Timber Nooks. Transducer Theory Loudspeaker Design

Transcription

1 Timber Nooks Transducer Theory Loudspeaker Design Matthew Nanney FA 4740: Transducer Theory March 8th, 2014

2 Table of Contents FUNCTIONAL DESCRIPTION... 4 GOALS... 4 ENVIRONMENT... 4 LISTENING PURPOSE... 4 VISUAL AESTHETICS... 4 SPL OUTPUT... 5 SUBJECTIVE DESCRIPTION OF SOUND QUALITY... 5 PRIORITIZATION... 5 TECHNICAL GOALS... 6 SIZE... 6 SPL... 6 FREQUENCY RESPONSE... 8 COLORATION, TIME RESPONSE... 9 DIFFRACTION AND SPEAKER SHAPE CROSSOVER DRIVER SELECTION WOOFER SELECTION Dayton Audio RS Reference Paper Woofer SB Acoustics SB17NRX Woofer ScanSpeak Classic P17WJ Woofer SB Acoustics SB17MCF Woofer SB Acoustics Satori MW16P Woofer TWEETER SELECTION Tang Band S 1 Tweeter Morel CAT /8 Tweeter Dayton Audio RS28F /8 Tweeter SB Acoustics SB26STAC 1 Tweeter SEAS 29TFF/W 1 1/8 Tweeter TESTING AND TUNING WOOFER PERFORMANCE TWEETER PERFORMANCE CROSSOVER PERFORMANCE OVERALL PERFORMANCE FINAL TESTING RESULTS OVERALL LOUDSPEAKER PERFORMANCE LEFT SPEAKER Frequency Response Integrated Frequency Response Harmonic Distortion Minimum Phase Horizontal Off- Axis Response Vertical Off- Axis Response Difference Plot Step Response Integrated Step Response Impulse Response Waterfall Plot

3 OVERALL LOUDSPEAKER PERFORMANCE RIGHT SPEAKER Frequency Response Integrated Frequency Response Harmonic Distortion Minimum Phase Horizontal Off- Axis Response Vertical Off- Axis Response Difference Plot Step Response Integrated Step Response Impulse Response Waterfall Plot WOOFER RESPONSE LEFT SPEAKER Frequency Response Minimum Phase Horizontal Off- Axis Response Vertical Off- Axis Response Step Response TWEETER RESPONSE LEFT SPEAKER Frequency Response Minimum Phase Horizontal Off- Axis Response Vertical Off- Axis Response Step Response WOOFER RESPONSE RIGHT SPEAKER Frequency Response Minimum Phase Horizontal Off- Axis Response Vertical Off- Axis Response Step Response TWEETER RESPONSE RIGHT SPEAKER Frequency Response Minimum Phase Horizontal Off- Axis Response Vertical Off- Axis Response Step Response BIBLIOGRAPHY

4 Functional Description Goals My speaker system will be used to mix in a normal living room type setting. The speakers will be used to mix sound effects and musical compositions for video games and film. The space that they will be used in limits the size of the speakers to that of bookshelf speakers, which coincides with the need for portability. Therefore, size takes priority with my design and will show impact on my decisions for SPL output and fidelity. I intend to use these speakers to listen backwards, or listening with the purpose of hearing the signal accurately reproduced in the system in order for the signal to be mixed based upon the actual recording, so they must be able to accurately reproduce recorded signals. 1 Environment The space that my speakers will be used in is a traditional living room setting inside of an apartment. The noise in my apartment that must be taken into account is that of the heating unit and the faint sound of cars passing by occasionally. Due to the size of the room, and also dependent upon my own budget for this system, I will design stereo speakers for my purposes with the goal of implementing them into a surround system upon expanding to a more appropriate space. Portability is a major concern of mine because I will be moving to Texas this summer by car, so keeping my speakers manageable in size and weight is vital to the overall design of the system. I plan to use the speakers in a variety of similar rooms, though the desk and spacing will be the same, and so acoustical treatment in said rooms will undoubtedly vary. Therefore, good off-axis response is important to my design in order to preserve clarity and proper imaging while listening to my speakers. Listening Purpose The intended purpose of the speakers is for mixing for video games and film, therefore the goal of them is to produce high fidelity sound while maintaining SPL outputs relative to what the listeners of my mix will be listening at when playing video games or watching a film. Accurate reproduction of my sounds through these speakers is important for mixing effectively, so these speakers will be used primarily for listening backward as explained in my design goals. When listening forward, or utilizing speakers to hear what the end-user will listen to, I have a good set of monitors to cover the Range Rule, or the range of systems that people will listen to my mixes on while playing video games or watching films. Visual Aesthetics Visually, my goal is to create a design that looks professional with decals to add flair. Most importantly, visual aesthetics are secondary so that more of my time can be spent on optimizing and tuning my speakers for their intended purpose. The size and weight of my speakers will need to be appropriate for portability while still being designed for the best sound quality possible within the size requirements. 1 David Moulton, Total Recording: The Complete Guide to Audio Production and Engineering (Sherman Oaks, CA: KIQ Productions, Inc. 2000),

5 SPL Output The SPL output for my speakers is going to be standard for film mixing established in the THX standard system. I will be listening to my speakers at a short distance away, so there will be minimal reduction in SPL levels from my speakers to me. Thus, I don t have to adjust my SPL output much for my preferred listening distance. Subjective Description of Sound Quality I desire for my speakers to have an uncolored response that provides an accurate reproduction of the source material. My speakers should have low listening fatigue so that I can mix for extended periods of time to be able to try out many options while sound designing within a session. Also, the speakers should have good low frequency response, which will be aided with the addition of a subwoofer into the system later on. A good off-axis response and clarity from my speakers is also important to the sound quality of the system. 2 Prioritization The size of my speakers must take full priority based upon the needs of portability in the immediate future. However, there is an important secondary emphasis upon the SPL output of my speakers to be able to meet standard reference level of mixing films with appropriate headroom. With the other two factors controlling a lot of my design, low frequency response is not my top priority, though I will try to aid my low frequency response wherever I can. Design Goal Balance 20% 50% Size SPL Figure 1. The requirements of size take top priority in my design, as seen through this pie chart of the balance of my design goals. 30% Low Frequency 2 AES Standards and Practices (New York: Audio Engineering Society, Inc. 1996). 5

6 Technical Goals Size For the purpose of both portability and to be used as desktop monitors, my loudspeakers need to be kept down in weight and size. Based upon my own measurements, they can be a maximum of 18 x 12 x 18 (Width x Depth x Height) to fit both of them upon my desk. Ideally, though, they would be around 15 x 10 x 12 in order for them to not completely take up my desk. 3 Also, this smaller size would be more capable of fitting onto smaller desks if I ever need to use my speakers with one. I know that I am comfortable lifting 50lbs. at a time, so my speakers could each weigh up to fifty pounds, but ideally if they weighed around 25lbs. each speaker would fit my goals of portability better. 4 With the size mentioned earlier, both speakers could fit into the backseat of my car so I know I could travel easily with them. Thus, my goals of portability are met with a size and weight that I am capable of dealing with when travelling. SPL Considering that I plan on using my loudspeakers for mixing film and video game sounds, they will need to meet the THX standard of a reference level of 85 db SPL with 20dB of headroom for 105 db maximum SPL in the main channels and a boost in the low frequency effects channel of 10dB for 115dB maximum SPL in that channel. 5 My goal is to achieve the 105 db max SPL output with my speakers and to address the low frequency effect channel upon expanding to a 5.1 or 7.1 system. Also, the range of 75dB to 85dB is the average listening level for people at home, where video games are mostly played, so mixing at that level would be appropriate to achieve a mix that will translate well into the end-users systems. 6 Concerning hearing safety, my loudspeakers will be at a reference level of 85dB, which meets the NIOSHA standard of 85dBa SPL per 8 hours of listening time, and I will ensure that I will not be listening to my loudspeakers at 85dB SPL for such extended periods of time for my own hearing safety. 7 These NIOSHA standards, also, allow for 3dB of variation for each halving of the total eight hours, resulting in my speakers being appropriate for the listening periods of four hours, which is 88dBa SPL, and any time shorter than that as well. After experimenting with my own listening preferences, I have discovered that I generally listen in a range of 78-85dB SPL when listening to films and video games, so having my loudspeakers at a reference level of 85dB SPL allows for me to mix at my preferred listening level and at the THX standard with ample amount of headroom. 8 The results of my listening 3 Matthew Nanney, 24 January 2014, Transducer Theory Speaker Size vs. Needed Space Measurement, Michigan Technological University. 4 Matthew Nanney, 25 January 2014, Transducer Theory Weight Measurement, Michigan Technological University 5 Tomlinson Houlman, Sound for Film and Television (Oxford: Focal Press, 2010), Richard Newell and Keith Holland, Loudspeakers: For Music Recording and Reproduction (Oxford: Focal Press, 2007), Kindle Edition. 7 Occupational Noise Exposure (Cincinnati, Ohio: National Institute for Occupational Safety and Health, 1998). 8 Matthew Nanney, 22 January 2014, Transducer Theory SPL Preference Measurement, Michigan Technological University 6

7 experiment can be seen in Figure 2, demonstrating that my desired SPL output from my loudspeakers meets and often exceeds my average listening level, so my loudspeakers will not have trouble producing needed SPL levels based upon my preferences. SPL Output (db) Pop/Rock Folk Electronic Film/Video Games Genre Figure 2. My preferred listening levels To achieve my desired SPL output, the overall sensitivity of my loudspeakers needs to be 85dB/Watt. With a 100W amplifier, my loudspeakers would be capable of producing 105dB max SPL; Figure 3 further represents the range of amplifier powers that I would be willing to use with my loudspeakers. This allows my loudspeakers to meet the THX standard and to be able of producing my preferred listening levels with plenty of headroom. 20 dbw db 0 Watts Figure 3. This graph represents Watts needed to produce a range of decibels. Important here is the range of 100W to 200W, showing that it isn t beneficial budget- wise to increase my amplifier to 200W for only a 3dB increase. 7

8 Concerning listening distance, Figure 4 shows the inverse square law in relation to loss of 6dB/m. 9 Based upon this law, my preferred distance of 55 (1.397 meters) from my speakers will result in an approximate 3dB loss in overall SPL. 10 I can will listen to my speakers likely within the range of one to two meters, resulting in a max loss of 6dB of SPL, which I conclude will be acceptable for mixing and my overall system SPL output based on my loudspeakers sensitivity coupled with my desired amplifier. 6 Inverse Square Law db Lost Distance (m) Figure 4. This graph represents the inverse square law in relation to decibels lost to meters. Shown here is that for every doubling of distance after 1 meter, there is a 6db loss of total SPL. Here is a range from 1m to 2m showing the range of my listening distances. Frequency Response Based upon my experimentation with low frequency preferences, I have been able to conclude that I desire my loudspeakers to be able to produce a F 3 of 60Hz. 11 However, with consideration of my budget, I would also accept my speakers being able to only solidly produce down to 80Hz. Further analysis of my low frequency experiment can be seen in Figure 5. After analyzing instrument frequency charts, I have determined that I would be able to mix most of my 9 Christopher Plummer, January , Transducer Theory Class Lecture, Michigan Technological University. 10 Matthew Nanney, 17 January 2014, Transducer Theory Listening Space Measurement, Michigan Technological University. 11 Matthew Nanney, 22 January 2014, Transducer Theory Low Frequency Preference Experiment, Michigan Technological University. 8

9 desired instruments with a frequency range of 60Hz to 20kHz, only losing some notes of lower instruments like the tuba, bassoon, bass, and harp. 12 A flat response over this range would be desirable based upon my purpose of mixing on my loudspeakers. Track (Genre) Main Theme - Inception (Film Score) BF4 Gameplay Preview (Video Game SFX & Score) Helm s Deep LOTR (Film Score) Fall Creek Boys Choir James Blake (Electronic) Lemon World The National (Alternative/Folk) Love Like a Sunset Part 1 Phoenix (Alternative/ Pop) Wake Up Arcade Fire (Alternative Rock) Canada Heidi Happy (Singer- Songwriter) Frequency No perceived difference (Hz) Frequency I could live with (Hz) Frequency I couldn t go any further (Hz) <45 60 >70 <50 65 >70 <40 55 >70 <50 70 >75 <50 65 >75 <55 70 >80 <50 65 >75 <60 70 >80 Figure 5. This table shows my low frequency preference according to specific genres and tracks. Overall, I concluded that a strong response down to 60Hz would be preferred, with an 80Hz lower limit as an acceptable alternative. Coloration, Time Response Based upon my size preferences and my bandwidth goals, I am going to use a vented box design for my loudspeakers. The vented box allows me to tune my box to extend my low frequency response below that of where the driver response begins to roll off. 13 The vented box will have an impact on my transient response, but that is a sacrifice I have decided to make in order to have extended low frequency response. My speakers will be sitting atop of my desk, hopefully resulting in added low frequency response from the flat surface below the loudspeaker acting like a wall behind it, similar to the effect the Yamaha NS-10s had when mounted on a 12 Frequency Chart, Independent Recording January Richard Newell and Keith Holland, Loudspeakers: For Music Recording and Reproduction (Oxford: Focal Press, 2007), Kindle Location

10 mixing console s meter bridge. 14 I will possibly be using foam pads underneath my speakers to tilt them upwards at an angle in order to control reflections from the desk to prevent any unwanted coloration that would poorly influence my mixing Diffraction and Speaker Shape The shape of my speakers will be rectangular, based on the experiment performed by Harry Olson Direct Radiator Loudspeaker Enclosures, which analyzed a set of shapes for loudspeaker design and their various on-axis frequency response variations showing that a rectangular enclosure produced a variation of ±3dB. 15 Thus, I will be using a rectangular shape for purposes of frequency response variation and ease of building technicality. The size of my speakers will need to be small enough to fit upon my desk, but still large enough to not diminish the quality of sound too much. The weight coincides with the size in which they need to be portable so that I can move them and fit them within my car when I travel. Therefore, I intend to have a mountable wood grill to attach over the front of my speakers to protect the drivers from damage during transport. I plan to use a mixture of material types for my speakers, specifically plywood and medium-density fiberboard (MDF) with consideration given to hardwood for aesthetic purposes. I will use internal dampening to help nullify some of the mid-range reflections that might otherwise bounce out through the cone of my driver and color my sound, thus counteracting my desired flat frequency response. 16 The edges of my speakers on the front panel will be rounded off to decrease reflections off the corners of the enclosure and decrease diffraction. Crossover For my crossover in my speakers I will be using an active 4th order crossover I will be using the MiniDSP PWR- ICE125 plate amplifiers with Ethernet control of the onboard DSP to control settings of my drivers and crossover. I will use symmetric crossovers, with my tweeter and woofer crossovers at 2kHz where there will be summation of 3dB to achieve a flat frequency response and avoid a dip at my crossover point. 17. I have chosen 4th order, because I have significant breakup in my woofer around 5kHz and I want to ensure my tweeter won t need to perform at much lower frequencies below my crossover point. To combat baffle step, I will be using the DSP settings to implement a high shelf filter to lower the increase in sensitivity in order to account for the shift from full space to half space due to the frequencies wavelengths becoming shorter than the baffle. For my crossover, I will set the MiniDSP to have a crossover at 2kHz with a filter type of - 24dB/octave (fourth order) for both speakers. For my tweeters I will have a high shelf starting at 10kHz set at approximately - 2dB to account for the increase in frequency output in my tweeters higher than 10kHz. Also, my whole tweeter output will be decreased 4dB to match with my woofer s sensitivity. I will use notch filters to fix certain bumps or 14 Ibid., Kindle Location Vance Dickason, Loudspeaker Design Cookbook (Peterborough, NH: Audio Amateur Press, 2006), Richard Newell and Keith Holland, Loudspeakers: For Music Recording and Reproduction (Oxford: Focal Press, 2007), Kindle Location Matthew Nanney, 12 February 2014, Transducer Theory Crossover Lab, Michigan Technological University. 10

11 dips at specific frequencies discovered while testing, but I haven t identified any needed notch filters from just my drivers frequency response plots. I have selected the SB Acoustics SB17MCF woofer and the SB Acoustics SB26STAC tweeter as my drivers. In Figure 6, the woofer and tweeter crossovers are modeled, demonstrating how a 4 th order crossover results in a relatively flat frequency response at the symmetric crossover frequency of 2kHz and the surrounding frequencies. It can been seen from this figure that the tweeter does not have to output high levels much lower than the crossover frequency because of the high order of the crossover. Also, the woofer s breakup isn t really noticeable in the graph, because the 4 th order crossover decays at - 24dB/octave and helps control the spike in sensitivity levels. Further smoothing around the crossover frequency will be handled during testing with the MiniDSP s filter settings to achieve a desired flat frequency response th Order Crossover Sensitivity (db) Woofer Xover Tweeter Xover Summation Frequency (Hz) Figure 6. This graph shows the woofer and tweeter with a 4 th order crossover at 2kHz. Two octaves before and after 2kHz have been included to show the true effect of the crossover s order on the woofer and tweeter s sensitivities. The summation is the resulting frequency response from the crossover. 11

12 Driver Selection Woofer Selection For my woofers, I am looking for a 6, 7, or 8 woofer that will have a flat frequency response from 60Hz to 2kHz. The desirable F3 for my woofer would be at 60Hz, within a critically damped vented box system, producing as many low frequencies as possible through the driver while maintaining a flat response. I want to crossover my system around 2-3kHz, so having a driver that doesn t have significant breakup until 4kHz for a 2kHz crossover or 6kHz for a 3kHz crossover is very important. I am looking to spend a combined cost of $125 on both woofers, but would be willing to expand my budget to $200 for both woofers. All of the woofers I have selected have sensitivity above 85dB, so they will all be able to give me my desired 85dB SPL level with 20dB of headroom from the addition of a 100W amplifier. For all of the modeling included with each woofer the box size was set to a standard of 0.7 cubic feet with box frequency adjusted to produce the lowest critically damped F3. Figure 7 lists my selections for woofers with important specifications that I considered when comparing them. Dayton Audio RS180-8 SB Acoustics SB17NRX36-8 ScanSpeak P17WJ00 SB Acoustics SB17MCF35-8* Satori MWP16-8 Diameter F3 (Critically 55Hz 45Hz 47Hz 43Hz 40Hz Damped) Sensitivity 89dB 89dB 88dB 88dB 87.5dB Power 60 Watts 60 Watts 150 Watts 60 Watts 60 Watts Handling Price $51.75 $62.40 $76.90 $65.05 $ Figure 7. This table shows the comparison between my selected woofers focusing on the specifications of diameter, F3, sensitivity, power handling, and price. *The woofer in bold is my choice for my loudspeakers. Dayton Audio RS Reference Paper Woofer 18 $51.75 The Dayton Audio 7 Reference Paper Woofer has a relatively flat frequency response up to about 3kHz, allowing me to utilize this woofer with a crossover at 2kHz or 2.5kHz depending on the order of the crossover. Based upon my experiments, I have concluded that within my vented box design I would be able to extend the low frequency response of this driver down to an F3 critically damped response of approximately 55Hz. With this woofer, I would actually be able to extend my expected system frequency response from a low end of 60Hz to roughly 55Hz. At such an affordable price, this woofer offers me ample low end and a flat frequency response to make it one of my top choices express.com/pedocs/specs/ dayton- audio- rs specifications pdf - Accessed 7 March

13 SB Acoustics SB17NRX Woofer 19 $62.40 The SB Acoustics 6.5 Woofer is in my ideal price range with acceptable low frequency response and a fairly flat response up to 3kHz. This woofer offers a very desirable F3 critically damped response down to 45Hz with the only real concern of this driver coming from a peak at around 3.5kHz. In order to compensate for this peak, I need to either have a lower crossover point of have a higher order crossover to ensure that the peak doesn t affect my overall frequency response sb17nrxc35-8/ - Accessed 7 March

14 ScanSpeak Classic P17WJ Woofer 20 $76.90 Vifa originally made this model of woofer, but manufacturing responsibilities have since been transferred to ScanSpeak. This model of woofer has been in a production for a long time, which I find desirable because that means that if I need to replace any of my woofers later on I will likely be able to use the same model. Also, it has a lot of desirable 20 woofers- 6-7/scanspeak- classic- p17wj woofer/ - Accessed 7 March

15 qualities at a relatively affordable price. Looking at the woofer s specifications, this driver has a flat frequency response from 200 Hz to 1 khz with what appears to be +/- 1dB of variation. There is a bump at 2kHz, but it is only a 2 or 3 db increase, which can be managed well with my active system. One of the desirable qualities of this woofer is there isn t any significant breakup that needs to be accounted for, so I can have a lower order crossover or cross it over higher in frequency if needed. With an F3 of approximately 47Hz, this woofer certainly exceeds my desires for low frequency response. Due to the affordability, flat frequency response to above 1kHz, low amount of breakup, and met requirements for F3 and sensitivity this driver is my first selection to use in my speakers. 15

16 SB Acoustics SB17MCF Woofer 21 $65.05 This SB Acoustics woofer is very similar to the slightly larger version listed earlier in my woofer selections. In comparison, though, this woofer has slightly less drastic breakup than its counterpart and therefore would be simpler to crossover in my design. With the same box design, I found this woofer to actually produce a slightly lower F3 around 43Hz. It has a pretty good off- axis response, with a soft roll off at both 30 and 60 degrees. This driver is very affordable, and the appropriate size for my desired boxes. The downsides of this driver would be that it doesn t have a flat response as high in frequency as some of the other woofers. However, its flat response from 200Hz to 3kHz is a lot smoother than the other SB Acoustics driver and thus this might be the optimal woofer for a higher crossover Accessed 7 March

17 SB Acoustics Satori MW16P Woofer 22 $ The SB Acoustics Satori MW16P is a high- end woofer that offers a lot of positives but really stretches my budget. This woofer has an impressive low frequency response with an F3 of 40Hz. The frequency response of this driver isn t the flattest with approximately +/- 3dB of variation, but it has really good off- axis response to 3kHz. Also, the breakup isn t particularly bad at any one point with a spread out breakup, allowing for flexibility with my crossover with only having to manage at most a +6dB peak past 3kHz satori- mw16p- 8/ - Accessed 7 March

18 Tweeter Selection For my tweeter selection I am considering tweeters that have a flat frequency response from 2kHz to 20kHz. However, I am willing to work with a tweeter that only goes to around 17kHz if it has an extremely flat frequency response or is a better price to fit my overall budget. My main concern with my tweeter is having a flat response down to 2kHz, because most of the woofers I have considered can only produce good responses up to 2kHz. Therefore, my tweeter optimally will have a flat frequency response to even below 2kHz, although if I have the proper woofer than having a crossover at 3kHz could be considered with the right tweeter. I am mostly considering silk and fabric tweeters to avoid any unwanted ringing or breakup past 20kHz. Figure 8 shows important specifications I have considered while analyzing tweeters. Tang Band S Morel Cat 308 Dayton Audio RS28F- 4 SB Acoustics SB26STAC* SEAS 29TFF/W Diameter 1 1 1/8 1 1/ /8 Free Air 450Hz 650Hz 530Hz 750Hz 950Hz Resonance Sensitivity 91dB 90dB 88dB 91.5 db 92dB Power 80 Watts 200 Watts 100 Watts 120 Watts 90 Watts Handling Price $75.15 $76.40 $54.75 $43.85 $53.60 Figure 8. This table shows the comparison between my tweeters on the specifications of diameter, free air resonance, sensitivity, power handling, and price. *The tweeter in bold is my first selection for use in my speakers. 18

19 Tang Band S 1 Tweeter 23 $75.15 The Tang Band 25mm Tweeter is at a fairly high price but has a relatively flat frequency response from 2kHz to 20kHz. With a flat response down to 2kHz, this tweeter will allow me to crossover my 2- way system at 2kHz while still maintaining an overall flat frequency response with any of my preferred woofers. With a sensitivity of 91dB, this tweeter is more than capable of meeting my specifications of 85dB SPL output express.com/pedocs/specs/ tang- band s- specifications pdf - Accessed 7 March

20 Morel CAT /8 Tweeter 24 $76.40 The Morel 28mm Tweeter has a fairly flat frequency response from 2kHz to about 17kHz. Also, it meets my sensitivity needs with a sensitivity of 90dB. With a higher price than some of my other tweeter options, the fact that this tweeter doesn t have a relatively flat response all the way to 20kHz is a major downfall. However, the response of this tweeter is really flat with little variation at high sensitivity. Therefore, I think that this tweeter would work very well in a system crossed over at 2kHz, because it remains flat in response until 2 khz, with only at most 5dB of variation express.com/pedocs/specs/ morel- cat specifications.pdf - Accessed 7 March

21 Dayton Audio RS28F /8 Tweeter 25 $54.75 The Dayton Audio 1 1/8 Tweeter has a flat response from around 900Hz to 10kHz, with an increase in sensitivity from 10-20kHz. The increase in sensitivity isn t drastic, though, raising approximately 3dB. With a Fs of 530Hz, I would be able to have a crossover a little above 1kHz without distorting the tweeter. A crossover that low is helpful because it ensures that I can use a variety of woofers with this tweeter. This tweeter has a lower sensitivity than my other options, but at 88dB it still meets my design goals. Also, this tweeter is very affordable, which helps me keep under budget if I decide to go with a more expensive woofer express.com/pedocs/specs/ dayton- audio- rs28f- 4- specifications pdf - Accessed 7 March

22 SB Acoustics SB26STAC 1 Tweeter 26 $43.85 The SB Acoustics 1 Tweeter offers a flat frequency response from 900Hz to 20kHz, one of the more impressive frequency responses out of the tweeters I selected. Another benefit of this driver is its off- axis response, which remains accurate until 7-8kHz with a smooth roll off until after 10kHz. At 91dB this tweeter certainly meets my needs for sensitivity. Also, this tweeter has a Fs of 750Hz, which would allow me to reasonably be able to have a crossover around 1500 Hz. With my goal to crossover close to 2kHz, this tweeter meets my needs and has a flat response below that frequency to allow for convenient roll off. Also, this is the lowest price of all my tweeters, making it an even better choice. Thus, I have chosen this tweeter to use in my loudspeakers, because it has a very flat response with little variation from at least 1kHz to 20kHz, it meets my sensitivity goals, it can be effectively crossed over at 2kHz, and it has good off- axis response c000-4/ - Accessed 7 March

23 SEAS 29TFF/W 1 1/8 Tweeter 27 $53.60 The SEAS 29TFF/W is a tweeter with relatively flat frequency response from 1kHz to above 20kHz. It is priced at an affordable $53.60 and fulfills my driver sensitivity goals with a sensitivity of 92dB. However, it has a higher Fs (950Hz) than the other tweeters selected, so I would have to be careful about crossing it over at 2kHz. Its off- axis response isn t terrible, but some of the other tweeters out perform it in that category Accessed 7 March

24 Testing and Tuning Woofer Performance Upon initial testing, my woofer demonstrated a relatively flat response close to what the driver specification sheets suggested it would have. The biggest concerns that I had to compensate for were a boost around 1500Hz and a lower boost around 100Hz. Having an active system with the Mini- DSPs I was able to adjust for these minor flaws through equalization, basically putting notch filters at these points and adjusting the Q and magnitude until it was just right. This resulted in a much flatter woofer response after my modifications. 24

25 Tweeter Performance After initialing testing my tweeter, I found it to have a much bigger ascending boost after 4kHz. The specification sheet had shown a mild bump, but I hadn t expected it to be so severe. Also, my tweeter was a lot louder than my woofer, so I certainly had to add a pad to my tweeter to get it to work in my system. To account for the boost after 4kHz, I added a high shelf to the tweeter s EQ. Also, I added a notch filter around 14kHz because of a sharp increase in that frequency region. Further analysis of the tweeter would present flaws around 2kHz and 5kHz, which were fixed via smaller notch filters just barely manipulating the response to get it within +/1 db. 25

26 Crossover Performance Initially I had planned for my crossover point to be at 2kHz and for my crossover to be fourth order. A fourth order crossover was the right choice, but with the crossover at 2kHz there were summation issues. To fix this issue, I shifted the tweeter s crossover point back to 2250Hz, which allowed for less summation and less power handling need from the tweeter because it doesn t have to go as low anymore. 26

27 Overall Performance When you take all of those changes and put them together you are able to change from a poor frequency response, such as that of the one I received through my initial test. To a frequency response that is +/1dB from approximately 70Hz to 20kHz, or my final loudspeaker performance. It is important to note that I added fiberglass in my speakers on the top, bottoms, and the side across form my vent opening to decrease resonance I was having around Hz. This can be seen in the difference between the two graphs within that frequency range. I didn t have to add any not filters for those frequencies, because the fiberglass helped control the resonance. 27

28 Final Testing Results These tests were done in a controlled environment on a ten- foot stand to reduce room effect and floor bounce on the testing results. The microphone was placed 16 away from the speaker, pointed level between the tweeter and the woofer at listening height. My final testing resulted in +/- 1dB responses in both speakers from 70Hz to 20kHz. Overall Loudspeaker Performance Left Speaker Frequency Response Unaveraged Averaged Integrated Frequency Response Unaveraged 28

29 Averaged Harmonic Distortion Minimum Phase 29

30 Horizontal Off- Axis Response 0º, 15º, 30º, 45º, 60º Vertical Off- Axis Response 0º, 15º, 30º, 45º, 60º Difference Plot Overall 30

31 +/- 5dB perspective Step Response Integrated Step Response 31

32 Impulse Response Waterfall Plot 32

33 Overall Loudspeaker Performance Right Speaker Frequency Response Unaveraged Averaged Integrated Frequency Response Unaveraged 33

34 Averaged Harmonic Distortion Minimum Phase 34

35 Horizontal Off- Axis Response 0º, 15º, 30º, 45º, 60º Vertical Off- Axis Response 0º, 15º, 30º, 45º, 60º Difference Plot Overall 35

36 +/- 5dB perspective Step Response Integrated Step Response 36

37 Impulse Response Waterfall Plot 37

38 Woofer Response Left Speaker Frequency Response Unaveraged Averaged Harmonic Distortion 38

39 Minimum Phase Horizontal Off- Axis Response 0º, 15º, 30º, 45º, 60º Vertical Off- Axis Response 0º, 15º, 30º, 45º, 60º 39

40 Step Response Impulse Response 40

41 Tweeter Response Left Speaker Frequency Response Unaveraged Averaged Harmonic Distortion 41

42 Minimum Phase Horizontal Off- Axis Response 0º, 15º, 30º, 45º, 60º Vertical Off- Axis Response 0º, 15º, 30º, 45º, 60º 42

43 Step Response Impulse Response 43

44 Woofer Response Right Speaker Frequency Response Unaveraged Averaged Harmonic Distortion 44

45 Minimum Phase Horizontal Off- Axis Response 0º, 15º, 30º, 45º, 60º Vertical Off- Axis Response 0º, 15º, 30º, 45º, 60º 45

46 Step Response Impulse Response 46

47 Tweeter Response Right Speaker Frequency Response Unaveraged Averaged Harmonic Distortion 47

48 Minimum Phase Horizontal Off- Axis Response 0º, 15º, 30º, 45º, 60º Vertical Off- Axis Response 0º, 15º, 30º, 45º, 60º 48

49 Step Response Impulse Response 49

50 Bibliography AES Standards and Practices. New York: Audio Engineering Society, Inc Dickason, Vance. Loudspeaker Design Cookbook. Peterborough, New Hampshire: Audio Amateur Press, Houlman, Tomlinson. Sound for Film and Television. Oxford: Focal Press, Frequency Chart. Independent Recording (accessed 24 January 2014). Moulton, David. Total Recording: The Complete Guide to Audio Production and Engineering. Sherman Oaks, CA: KIQ Productions, Inc Newell, Richard, and Holland, Keith. Loudspeakers: For Music Recording and Reproduction. Oxford: Focal Press, Kindle Edition. Occupational Noise Exposure. Cincinnati, Ohio: National Institute for Occupational Safety and Health Plummer, Christopher. FA 4740 Transducer Theory. Houghton, Michigan, Spring Michigan Technological University. 50