible to the calculated dimensions and ended up with a x x enclosure. The rest of the calculated parameters from AJDesigner are as follows: 5

6 Vb = Liters Fb = 29.5 Hz F3 = Hz Lp = cm AJDesigner predicted a response with a small shelf around the 40 Hz range and then the run-off being at around 30 Hz. From the frequency sweep we conducted we determined this was very close to the actual response. The subwoofer became distinguishable around 28 Hz and then had a high frequency run-off close to 550 Hz. 3.0 Results We were able to achieve a flat response between 35Hz and 15kHz. Our initial reading with filters based solely on manufacturer provided ranges created dips between the drivers. this is likely attributed to testing my the manufacturers in perfect situations and not in the field. by making the overlap between components slightly larger, we were able to compensate. The system was tested with trap/house music, jazz, rock, rap, R&B/funk, and classical. Below are the results of each. Trap/House: Notorious by Malaa This genre produced a strong, low presence and fast transient response. We experienced a slight buzz on low beats which wa remedied by tightening the screws attaching the woofer. Jazz: Maybe by Dave Grusin Our system reproduced crisp and clean high end, with enjoyable brilliance. The system also created significant liveliness, with a full sounding response from the middle and high ranges. The overall result was a warm sound with definition and texture. Rock: Only the Young by Journey The lead vocalist has a range that fit perfectly in the mid range driver, which allowed the lyrics to be more well defined. An increase in brilliance was also encountered. This was accompanied by a sound with significant texture. Rap: Gummy by Brockhampton Initially, some rattle was experienced from the extreme sub-bass frequencies. This was remedied by raising the low end cut off of the subwoofer to 25Hz. We found the bass response not to be as aggressive in our system as a typical rap system. Our systems high amount of blend was not asnappeling in this genre as in the previous choices. The sonic experience lacked brilliance. R&B/Funk: Everyday People by Sly and the Family Stone This system was well suited for this genre, supporting a sound rich with warmth and texture. However, the overall sound lacked liveliness in the mid-high range and noticeably less brilliant. Classical Symphony #7 Beethoven 6

7 This system provided brilliance, nearly to a fault. The more extreme high frequencies occasionally become overpowering. This was offset by the warmth created. Liveliness was also decreased. We all agreed that the speakers exceeded our expectations. Given the price of the drivers we felt they all performed well with vibrant mids and crispy highs. The sub also was audible down to 30 hertz. As far as improvements to the system adding a second 3-way to be able to play in stereo would be a plus and open many doors. Excluding that, better enclosures would help minimize rattle and increase sound quality. To look at the system as a whole we can t neglect the transmission of the sound which went through the room. A treated room would help create a more balance sound. Last minute preparations would include double checking all screws, adding wood glue to all the joints, breaking in the new 10-inch driver more, as well as double checking all connections. Making sure everything is soldered and wire impedance is minimized. 7

8 4.0 References McCarthy, R. (2007). Sound systems: Design and optimization: Modern techniques and tools for sound system design and alignment (2nd ed.). Oxford: Elsevier/Focal Press. Raymond, Jimmy. AJ Design Software. AJ Design Software, 8

9 Appendix A: Activity Logs 9

10 Activity Log for: Derek Role: Tuner and Time Keeper Activity Date Start Time End Time Time Spent Constructed sub 4/3 6:00 9:00 3 hours Finished sub construction and designed the crossovers for the system and tuned 4/4 7:00 9:15 3 hours Selected new tweeter and subwoofer driver 3/6 9:00 10:10 1 hour 4/4 9:20 10:45 1 hour 25 Typed up portion of the design documentation minutes Started work and started troubleshooting the tweeter swap 3/27 10:30 11:30 an hour 10

11 Activity Log for: Devin Role: Sub Designer and Shop Liason Activity Date Start Time End Time Time Spent Component Research and Order 3/22 10:30 am 12:00 pm 1.5 hrs Subwoofer Design and Shop Submission 3/23 1:00 pm 3:00 pm 2 hrs Part Home Depot 3/26 5:00 pm 5:30 pm 0.5 hrs Replacement Tweeter Installation 4/3 9:45 am 10:15 am 0.5 hrs Subwoofer Construction 4/3 6:00 pm 8:00 pm 2 hrs System Tuning 4/4 6:00 pm 10:30 pm 4.5 hrs 11

12 Activity Log for: Zack Bennett Role: Constructor and Scribe Activity Date Start Time End Time Time Spent Selected new tweeter 3/6 9:00am 10:10am 1h 10m Assisted in attempted new tweeter 3/27 10:30am 11:30am 1h installation Researched existing components intended 4/2 10:30am 11:00am 30m frequency responses. 4/3 6:00pm 9:00pm 3h Constructed subwoofer from components 4/4 7:00pm 9:00pm 2h System Tuning Summarized Findings 4/4 9:00pm 10:30pm

13 Appendix B: (DSP) System Tuning Parameters 13

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17 Appendix C: Frequency Response Measurement 17

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19 Appendix D: Subwoofer Design Documentation 19

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