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Welcome to the weblife of:   J.G. (JACK) BOUSKA   Updated:   31 July 2007


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These days, it's virtually mandatory to have your own webpage ..... All my life I have been making waves. When I'm not rocking the boat, or enjoying time with my family, I lead the dual lives of Geophysicist, and Audiophile.

You can expect the contents of this site to reflect my passion in both areas. My personal bias towards function over form will most certainly be reflected in this homepage, hence my use of this space as an electronic repository to archive some of my Geophysical publications, and a record of various audio/electronics projects, and of course my speaker building projects.

Apologies for the year delay in updating my web page, and any frustration caused by the static content. If you are interested in reading more regarding the “Impact Stack” loudspeaker system, I have posted a comprehensive description of the design philosophy, construction techniques, and performance measurements of the system on the Lansing Heritage website:

  • DIY Axially symmetric oblate spheroid CD waveguides, in solid Oak.

  • Factors Affecting Sonic Quality of Mid & HF Horns & Waveguides.

  • Some images of my recent waveguide construction on the "Horn system pictures" thread.



  • Contents of the webpage, with quick jump links: (or just scroll down)


    Archive of previously published material relating to Seismic acquisition and processing:


    Archive of my audio related articles, previously published in the LLDIYHiFi Newsletter:


    Four keynote references which provide some background information related to my design philosopy:

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    Some brief information on my current Audio system:

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    The room as it was in Muscat Oman

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    The room as it is presently in Calgary Alberta

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    The room as it is presently in Calgary Alberta



    J.Bouska audio system configuration philosophy.

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      The design criteria for this system are intended to mimic studio monitor requirements:
    • 1) Wide bandwidth (starting below 10hz extending above 20khz)
    • 2) Realisticly wide dynamic range (at least 125db SPL peaks, undistorted)
    • 3) Flat bandwidth with smooth anechoic on axis response (max rate of change < 3db between 1/2 octave bands)
    • 4) Flat bandwidth with even distribution of full field power response at listening location (Smooth white / pink noise spectrum)
    • 5) Low distortion (Harmonic and IM < 0.1% midband)
    • 6) Less than 1 db power compression, all amplitudes up to 120db SPL
    • 7) Stable stereo imaging (via controlled acoustic dispersion and absence of early reflections)
    • 8) Natural sounding speech and music (freedom from any identifiable timber or tonality.)
      The ETF and SpeakerWorks software packages provide valuable tools to verify my efforts in approaching the above design goals.
      (click to visit the ETF website:www.etfacoustic.com)
      (click to visit the SpeakerWorks website: www.audua.com)


    System performance verification via acoustic measurements:

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    How closely does the final system match my design specifications? Quite closely in many respects. The ultra wide (11 octave) response means that the system can retrieve all the deep bass that is encoded on modern digital media.

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    The supurb impulse response is reflected in very respectable phase response.

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    The rapid energy decay, and smooth high frequency response (especially for a horn loaded compression driver) seen here in the remarkable waterfall plot, imply very little energy storage, which translates into high resolution capability, even at high volume levels.

    Again, you can click here to view the most recent set of measurements of my audio system. Tests include: impulse response, frequency, phase, waterfall and pink noise analysis.

    The electronic equipment used in my audio system:

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    • Digital source: Denon CD (used as a transport, with digital feed into pair of 2496 Xovers)
    • Phono: Linn LP12, Ittok, Asak, Valhalla
    • Preamp: Meridian 101, used for phono pre-preamp and RIAA
    • Speaker crossover: pair of 5 way Digital DSP, Behringer DCX2496 li> five way Volume control: passive ballanced ganged pots, between the Xover and amplifiers
    • Amplifiers: Four Tripath TA104 eval boards (eight channels), eight channels of LM3875 amplifiers, and one TA2021 eval board.
    • Speaker cable: 6 gauge litz wound copper


    The transducers used in my Six-Way-Digital-Active audio system:

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    • (To see a page ONE of the JBL-1401nd specifications, click here.)
    • Upper Woofer: Four 14" JBL 1401nd direct radiators (96db/watt sensitivity each. 300+ watts, displacement limited, 1200w peak power handling) each mounted in 23L sealed cabinets. Band limited 60hz - 250Hz. Driven by 750 watt(rms/4 ohm) Tripath TA104a amplifiers, crossed over at 80Hz 6db/octave, and 320Hz 6db/octave Note: these are high-sensitivity, ultra low distortion (1st and 2nd harmonic distortion <0.3%) drivers that can move prodigious amounts of air! (The 4 drivers are capable of >130db continuous output SPL in this system) (click to visit the Jbl heritage website:www.audioheritage.org)


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    • (To see a page ONE of the JBL-2269h specifications, click here.) (click for additional specifications at the Jbl heritage website)
    • Low Frequency Driver: Pair JBL 2269H, 460 mm (18 in) dia., 100 mm (4 in) Dual Coil
      Dual Gap neodymium Differential Drive® VGC™ direct radiator driver
      Woofer is capable of a peak-to-peak maximum excursion of 89 mm (3.5").
      Transducer Power Rating : 2000 W (8000 W peak), 2 hrs
      Long-Term System Power Rating : 1200 W (4800 W peak), 100 hrs.
      Maximum SPL (1m) : 25 Hz - 200 Hz: 129 dB-SPL cont avg (135 dB peak, greater than 140db max SPL per pair)
      System Sensitivity : 25 Hz - 200 Hz: 96 dB-SPL, 1W (2.83V) @ 1m
      loaded in two 4Meter long, tapered transmission line enclosures, each driven by 1250 watt (rms/8 ohm) bridged Tripath TA104a amplifiers, crossed over at 80 hz 6db/octave.

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    The above amplifier complement can deliver over Eight kilowatts of continuous power output, and drives a speaker system with an average mid band sensitivity of 105db / watt, this is a combination that can comfortably exceed the 125db peak requirement to aproximate real life dynamic range reproduction.
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    In the current incarnation, the compression driver tweeter and 10" midranges are aligned with a flat front, but staggered voice coils. The digital Xover is used to delay the midrange signal so that the time of flight for first arrival of acoustic impulse is identical at the listening position for the three drivers, thus achieving a good phase response.


    Dimensions and layout of the listening room:

    • 8ft high
    • 14 feet wide
    • 18.5 feet deep
    • Total volume of listening room: 2083 cu.ft.
    • Speakers 9 feet apart, aprox 11 feet from listener to each speaker.
    • Room has untreated walls, and an RT60 of aprox 0.4 sec wideband
    <... 14 feet wide ....>
    |---------------------| ^
    |W    L<-9ft->R      W| .
    |     \         /     | .
    |      \       /      | .
    |  11ft \     / 11ft  | .
    |        \   /        |18.6feet
    |         \X/         | long
    |                     | .
    |                     | .
    |                     | .
    |                     | .
    | Ceiling = 8ft high  | .
    |---------------------| v
    
    Speakers at position marked L and R, with the woofers 
    marked with W, the listening position is marked with X
    
    
    Acoustic regions are denoted by the following definitions:
    
      |Region X    | Region A   |  Region B  |  Region C   |
      |            |dominated by|dominated by|dominated by |
      |            |normal modes|diffraction |  specular   |
      |            |            |   and      | reflection  |
      |            |            | diffusion  |ray acoustics|
      +------------+------------+------------+-------------+
    0 hz         565/L          F            4F
                 30hz         156hz        624hz
    
    where F = 11250 * sqrt(Rt60/Vol) 
    
    X to A = 565/L = 565/18.5 = 30hz
    F = 11250 * sqrt( 0.4sec / 2083cuft) = 156hz
    
    Note:to view ascii art correctly, use font = Courier (regular, size 10)


    Comments:

    Although this is not a large listening room, it does have very good low frequency modal support, and relative freedom from bass boom or overhang. (apart from a 30Hz resonance) The position of the speakers and listening position allow for natural suppression of side wall reflections, and the rear wall is approximately 8 feet behind the listener, allowing the Hass fusion effect to take place. The room walls and cieling are highly reflective, however the floor has wall to wall carpet, with thick underlay, which provides adequate mid and high frequency damping.


    Most recent improvements:

    • - The last three years have seen major changes in the system:
    • 2003: All of the electroncs were replaced, with analogue filters and amplifiers replaced by digital equipment
    • 2004: I moved house, and aquired a very good listening room, full masonary (cement walls, floor, and ceiling!). As a bonus, the dimensions provide good modal support down to 30Hz, with no overlapping modes.
    • 2005: The midrange and tweeter cabinets and drivers were augmented, with a full rebuild of the speaker cabinets, taking advangate pro-audio quality drivers from JBL, and innovative ideas in loudspeaker system design and cabinet construction.
    • 2005: Added Oblate Spheroid Waveguide horns to the Tad 2002 and JBL 2441 compression drivers

    • -Starting at the input working towards the output :
    • 2003:
    • -Obtained a new CD unit from D.Benjamin, a Dennon DCD-1520, which I used as a transport.
    • -Revived the dead Valhalla board in my Linn LP12, (with Asak & Ittok), I now have vinyl running again after 5 years going without. The Linn motor has a 60hz spindle on it, so I could not use it straight from the mains, had to fix my Valhalla to get it running again. I am temporarily using an old meridian 101 as the pre-preamp and RIAA gain stage.
    • -Installed a Behringer Ultradrive DCX2496 to act as DAC, Preamp, Active digital Xover, and response tailoring all in one! A very useful, and good sounding unit indeed!
    • -The DCX has three inputs, I am using one as an SPDIF (digital) input direct from the digital out of the CD player. I am using the other two as 24bit 96khz A/D converters for the turntable input. Switching between inputs is from the front panel of the DCX and very convenient. Digital input straight from the CD to the DCX avoids an unnecessary D/A - A/D step between the CD and xover.
    • -the flexibility, quality, and price performance of the DCX is remarkably good.
    • -Volume control is accomplished with a ganged potentiometer (12 wafers), allowing me to run the DCX with digital in, at full dynamic range for the Sharc DSP and output DAC's, then I run each of the six DCX balanced outputs into a balanced stereo pot, which acts as a phase splitter, allowing me to run the subsequent power amplifiers in bridged mode (balanced line feed all the way to the speaker load)
    • -Placing the volume control on the output of the DCX achieves the best of both worlds: maximizing the dynamic range of the signal in the digital domain, and putting the volume control just ahead of the analogue input to the power amps, which yields the best S/N performance. When a volume control was used on the input to the DCX (which was only viable with analogue inputs), it yielded noticeably poorer sound quality at low volume levels. (less bits being used inside the DCX)
    • -I also managed to get my giant TA104 Tripath amplifier rig running (flawlessly hum free now), as well installing a smaller TA2021B Tripath to drive the tweeters.
    • -The amp-speaker configuration is as follows:
    • -Bass: Two stereo TA104 boards, bridged, driving a pair of 18" Altecs, peak output aprox 1250 watts per channel, Bandlimited 10hz to 110hz. (6db/oct)
    • -Mid: Two stereo TA104 boards, bridged, driving four 10" JBL, peak output aprox 1250 watts per channel Bandlimited 110hz to 1.1khz. (6db and 24db/oct)
    • -Treble: One TA2021B, (internally bridged), driving a pair of TAD 2002 compression drivers on custom horns, sensitivity over 110db/watt, peak output aprox 15 watts per channel, Bandlimited above 1.1khz (24db/octave)
    • -The above amplifier rack could produce as much as 5 KW output power, however for the purpose of dynamic range, I am more interested in peak voltage swing, rather than high power output.

    • 2004: venue change to new house with 8' x 14' x 18.5' listening room

    • 2005
    • - full rebuild of speaker cabinets, adding pair 2"exit JBL-2441 compression drivers as lower midranges, and four 14" JBL-1401ND direct radiators as upper bass drivers. System is now five way, as follows
    • - Lower Bass: pair 18" Altec 3182 drivers in 4m transmission line cabinet.
    • - Upper Bass: four 14" JBL-1401ND drivers in 23L sealed cabinets.
    • - Midrange: four 10" JBL 2123 drivers in 7L sealed cabinets.
    • - Lower Treble: pair 2" exit JBL 2441 Alnico compression drivers
    • - Upper Treble: pair 1" exit TAD-2002 Alnico compression drivers
    • - added second Behringer DCX-2496 for five way system capability
    • - rewired volume control using better potentiometers, and adding extra wafers for five way system capability

    • 2005
    • - Purchaced a lathe, and turned four Oblate Spheroid waveguide horns (using Earl Geddes formula).
    • - Waveguides are true constant directivity (CD) types, with coverage angles of +/- 40 degrees over the full bandwidth of each device
    • - The four horns were hand turned by me on a lathe from a solid block of French Oak
    • 20010
    • - Purchaced a JBL VT4880A Vertec speaker
    • - Removed 2269h drivers, and installed into the 4m transmissionline cabinets
    • - Installed the Altec 3182 drivers in the Vertec cabinets
    • - configured the loudspeaker system to use six-way active digital crossover
    • - configured the crossover to be 100% first order (6dB/octave) for minimum phase and optimum impulse response


    Future work planned:

    • - Ceiling absorbers, Helmholtz resonator for additional damping of 30hz and 60hz room modes.
    • - Digital speaker and room correction filters implemented using ADSP-21061 SHARC EZ-Kit lite boards.
      Why should I let 20 years of Geophysical digital signal processing expertise go to waste, when I could be codeing up Weiner match filters to achieve the exact response I want in the digital domain.


    Some brief images related to past incarnations of my Audio system:

    (To see a description of the components in this picture, and other listening rooms, etc, click image.)



    Join the club

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    Page owner: Jack Bouska, email (please delete the xyz in bpxyz -> bp before sending e-mail): bouskajg@bpxyz.com