Open Baffle w/ 2 Drivers - Acoustic Response 5/03/11. Copyright 2011 by Martin J. King. All Rights Reserved.

Transcription

1 Open Baffle w/ 2 Drivers - Acoustic Response 5/3/11 Software : by Martin J. King MJKing57@aol.com Copyright 211 by Martin J. King. All Rights Reserved. Configuration : Extended Range Driver w/ Bass Driver Mounted on an Open Baffle Unit and Constant Definition cycle := 2 π rad Hz := cycle sec Air Density : ρ := 1.25 kg m 3 Speed of Sound : c := 344 m sec Part 1 : Thiele-Small Consistent Calculation Detailed User Input (Edit This Section and Input the Parameters for the System to be Analyzed) Power := 1 watt (Input Power) Applied Voltage Reference ---> R ref := 8 Ω Extended Range Driver Thiele / Small Parameters : Fountek FR88EX f d := Hz V ad :=.62 liter R e := 6.1 Ω Q ed :=.878 L vc :=. mh Q md := Bl 3.13 newton 1 1 := Q td := + amp Q ed Q md S d := cm 2 Q td =.656 Bass Driver Thiele / Small Parameters : Eminence Alpha 15" High Efficiency f d := 41 Hz V ad := 26 liter R e := 5.88 Ω Q ed := 1.53 L vc :=.84 mh Q md := 7.23 Bl 7.7 newton 1 1 := Q td := + amp Q ed Q md S d := cm 2 Q td = 1.263

2 Crossover Definition For Even Order Crossovers : Type 1 = Linkwitz-Riley Type 2 = Bessel Type 3 = BEC Type 4 = Butterworth Low Pass Filter High Pass Filter f LP := 2 Hz f HP := 4 Hz (Filter Frequency) LP order := 2 HP order := 2 (Filter Order :, 1, 2, 3, or 4) LP type := 1 HP type := 1 (Filter Type : 1, 2, 3, or 4 for even order only, for odd order this entry is ignored) Crossover Phase Connection LP phase := 1 HP phase := 1 (Phase : 1 = in phase, -1 = out of phase) Low Frequency Boost LP boost := 6. db Sub High Pass Filter (Use to Limit Low Frequency Woofer Displacement) f sub := 2 Hz SHP order := SHP type := 4 (Filter Frequency) (Filter Order :, 1, 2, 3, or 4) (Filter Type : 1, 2, 3, or 4 for even order only, for odd order this entry is ignored) End of Detailed Input End of Part 1 Input

3 OB Driver Impedances (Red Curve - Woofer, Blue Curve - Extended Range Driver) 9 Phase (deg) arg( Z Lr ) deg ( ) arg Z Hr deg r Impedance (ohms) Z Lr Z Hr r Frequency (Hz) Driver RMS Displacements (Red Curve - Woofer, Blue Curve - Extended Range Driver) 5 RMS Deflection (mm) x Lr mm x Hr mm rdω Hz Frequency (Hz)

4 Part 2 : Detailed SPL Response Calculation Calculation Includes : Position of Drivers on the Baffle. Open Baffle Defraction for the Drivers. Floor Reflection for the Drivers. Geometry Coordinate System : Origin is the lower left corner of the front baffle y = horizontal direction z = vertical direction The variables num_r, n_low, and n_high control the number of simple sources used in the calculations. Increasing each will improve accuracy at the expense of longer calculation times. Increase each variable until final plotted SPL stops changing at which point the solution has converged. Enclosure Geometry Input X := 2ft (Front Baffle Distance from Rear Wall > Depth of Enclosure) Y := 1.5 ft (Front Baffle Distance from Side Wall) θ := 45 deg (Rotation Towards Room Center) Z := 8ft (Floor to Ceiling Distance) stand := m (Height from Floor to Bottom Edge of Front Baffle) num_r := 1 (Number of Points per Unit Length of Baffle Edge) Corner Coordinates Y coordinate Z coordinate y o y o1 y o2 y o3 := 2 in (Bottom Right Corner) := 2 in z o1 := 38 in (Top Right Corner) := in z o2 := 38 in (Top Left Corner) := in (Bottom Left Corner) Extended Range Driver Geometry Input y dc := 12 in (Driver Center y Coordinate) z dc := 32 in (Driver Center z Coordinate) n_high := 4 (Number of Points Across Diameter) Woofer Driver Geometry Input y w1 z w1 := 1 in (Lower Driver Center y Coordinate) := 1 in (Lower Driver Center z Coordinate) n_low := 1 (Number of Points Across Diameter)

5 Listening Position (Default Location is at 1 m Distance Along the Driver's Axis) n_listen = radius := θ := deg z p := z dc 1 m (Listening Position Relative to Speaker) (Calculation Radius, Effective Radius is Greater if y p is Changed from Default) ( deg is along the Driver's Axis, -8 deg < θ < 8 deg) (Default Height is Equal to Driver Height) n_listen = 1 X p := 1ft Y p := 7ft Z p := z dc + stand n_listen := (Listening Position Relative to the Room Corner) (Default Height is Equal to Driver Height) (Method Selection) Floor Condition Reflect := 1 ( = hardwood or concrete, 1 = carpeted) Refective Surface Selections (if 1 reflective surface is included, if reflective surface is removed) Inc_floor := 1 Inc_rear := Inc_side := Inc_ceiling := (Floor, Z = ) (Rear Wall, X = ) (Left Side Wall, Y = ) (Ceiling)

6 Extended Range Driver and Woofer : Simple Source Pattern with Baffle Edge Outline z d z w.6 z o y d, y w, y o

7 Three Dimensional View Axis Length (m) axis := 2 <---- Change value of "axis" to rescale plots Room Corner is the Origin 2 Side view z driver z outline z woofer Side View - looking out from side wall z mic x driver, x outline, x woofer, x mic 2 Front View z driver z outline z woofer Front View - looking towards rear wall z mic y driver, y outline, y woofer, y mic 2 Top View y driver y outline y woofer Top View - looking down from ceiling y mic x driver, x outline, x woofer, x mic

8 Plotted Response for the Extended Range Driver Dashed Red - Infinite Baffle Response Dashed Magenta - Baffle Response Dashed Brown - Crossover Response Solid Red - Combined Response SPL (db) SPL IBr X_over r SPL BFr SPL nr rdω Hz Phase (degrees) Phase r deg SPL (db) rdω Hz SPL Hr rdω Hz Frequency (Hz)

9 Plotted Response for the Woofer Driver Dashed Red - Infinite Baffle Response Dashed Magenta - Baffle Response Dashed Brown - Crossover Response Solid Red - Combined Response SPL (db) SPL IBr X_over r SPL BFr SPL nr rdω Hz Phase (degrees) Phase r deg SPL (db) rdω Hz SPL Lr rdω Hz Frequency (Hz)

10 Plotted System Response for the Extended Range and Woofer Open Baffle Design Phase (degrees) Phase r deg rdω Hz SPL (db) SPL r 95 SPL 9 Lr 85 8 SPL Hr rdω Hz Frequency (Hz)

11 System Time Response for an Impulse Input 4 Woofer Sound Pressure in Time Domain 2 p wooferr Pa rdt 1 System Sound Pressure in Time Domain 5 p summedr Pa rdt Time (sec)