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Thread: ALtec Model 19-XO upgrade discussion

  1. #136
    Senior Member DavidF's Avatar
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    Quote Originally Posted by Zilch View Post
    " ...
    Note: M19 box is too big for its driver.... "
    Por favor, please expand. Thought that the M19 box ('bout 9.4 ft3 I think) was still a little shy on volume for lowest bass extension and flat(ter)bass. Don't know that, just my thinking based upon unverified TS specs. A smaller box was used in the 846 but tuned way differently. May try to build some boxes some day and the difference between 6-7.0 and 9.4 ft3 is significant in my environment.

    David F
    David F
    San Jose

  2. #137
    RIP 2011 Zilch's Avatar
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    Earlier in this thread:

    http://audioheritage.org/vbulletin/s...472#post138472

    Read on to the next page.

    416B/C parameters are in the box modeling databases. It's A/Z that are not published anywhere, so for those, I use some measured ones from the Altec Forum.

    Doing that, 846 et al. is too small for its woofer, and M19 is too large for its, subject to verification, of course. The tunings are also not optimum. Recalc before building anything, tho. I just click buttons here....

  3. #138
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    Quote Originally Posted by Zilch View Post
    Its function is described in the M19 crossover sims I posted. It establishes the attenuation at the very high end, i.e., the starting point for the contour rolloff of the mids. What I never found out is why it was derved from the LF path....
    Any thoughts on adjusting the acoustic phase alignment between the drivers?
    I assume the Altec engineers had a definitive reason for the component placement.

    Gents,
    A newby here; to the Lansing Heritage Forum.

    I have been lurking for some time with much interest for the not so simple task of passive crossover design, simulation, electrical and acoustic testing. I love the accomplishes of Zilch the “Curve Junkie” and others on this Forum.
    IMHO, obsession is everything, therefore, if a little is good and a lot is better then way too much is just about right!!!

    Excuse my verboseness, while I ramble a bit.
    If you want to skip my introductory gibberish skip to;
    Inductor - World's Worst Passive Component?

    I am experienced in analog circuit design and simulation with an intense passion and interest for music reproduction. More recently I have added high-definition video sound reproduction (Blu-ray, PCM, DTS-HDMA, Dolby HD True Audio) to the task for my sound system.

    My technical background is in Electronics Engineering with 40 years of R&D with experimental systems and data acquisition experience. However, I hobby with passion in many technologies and crafts.
    I am by no means an expert on crossover design and I have great respect and appreciation for those that have an in-depth understanding of the numerous element of this technology.
    I have avoided it until now. One of the speaker system characteristics I would like to explore more is the issue of coherent phase relationship (phase coherent, phase aligned, transient accurate) between the driver & crossover and how that effects speaker performance. Without a doubt, the acoustic output/performance of the driver is the most difficult to accurately measure, heaven knows I’ve tried.

    30 years ago, I fabricated a pair of walnut veneered, custom A7X-VOTT (511B, 802-8G & 416-8B in an 828 cabinets with the LF horn flipped, reflex port at the bottom & the 511B horn inside the top part of the cabinet) for my listening pleasure.

    The drivers are bi-amp’ed with Crown D-75 & D-150A-II. The active crossover is a custom Salley-Key 500Hz-18dB/octave HP with a derived LP (6dB/octave). Yep, I’m aware of the derived crossover foibles (+4dB LP peak at xover point and LP 6dB/octave slope issues). IMHO, given, all the optimization variables surrounding sound reproduction the issues of a derived LP filter isn’t that big of a negative.
    As with most owners of large speakers (200-lbs each), they were placed on the floor in the room corners. Several years ago, I hung them in the ceiling corners (reflex port & woofer on top) and the performance of the bass was enhanced substantially.

    Oh yeah, my interest in passive crossovers:
    So with all the HD video with true hi-fi sound tracks, I have taken up the challenge of building some better surround sound speakers.
    I used a Yamaha DSP-1 and upgraded to the DSP-3000 for 2-channel surround sound effect for many years and have since moved on to a pre-amp processor that can better handle the music and AV 7-channel (I don’t need a sub-woofer) program material with surround sound effects. I was using some small Klipch surround sound speakers (6.5" base driver) and I have come to appreciate more bass in the AV surround sound low frequency effects (LFE). I am also hoping to enhance the imaging between the VOTT and the side surround sound speakers. If I’m successful I will make a pair of center channel speakers driven in mono-mode.

    For the SS side speakers, I’m attempting to clone some Altec Model 14 with a M931-1 horns, GPA 902-8A and GPA Model 3127. I have some 1.5-1.75 cu-ft base-reflex enclosures that I will rework to install the components. I’m assuming these drivers better match the VOTT sound field and will enhance surround sound imaging.

    I have spent some time evaluating and running sims of the various crossover topologies to include the Model 19. All I can say is, it is easy to make an electrically ideal crossover (Bessel, Linkwitz-Riley, etc. alignment) however the drivers are not perfectly stable (impedance, etc.) nor are they an acoustically ideal transducers (as I read in one article – ‘electrically summed is not the same as acoustically summed’) therefore I anticipate the ideal text-book crossover will fail the primary task every time. That is, getting the most out of the drivers installed in the enclosure. In my sims I include a summation node for the HP & LP outputs and the electrically summed node is anything but flat for the Altec Model 19 xover.
    I can only anticipate Altec is aligning the phase of the drivers to produce an acoustically optimal system response? What else is there?

    With respect to passive crossover components I have made a couple of measurement observations, I would like to share with the Forum.

    I’ll start with a proposition: would you want a power amp with a dampening factor of < 20 and/or the THD > .5%? No, of course not!! Well, if the low-pass series inductor is not optimal the woofer will end up being driven by a low dampening factor and high distortion level. The HP crossover doesn’t have the dampening factor problem however the distortion can be excessive. So if I’m going to live with a passive crossover, what is the optimal inductor to minimize the inductor’s possible negative characteristics?

    Inductor - World's Worst Passive Component?
    In the article “Design of Passive Crossovers” by Rod Elleiot (http://sound.westhost.com/lr-passive.htm) he wrote the inductor is the “World's Worst Passive Component”.

    Given my observation there are two inductor characteristics that I want to minimize. Series DCR and inductor distortion caused by the core material. Even a small series DCR kills the dampening factor of a great amp and an inductor with a ferrite core will increase the distortion level to the woofer. These points are discussed in many articles however I have yet to see it quantified and would want it here from others that have tested crossover distortion. The dampening factor is the easy one to calculate but until now I was not aware of the distortion levels caused by the inductor cores. The dilemma, air core inductors are large, expensive, have the lowest distortion but the highest DCR while the ferrite/iron core inductors are less expensive, have the lowest DCR and the highest distortion.

    Dampening Factor:
    The low frequency (< 500Hz) dampening factor to the woofer is easy to calculate. For 20 ft of #14AWG speaker wire the DCR is .1 ohms and an Erse 2mH @ #14 AWG air core inductor has a DCR of .31 ohms. Therefore, the system dampening factor for the woofer with a nominal 8-ohm impedance will be < 19.5. If I desire a dampening factor of 40-50 the DCR budget for the combined speaker wire and crossover inductor is < .20 ohms. Given that 20 ft of 14 AWG speaker wire would limit the dampening factor to 80 and I desire to keep the dampening factor > 40 the crossover inductor is the dominate factor. To show that not all air-core inductors are created equal, the Jantzen 2.2mH @ 14 AWG Copper Foil Inductor has a DCR of .42 ohms. With the foil inductor the dampening factor would be < 16. The foil inductor’s larger DCR indicates the Jantzen #14 AWG foil design is not an optimal inductor without even discussing whether the foil design is useful at audio frequencies, since the additional DCR would indicate a greater wire length to develop the inductance value; (RE: DCR for #14 AWG non-foil inductor design). DCR is defined by the inductors wire gage and length. To optimize the inductance (minimize the wire length) the inductor would want to be fabricated by the dimensions of a Brooks coil. A Brooks coil of 2.2 mH @ 14 AWG inductor would have a DCR of .26 ohms. The link below describes the principles of a Brooks coil, “An introduction to the air cored coil” http://info.ee.surrey.ac.uk/Workshop/advice/coils/air_coils.html. With #12 AWG magnet wire, (something I have yet to find readily available or in the Parts Express catalog, Solen has a 2.2 mH #12 AWG @ .24 ohms for $47 USD each) the Brooks coil designed 2.2 mH inductor should have a DCR of .18 ohms. The woofer dampening factor would now be on the order of 28. Increasing the speaker wire to #10 AWG, a reduction in wire DCR to .047 ohms, I can get the dampening factor above 35. This is where bi-amping shines, since the passive crossover DCR dominates the reduction in dampening factor and a bi-amped system would have a dampening factor of 170 with #10 AWG and an optimized passive crossover speaker system struggles to get to 40.

    Inductor Distortion, P-Core :
    The Jantzen P-Core inductors (I purchased several values to use in my crossovers) can substantially reduce the series DCR however the distortion created by the core material is not a desirable tradeoff, IMHO (I returned the P-Core - I wouldn’t use then after the THD discovery). To test the inductor distortion levels I did some simple comparative tests using a low-distortion Tek Sig-Gen (.002%) and a couple of Tek THD analyzers to measure inductor-induced distortion. My test circuit is a Crown D-75 driving the series inductor (DUT) 6dB/octave LP filter with a 10-ohm load. I used one analyzer to measure the amp THD and another to measure the THD across the 10 ohm load resistor. While my measurements are a single data point I anticipate most inductor core materials will perform with similar distortion levels as the P-Cores. I assume core material hysteresis is the culprit. The DUT is a 1.1 mH no-name air-core and a 1.0 mH Jantzen P-Core @ #15 AWG with a DCR of .09 ohms. The THD across the resistor measures a THD of .015% at –3dBV with air-core and with the Jantzen P-Core I measured a THD of .23% at –3dBV. Even at the lower less reactive frequencies the P-Core indictor had distortion levels of 5-10 times greater than the air-core inductor.

    I also tested the inductors in an 18 dB/octave HP circuit configuration and the shunting P-Core inductor measures THD levels 2 times @ -3dBV and 5-6 times @ -10 dBV (@ 500Hz the THD was .93%) over the air core inductor.

    My thoughts:
    #14 AWG is not sufficient to maintain an adequate woofer dampening factor (especially if the speaker wire is of any length (I have speaker wires more then 40 ft) and the P-Core inductor adds significant distortion around the crossover point. If there is P-Core in the HP & LP filters then both drivers will be inducing distortion around the crossover point.

    Arguments:
    The difference between a dampening factor of 16 and 35 not audible in the LP filter and inductor induced THD levels of .25-.9% around the crossover point is lost in the overall speaker/room acoustics distortion levels?

    Subjectively:
    If I can measure it and the minimize artifact by simple selection of a specific component parameter then it is a worthwhile pursuit. Hence, I just purchased 900 ft of #12 AWG magnet wire and I will wind my own, Brooks coil design, air-core inductors; wish me well in this endeavor. I will report back on the results of the fabricated inductors.

    I would like to hear from others that have made similar observations and/or measured other inductor cores with more favorable measurements supporting ferrite core inductors.

  4. #139
    RIP 2011 Zilch's Avatar
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    Reworked and presently under evaluation:



    Sims here:

    http://audioheritage.org/vbulletin/s...971#post197971

  5. #140
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by Zilch View Post
    Reworked and presently under evaluation:
    How did you fit a pair of Model 19s in your "listening area"?

    Are you listening to actual Altec built cabinets or some amalgamation of bits?


    Widget

  6. #141
    RIP 2011 Zilch's Avatar
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    Quote Originally Posted by Mr. Widget View Post
    Are you listening to actual Altec built cabinets or some amalgamation of bits?
    Call me "Mr. Eclectic" this week....

  7. #142
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    Quote Originally Posted by Zilch View Post
    Reworked and presently under evaluation:



    Sims here:

    http://audioheritage.org/vbulletin/s...971#post197971
    Zilch, and conclusions/observations on this?

    fcc

  8. #143
    RIP 2011 Zilch's Avatar
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    None from me directly.

    Skywave-rider built it, and posted results in the 9844-8B thread....

  9. #144
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    Quote Originally Posted by Zilch View Post
    None from me directly.

    Skywave-rider built it, and posted results in the 9844-8B thread....
    Thanks Zilch, you just tied all these threads (and the econowave) together for me.

    fcc

  10. #145
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    a new set of model 19 crossovers on ebay

    for anyone interested i just seen a new set of model 19 crossovers on ebay .ebay.com/itm/Altec-n1201-Model-19-crossovers-pair-/290638620636?pt=Speakers_Subwoofers&hash=item43ab6 967dc

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