Speaker Design Proposal

Transcription

1 Speaker Design Proposal Home Theatre Speakers Alison Pittsley

2 Table of Contents Design Goals... Box Size Requirements... SPL... Power Requirements... Frequency Response... Woofers... Tweeters... Crossover... Box Shape & Materials... Cost... Bibliography...

3 Design Goals This system consists of a stereo pair that will maly be used for television or film sound reproduction, but may occasionally be used for music reproduction as well. Enjoyment of the listeng experience, rather than critical listeng, is more valuable this design. I usually listen at fairly low SPL levels, but I also want these speakers to be close to THX standards for sound reproduction. Ideally, these speakers would have low power requirements and the frequency response would cover almost all of the audible range, but certa sacrifices are acceptable to keep the design around $ or less. Box size is flexible, but it must be big enough to be a floor standg speaker. Achievg good low frequency response is more important than high SPL, but both are desired if possible. Sce box size is flexible, cost is the most limitg factor for this design. Box Size Requirements The size specifications for these speakers are relatively flexible sce they will be placed on either side of a television that has open space around it. This home theatre setup will be fairly permanent so mobility is not a large factor. The preferable box size is smaller than tall by. wide by. deep, but these are arbitrary measurements assumg that these will be floorstandg speakers flankg the television. The speakers will need to have the correct size and aimg to cover the listeng area a by by room with an average listeng height of. feet. A drawg and approximate values of the listeng area are shown below. The walls of this room are relatively absorptive, so off axis response will not have a huge impact at the listeng area; this means than that on axis response is paramount, and off axis response will not have much impact on driver choice. Figure : Approximate Listeng Area

4 Ear Height Max Ear Height M (sittg a chair) Ear Height Avg.. (sittg on a high bed) Ideal Ear Distance From Speakers Room dimensions wide by long by high Table : Approximate Listeng Room Dimensions and Positions SPL My listeng levels are generally much lower than average, around dba if the noise floor is low enough. Considerg that the noise floor the tended space for these speakers is higher than the room I based my preferences on, the average listeng level will probably be closer to or dba. It is also important to consider that I will not be the only one listeng to these speakers, so a more universal standard of SPL capabilities is beneficial. Each speaker THX systems are calibrated to a reference level of SPL with a C-weighted level meter, and have a maximum, undistorted, level of SPL. Havg speakers that are capable of THX standards is ideal, but lower SPL output is acceptable if necessary. Takg my listeng preferences to md, maximum SPL as low as dba would be acceptable. With these two values, dbc and 9 dba, and takg crest factor to account these speakers would have to be able to produce a maximum of dbc and dba, respectively. Room Level Comfortably low listeng level Mixg Level Rockg out to a really good song level Begng of discomfort dba dba dba dba 9 dba Table : My SPL preferences based on levels taken Walker Tomlson Holman, Sound for Film and Television, (Focal Press, 99), - 9. Alison Pittsley, experiment, (SPL Preferences, Michigan Technological University, Michigan January, ).

5 Power Requirements Ideally, power requirements would rema low, with driver sensitivities db or above. Given that the listeng area is about meters away from each speaker, watt of power would be enough to deliver the average listeng SPL; higher sensitivities would easily allow smaller amplifiers to produce maximum SPLs over dba. Havg high driver sensitivity is a very important sce many home theater receivers do not provide more than W per channel. Assumg a maximum of W, dbw is the most that could be gaed by usg more power so a driver with the sensitivity of db would have a maximum of db after considerg the crest factor. To reach the maximum of dbc for a THX system, the sensitivity of the drivers would have to be db or above; considerg sensitivities above approximately 9 db are less coon and more expensive, a good balance of power capabilities and cost must be found for each driver. (W) to deliver SPL (dba) at Meters (M) dbw Table : Example power requirement chart, driver sensitivity = db W/m (W) to deliver SPL at Meters (M) dbw (dba) Table : Example power requirement chart, driver sensitivity=9 db W/m Christopher Pluer, lecture, (course on Transducer Theory, Michigan Technological University, Michigan January, ).

6 Frequency Response Given that this system will be used maly for television or films, some might thk that the low frequency limit could be high because vocal frequencies wouldn t be affected until around, the vocal frequency range for humans beg about to. k. Though dialogue is usually considered, on the surface, to be the drivg force TV and films, there is so much more sound volved counicatg stories, much of it outside the vocal range. Knowg this, but not knowg how much low frequency usage is coon film mixg, I used THX standards for an idea of the required frequency response for films and TV. Speakers THX systems are calibrated to the X-curve, which begs to roll off around and is about db down around. Figure : X Curve In addition to fdg the THX standards, I also did an experiment to fd my own low frequency extension preferences while listeng to music. For this experiment I loaded four songs that represent the kd of music I like to listen to to Logic Pro and put a high pass filter on all of them. Playg each song and my preferred listeng level, I swept the filter higher until I noticed significant change the quality of the music. Dog this I found the frequencies where I thought that low frequency loss was acceptable, and the pot at which I thought the loss was not acceptable (results of this experiment are shown on the next page). Usg this formation, and keepg the THX standards md, the highest low frequency limit that could be considered is around, with beg the middle ground, and beg ideal. Ken Ellis, Sound and Light SALT Manual, Last modified 9,, Brian Florian, Learng from History: Cimema Sound and EQ Curves. Last modified,. Accessed January,. article- curves- -.html.

7 Song Title (Artist) Maximum loss () Acceptable loss () Thunderstruck 9 (AC/DC) Circle the Dra (Katy Perry) Juke Box Hero 9 (Foreigner) The Luckiest (Ben Folds) Table : My low frequency extension preferences Woofers To beg the woofer selection process I searched for woofers my price range that had large frequency ranges and high sensitivities. With these parameters, I came up with the followg list to compare. Woofer Cost sen. power (W) Max SPL (db) Q_ts F_s () Box Volume V_b (ft^) Seas CARLY $.... Aura NS--A $ Seas CARCY $..... Peerless HDS Nomex $. 9. NA..9. Peerless HDS " GF Cone $ Peerless HDS PPB " Midwoofer $. NA....9 Peerless HDS." GF Cone $ Peerless HDS." Alu Cone $ Peerless HDS PPB." Midwoofer $.. NA...9. Peerless SDS." Midwoofer $9. NA Seas LRLY/P $...9. W- $....9 Dayton RS- $ Table : Woofer Spec Spreadsheet f_ () Alison Pittsley, experiment, (Low Frequency Extension Preferences, Michigan Technological University, Michigan January, ).

8 Usg W Speakers, I modeled the system frequency response of all these drivers assumg a SBB_ alignment (box volume and f_ shown above table). From these models I easily chose five drivers to exame more closely. They were: Seas CARLY Aura NS--A Seas LRLY/P TB W- Dayton RS- #* %&' From this pot I closely examed frequency response of the drivers and of the system. The qualities I took to account were, order:. Lowest extendg/flattest system response. Flattest driver response. Highest driver response (as least for crossover at ). High sensitivity (All drivers meet mimum sensitivity requirement) Frequency [] (./,//,/9/,:/;9<,.9<,=/>/?,//,@/;?,9?,//,@,%A,-%A,>?,B%,?/C//,>C;/,@C,> ;9/?,:9D,9,,"E,;,/FG,H9;=/G,,IF,EG#-,+9;F,JK*A,=@9.9/,?@F>/,%GL=A,9=>;@M/?,F9,"=G (./,9;@?,;@/,:/;9<,L%%,NM,@,>,>;;>F/?,/9/,9,>,@@@F/,:>;/,:>/?,9,F./,>>=/F/,C@H/,9,F.@ /@@,?@H/G,(./,@=/?>/,@,=/>/?,@,//,>@,<@F.9F,:>;/G Figure : W- Frequency Response 9 9 SPL [db] Figure : Seas LRLY/P Frequency Response Impedance [ohm]!! RoHS compliant product www ,+ Figure : Seas CARLY Frequency Response ;:+>-@<=-+ =+.BF,=,BF+ <D+9+ ;+9<+.+ +<D+NG QORSQ"&+SRTPU"Q!P ++++%P!ORRPQUPU+%PNVPQ!'+%"QWP ++++X(O%H+HP%R+R"YSRVR+TOJP%+Z+ ++++&OQW+HP%R+R"YSRVR+TOJP%+Z ++++!("%"!HP%SXHS!+XPQXSHS[SH'++\#J#F^ [OS!P+!OS&+US"RPHP% ++++[OS!P+!OS&+(PSW(H [OS!P+!OS&+%PXSXH"Q!P [OS!P+!OS&+SQUV!H"Q!P+\PNVS["&PQH^ O%!P+"!HO% %PP+"S%+%PXOQ"Q!P RO[SQW+R"XX "S%+&O"U+R"XX+SQ+SP!+`"&P XVXTPQXSOQ+!ORT&S"Q!P XVXTPQXSOQ+RP!("QS!"&+%PXSXH"Q!P PP!HS[P+TSXHOQ+"%P" Ge cg*c G/ dc ##Gd cg$/ #Gb #Ge #bc $ OFb])cc (a )c J $c J $$Gc `+XT& )/ FF #/ FF OF- F( QE" (a FFEQ Q-EF -CG;F ++++"S%+W"T+(PSW(H /Gc FF

9 Frequency Response (W, m) Figure : Dayton RS- Frequency Response 9 deg -9 - Figure : Aura NS Frequency Response Impedance k k k k k TA TA ) tab db db Lear Exc Limit Distortion (W, m) Lear Exc Limit 9 - Pha - Mag k k ms Exc Dly Pha - Mag k k ms Exc Dly Figure Driver Parameters : W- SBB_ Box Response Parameters Driver: System Type: Nomal Diameter Nomal Power Sensitivity (W/m) Free Air Resonance Total Q Electrical Q Mechanical Q Equivalent Volume Nomal Impedance DC Resistance Max Thermal Power Max Lear Excursion Max Excursion Voice Coil Diam. Driver Notes: D = P = SPL = f(s) = Q(ts) = Q(es) = Q(ms) = V(as) = Z = R(e) = P(t) = X(max) = X(lim) = D(vc) =..... db SPL Ohms Ohms NOTE: X(max) was estimated based on the nomal driver NOTE: S(D) was estimated based on the nomal driver System Notes: Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q th Order Vented Box V(B) = Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) = System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance N = I = P() = D = My Company My Address, le....9 (=normal, =iso) m Figure Driver 9: Parameters Seas LRLY/P SBB_ Box Parameters Driver: System Type: Response Nomal Diameter Nomal Power Sensitivity (W/m) Free Air Resonance Total Q Electrical Q Mechanical Q Equivalent Volume Nomal Impedance DC Resistance Max Thermal Power Max Lear Excursion Max Excursion Voice Coil Diam. Driver Notes: D = P = SPL = f(s) = Q(ts) = Q(es) = Q(ms) = V(as) = Z = R(e) = P(t) = X(max) = X(lim) = D(vc) =.... db SPL Ohms Ohms NOTE: X(max) was estimated based on the nomal driver NOTE: S(D) was estimated based on the nomal driver System Notes: Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q th Order Vented Box V(B) = Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) = System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance....9 N = I = P() = D = My Company My Address, le (=normal, =iso) m

10 TA TA db db Lear Exc Limit Lear Exc Limit Pha - Mag k k ms Exc Dly Pha - Mag k k ms Exc Dly Figure : Seas CARLY Box Parameters System Type: SBB_ th Order Vented Response Box Driver Parameters Driver: Nomal Diameter Nomal Power Sensitivity (W/m) Free Air Resonance Total Q Electrical Q Mechanical Q Equivalent Volume Nomal Impedance DC Resistance Max Thermal Power Max Lear Excursion Max Excursion Voice Coil Diam. Driver Notes: D = P = SPL = f(s) = Q(ts) = Q(es) = Q(ms) = V(as) = Z = R(e) = P(t) = X(max) = X(lim) = D(vc) = db SPL Ohms Ohms NOTE: X(max) was estimated based on the nomal driver NOTE: S(D) was estimated based on the nomal driver System Notes: db - - Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q V(B) = Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) = System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance N = I = P() = D = My Company My Address, le My Address, le My Country System Name: Designer: My Name Title: My Title Rev Date: Seas CARLY (SBB) th Order Vented Box (=normal, =iso) m My Phone Rev: Figure Driver : Parameters Dayton RS- SBB_ Box Parameters Driver: System Type: Response th Order Vented Box Nomal Diameter Nomal Power Sensitivity (W/m) Free Air Resonance Total Q Electrical Q Mechanical Q Equivalent Volume Nomal Impedance DC Resistance Max Thermal Power Max Lear Excursion Max Excursion Voice Coil Diam. Driver Notes: D = P = SPL = f(s) = Q(ts) = Q(es) = Q(ms) = V(as) = Z = R(e) = P(t) = X(max) = X(lim) = D(vc) = db SPL Ohms Ohms NOTE: X(max) was estimated based on the nomal driver NOTE: S(D) was estimated based on the nomal driver System Notes: TA Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance My Address, le My Address, le My Country 9 V(B) = Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) = N = I = P() = D = My Company System Name: Designer: My Name Title: My Title Rev Date: Dayton RS- (SBB) th Order Vented Box (=normal, =iso) m My Phone Rev: Lear Exc Limit - - Mag k k ms Exc Dly Figure : Aura NS SSB_ Response System Type: Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q th Order Vented Box V(B) = Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) =.... System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance N = I = P() = D = (=normal, =iso) m System Notes: My Company My Address, le My Address, le My Country System Name: Aura NS--A (SC) th Order Vented Box My Phone 9 Designer: Title: My Name My Title Rev Date: Rev:

11 From these choices I cut the drivers that had an f_ above. The fal two options were the Aura NS--A and the Seas CARLY; I chose the Aura because it had a higher sensitivity, a higher frequency extension, and the Seas low frequency response was not superior enough to outweigh the benefits of the Aura. When choosg drivers I left the prices out of my spreadsheet so they would not affect my decisions; once I fally looked up the prices, I realized that I had chosen a driver that was only $. and thought I must have made a mistake. I did; I had entered as the f_b when it was really ; this factor had been a huge part my decision-makg process. The correct system response, as seen above Figure, is not nearly as attractive as the one that was correct. With the correct system response, the Aura is not as attractive as the Seas terms of low and flat frequency response, but all the qualities I liked about the Aura itially were still there, so decidg whether to keep the Aura, or use the Seas, was very difficult. Initially when comparg the fal drivers, I used f_bs for SSB_ alignments because it is the best terms of low tung and transient response, with the SC_ comg just below it quality. After I realized that I chose the Aura s based on the lower f_b of, I noticed that the Aura s f_b with the SC_ alignment is. Given that this alignment gave the type of f_b I needed to get a nice system response and keep the high sensitivity and high frequency extension, I decided to stick with the Aura s. Usg the Aura s, I experimented with the number of drivers and box volume to see if I could come up with a better response. With this, I decided to use four woofers each speaker, separatg the drivers to two spaces, with two drivers each space. TA TA db db Lear Exc Limit - Mag k k ms Exc Dly - - Lear Exc Limit - Mag k k ms Exc Dly Driver Parameters Driver: Box Parameters th Order Vented Box System Type: Figure : Aura NS SC_ Response Nomal Diameter Nomal Power Sensitivity (W/m) Free Air Resonance Total Q Electrical Q Mechanical Q Equivalent Volume Nomal Impedance DC Resistance Max Thermal Power Max Lear Excursion Max Excursion Voice Coil Diam. Driver Notes: D = P = SPL = f(s) = Q(ts) = Q(es) = Q(ms) = V(as) = Z = R(e) = P(t) = X(max) = X(lim) = D(vc) = db SPL Ohms Ohms NOTE: X(max) was estimated based on the nomal driver NOTE: S(D) was estimated based on the nomal driver Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) = Figure : Aura NS Double Driver System Type: Response Box Volume Closed Box Q Box Frequency M Rec Vent Area Vent Surface Area Vent Length Compliance Ratio Box Loss Q th Order Vented Box My Address, le Vance Dickanson, Loudspeaker Design Cookbook, System (Peterborough, Notes: New Hampshire: My Address, le Audio My Address, le My Country My Phone My Address, le System Name: My Country Amateur Press, ),. System Name: System Notes: System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance V(B) = N = I = P() = D = My Company Designer: My Name Title: My Title Rev Date: Aura NS--A (SC) th Order Vented Box (=normal, =iso) m Rev: V(B) = Q(tc) = F(B) = S(vM) = S(v) = L(v) = alpha = Q(B) = System Parameters No. of Drivers Isobaric Factor Input Power SPL Distance... N = I = P() = D = My Company Designer: My Name Title: My Title Rev Date: Aura NS--A (SC) th Order Vented Box (=normal, =iso) m My Phone Rev:

12 Tweeters To beg the tweeter selection process I searched for tweeters my price range that extended lower than (assumg a crossover at ) and with high sensitivities. With these parameters, I came up with the followg list to compare. Tweeter Cost F_s sensitivity power (W) f_ () impedence (ohms) Max SPL (db) Dayton DCSF- $.. 9 Seas H9 $ Seas H $. 9 9 Vifa BCTG- $... Vifa BCSC- $ Vifa XTSC9- $ Vifa DTG- $... Vifa XTTG- $. NA Vifa XT9TD- $.. 9. Vifa XTBG- $ Fostex FTD $9. 9 ScanSpeak D/9 $. 9.. ScanSpeak D/9 $ ScanSpeak D/9 $ Fostex FTD $. 9 Audax TWX $. 9. Morel CAT - $9. 9 Morel MDT S $. 9 Dayton DCSFS- $..9 9 Dayton RSA- $. 9. Table : Tweeter Spec Spreadsheet

13 Lookg at the specs for these tweeters I cut the ones with the least flat responses and highest frequency extensions first, as well as any tweeter with a nomal impedance below ohms, and ended up with the followg to compare more closely: Fostex FTD ScanSpeak D/9 Audax TWX Figure : Fostex Frequency Response Figure : Audax Frequency Response Figure : ScanSpeak Frequency Response

14 Of these tweeters, I chose the one that I thought had the best balance between:. Low frequency extension. Smooth low frequency roll off. Flat high frequency extension through k. Off axis response close to on axis response. High sensitivity (All drivers meet mimum sensitivity requirement) With the idea of a first order crossover md, it was important to have low frequency extension with a smooth roll off. Two of the three of the fal tweeters had really smooth roll offs so I had to take flatness of the high frequencies, off axis response, and sensitivity to higher account for my fal selection. I I ended up choosg the ScanSpeak D/9, even though the off axis response is very consistent at high frequencies, because it has flat response on axis and a high sensitivity; because the room these will be placed is non-reverberant the off axis response will not have a very big impact on the listeng area. Crossover A first order crossover is the only conventional crossover whose combed output reconstruct the put waveform. This is the reason I put such high value on havg a woofer and tweeter that extended above and below, respectively. With the ScanSpeak D/9 tweeter and the Aura NS--A woofer a first order crossover at makes a smooth roll off of both the highs and lows, makg for a smooth transition between the tweeter and the woofer. However, a second order crossover gives a much safer drop db at the tweeter resonant frequency and will probably allow the tweeter a longer life than a first order crossover. Crossover Model Relative db - - Frequency Response () Tweeter st order ailter Woofer st order ailter Zeroed Tweeter Resonse Zeroed Woofer Resonse Tweeter nd order ailter Woofer nd order ailter Figure : Crossover model of ScanSpeak D/9 tweeter and Aura NS--A woofer Philip Newell, and Keith Holland, Loudspeakers for Music Recordg and Reproduction, (Elsevier Ltd., ),.

15 For these reasons, I decided to go with a second order Lkwitz-Riley crossover, which sums to a flat magnitude. 9 As stated before, the woofer section, these speakers will have four drivers split to two sections. This provides an opportunity to extend low frequency response by compensatg for the baffle step loss with a. crossover on the low end. Two woofers will cover the low and mid frequencies, and the other two will only cover low frequencies. This makes the speakers more consistent on the vertical axis. With the. crossover added on the low end, the fal design will be a second order Lkwitz-Riley. way crossover. Figure 9: Example. Way Crossover Figure : Example. Filter Response Box Shape & Materials The boxes are tended to be floor standg, approximately.ft tall by.ft deep by.ft wide. I had origally planned on makg rectangular speakers with rounded edges to reduce edge diffraction, but the effectiveness of this is rather limited. With a rectangular design, the drivers were to be placed different distances from the edges of the speakers, which makes a big improvement the diffraction loss. I opted for the more complex diamond shape because I like the look, and because the -degree angles off the front baffle help to reduce diffraction loss a great deal more than rounded or chamfered edges. With the syetrical look of the diamond shape, I chose to keep the drivers center on the baffle to keep the syetrical look. 9 Vance Dickanson, Loudspeaker Design Cookbook, (Peterborough, New Hampshire: Audio Amateur Press, ),. Christopher Pluer, lecture, (course on Transducer Theory, Michigan Technological University, Michigan Feburary, ). Paul Spencer, Red Spade Audio Blog, "Etude TL crossover." Last modified 9,. Accessed April,. audio.blogspot.com///etude- tl- crossover.html. Lkwitz Lab, Diffraction from baffle edges. Last modified //. Accessed January 9,. John L. Murphy, Introduction to Loudspeaker Design, (Andersonville, TN: True Audio, 99),.

16 The box material needed to be stiff enough so that the speakers will not resonate with the drivers. To achieve stiffness of the box I decided to use two layers of wood. On the outside, ¾ birch plywood with the highest ply possible to crease rigidity, and on the side, ¾ MDF which is heavy and will vibrate less tandem with the driver. The MDF will also be used a brace that separates the box to two sealed enclosures (besides the ports). Each box will have two tung ports, one for each enclosure. These ports will be located on the back diagonal of the boxes so that the box noise will not be directed at the listeng area, nor will it be reflected off the wall behd it. Once the boxes are constructed, the unique shape and wood gra will create a nice aesthetic. I plan to keep this natural look by usg natural wood sta, and possibly a clear glossy coat to a more fished look. Figure : D Renderg of Speaker Design Philip Newell, and Keith Holland, Loudspeakers for Music Recordg and Reproduction, (Elsevier Ltd., ),.

17 Cost The budget for these speakers is around $, with limited flexibility for better quality. My itial thought was that each driver could cost no more than $, which was one of the limitg factors when fdg drivers to compare. This would have left about $, which would not have been enough to cover wood and crossover costs. The low cost of the woofers and tweeters leaves enough money for wood and crossover materials, addition to less significant costs like shippg, glue, and sta. Quantity Cost Total Woofer $. $9. Tweeter $. $. Baltic Birch x $. $. MDF x $. $. Total: $. Table : Current Speaker Budget

18 Bibliography Custom Car Stereo, "Xover Calculators." Accessed April,. Dickanson, Vance. Loudspeaker Design Cookbook. Peterborough, New Hampshire: Audio Amateur Press,. Ellis, Ken. Sound and Light SALT Manual. Last modified 9,. Florian, Brian. Learng from History: Cimema Sound and EQ Curves. Last modified,. Accessed January,. Holman,Tomlson. Sound for Film and Television. Focal Press, 99. Kg, Mart J. Simple Sizg of the Components a Baffle Step Correction Circuit.. Lkwitz Lab, Diffraction from baffle edges. Last modified //. Accessed January 9,. McCarthy, Bob. Sound Systems: Design and Optimization. Burlgton, MA: Elsevier Ltd.,. Murphy, John L. Introduction to Loudspeaker Design. Andersonville, TN: True Audio, 99. Newell, Philip, and Keith Holland. Loudspeakers for Music Recordg and Reproduction. Elsevier Ltd.,. Pittsley, Alison. Experiment, (Low Frequency Extension Preferences, Michigan Technological University, Michigan January, ). Pittsley, Alison. Experiment, (SPL Preferences, Michigan Technological University, Michigan January, ). Pluer, Christopher. Lecture, (course on Transducer Theory, Michigan Technological University, Michigan January, ). Pluer, Christopher. Lecture, (course on Transducer Theory, Michigan Technological University, Michigan Feburary, ). Spencer, Paul. Red Spade Audio Blog, "Etude TL crossover." Last modified 9,. Accessed April,.