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

Friday, 18 January 2019
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 Projects ( planned or in progress )

If the first watt sucks, why continue?

Open Baffle with Eminence Alpha 15A 2 meter Bass Pipe
ELTAX Modification PC Satellite
Horn Modification Tube RIAA-Amp
Olson-Style Manifold Horn

= finisehd     = in progress     = canceled


July 2014: New project ( Turntable ) is started...

The base is made from walnut, 40mm (1,6 inch) thick.
I will use an AC Motor of the Thorens TD160 mkII, also the platter bearing.
The table is completely solid, with holes cut, of course, for the motor, bearing, and arm mounting.

Building the base from walnut.

A long way to go...

I'm using the Rega RB300

First hole, the main bearing.
I used 40 mm ( 1,57 inch ) Walnut for the Turntable. It's build out of 4 piece walnut to avoid distortion. All holes are machined with high precision.
The distance of mid platter to the tone arm pivot must be exactly 222 mm ( 8,74 inch )for the used Rega RB 300 tonearm.

The used Synchronous motor is from an old Thorens TD 160 Mk II. Also the Platter is from the TD160 Mk II

After weeks of calculating and building the Project is now finished...

The Spikes are from eBay...

Motor: Thorens TD 160 Mk II Synchronous 230 VAC/50 Hz
Platter: Thorens TD 160 Mk II Aluminium 300 mm / 1,5 kg, Belt driven
Cartridge: Denon DL110

This turntable/tonearm combination was evaluated by 3 of my friends over the last weeks.
The TT1 is very quiet even with old and frequently played records. It further surprises by producing a stable, solid soundstage with a respectable representation of front-to-back depth on suitably recorded albums.

The 180g pressing of Cat Stevens 'Tea For The Tillerman', further shows how the bass is tight, tuneful, fast and weighty.

Next step: Extended Synchronous Motor

TYP LSR 11/16

New Cartiridge is added (2 oct. 2014).

This is a legendary cartridge, considered one of the best MM designs ever made.
During its lifetime it appeared in somewhat different versions, the differences between them are primarily in the styli - with the SL or SLa having the tapered aluminium cantilever and the SS (top version made) having a beryllium cantilever.

 Frequency Range 5-50k Hz (AT20)
5-45k Hz (AT15)
 Channel Seperation @1kHz (db)   >30db AT15/20SLa
 >33db AT15ss
 >35db AT20ss
 Channel Seperation @10kHz (db)   >25db AT20SLa
  >30db AT20ss  
 Channel Balance @ 1kHz (db)  <0.75db
 Output Voltage (mV @ 5cm/s))   2.7 mV
 Compliance, dynamic (100Hz)  9.5 x 10-6cm/Dyne
 Stylus type   Nude Square shank Shibata 
 Cantilever     Tapered Aluminium (SLa)
 Beryllium (SS) 
 Tracking force range (g)  0.75 to 1.75 
 (1.25g nominal) 
 Tracking angle  20
 Coil DC resistance (ohm)  500 ohm
 Weight (g)  8g
 Suggested resistive Load  (ohm)  47k ohm
 Suggested capacitive load  100 - 200pf
 Replacement Stylus     ATN20SLa, ATN20ss
 ATN15SLa, ATN15ss 

The Audio Technica AT20SLa cartridge features a wide frequency response, with a smooth curve resulting in a natural and uncoloured sound, without the high frequency harshness which results from peaky response.

A major side benefit of smooth high frequency performance is decreased groove wear.

Very interisting movie about Tonearm Tracking Error made by Seb from

Open Baffle

October 2012: New project ( Open Baffle ) is started...

The joiner (Dennis) is now working on the 1,2 inch ( 30mm ) Baffle...



Looks very good, thanks Dennis!

Baffle Size: 19 x 40 inches / 48 x 100 cm

Drivers: Eminence Alpha 15A, Jordan JX92 and Audax HD13D34

Eminence Alpha 15A

  • Resonant Frequency (fs) 41Hz
  • Total Q (Qts) 1.26
  • Surface Area of Cone (Sd) 856 cm2
  • Sensitivity 97.2dB

  • Jordan JX92 Fullrange

  • Resonant Frequency (fs) 51Hz
  • Total Q (Qts) 0.56
  • Surface Area of Cone (Sd) 78.5 cm2
  • Sensitivity 85.3dB

  • Embracing a range of almost nine octaves, the JX92 offers the widest bandwidth of any single drive unit available.
    This not only provides an exceptionally smooth, high-definition, crossover-free sound quality but allows for a very diverse range of applications.

    Audax HD13D34

  • Resonant Frequency (fs) 1012Hz
  • Total Q (Qts) 1.01
  • Sensitivity 91dB

  • Companies like Spendor and Rogers have used these in studio monitors. Natural timbre strong play.
    Without ferrofluid. Solid aluminum front panel.

    Crossover: 12dB @ 200Hz Woofer, 12dB @ 400Hz Midrange and 12dB @ 8kHz Tweeter

     Crossover Circuit (under construction)

    First Crossover Measurements ( October 2012 ):

    Target Response and measured Frequency Response (Nearfield)

  • Some problems (1.6kHz, 2.5kHz and 10kHz) with the Mid-Band (JX92). That is to solve with Notchfilters.

  • Frequency Range between 1kHz and 3kHz is now (almost) ok. A Notch Filter is added to the Fullrange Driver JX92.
    The peak is reduced with 5dB.

  • Yellow Curve without Notch Filter
  • Green Curve with Notch Filter (6R8, 22u and 0m68)

  • Date: February 2013 - Crossover Simulation
  • Woofer fc: 200 Hz, Midrange fc: 200 Hz / 3700 Hz, Tweeter fc: 3700 Hz

  • Date: February 2013

     Final Crossover Circuit

    Date: May 2013 - Crossover Simulation
  • Woofer fc: 200 Hz, Midrange fc: 200 Hz / 3600 Hz, Tweeter fc: 3600 Hz
  • Impedance correction @ 200Hz and @ 13000 Hz

  • Date: May 2013

     First listening Test's

    Source: Marantz Marantz CD-63 MK II Ken Ishiwata Signature
    Amplifier: Modified SE Amplifier with EL34, 2 x 6 Watt
    Speakers: Open Baffle Project Loudspeakers
    Cables: The Reference LS-602 and DIY Silver Cables
    Room (W, D, H): 5,50mtr x 4,20mtr x 2,45mtr
    Music: Jack Johncon, Huge Masakela, Lou Reed, Diana Krall, Yellow, Sonnie Rollins, Ray Brown

    When I first saw this speaker standing in my living room - they like two of the rocks from the Stonehenge ruins.
    The first thing about my OB's that really shocks people who think they know open baffles is that they are so strong in the bottom end.
    They are concert level loud and are quite explosive at the bottom.
    Specialy Ray Brown's Bass on "Moonlight Serenade" is realy impressive.

    Next surprice is Diana Krall and Jack Johnson.
    The voices are very clear, that because the complete midrange is reproduced by one fullrange driver (Jordan JX92) over more then 4 octaves ( 450Hz - 8kHz).
    The JX92 with his aluminium cone has low distortion throughout the midrange plus a very open and detailed midrange for optimum voice reproduction. Not only do most of music's fundamental notes reside in this band but also more than 90% of their most important harmonics.

    I doubt about the tweeter, the AUDAX H13D34.
    May be i try a Ribbon Tweeter like the Fountek NeoX 2.0 Ribbon Tweeter...

    Strength of my OB:
    - deep bass
    - nearly no time delay
    - very low colouration
    - open sound
    - easy to built

    Last step: Painting...

    to be continued...

     Sigfried Linkwitz Interview - Orion and Pluto Open Baffle Loudspeakers

    Olson-Style Manifold Horn

    This Horn project is canceld!

    It is based on the Olson-Nagaoka design which was first suggested by Harry Olson in 1937.

    Drawing by H. Olson 1937

    It will be something like that...

    Using the Jordan JX-92 Fullrange driver ( because i have 2 drivers in stock ), the constuction plan has to be recalculated because the original plan is used for the Fostex FE127e.

    Jordan JX-92

    Have a look at the Frugel-Horn Site for more information about Horn-Speakers.


    Project successfully finished

    Modification: ELTAX Concept 500

    Floor standing Bass Reflex Loudspeaker

    Two loudspeakers for 140 euro...

    • System: 3 way Bass Reflex
    • Woofer: 2 x 130mm shielded
    • Tweeter: 25mm dome neodynium
    • Sensitivity ( 2.83V / 1m ): 88dB
    • Frequency range ( +/- 3dB ): 48 - 19000Hz
    • Dimensions ( HxWxD ): 900mm x 185mm x 260mm

    • Fs: 72.6 Hz
    • Re: 7.8 ohms
    • Qts: 0.70
    • Qms: 4.00
    • Qes: 0.85
    • Mms: 7.0grams
    • Vas: 7.24 liters
    • Sd: 86.6 cm2
    • Fs: 1480 Hz
    • Re: 7.26 ohms
    • Qtc: 1.47

    The first listening test is disappointing...
    • The bas range is ok for that money...
    • The midrange is spongy, unclear and blurred
    • The tweeter is to loud ( +3dB )
    Looking to the crossover network, i understond why.

    Original Network Circuit

    Original network

    3 coils and 1 capacitor for 3 drivers?
    • 1.51 mH woofer ( 6 dB )
    • 0.21 mH midrange ( 6 dB )
    • 0.53 mH and 4.7 uF tweeter ( 12 dB )
    No impedance correction circuit?

    Next step: measuring of the impedance of the loudspeaker.
    I decided to add a RC circuit to the woofer and midrange driver.

    Concept 500 Impedance Curve measured with ARTA (Limp)

    Impedance without compensationImpedance with RC-compensation

    The irregularity at 220 Hz is caused by enclosure resonances ( Enclosure height 80cm )

    Here the calculation:
    344 m/s divided by Frequency Hz = Wavelength in meters

    (344 / 220) / 2 = 0.78 meter or 78 cm

    Calculate here Enclosure Resonances

    Here the picture of the modified crossover network with Zobel circuits for bass and midrange.

    modified crossover

    Modified crossover

    The reason to use "Zobel" circuits is to let the crossover network function properly.

    The crossover network is still under construction and a attenuation circuit ( -3dB ) will be added to the tweeter.

    Look here for more explanation about "Impedance Equalization" and calculations

    Crossover frequencies
    Lowpass woofer: 750Hz ( 6dB Bessel alignment ) Inductor: 1.5mH
    Lowpass midrange: 4200Hz ( 6dB Bessel alignment ) Inductor: 0.21mH
    Highpass tweeter: 4200Hz ( 12dB Bessel alignment ) Inductor: 0.52mH, Capacitor: 4.7uF

    Impedance equalization
    • Resistor   : 4.7R 10 watts
    • Capacitor : 33uF bipolar 50VAC

    Tweeter attenuation
    • Resistor serial : 1R 5 watts
    • Resistor parallel : 15R 5 watts

    Until now i didn't measure the Frequency Response, because i was curious if it's possible to tune the network by ear...

    Acoustical Measurements of the Loudspeaker

    Frequency Response: original Crossover Network
    Port:  closed  -  open
    Frequency Response: new Crossover Network
    Port: open

    ** note the different resolutions of the Frequency Response Plots (left side: 5dB, right side: 10dB)

    The aim of the crossover optimization was to optimise with as few resources which should also fit on the existing crossover board.
    The enclosure also leads despite 2 ring stiffeners due to the small thickness of 13 mm a busy life of its own.
    But for a handful of dollars ( 10$ ) are you able to optimise this loudspeaker in the good direction

    A listening test will come soon...

    Project successfully finished

    PC Loudspeaker

    Project successfully finished

    Satellite Loudspeakers for Personal Computer

    for my son Rik

    System:Sealed Enclosure
    Alignment / Qt:0.66 ( better impulse respons )
    f-3dB:130 Hz
    Network:Highpass 6 dB @ 4000 Hz
    Bass/Midrange: NA 130 ( out-of-production )
    fs: 64.32 Hz
    Re: 5.9 ohms [dc]
    Qes: 0.34
    Qms: 2.18
    Qts: 0.30
    Mms: 5.59 grams
    Rms: 1.03 kg/s
    Cms: 0.001095 m/N
    Bl: 6.23 Tm
    ETA: 0.71%
    Sd: 78.45 cm2
    Vas: 9.7 ltr
    SPL: 91.92 dB @ 2.83V/1m
    Tweeter: SC 10 N ( Visaton )
    fs: 1700 Hz
    Re: 6.9 ohms [dc]
    Mms: 0.1 grams
    Bl: 1.3 Tm
    Sd: 5 cm2
    SPL: 90.1 dB @ 2.83V / 1m

    recommended cutoff frequency: 4 kHz/12 dB

    Because a Subwoofer is used, f-3dB @ 130 Hz is perfect...

    MDF 18mm
    4 pieces180 x 320mm
    4 pieces156 x 320mm
    4 pieces120 x 180mm

    Inside measurements:
    12cm x 18cm x 24cm=5.18ltr
    Vb = (5.18ltr - DrviverVol = 0.3ltr)=4.88 ltr

    New Network: 12dB Crossoverfrequency (acoustical: 2.5kHz, electrical: 1.7kHz)

    The network is totaly recalculated. One capacitor is not working...

    Now it's a 12db network with impedance compensation for Midwoofer and Tweeter. There are problems at 6.5 kHz and 10kHz.
    This is caused by the Tweeter...
    But i don't change this because the network components would be 4 times the money as the both drivers...

    And, the speaker is used as PC loudspeaker and not as HiFi loudspeaker.

    Calculated and optimized Frequency-Response

    The final PC monitor-loudspeaker

    JX92 Horn

    This project is in progress ( almost finished )

    My plan is to add a Tweeter to the JX92-Horn.

    Looking for a suitable Tweeter, i found the Swans TN-28.

    The absence of a mounting flange on the TN-28 allows flexible placement and diverse cabinet design. The TN-28 can be placed on top of a cabinet to reduce diffraction effects and align acoustical centers of transducers.

    The solid aluminum case enclosing the magnet system provides effective cooling.
    The special weave of the fabric results in better axial symmetry of the entire moving system.
    The tweeter has very smooth on-axis and off-axis frequency response delivering excellent acoustic power dispersion. The TN28 creates an accurate imaging source and is distinguished by exceptionally transparent and balanced sound.


    Frequency response of the Swans TN-28

    The crossover frequency will be around 3000Hz, because the JX92 response falls back a bit at thet frequency.
    So, my idea is to use a 12dB lowpass filter and a 6dB highpass filter.

    At the moment i'm busy to measrue both drivers, impedance curve and frequency response. This data i need to design the crossover network and the impedance equalization for the JX92.

    If you choose a crossover point in a range where the driver's frequency response is changing rapidly off-axis, the off-axis response will have large response anomalies which degrade the power response the listener perceives.

    Frequency response at listening position of the original construcuion without filters.
    Measured with ARTA

    20 Hz - 20 kHz   ± 12.5dB - too sad for words...

    The crossover network is calculated. It's a lowpass filter with 12dB and a highpass filter with 6dB.

    The choosen crossover frequency is 4800Hz and not 3000Hz as planned.

    This is done because:
    • the resonant frequency of the tweeter is 1700Hz, to low to cut at 3000Hz
    • the power response of the JX92 fullrange driver fits beter at 4800Hz

    Lowpass 12dB, highpass 6dB crossover filter (4800Hz) and -4 dB attenuator for tweeter.

    The rising impedance of the JX92 is compensated with a Zoble circuit (5.6ohm and 6.8uF)

    Impedance- and phase of the complete loudspeaker

    Now i will listening a lot of my CD's and LP's.
    Perhaps i have to fine-tuning the
    • crossover network...
    • or the Horn damping...
    • or the acoustical properties of my listening room...

    • perhaps all?

    Phono Project

    Project successfully finished

    The idea is to rebuild the MC676-RD Tube Phono Pre-amplifier. The Output Impedance will be ca. 52kOhms.
    Because this is var to high i will use the Tube Buffer Amplifier.

    Calculate Amplification and Output Impedance of a Grounded-Cathode-Amplifier



    Frequency Response 10Hz - 30kHz ± 0.35dB

    Simulation is done with B2 Spice A/D v4.2 Lite

    Here you can download B2 Spice A/D v4.2 Lite

    to be continued...

    Bass Pipe

    2 meters Bass Pipe ( Project successfully finished )


    Finished Pipe

    The idea is simple:
    remember an organ... Pipes, a lot of pipes. Small sized and sometimes very big ones.
    So, i took a PVC tube with 8 inches diameter and 2 meters log, mounted a 8 inch woofer and tried to get some bass.


    Nearfield measurement with second order lowpass filter ( 10mH and 120uF )

      TSP of used woofer:
    Re: 6.8 Ohm
    fs: 32Hz
    Qts: 0.33
    Vas: 98 liters
    SPL: 92dB

    To calculate the resonant-frequency of this 2 meter tube:
    fs = c / ( 4 * l )
    c = 343.2 meters ( speed of sound )
    l = length of tube in meters and 4 because is a quater-wave-pipe

    Resonant frequency of the pipe = 343.2 / ( 4 * 2 ) = 42.9 Hz


    Woofer Base

    Woofer impedance


    Impedance ( no filter and no filling )

    Impedance ( with filter and filling )


    Second Order 12dB crossover network, Butterworth alignment - crossover frequency: 145Hz, Q: 0.745

    Now these speakers imaged almost exactly as the original, and were as detailed. These speakers are failry effieienct (90db) and will not require a powerful power source. I listen to a pair with a Single Ended Tube Amlifier delievering 6 watts @ 8ohms.

    I dare someone to make me a better speaker for $95 a speaker.