2-way Monitor Design Statement

Transcription

1 2-way Monitor Design Statement FA 4740 By: Dj Puuri February 12, 2010 Spring

2 1. Function Goals a. Speaker application and specifics This speaker will be a 2- way system. As described in The Introduction to Loudspeaker design this will consist of a tweeter and one woofer. 1 This speaker is intended for use as a studio monitor. The objective in designing this speaker is to design and build a product that costs less and performs better then what could be purchased for this particular application. Some specific goals of this speaker are as follow. 1.Cost $600- $700 2.Small in overall size 3. Aesthetically pleasing finished product 4. Capable of 83 db SPL (with 20 dbspl headroom, 103 dbspl max ) 2 5. Large frequency range (20Hz- 20K) 6. Look comparable to something purchased for use as monitor Specific size of the enclosure will be decided upon once drivers are further evaluated. At this time the enclosure must be easily transported. 1 John L. Murphy, Introduction to Loudspeaker Design (Riverside: True Audio, 1998), pg. # Bob Katz, How To Make Better Recordings in the 21 st Century, software.com/k- System.html (accessed February 11,2010). 2

3 2.Technical Goals b. SPL Capabilities My intended mixing position is going to be within a meter of these speakers. With that in mind a db SPL rating of 83 at 1W/1M will require 64 watts of power to reach 103 db SPL. 3 4 I will be using a 130watt per channel stereo power amp to power these monitors so this should not be a problem. c. Driver Evaluation With a budget of $100 per driver my design was quickly modified after researching drivers. I intended to build a 2- way monitor system with a closed enclosure. I found very few drivers within my price range that had an EBP less then The formula for calculating this is as follows. EBP= fs/qes This information led me to change my enclosure from sealed to one requiring a port. Not only are drivers more affordable I can lower my (f3) and increase my frequency range. I have included a driver modeled for a sealed enclosure this was researched prior to changing my design. 3 John L. Murphy, Introduction to Loudspeaker Design, pg. #12. 4 DJ I. Puuri, SPL Testing, January 18, 2010, raw data, Home and Auto, Houghton 5 Vance Dickason, Loudspeaker Design Cookbook, 7 th ed. (New York: Audio Amateur Pubns, 2005), pg. # 34. 3

4 The Drivers I modeled are: 1. M6a Bass- Midrange by Swans 2. Hi- Vi F6 3. Peerless 8in 4. TangBand W Dayton Hi- Vi D6G The M6a was modeled in winspeakerz along with the rest of my drivers. (All models included in appendix A) This drivers EBP= 109 so it was modeled in a vented enclosure. As on can be seen in figure 1.1 there is a spike in the frequency response around 3K. Upon modeling and matching this driver with a tweeter the M6a was discarded. The reason being a 4 th order crossover would be needed in order to compensate for this spike. This would be too expensive for my budget. 6 Fig 1.1 M6a Frequency Response 6 Madisound Speaker Component Assisting speaker builders for more than 25 years., (accessed January 27,2010). 4

5 I then evaluated the Hi- Vi F6. This driver had an EBP=100 making it more suitable for a vented enclosure. Figure 1.2 shows a model done in winspeakerz for this particular driver. Fig 1.2 F6 model This driver was promising with an f3 of 45Hz and a box volume of.424 cu ft. it met most of my requirements. This woofer cost $46.30 each I could afford a bit more in my design so I continued my research. 7 In order to not change my design to vented I contemplated going with an 8in driver. This would be done in order to lower my f3, widening my frequency spectrum. I then modeled a peerless 8in woofer. This driver had an EBP= Madisound Speaker Component, (accessed January 27,2010). 8 Parts- Express.com- Speakers,SpeakerBuilding, Home Audio amd Video, Pro Audio, Electronic Parts & Accessories PARTS EXPRESS, Speakers, WOOFER, express.com (accessed February 05, 2010). 5

6 Figure 1.3 Peerless 8in This driver called for a much larger enclosure then I was willing to use in my design. I then modeled the TangBand 6.5in. This driver has incredible excursion, an Xmax of 8mm. 9 I first found this driver while researching a fellow speaker builder s design. 10 The TangBand 6.5in was used in a 3- way MTM speaker design done by Zach Carlson. Upon examining specs for this driver I found it had an fs=40hz. This is lower then what I desired for my design. It had an EBP=82 making it more suited for a vented enclosure. I decided to model this driver in winspeakerz. 9 Parts- Express.com- Speakers,SpeakerBuilding, (accessed February 05, 2010). 10 Zach, Carlson, Zac MTM Speakers VPA Wiki, (accessed February 2010). 6

7 Fig 1.4 TangBand 6.5in Model As can be seen in figure 1.4 the box volume this driver is modeled in is 1.26 cuft. A golden ratio box design for this would give me an enclosure with dimension heigh, 8.49 wide, and deep. 11 This would still be a portable enclosure. Making this driver acceptable for my design. These dimension are figured larger then need and will be adjusted slightly once drafting is started for this project. After considering the low f3 (35 Hz) this driver offers, the price, the max SPL (88dB SPL) enclosure size, and its successful use in other projects I decided to use this driver in my design. 11 John L. Murphy, Introduction to Loudspeaker Design, pgs

8 The Dayton classic 6.5 modeled lacked linear excursion it had an Xmax of 3.15in. I was also concerned with its frequency response this can be seen in figure It is not very smooth and spikes at about 1.8K this is around where I would place my cross over. Fig.1.5 Dayton Classic 6.5 Frequency response This woofer while very affordable at $23.77/unit has a sensitivity of 87 db SPL this is less then the TangBand. It was then discarded Parts- Express.com- Speakers,SpeakerBuilding, (accessed February 05, 2010). 13 Parts- Express.com- Speakers,SpeakerBuilding, (accessed February 05, 2010). 8

9 The Hi- Vi D6G was the last driver I modeled. It s specs where along the line of what I was looking to use in my design.(see appendix b spec sheets) It even modeled well in a vented enclosure with a considerably smaller Vb.4 cubic ft. This can be seen in figure 1.6 below. I decided on the TangBand 6.5 over this woofer because I felt I was purchasing a better quality product. I didn t mind spending the extra money for a lower f3 despite having a larger enclosure. Fig.1.6 Model for Hi-Vi D6G Woofer d. Tweet Choices Now that I had decided on the TangBand 6.5 as my woofer for my monitor it was time to turn my attention to tweeters. 9

10 Tweeters Researched Where 1. Scan Speak Discovery 1 2. Seas 27TDFC 3. Morel CAT Jantzen JA Seas 29TFF 6. Eton 25 SD1 These tweeters were all chosen with there sensitivity in mind I wanted something around 90 db SPL and was willing to pay up to $100 dollars each. These tweeters all have sensitivities around 90 db Spl from 1k to 20k. (see appendix c Tweeter specs). All of these tweeters were also capable of handling the power I needed. After careful examination I decided on the Eton SD 1. Its frequency plot carried a bit lower down in frequency to around 750Hz before it dropped below 90 db SPL. (Fig 1.6) It also has a power rating of 100 W. 14 Fig 1.6 Eton SD 1 14 Madisound Speaker Component, (accessed January 27,2010). 10

11 The Eton SD 1 will be paired the 6.5 in TangBand W woofer in my 2- way monitor design. The low distortion shown in fig 1.6 for this tweeter is a bonus I am intending this tweeter to add to the clarity of this speaker. It also prices out on at $76.60 each. This is slightly under my budget of $100 per tweeter. 11

12 e. Crossover After deciding upon the Tangband W and the Eton SD 1 for my 2- way monitor, it was time to decide the cross over point. This was done by carefully plotting the frequency curves for both woofer and tweeter. (fig. 1.7) 15 Fig 1.7 Crossover Plot W and SD 1 This plot was done with a 2 nd order 12 db/ octave crossover on both the woofer and tweeter. A cross over point of 1500 Hz was chosen. The woofer shows a frequency spike at around 4K. The 2 nd order crossover modeled does not lower this enough. It is my intention to use a 3 rd order Butterwoth crossover on both the woofer and tweeter. 15 DJ I. Puuri, Crossover Plot, chart, in Crossover Plot (Houghton, 2010), pg.#2. 12

13 f. Crossover Parts and Schematic Once a cross over frequency and the impedances of both the woofer and tweeter are known parts and schematics for your design can be easily modeled in winspeakerz. (Fig 1.8 and 1.9) Fig 1.8 Crossover Parts Fig. 1.9 Crossover Schematic 13

14 g. Tweeter Attenuation I anticipate having to attenuate my tweeter in these monitors. This is a common occurrence in speaker building and should be anticipated Figures 1.10 and 1.11 show both the parts and schematic for the tweeter attenuation circuit for this 2- way monitor design. Fig 1.10 Tweeter Attenuation Parts Fig 1.11 Tweeter Attenuation Circuit Schematic 16 Christopher Plummer, Discussion With Professor, interview by author, February 10, PHILIP NEWELL and Keith Holland, Loudspeakers for music recording and reproduction,chapter5. 14

15 h. Baffle Step Correction Circuit Baffle step is the frequency at which the sound field transitions from radiating into full space to radiating into half space. 18 A baffle step circuit should be designed and installed before the woofer in order to counter the affects of baffle step. This can easily thru entering your woofer impedance and baffle width along with the sensitivity rating into any calculator found on- line. There are also schematics for the circuit readily available on- line. Figures 1.12 and 1.13 show calculations for my particular design along with a schematic of the circuit. 19 (it should be noted my baffle size is an estimate at this time) Fig 1.12 Baffle Step Calculations For 2-Way Monitor Design 18 King, Martin J. Simple Sizing of the Components in a Baffle Step Correction Circuit. Technical Paper. Martin J. King, wave.com/general/bsc_sizing.pdf (accessed February 11,2010). 19 Baffle Step Correction/Componsation (BSC) Circuit Calculator for Speakers. DIY AUDIO PROJECTS- DO- It- Yourself- Hi- Fi for Audiophiles. Step- Correction- Circuit- Calculator/(accessed February 12, 2010). 15

16 Fig 1.13 Baffle step Correction Cicuit i.enclosure Design When designing an enclosure for speakers there are a number of considerations. An example of this would be in my particular 2- way monitor design clarity is a major concern. A few things I intend to do to my enclosure are rounding the edges and flush mounting all drivers. This will help me with diffraction effects and other early reflections This enclosure will also be dual layers of MDF and Birch Plywood. Doing this along with damping the inside of the enclosure with fiberglass insulation will help combat unwanted resonance. Internal bracing will also be added to add strength to the sidewalls and keep resonances to a minimum. 22 Calking all joints and multiple layers quality paint will make the vents the only point air will travel in and out of this enclosure. This is important in making sure your enclosure does not have unwanted buzzes. 23 Previous experience in constructing woofer enclosures for car audio systems has led me to desire a matte black finish for this enclosure. This will be 20 PHILIP NEWELL and Keith Holland, Loudspeakers for music recording and reproduction,pgs Index. (accessed February 12, 2010). 22 John L. Murphy, Introduction to Loudspeaker Design, chapter4. 23 John L. Murphy, Introduction to Loudspeaker Design, pg

17 accomplished by using matte black auto paint purchased from Napa auto parts store. This should ensure a quality finish and mesh nicely with my personal taste. Exact size and prints for these enclosures will be available once drafting begins at this time they are to be rectangular in shape dimensions can be estimated from the box volume modeled in winspeakerz. This will however be modified and exacted once drafting is complete. f. Final Thoughts Zaph audio rates the TangBand W as overall nice and certainly unique. 24 I am pleased with my choices for my 2- way monitor design The TangBand W and the Eton SD1 will give me a good overall db SPL. My choice of crossover point and crossover will ensure my desired frequency response. All products are with in my budget. Woofers $200 Tweeters $175 Crossover $200 Materials/Finish $125 Total $700 It should be noted that at this time I have allocated $100 extra in my budget. This is done to ensure quality crossover parts can be used in my monitors. 24 Zaph Audio, (accessed February 11, 2010). 17

18 Appendix A M6a model in winspeakerz 18

19 Hi-Vi F6 modeled in winspeakerz Peerless 8in modeled in winspeakerz 19

20 TangBand W Modeled in Winspeakerz Dayton Classic 6in modeled in winspeakerz 20

21 Hi-Vi D6G modeled in winspeakerz 21

22 Appendix B Driver Spec Sheets From Madisound.com and Parts-Express.com 22

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28 Appendix C Tweeter Spec Sheets Taken From Madisound.com 28

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33 Appendix D Crossover Plot and Data Prepared By: DJ Puuri HZ dbspl Woofer dbspl Tweeter Summatio n Tweeter Xover Woofer Xover

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36 Bibliography "Baffle Step Correction / Compensation (BSC) Circuit Calculator for Speakers." DIY AUDIO PROJECTS - Do-It-Yourself Hi-Fi for Audiophiles. echnical/baffle-step-correction-circuit- Calculator/ (accessed February 12, 2010). Carlson, Zach. "ZAC MTM Speakers - VPA Wiki." (accessed February 05, 2010). Dickason, Vance. Loudspeaker Design Cookbook. 7th ed. New York: Audio Amateur Pubns, Dynaudio Acoustics Home. (accessed January 12, 2010). Index. (accessed February 12, 2010). Katz, Bob. "How To Make Better Recordings in the 21st Century." Unbenanntes Dokument. (accessed February 11, 2010). King, Martin J. SImple Sizing of the Components in a Baffle Step Correction Citcuit. Technical paper. Martin J. King, (accessed February 11, 2010). Madisound Speaker Components Assisting speaker builders for more than 25 years. (accessed January 27, 2010). McCarthy, Bob. Sound Systems: Design and Optimization Modern Techniques and Tools for Sound System Design and Alignment. New York: Focal Press, Meyer Sound Laboratories Inc (accessed February 11, 2010). Murphy, John L. Introduction to Loudspeaker Design. Riverside: True Audio, NEWELL, PHILIP, and Keith Holland. Loudspeakers For music recording and reproduction. New York: Focal Press,

37 Parts-Express.com - Speakers, Speaker Building, Home Audio and Video, Pro Audio, Electronic Parts & Accessories PARTS EXPRESS, Speakers, Speaker Parts, Guitar speakers, Bass speakers, Woofers, Drivers, speaker upgrades and replacement speakers. Eminence Speaker, JBL speakers, B&C, EV, Peavey, Pyle, Tang Band, Hi Vi, Peavey, Usher, Dayton Audio, Selenium, Goldwood, Morel, Vifa, Peerless, JBL speakers, Eminence woofers, WOOFER. (accessed February 05, 2010). Plummer, Christopher. "Discusion With Professor." Interview by author. February 10, Puuri, DJ I. "Crossover Plot." Chart. In Crossover Plot. Houghton, Puuri, DJ I. SPL Testing. January 18, Raw data. Home and Auto,Houghton. Zaph Audio. (accessed February 11, 2010). 37