Resource to calculate, building and measuring Hi Fi Loudspeakers and more...




 


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    Loudspeakers

Calculate Enclosure Resonances  Onken Bass Reflex Calculator  Acoustic Power Calculator  TQWT Calculator  Sealed Box Calculator  Vented Box-Calculator  Bass Horn  Back Loaded Exponential Horn  Thiele's Alignment based on QT Transmission Line Calculator Calculate Enclosures Sixth-Order Bandpass Subwoofer-Calculator Port-Calculator Passive Radiator Calculator new Qts with Series Inductor TSPCalculator Driver Reference Efficiency Calculate maximum Sound Pressure Level Loudspeaker Protection Amplifier Power Required  

    Networks

Impedance Equalization Circuit Calculate Q of Second Order Network   6dB, 12dB, 18dB & 24db Crossover Filters Attenuation Circuit  Calculate Baffle Diffraction Loss Series Resonant Circuit   Series Resonant Circuit For Tube Amp   Parallel Notch Circuit   Calculate passive RIAA EQ Network

    Diverse

Cable Length & High Frequency Loss   Grounded-Cathode Amplifier Calculations   Calculate Stepped Attenuator Search Resistor Calculate Resistor Values From Color Codes Calculate Inductive And Capacitive Reactance Calculate Led Resistor Calculate Input And Ouput Impedance

    Acoustics

Speed of Sound in fibrous material   Wavelength - Frequency Calculator   Calculate Room Modes Calculate optimal Room Dimension Reverb (RT60) Calculator Amount of Standig Waves In A Rectangle Room Calculate your Bass Trap, Panel Absorber, Slot Absorber, Skyline Diffusor or Quadratic Residue Diffusor

    Turntable

Calculate Tonearm / Cartridge Capability Calculate Passive RIAA EQ Network

    Equivalents

Convertion-Calculator





    Thiele's Alignment based on QT

Thiele's method is to choose an alignment based on QT.
Alignment Box design
Order No Type Ripple(dB) f3/fs fB/fs VB/VAS QT
Quasi Third Order 1 QB3 --- 2.68 2.000 0.0954 0.180
2 QB3 --- 2.28 1.730 0.1337 0.209
3 QB3 --- 1.77 1.420 0.2242 0.259
4 QB3 --- 1.45 1.230 0.3390 0.303
Fourth Order 5 B4 --- 1.000 1.000 0.7072 0.383 optimally flat
6 C4 --- 0.867 0.927 0.9479 0.415
7 C4 0.13 0.729 0.829 1.372 0.446
8 C4 0.25 0.641 0.757 1.790 0.518
9 C4 0.55 0.600 0.716 2.062 0.557
9.5 C4 1.52 0.520 0.638 2.60 0.625




Example:
  • fs = 30.4 Hz

  • Vas = 125.9 liters

  • Qe = 0.249

  • Qm = 3.9934

  • Rs = 7.4 ohm
EBP = fs/Qe = 122 --> vented

With 0.5 Rext external, QT = 0.249

Looking at the table, this QT suggests
alignment No3 ( QB3 ), giving:

Vb = 28.23 liters
fb = 43.2 Hz
f3 = 53.8 Hz
 
fs [Hz] :
Vas [liters] : Vas [cu.ft.] :
Qe [] :
Qm [] :
Re [ohms] :
Rext [ohms] :
 
EBP [] :
QT [] :
Vb [liters] : Vb [cu.ft] :
fb [Hz] :
f3 [Hz] :
 
Port calculations

  Dv : [cm] Lv : [cm] Pa : [cm2]
  Dv : [inches] Lv : [inches] Pa : [sq.inches]
 
If you change the pipe diameter [Dv], click on 'Port' to recalculate Port length.



GLOSSARY OF SYMBOLS
  • fs - resonance frequency of driver in free air
  • Vas - volume of air having same acoustic compliance as driver suspension
  • Qe - Q of driver at Fs considering system electrical resistance only
  • Qm - Q of driver at Fs considering system nonelec-trical resistances only
  • Re - dc resistance of driver voice coil
  • Rext - dc resistance of crossover-filter-coil and speakercable

  • EBP - efficiency bandwidth product
  • QT - total Q of driver at fs including all system resistances
  • Vb - net internal volume of enclosure
  • fb - Helmholtz resonance frequency of vented box
  • f3 - alignment (-3dB) cutoff frequency

  • Dv - Diameter of the bass reflex pipe
  • Lv - Length of the bass reflex pipe
  • Pa - Area of the bass reflex pipe

    Tuning Lv
Lv now cm
Fb you want Hz
Fb measured Hz
 
Lv cm
new length Lv is cm





    Transmission Line

A transmission line enclosure is a waveguide in which the structure shifts the phase of the driver's rear output by at least 90°, thereby reinforcing the frequencies near the driver's Fs. Transmission lines tend to be larger than ported enclosures of approximately comparable performance, due to the size and length of the guide required (typically 1/4th the longest wavelength of interest).

The design is often described as non-resonant, and some designs are sufficiently stuffed with absorbent material that there is indeed not much output from the line's port. But it is the inherent resonance (typically at 1/4 wavelength) that can enhance the bass response in this type of enclosure, albeit with less absorbent stuffing. Among the first examples of this enclosure design approach were the projects published in Wireless World by Bailey in the early 1970s, and the commercial designs of the now defunct IMF Electronics which received critical acclaim at about the same time.

A variation on the transmission line enclosure uses a tapered tube, with the terminus (opening/port) having a smaller area than the throat. The tapering tube can be coiled for lower frequency driver enclosures to reduce the dimensions of the speaker system, resulting in a seashell like appearance. Bose uses similar patented technology on their Wave and Acoustic Waveguide music systems. Bowers & Wilkins have used this approach in their flagship Nautilus speaker as well as smaller straight tapering tubes in many of their other lines.




  Driver
 Cabinet
  fs : Hz Sd : cm2   Inside width : cm
 



 
Classic tuning
  Cabinet height [h] : cm
  Depth behind driver [a] : cm
  Depth at TML port [c] : cm
  Depth at base [b] : cm
  Length of TML duct [LTML] : cm
  Resonant frequency [fb] approximately : Hz at 275 m/s
  Classic: the unfold length is 1/4 of the resonance frequency's wave length
Low tuning
  Low tuning [h] : cm
  Length of TML duct: LTML = cm
  Resonant frequency [fb] approximately : Hz at 275 m/s
 
  Low tuned: the unfold length is 1/3 of the resonance frequency's wave length


Half of transmissionline is to be filled with damping material (dark gray in the picture)

Therefore, the velocity of speed in the TML duct drops by 20% to approx. 275 m/s

Take a look at 'Definition Transmission Line'








    Calculate change of Speed of Sound
in fibrous material



c= speed of sound in air = 344 meters or 1128.6 feet
c'= speed of sound in long fiber wool
P= packing density of the fibrous material = 8kg/m3



Speed of sound in air [c]: m/s
Packing density of the fibrous material [P]: kg/m3
 
Speed of sound in long fiber wool [c']: m/s






    New Qts with series inductor



Driver Qes = Driver Qms =
Driver Re = Ohm R = Ohm
      R is the resistance of the wiring, typically 0.5 ohm 
  original Qts =
new Qts =    






    Attenuation Circuit

divider
Speaker impedance: Ohm
Damping: dB
  Series resistance R1: Ohm
  Parallel resistance R2: Ohm



 
Calculate here the attenuation and new driver-impedance of an existing attenuation circuit or with resistors different then calculated before.

Important:
Impedance from this circuit has to be as close as possible to the original driver impedance. If the difference is >0.25 ohm the filter function is deviating of the computations.

Enter R1, R2 and the driver impedance.
The impedance and attenuation of the circuit including the driver will be calculated.


This can be usefull if you have to use resistors with a different values then calculated for the attenuation circuit.

Driver impedance:  ohm
Series resistance R1  ohm
Parallel resistance R2  ohm
Driver impedance (incl. attenuator):   ohm Damping:   dB
Driver impedance difference:   ohm
Message: 
 



    Impedance Equalization Circuit (Zobel)


An Impedance Equalization Circuit is used to counteract the rising impedance of a voice coil caused by inductive reactance. The cause of this impedance rise is due to the speaker's voice coil inductance (Le).

Example:

For a midwoofer you calculate a Lowpass Butterworth 2nd order filter with a cutoff frequency at 4.5 kHz with the nominal impedance Re (from datasheet) of 8.0 ohm

The calculated inductor is 0.4 mH and 3.1uF for 4.5 kHz cutoff frequency.


Impedancecurve Fullrange driver measured with ARTA - LIMP

no compensation - 13.3ohms at 4.5kHz

with compensation - 7.3ohms at 4.5kHz

Take a look at the impedance plot of this fullrange driver. The impedance at 4.5 kHz is not 8.0 ohm,
but more than 13ohms!

At this impedance you inductor has to be 0.28 mH and not 0.4 mH
and the capacitor should be 4.4uF and not 3.1uF.

This wrong inductor and capacitor would create a wrong crossover frequency and not as assumed a crossover point of 4.5 kHz!

The importance to use impedance compensation should be clear now...


 
Re = Ohms R = Ohms
Le = mH C = uf

Advantage:
the crossover filter works better, because the driver impedance is more stable over a wider frequency range.






© mh-audio 2010