2012-04-26 fa4740 initialdesignstatementrev 09 · 2012-04-26 · page7!of!55! use%...

arbor. DESIGN STATEMENT

Chelsea Leighton FA 4740: Transducer Theory

April 26, 2012

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Table of Contents Overview ...................................................................................................................................................... 4

Initial Design Statement ............................................................................................................................... 5

Application ................................................................................................................................................... 6

Size ........................................................................................................................................................... 6

Aesthetics ................................................................................................................................................ 6

Use ........................................................................................................................................................... 7

Sealed-‐box vs. Vented-‐box ...................................................................................................................... 7

Frequency Response ................................................................................................................................ 8

Active vs. Passive Crossover .................................................................................................................... 8

Sound Pressure Level ............................................................................................................................... 9

Supporting Equipment ............................................................................................................................... 10

Amplifier ................................................................................................................................................ 10

Crossover ............................................................................................................................................... 10

Additional Speakers ............................................................................................................................... 11

Design Goals .............................................................................................................................................. 11

Preliminary Design ..................................................................................................................................... 12

Initial Sketches ....................................................................................................................................... 12

Edge Diffraction ..................................................................................................................................... 12

Speaker Placement ................................................................................................................................ 13

Materials & Construction Methods ....................................................................................................... 14

Working Design Statement ........................................................................................................................ 15

Drivers ........................................................................................................................................................ 16

Woofers ................................................................................................................................................. 16

ScanSpeak 18W/8434G00 – Third Choice .......................................................................................... 17

Morel CAW 638 – Second Choice ...................................................................................................... 18

ScanSpeak P17WJ-‐00-‐08 [Vifa P17WJ-‐00-‐08] – First Choice .............................................................. 18

Tweeters ................................................................................................................................................ 20

Seas Excel T25CF001 – Third Choice .................................................................................................. 20

ScanSpeak D2905/930000 – Second Choice ...................................................................................... 21

Seas Prestige 27TDFNC/GW – First Choice ........................................................................................ 21

Current Sketches .................................................................................................................................... 22

Materials & Construction Methods ....................................................................................................... 22

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Brace ...................................................................................................................................................... 22

Vent ....................................................................................................................................................... 23

Appendices ................................................................................................................................................ 24

A. Newell’s Active vs. Passive Crossover Analysis .................................................................................. 24

B. Working Drafting Packet .................................................................................................................... 26

Bibliography ............................................................................................................................................... 54

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Overview This report covers the first two phases of speaker design for “Arbor”: the preliminary and working stages. The preliminary section focuses on all limiting factors that were considered at the start of the project, including the client’s personal loudspeaker preferences, proven loudspeaker designs comparable to what might be built, supporting equipment to be utilized, and the preliminary design sketches. Phase two of the project provides further insight into the current direction for cabinet design and construction of Arbor, and also includes further detail regarding how and why some of those basic design decisions were made. Also addressed are the different drivers (both tweeters and woofers) that were considered for Arbor. Ultimately, a final recommendation for the most suitable woofer and tweeter for this project are stated, and the working design sketches are provided.

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Initial Design Statement “Arbor” requires that a left/right pair of loudspeakers be built which are appropriate for use in a small college dorm room setting. The final location of the loudspeakers, combined with the request that they also be easily portable, immediately limits the size of the cabinets to that of a bookshelf speaker. In this case, the size of the loudspeaker is always the most important element when compared to other design considerations. Due to the size requirements, this will be a two-‐way system, which automatically locks in the need for only one crossover point. An active crossover is highly desired due to its ease of tuning. To accomplish this, the system will need to be powered by four separate channels of amplification. The drivers should be a woofer, with a diameter anywhere from 6.5” to 7,” and a soft dome tweeter that is liquid filled for cooling purposes. The sensitivity to aim for is at least 87 dB sound pressure level at 1 Watt at 1 meter. A good amount of system head room was important to the client as they often listen to highly dynamic music. Another important element to the client was the ability to have good bass response. The small box size makes this a much more difficult goal to reach. Porting the cabinet will allow extra low frequency extension to help solve this problem, while also giving the speakers a much more mellow sound. This, in turn, supports the wish for the system to be less fatiguing and harsh, elements often connected to closed-‐box designs. It was not as important to the client that the loudspeakers have good spatial accuracy, so the reduced accuracy of a vented box is not an issue. To give the loudspeakers more rigidity and isolation, the boxes should be milled entirely from 1” aluminum blocks. Should this prove to be too complicated or expensive during the actual building process, the boxes should simply be made out of wood “laminated” on the outside with quarter-‐inch aluminum, or made completely out of wood. Bracing the box will also help add stability to the cabinet’s overall structure and is highly recommended, especially if the main structure is not block aluminum. Every step of the way, the budget for the loudspeakers themselves should be taken into account, with $800.00 being the target cutoff amount.

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Figure 2: Milled aluminum subwoofer enclosure. (Source: AVForum)

Figure 3: Magico Q1 two-‐way speaker. (Source: Magico)

Application

Size The completed pair of loudspeakers will be used by a college student in a room with very limited space and few placement options, so the smaller and more portable the system, the better. Floor standing speakers are not an option, and unconventional speaker locations (such as high overhead or unevenly spread in the room from the listening location) might be required.

Two-‐way bookshelf size speakers would be preferable because of their small dimensions and easy portability. The Phase Technology V62 two-‐way bookshelf speaker, loudspeakers that I am already personally familiar with and are comparable to this project’s goals, (Figure 1) has the target size we should aim for with dimensions of 8.25” (W) x 13.25” (H) x 9.53” (D) and a weight of 10.5 pounds.1 This is the smallest acceptable speaker box size for this project. The absolute maximum acceptable box size for Arbor would be 11.00” (W) x 23.19” (H) x 16.68” (D) and no more than twenty-‐five pounds.

Aesthetics Although not of paramount importance, our client would prefer a design that was visually appealing and relatively unique. Mention has been made of building the cabinet out of either a clear material (such as Plexiglas) or milling it out of a metal such as aluminum. Indeed, people have successfully made milled aluminum speakers before, such as the sub in Figure 2.2 Another option would be to utilize both the clear and metallic elements to create an enclosure. A company named Magico has already had such a speaker on the market, as seen in Figure 3, but for the unrealistic price of $25,000.00 per pair. 3 4 No matter what the speaker cabinet ends up being made out of, it would be nice if the diver cones themselves were metallic looking.

1 “V62,” Phase Technology, accessed January 15, 2012, http://www.phasetech.com/products.html?product_id=V62&vc=1. 2 michael hurd, August 25, 2011 (9:30 p.m.), comment on Schino, “aluminum speaker enclosure. okay or not?,” AVSForum (forum) August 25, 2011 (8:41 p.m.), http://www.avsforum.com/avs-‐vb/showthread.php?t=1356426. 3 “Q1,” Magico, accessed January 15, 2012, http://magico.net/Product/Q1/Q1_03.php. 4 Stephen Mejias, “The Magico Q1 and the Grand Opening of EarsNova,” Stereophile, January 16, 2011, http://www.stereophile.com/content/magico-‐q1-‐and-‐grand-‐opening-‐earsnova.

Figure 1: Phase Technology V62 bookshelf speaker. (Source: Phase Technology)

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Use These speakers will mostly be used to listen to music, but could also be employed for movie and television audio playback. Our client’s taste in music is rather eclectic, being an active listener to virtually all major genres. When asked to rate his top five flavors of music, our client replied: electronic, pop, rock, jazz, and classical in order of interest with electronic being the most listened to type.5

Sealed-‐box vs. Vented-‐box Electronic music tends to require more low frequency extension which can be a difficult demand for small speakers to meet. One path often looked to for resolution of this issue is the use of a “reflex loaded cabinet” with one or more ports or vents incorporated into the loudspeaker instead of using a closed box design. This method relies on resonance and its interaction with the “air spring” within the port. “In these systems, the mass of air inside the ports resonate with the spring which is created by the air trapped within the cabinet. If the resonant frequency is chosen to be just below where the driver response begins to roll-‐off, then the overall response can be extended.”6 However, this technique does introduce a few issues.

One issue, “vent leakage,” can occur when midrange frequencies produced from the back of the driver leak from the port and interfere with the sound waves radiating from the cone at the front of the speaker. Reduced transient response is another symptom that can make the audio image seem blurred as there is an increased impulse response. The difference between sealed-‐box and ported-‐box decay times can be seen in the two waterfall plots in Figures 4 and 5. It can clearly be seen that the response time of the closed-‐box system (Figure 2) has much less lag compared to that of the ported system (Figure 3), especially at lower frequencies. Also, “…vented boxes will typically be under-‐dampened compared to closed boxes [and there] will be more ripple in the transient response for a vented box than for a closed box.”7 The choice to use a ported system for the Arbor design must be made very carefully because our client also listed jazz and classical music as material that would be played through these speakers often. Jazz and classical music employ highly contrasting dynamics and sudden transients which, as just discussed, would be susceptible to being blurred. Also, this type of music requires more headroom than a conventional system of up to 20 dB.8

5 Tyler Leighton, chat message to author, January 15, 2012. 6 Philip Newell and Keith Holland, Loudspeakers for Music Recording and Reproduction (Oxford: Focal Press, 2007), 320-‐33. 7 John L. Murphy, Introduction to Loudspeaker Design (Andersonville: True Audio, 1998), 27-‐9. 8 Christopher Plummer, (lecture, FA 4740: Transducer Theory, Houghton, MI, January 11, 2012).

Figure 4: Waterfall plot of a small closed-‐box loudspeaker. (Source: Newell and Holland)

Figure 5: Waterfall plot of a small ported loudspeaker. (Source: Newell and Holland)

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Figure 6: Basic active crossover system layout.

During my research, I was able to further develop opinions pertaining to loudspeaker design. One of the most distinct results I found was that I prefer ported speaker cabinets instead of a fully sealed-‐box design for two-‐way systems. It is true that a closed-‐box design has better transient response and depth reproduction, but they also tend to have a harsher sound with less bass. For this reason, I tend to find closed-‐box designs less listenable, especially when they are meant to be standalone units without a supporting subwoofer, just as the Arbor system is meant to be.

Frequency Response It would be wonderful if the set of speakers for Arbor could cover the entire hearing range of 20 Hz to 20,000 Hz, but this is not realistic. Besides, it is most important that a pair of loudspeakers be able to remain consistent over the most essential frequencies. To reinforce that point, it is generally accepted by professionals in the audio field that“…excellent loudspeaker frequency response consists of a range from 30 kHz to 17 kHz.”9 As this is already an industry standard, I feel it is important to attempt to at least meet or even exceed these standards. However, given the physical size of the loudspeakers will be small, it is likely that any woofer used in the system will be physically small as well and thus unable to produce the wavelengths needed to reach substantially lower frequencies. The only possible way to reach low notes would be to port the cabinet, but even that might not go far enough to reach 30 Hz. To be more practical, I think it is only fair to adjust our acceptable lower limit by the probable size of the woofer to be chosen. Referring back to the Phase Technology V62, we will use this as our model. It comes equipped with a 6.5” woofer and is capable of outputting frequencies as low as 58 Hz. Therefore, the target minimum frequency range for my design will be an outer wall limit of -‐3 dB at 58 Hz and 17 kHz with as flat of a frequency response curve as possible in between. Also, the woofer diameter should be at or between 6.5” and 7”.

Active vs. Passive Crossover Also having to do with the frequency response is the crossover. There are two basic types of crossovers: active and passive. Active crossovers involve processing the signal before it is amplified to help separate the frequencies into high and low. Although this allows for much more control over a system at any given point in time, it also calls for extra equipment (adding greatly to the system expense) and more physical space to house that equipment. (A diagram detailing the basic active crossover system layout can be seen in Figure 6.10) In this case, we will be utilizing an active crossover because its overall accuracy, and the convenience of easy tuning, outweighs money and space issues. (Whether active or passive crossovers are “better” is occasionally a point of dispute point within the audio community. It is generally understood that active is better, but the extra costs associated with such a system often can make it difficult to implement. To see a list of one expert’s analysis of the pros and 9 David Moulton, Total Recording: The Complete Guide to Audio Production and Engineering (KIQ Productions, 2000), 133-‐35. 10 “Digital Crossovers,” miniDSP, accessed January 21, 2012, http://www.minidsp.com/applications/digital-‐crossovers

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0

10

20

30

40

50

60

70

80

90

Jazz Electronic Rock (Classic) Pop Classical

SPL in dBA

Heavy Concentrapon

Easy Listening

Rocking Out

Figure 8: Average preferred sound pressure level measured in dBA depending on activity and genre of music at 1.5 meters distance.

Figure 7: A second order LCR passive crossover.

cons for each type of crossover, please refer to Appendix A: Newell’s Active vs. Passive Crossover Analysis.) However, should problems arise with using an active crossover, passive crossovers could also be used. The following details this method: Given that this is a typical consumer setting, using a typical passive crossover made of electronic components in the cabinet should work just fine. Due to the fact that these speakers will be a two-‐way system, one two-‐way crossover is needed per cabinet. If money becomes an issue, I would opt for a second order crossover as first order crossovers require special drivers that could get very expensive. Figure 7 is an example of a second order LCR (inductor, capacitor, and resistor) passive crossover for a two-‐way system very similar to what will be needed for Arbor.11 The best crossover point frequency will need to be determined once the drivers have been selected because it is dependent on their range – generally, the location of this point is where the two frequency ranges for the drivers meet. It is also desirable for this point to be out of the range of the human voice. The final location of this point will become more apparent once the speaker is built and testing and tuning can begin to take place, a process which will be greatly simplified due to the use of an active crossover.

Sound Pressure Level I discovered that my preferred listening levels changed depending on the type of music and activity I was completing while listening, as portrayed in the graph in Figure 6. The time of day at which I listened greatly affected the sound pressure level (SPL) I desired. In general, when I first woke up in the morning, I liked everything to be quiet so my “Heavy Concentration” level would turn into my easy listening level in the morning. (It is important to note that Figure 8 is based on levels taken in the evening time). I also enjoyed quieter levels after long periods of silence. Inversely, the longer I was in a noisy situation, the higher SPL I thought was needed.

The SPL average levels required for Arbor should not need to surpass the levels I determined

11 “The Audio Pages: Design of Passive Crossovers,” Elliot Sound Productions, accessed January 15, 2012, http://sound.westhost.com/lr-‐passive.html.

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Table 1: Crown XTi SPL response.

Figure 9: Crown XTi 1002 amplifier.

Figure 10: dbx DriveRack PA.

to be sufficient, the highest of which was 87 dBA SPL. Part of what I am taking into account here is the fact that the levels I was listening at were for the same purposes as what the client will be using their speakers for – background music while studying, easy listening for when a little less concentration is needed for the task at hand, and the occasional “rock out” session. I also took into account that the room I did my listening in is a space of approximately the same size as where the client will be using their speakers from this project. The smaller the space, the closer the listener is to the source (in general), the lower the SPL that needs to be output. If we assume that 87 dBA was the sensitivity of the speaker (87 dBA at 1 Watt at 1 meter), the following levels would be possible using the Crown XTi 1002 amplifier configured for eight ohm output impedance and stereo outputs (non-‐bridged):

Power Requirement (Watts)

Signal Strength (dBW) Sound Pressure Level at 1 Meter (dB)

1 0 87 2 3.0103 90 4 6.0206 93 8 9.0309 96 16 12.0412 99 32 15.0515 102 64 18.0618 105 128 21.0721 108 256 24.0824 111

Note that the decibel watt or dBW is also given. This column represents the signal strength as compared to one watt in decibels and was calculated using the following equation: !" = 10 log!"(!) .

Supporting Equipment

Amplifier Two Crown XTi 1002 amplifiers, pictured in Figure 912, will be used in this system, so the speakers do not need to be self-‐powered. This amplifier provides 700 watts of power per stereo channel at two ohms impedance, 500 watts at four ohms, and 275 watts at eight ohms impedance, which will supply enough power to allow the system to easily handle peaks during high-‐level listening sessions by providing more than 20 dB of headroom.

Crossover The active crosser to be paired with this system is the dbx DriveRack PA which features a built in graphic equalizer, a pink noise generator, and twelve notch filters, among other things. It is pictured in Figure 10 below.13

12“Crown XTI 1002,” Key Music, accessed February 18, 2012, http://www.keymusic.com/en/product/Crown-‐XTi1002 13 “dbx DriveRack PA+,” Parts Express, accessed February 18, 2012, http://www.parts-‐express.com/pe/showdetl.cfm?Partnumber=246-‐171

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25

25

50

Design Emphasis

Sensipvity

Bandwidth

Enclosure

Figure 11: Major design decision area visual representation.

Additional Speakers It should not be assumed that the Arbor speakers will be played with a separate subwoofer in a 2.1 configuration. Although this setup is a possibility in the future, for now, no subwoofer will be used, so this pair of speakers must be able to sound good on their own.

Design Goals Out of the three major design decision areas as seen in Figure 11, enclosure is most important because the speakers must be of a very specific size to fit within the listening environment. It is also important that the speakers are listenable for relatively long periods of time. The bandwidth and sensitivity are equally less important than the size in this case. The overall bandwidth we are aiming for is 58 Hz to 17 kHz with a relatively smooth frequency response curve. In order to achieve that low frequency range, the speaker cabinet must be ported which will make depth less obvious. However, porting will also help to solve the issue of producing a fatiguing sound. The sensitivity should be set at around 87 dB at 1 Watt at 1 meter within 5 dB. Another important design goal that has yet to be mentioned is the budget. Although not a strict budget, we should aim to spend around $800.00 on this pair of speakers, and not go over $1000.00. Probably the least important item on the list is the final ascetics. It would be nice to have a good looking set of speakers, but it is far more important that they sound good than look good.

In order of importance, here the major considerations once more:

1. Size 2. Long listening ability, less fatiguing 3. Budget 4. Bandwidth/low frequency performance 5. Sensitivity 6. Depth 7. Aesthetics

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Figure 14: Basic Project TDL design.

Figure 12: Box side view.

Figure 13: Box front view.

Preliminary Design

Initial Sketches The initial design plans for Arbor can be viewed in Figures 12 through 14 below. The box size has been set to the dimensions of 17.5” high by 7.75” wide by 12 “ deep, although the inner dimensions will be one inch less for each measurement, giving a total box volume of approximately 1225 inches cubed. These dimensions might be subject to change slightly in the future. This basic size of the cabinet was reached based on the fact that the box needed to be relatively portable while still being large enough

to allow for acceptable conditions regarding base response and venting. Also, the end location for the speakers will be in a relatively small dorm room where space will come at a premium, further enforcing the need for setting size constraints on the box design early on.

Edge Diffraction Notice that the edges of the boxes in the renderings are beveled and that the speakers are mounted flush to the “face” surface of the cabinet. Both of these design elements were implemented in an attempt to combat edge diffraction. “[Edge diffraction] occurs when some of the energy radiated by a driver is re-‐radiated at a later time from the cabinet edges. [It] causes tonal balance problems by increasing energy to the listener at some frequencies and reducing energy at other

frequencies. Diffraction also causes smearing of transient sounds, distortion of spatial cues, and creates a "boxy" sound.”14 This effect can be seen more clearly in Figure 15, where the waves are bouncing off of the box surface, creating a “second point source.” Figure 16 shows what happens when the edges of the cabinet are beveled, helping to remedy the issue of edge diffraction.

14 “Diffraction,” THIEL Audio, accessed January 28, 2012, http://thielaudio.com/THIEL_Site05/Pages/Tech/diffraction.html

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Figure 15: Loudspeaker box with edge diffraction.

Figure 16: Loudspeaker box with beveled edges to combat edge diffraction.

Figure 17: Typical dorm room layout.

In an ideal situation, the driver would be mounted completely centered at the end of a lengthy, solid cylindrical object.15 In the case of Arbor, the overall box shape is rectangular to make placement of the speakers in a dorm room more feasible without the use of speaker stands; this way, the speakers could be set on almost any flat surface either horizontally or vertically.

Speaker Placement More than likely, the speakers themselves will be placed directly at ear level (i.e. on a desk or dresser) in comparison to where the listener sits. Alternatively, due to lack of space, there is the possibility that the loudspeaker might also be placed well above ear level, with the highest possible position being where the horizontal top is just below the ceiling. Judging by the height of our client, if the speakers were to be placed at ear level (while standing upright) the midpoint of the speakers would need to be flush with the listener’s ears at three feet, nine inches high. When the listener is standing, this “midpoint” for ideal speaker listening would change to be about five feet, six inches. Also, the client has a preferred listening distance of no less than four feet. Due to the small size of dorm rooms, our best chance at meeting this specification would be to keep the depth of the speaker box small. To give a better idea of the size of room our client will be listening in, Figure 17 provides a dimensioned diagram of an average dorm room layout at Michigan Technological University.16

15 “Understanding Cabinet Edge Diffraction,” Unrah, Andy, accessed January 28, 2012, http://www.speakerdesign.net/understand.html 16 “Room Layout Types: Wads Two Person,” Michigan Technological University, accessed January 28, 2012, http://www.mtu.edu/housing/residence-‐halls/incoming/buildings/

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Materials & Construction Methods The primary construction material used within this design will be medium-‐density fiberboard (MDF). This type of wood product was chosen due to its uniform density and manageable cost. It will be used to construct the inner skeleton of the box, including all joints and bracing, and, other than the hole needed for the port, would be used to create a fully enclosed cabinet. The only other outlet from the inside of the box would be a small, sealed hole on the back that would allow wires to travel from the drivers, through the backboard, and out to connectors mounted on the back. This would facilitate connection of the drivers to the amplifiers. Aluminum sheeting will then be applied over this MDF skeleton. Not only will this provide an appealing visual aesthetic, it will also act as a second barrier between sound waves created within the cabinet and outside of the cabinet, thus reducing interference which could impact the overall sound of the system. Mounting the drivers flush to the front face of the cabinet is another way that this design will help prevent wave interference.

Baffle step is something else which needs to be proactively addressed. It is easily identifiable graphically by a 6 dB drop in bass response. “As an approximation, the rise begins at the frequency whose wavelength is 8 times the smallest dimension of the baffle.”17 In the case of Arbor, this means that the baffle step would occur at approximately the speed of sound (13,397 inches/second) divided by the width of the speaker, the product of which is multiplied by one eighth. This gives an approximate baffle step of 248 Hz. Unfortunately, other than increasing the smallest dimension of the overall speaker cabinet (something that has already been ruled out as an option) there is little that can be done to reduce baffle step. However, if the speaker is placed on a shelf, there is a possibility that the system might act as if it were soffit mounted, giving it an “endless baffle” in which there would not be baffle step. For this to work, though, the box and shelf dimensions would need to be very precise, so this would not be a very reliable solution.

17 “Baffle Diffraction Step,” Jason M. Neal, accessed January 28, 2012, http://www.t-‐linespeakers.org/tech/bafflestep/index.html

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Working Design Statement Arbor requires that a left/right pair of loudspeakers be built which are appropriate for use in a small college dorm room setting. The final location of the loudspeakers, combined with the request that they also be easily portable, immediately limits the size of the cabinets to that of a bookshelf speaker. In this case, the size of the loudspeaker will be determined by the required inner volume of the box, represented by the dimensions 16” x 7.5” x 10”. Due to the size requirements, this will be a two-‐way system, which automatically locks in the need for only one crossover point. This will be handled by the dbx DriveRack PA active crossover system. To accomplish this, each individual loudspeaker will be powered by a Crown XTi 1002 amplifier to provide separate power sources for each driver, supplying enough power to give at least 20 dB of headroom. The drivers will be a ScanSpeak P17WJ-‐00-‐08 woofer, with a 6.5” diameter, and a Seas Prestige 27TDFNC/GW soft dome tweeter that is liquid filled for cooling purposes. Porting the cabinet using an SC4 alignment with a QL of seven will allow extra low frequency extension to help solve the problem of limited low bass response, while also giving the speakers a much more mellow and blended sound. This, in turn, supports the wish for the system to be less fatiguing and harsh, elements often connected to closed-‐box designs. It was not as important to the client to have good spatial accuracy, so the reduced accuracy of a vented box is not an issue. To give the loudspeakers more rigidity, the boxes have been reinforced with a figure eight brace. This is especially important since the box is primarily made out of wood with an inner layer of ¾” baltic birch, ⅛” loaded vinyl, and a ½” maple exterior. Every step of the way, the budget will be taken into account, with $800.00 being the target amount and $1000.00 being the cutoff.

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Table 2: Woofer comparison chart. Note that the boxes highlighted in red indicate specific reasons for that driver being eliminated from consideration.

Drivers

Woofers Generally speaking, a woofer is a “…speaker driver that handles the low frequency signals of a sound wave.”18 Woofers are not to be confused with subwoofers which are used to produce extremely low frequencies -‐ usually 80 Hz and below. Sizes for woofers range anywhere from four inches to fifteen inches, but are most often utilized within the four inch to ten inch boundaries.19 There were ten individual woofers that were compared and considered for use in Arbor. They are as follows:

• Fostex FW168N • Peerless HDS-‐P830874 • Morel CAW 638 • Peerless SDS-‐P830657 • Morel EW 638 • ScanSpeak 18W/8434G00 • Morel MW 166 • ScanSpeak P17WJ-‐00-‐08 [Vifa P17WJ-‐00-‐08] • Morel SCW 636 • Seas Prestige L16RNX

To evaluate these drivers, a general comparison chart was created, detailing size, resonant frequency (fs), sensitivity, price, power handling, frequency range, and maximum excursion (x-‐max), as seen in Table 2.

SCW 636 **CAW 638 FW168N MW 116 EW 638 Range 40 Hz – 4 kHz 43 Hz – 5 kHz 40 Hz – 9 kHz 30 Hz – 5 kHz 40 Hz – 4 kHz F3 (SC4, QL=7) -‐-‐ 35 Hz -‐-‐ 28 Hz -‐-‐ VB (SC4, QL=7) -‐-‐ .88048 ft3 -‐-‐ 1.8413 ft3 -‐-‐ Fs 40 Hz 43 Hz 40 Hz 46 Hz 39 Hz Power Handling 150 W 150 W 34 W 150 W 150 W Price $351.80 $130.60 $169.20 $118.50 $185.90 Sensitivity 87 dB 86 dB 89 dB 86 dB 87 dB Size 6" 6" 6.5" 6” 6" X-‐max 5 mm 6 mm 5 mm 4.25 mm 6 mm

Based on price, the following drivers were ruled out: Morel SCW 636, Fostex FW168N, and Morel EW 638. From here, each of the remaining woofers were modeled using WinSpeakerz, for both the SBB4 and SC4 fourth order vented box alignments with a leakage of QL=7, and compared. According to the

18 “Audio Glossary: Definitions,” John M. Anning, accessed January 28, 2012, http://www.nu9n.com/audio_glossary.html 19 “Woofers,” Parts Express, accessed January 28, 2012, http://www.parts-‐express.com/speakers.cfm

SDS-‐P830657 *P17WJ-‐00-‐08 HDS-‐P830874 L16RNX ***18W/8434G00 Range 40 Hz – 4 kHz 37 Hz – 5 kHz 50 Hz – 4 kHz 45 Hz -‐ 2 kHz 53 Hz – 3 kHz F3 (SC4, QL=7) 35 Hz 48 Hz 52 Hz 48 Hz 45 Hz VB (SC4, QL=7) 1.7254 ft3 .6679 ft3 .5429 ft3 .33891 ft3 .8331 ft3

Fs 45 Hz 37 Hz 58 Hz 39 Hz 50 Hz Power Handling 60 W 150 W 75 W 80 W 170 W Price $24.75 $76.90 $56.00 $93.25 $73.75 Sensitivity 88 dB 88 dB 88 dB 85 dB 89 dB Size 6.5” 6.5” 6.5” 5" 6.5” X-‐max 3.46 mm 6 mm 5.38 mm 6 mm 4.2 mm

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Figure 18: SC4, QL=7 alignment, 170 W.

Loudspeaker Design Cookbook, “The Super Fourth-‐Order Boom Box [SBB4] is characterized by a large box, low tuning (longer vent length), and good transient response…,” while “The Fourth-‐Order Sub-‐Chebyshev is roughly the same size and f3 as the SBB4, but has different tuning.”20 I decided to look at the SC4 box outcomes (as seen in Table 2) due to the possibility of producing a smaller box size and was able to rule out the Morel MW 166 and Peerless SDS-‐P830657 based on box volumes that were still too large. Similarly, the Peerless HDS-‐P830874 was ruled out due to a high f3 in comparison to the remainder of the batch. (F3 is the point at which the low bass response dips to three dB below the average SPL. This is the point when a perceived sound level difference can be detected by the human ear.) The next woofer to be taken out of those to be considered was the Seas Prestige L16RNX due to it having the lowest power handling capability and sensitivity out of the remainder. The three resulting woofers are listed below, along with their WinSpeakerz plots and the reasoning behind their ultimate ranking. For further information regarding these three drivers, please refer to Appendix C for individual driver specification sheets.

ScanSpeak 18W/8434G00 – Third Choice

Although the SC4 alignment being considered for this driver looked okay when considering factors such as phase response, it was ultimately put in third place because it left little headroom – as the power supplied by the amplifier increased, the linear excursion limit was quickly reached. The linear excursion limit is the mechanical limit point where the driver will actually physically pull apart when reached. Another factor that played into the “demotion” of this woofer was an issue at 1000 Hz visible within the frequency response graph. There could not be a worse place for interference as the area that this frequency response represents is essential to understanding speech.

20 Vance Dickason, Loudspeaker Design Cookbook 7th Edition (Peterborough: Old Colony Sound Lab, 2006), 62.

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Figure 21: SBB4, QL=7 alignment, 150 W.


Morel CAW 638 – Second Choice

The Morel was the runner up for two reasons. Much like the ScanSpeak in third place, there was a slight anomaly around 1000 Hz that was not ideal. Also, as seen in Figure 19 above, the phase response of this driver was off the charts in comparison with the other choices and, although there was a more acceptable amount of headroom before hitting the linear excursion limit than the 18W/8434G00, it was much less than that offered by the ScanSpeak P17WJ-‐00-‐08.

ScanSpeak P17WJ-‐00-‐08 [Vifa P17WJ-‐00-‐08] – First Choice

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Figure 22: ScanSpeak P17WJ-‐00-‐08 woofer.

The first choice in woofers for Arbor is the ScanSpeak P17WJ-‐00-‐08. It should be noted that this driver was initially produced by Vifa and that it has a long, positive track record for being an all-‐around good driver for non-‐precision listening. Beyond its good reputation, this driver was chosen due to its relatively low f3 point, good delay response, smooth frequency response, large headroom and acceptable box size. As can be seen in Figures 20 and 21, I looked into both the SBB4 and SC4 box alignments for this driver. In this case, it appears that the SC4 alignment produce the best overall results. Upon testing the different QL values for this alignment, I then determined that a QL of seven made the most sense based on box size and relative difference between results.

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Table 3: Tweeter comparison chart. Note that the boxes highlighted in red indicate specific reasons for that driver being eliminated from consideration.

Tweeters Tweeters are drivers that handle the high frequencies in a system. In almost all cases, they are self-‐contained, meaning that their movement produces no change in pressure within the speaker cabinet itself. In a two-‐way system, this translates into not needing to physically separate the woofer and the tweeter within the cabinet. One of the main distinctions between tweeters is the resonant frequency – the lower this is the better. This information, along with many other comparison items, can be viewed in Table 3 below. The specific tweeters compared in this chart are:

• Fostex FT28D • ScanSpeak D2905/930000 • Morel ET 448 • Seas Basic 29TFF/W • Morel MDT 12 • Seas Excel T25CF001 • Fostex FT28D • ScanSpeak Classic D2905/950000 • ScanSpeak Illuminator

D3004/662001 • Seas Prestige 27TDFNC/GW

29TFF/W *27TDFNC/GW **d2905/930000 FT28D ***T25CF001 Frequency Range

2.2 – 25 kHz 2.5 – 30 kHz 700 Hz – 20 kHz 1 – 50 kHz 2 -‐ 25 kHz

F3 1000 Hz 1,000 Hz 1,500 Hz 1,750 Hz 1,100 Hz Fs 950 Hz 750 Hz 650 Hz 850 Hz 700 Hz Power Handling 90 W 90 W 150 W 40 W 90 W Price $52.00 $96.55 $122.55 $68.20 $107.15 Sensitivity 92 dB 90.5 dB 90 dB 90 dB 91 dB FT48D 25SD-‐1 D3004/662001 D2905/950000 MDT12 Frequency Range

800 Hz – 30 kHz

2 -‐ 25 kHz 800 Hz -‐ 30 kHz 900 Hz – 30 kHz 1.8 -‐ 25 kHz

F3 1000 Hz 600 Hz 600 Hz 1,050 Hz 1,300 Hz Fs 600 Hz 1 KHz 500 Hz 550 Hz 1 KHz Power Handling 50 W 100 W 90 W 150 W 80 W Price $96.25 $76.60 $232.65 $140.15 $34.90 Sensitivity 93 dB 90 dB 91.5 dB 90 dB 89 dB

Immediately, the Illuminator D3004/6620-‐01 and Classic D2905/9500 were eliminated due to price, and the MDT12 was eliminated due to a combination of low power handling capabilities and low sensitivity, and the FT48D and FT28D due purely to low power handling capabilities. The resonance frequency was the next element that determined which tweeters were acceptable or not, with the higher frequencies scoring worse. This resulted in the dismissal of the 29TFF/W and the 25SD-‐1, leaving the top three choices as: the Seas Excel T25CF001, the ScanSpeak D2905/930000, and the Seas Prestige 27TDFNC/GW, all of whose specification sheets can be found in Appendix D.

Seas Excel T25CF001 – Third Choice The Seas line seems to have made a name for itself as being a little brighter and sharper than some of their competitor’s tweeters without becoming “too harsh”. Knowing that our client enjoys music with lots of transients, especially jazz, this seemed like the perfect fit. While this specific tweeter met almost all desired criteria, it did not beat out the Seas Prestige, partially because it had a lower high-‐frequency

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Figure 23: Seas Prestige 27TDFNC/GW tweeter.

drop off point and a higher f3 value. Beyond that, in my opinion, there just wasn’t enough difference between the two to make a forty dollar price difference per pair.

ScanSpeak D2905/930000 – Second Choice This tweeter was still in the running due to its high power handling and low frequency extension and resonance frequency. However, it also had its drawbacks; the extended high frequency range drops off well before that of the Prestige. Also, the ScanSpeak had a relatively high f3 which would make finding a good crossover point more difficult.

Seas Prestige 27TDFNC/GW – First Choice There are several reasons that make this tweeter the right choice for Arbor. For starters, this design features a fully protected front of the tweeter which (at $97.00 per replacement) was very desirable for a college dorm room setting. The Prestige also had a great frequency range, with a high extension that appears to go beyond 40 kHz, comparable sensitivity and power handling, and a relatively flat overall frequency response. The only downside to this tweeter is that is has a little bit of a higher resonant frequency than the rest. However, this was easily overshadowed when taken into account with all other parameters.

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Figure 25: SC4, QL=7 box dimensions for the ScanSpeak P17WJ-‐00-‐08.

Figure 24: Working box design.

Working Design

Current Sketches The basic working model for what the Arbor speakers should look like can be seen in Figure 24 with more detailed drawings in Appendix B: Working Drafting Packet.

Materials & Construction Methods There are three main layers to the speaker box: the first layer is ¾” baltic birch, the second is ⅛” loaded vinyl to help reduce mechanical noise caused within the box, and the third layer is ½” maple. The choice to use wood on the outside of the box was in part due to the cheaper cost of wood verses aluminum, and because it is easier to manipulate. Each layer will be glued together with the only unglued portions of the box being screws used to mount the drivers, the terminal plate, and the back of the box (this will act as the main access point for future tuning and adjustments.) The ideal internal box volume for the chosen woofer is .6679 cubic feet – the tweeter has zero effect on the box size because it is completely enclosed in the back, unlike the woofer. It is always preferable to have more room within the loudspeaker box than too little as space can always be taken up during the tuning process by adding dampening material. Taking this into account, I used the box calculator within WinSpeakerz to round up the dimensions of the ideal box volume to easy-‐to-‐handle numbers within a half inch – note that these dimensions included allowances for the volume taken up by the drivers and brace within the box. This gave an overall box volume of .69444 cubic feet, as seen in Figure 25.

Brace A brace is required within the speaker box design to provide additional support when extremely ridged materials (such as thick blocks of metal) are not in use. Because wood is the primary material used within the box, a brace is required to help discourage box flexing. There are many brace variations, but it is generally accepted that the more solid the brace construction material, the better. In this case, the brace will be made out of ¾” baltic birch cut in a figure eight configuration, as can be viewed in Appendix B: Working Drafting Package. This brace will slide into notches along the inside sides of the box and glued into place.

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Figure 26: SC4, QL=7 vent alignment for the ScanSpeak P17WJ-‐00-‐08.

Vent The larger the vent diameter, the less likely it is to produce noise. However, the larger the vent diameter, the longer the vent itself must be. As such, I experimented in WinSpeakerz to produce a vent size that was of a “normal” measurement (within .25 inches in diameter). The results can be seen in Figure 26 with a vent diameter of 2 inches and length of approximately 6.328 inches. When the speaker is built, the vent length should be cut longer than this to allow for changes during the tuning process. Also, it is important to note that the vent used in this design is not flared -‐ this would change the vent surface area and, therefore, the required length.

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Appendices

A. Newell’s Active vs. Passive Crossover Analysis “The list of advantages in favor of active crossovers and multi-‐amplification is impressive:

1) Loudspeaker drive units of different sensitivities may be used in one system without the need for lossy resistive networks or transformers. This can be advantageous because drive units of sonic compatibility may be electronically incompatible in passive systems.

2) Distortions due to overload in any one band are captive within that band, and cannot affect any of the other drivers.

3) Occasional low frequency overload do not pass distortion products into the high-‐frequency drivers, and instead of being objectionable may, if slight, be inaudible.

4) Amplifier power and distortion characteristics can be optimally matched to the drive unit sensitivities and frequency ranges.

5) Driver protection, if required, can be precisely tailored to the needs of each driver. 6) Complex frequency response curves can easily be realized in the electronics to deliver flat (or as

required) acoustic responses in front of the loudspeakers. Driver irregularities can, except if too sharp, be easily regularized.

7) There are no complex load impedances as found in passive crossovers, making amplifier performance (and the whole system performance) more dynamically predictable.

8) System intermodulation distortion can be significantly reduced. 9) Cable problems can be dramatically reduced. 10) If mild low frequency clipping or limiting can be tolerated, much higher SPLs can be generated

from the same drive units (vis-‐á-‐vis their use in passive systems) without subjective quality impairment. (See 2 and 3 above.)

11) Modeling of thermal time constraints can be incorporated into the drive amplifiers, helping to compensate for thermal compression in the drive units, although they cannot totally eliminate its effects.

12) Low source impedances at the amplifier outputs can damp out-‐of-‐band resonances in drive units, which otherwise may be uncontrolled due to the passive crossover effectively buffering them away from the amplifier.

13) Drive units are essentially voltage-‐controlled, which means that when coupled directly to a power amplifier, (most of which act like voltage sources) they can be more optimally driven than when impedances are placed between the source and load, such as by passive crossover components. When ‘seen’ from the point of view of a voice coil, the crossover components represent an irregularity in the amplifier output impedance.

14) Direct connection of the amplifier and loudspeaker is a useful distortion reducing system. It can eliminate the strange currents which can often flow in complex passive crossover.

15) Higher order filter slopes can easily be achieved without loss of system efficiency. 16) Low frequency cabinet/driver alignments can be made possible which, by passive means, would

be more or less out of the question. 17) Drive unit production tolerances can easily be trimmed out. 18) Driver ageing drift can easily be trimmed out

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19) Subjectivity, clarity and dynamic range are generally considered to be better on an active system compared to the passive equivalent (i.e. same box, same drive units). […]

20) Out of band filters can easily be accommodated, if required. 21) Amplifier design may be able to be simplified, sometimes to sonic benefit. 22) In passive loudspeakers used at high levels, voice-‐coil heating will change the impedance of the

drive units, which in turn will affect the crossover termination. Crossover frequencies, as well as levels, may dynamically shift. Actively crossed-‐over loudspeakers are immune to such crossover frequency changes.

23) Problems of inductor sitting (to minimize interaction with drive unit voice coils at high current levels) do not occur.

24) Active systems have the potential for the relatively simple application of motional feedback, which may come more into vogue as time passes.

Conversely, the list of benefits for the use of passive, high level crossovers for studio monitors would typically consist of:

1) Reduced cost? Not necessarily, because several limited bandwidth amplifiers may be cheaper to produce than one large amplifier capable of driving complex loads. What is more, the passive crossovers for the 1000 watt Kinoshita studio monitors […] cost over 3000 euros.

2) Passive crossovers are less prone to being misadjusted by misinformed users, who think that crossovers are some sort of ‘adjust to taste’ tone controls. On the other hand, passive systems have a tendency to misadjust themselves with age.

3) Simplicity? Not really, because very high quality, passive, high level crossovers can be hellishly complicated to implement, not to mention the amplifiers which are needed to drive them.

4) Ruggedness? No, because the electrolytic capacitors (necessary for the large values) are notorious for ageing, and gradually changing their values.”

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B. Working Drafting Packet

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C. Woofer Specification Sheets

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D. Tweeter Specification Sheets

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Bibliography Anning. “Audio Glossary: Definitions.” Accessed January 28, 2012,

http://www.nu9n.com/audio_glossary.html#s. Dickason. Loudspeaker Design Cookbook. Peterborough: Old Colony Sound Lab, 2006. Elliot. “The Audio Pages: Design of Passive Crossovers.” Accessed January 15, 2012, http://sound.westhost.com/lr-‐passive.htm. Key Music. “Crown XTI 1002.” Accessed February 18, 2012, http://www.keymusic.com/en/product/Crown-‐XTi1002. Madisound. “Madisound Speaker Store.” Accessed February 18, 2012,

http://www.madisoundspeakerstore.com/ Magico. “Q1.” Accessed January 15, 2012, http://magico.net/Product/Q1/Q1_03.php. Mejias. “The Magico Q1 and the Grand Opening of EarsNova.” Stereophile http://www.stereophile.com/content/magico-‐q1-‐and-‐grand-‐opening-‐earsnova. Michigan Technological University. “Room Layout Types: Wads Two Person.” Accessed January 28, 2012,

http://www.mtu.edu/housing/residence-‐halls/incoming/buildings/. miniDSP. “Digital Crossovers.” Accessed January 21, 2012, http://www.minidsp.com/applications/digital-‐crossovers. Moulton. Total Recording: The Complete Guide to Audio Production and Engineering.KIQ Productions,

2000. Murphy. Introduction to Loudspeaker Design. Andersonville: True Audio, 1998. Neal. “Baffle Diffraction Step.” Accessed January 28, 2012

http://www.t-‐linespeakers.org/tech/bafflestep/index.html. Newell and Holland. Loudspeakers for Music Recording and Reproduction. Oxford: Focal Press, 2007. Parts Express. “dbx DriveRack PA+.” Accessed February 18, 2012,

http://www.parts-‐express.com/pe/showdetl.cfm?Partnumber=246-‐171 Parts Express. “Woofers.” Accessed January 28, 2012,

http://www.parts-‐express.com/speakers.cfm. Phase Technology. “V62.” Accessed January 15, 2012, http://www.phasetech.com/products.html?product_id=V62&vc=1.

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Plummer, Christopher. Lecture for FA 4740: Transducer Theory, Houghton, MI, January 11, 2012 THIEL Audio. “Diffraction.” Accessed January 28, 2012, http://thielaudio.com/THIEL_Site05/Pages/Tech/diffraction.html. Unruh. “Understanding Cabinet Edge Diffraction.” Accessed January 28, 2012,

http://www.speakerdesign.net/understand.html.

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