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Thread: Has Anyone Ever Seen These?

  1. #1
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    Has Anyone Ever Seen These?

    They came with a bunch of JBL stuff that I bought. I've never seen them before.
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  2. #2
    Senior Member 1audiohack's Avatar
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    Nope but they’re hella cool!!

    Barry.
    If we knew what the hell we were doing, we wouldn't call it research would we.

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    Senior Member martin_wu99's Avatar
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    Cool!
    46 lover

  4. #4
    Senior Member RMC's Avatar
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    Hi Robert,

    Real cool. Never seen them either. Collector's items.

    I guess these were given to JBL dealers or sound contractors to help them in designing pro sound systems (Horn Performance Data), or consumer vented boxes for the "Loudspeaker System Calculator" based on driver model numbers (124A, 136A, etc).

    These are probably from the seventies. The copyright on the Loudspeaker Calculator seems like 1975. Plus on the Horn Performance one the 2205 driver mentioned was launched in 1971 or so as seen in an old JBL catalog.

    The Loudspeaker Calculator looks like a first "helping hand tool" contribution for proper vented box tuning following the work of Thiele and Small published in the JAES in 1971-2-3. And it already has Metric data calculations on it!

    The format of the latter reminds me of an old (1973) two-sided metric converter I have and still use once in a while.

    Later, JBL made a different and very useful tool to help folks tune their vented boxes (can't remember the year of this one but most probably 80's). I found this large-size one at the time in a European Sound Reinforcement magazine. Its made after a similar, but smaller-size, chart published by Small in his papers.

    The beauty of this chart is that its NOT limited to JBL drivers nor to specific models, as with the calculator mentioned above. It will give required port dimensions, and other such options, based on Vb and Fb desired. Naturally, one can also see what a given set of port dimensions/Vb will tune the box to what frequency. Used it many times in the old days before software programs were widely available to consumers.

    I'll post pictures of the Metric converter and JBL box tuning chart shortly. Regards,

    Richard

  5. #5
    Senior Member RMC's Avatar
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    Hi Robert,

    As indicated earlier, you will find pictures of the Metric converter and more importantly the JBL tuning chart mentioned, plus bonus charts from Mc Cauley Sound (2 similar ones), the latter giving more detailed explanations but a smaller chart size to work with...

    Metric converter: Find the unit to convert (origin/destination) and for one such unit you can read the equivalent right there, plus by pulling slowly the cardboard inside the calculator you get other results for two to ten such units. Today its more or less "obsolete" but a while ago it was real nice to have.

    As for the JBL and Mc Cauley Sound tuning charts, one called "Alignment Graph" ?? by Mc Cauley, there's no indication these being copyrighted stuff, and as mentioned previously they are derived from Small's work. Both Small & Eargle's such charts are much smaller size with both Metric/Imperial measures, which could make things a bit more confusing at times.

    JBL's large size one is Metric only since it was published in a European Sound Reinforcement Magazine. However, for those who prefer "British Imperial" units the Mc Cauley ones fit the bill. The two Mc Cauley's are pretty much the same but for a few cosmetic changes: title, driver list, example explanations....

    If someone intends to play with these charts, for fun/nostalgia, checking a box Fb knowing vent dimensions and Vb, for lack of design software or archiving purposes for e.g., and would like to see a better or clearer copy, let me know I may scan them when I have time. The dotted line with scissors outside the JBL chart clearly shows it was meant to be cutout, probably copied, and used on box tunings...

    So you have vent diameter in mm, vent surface area and vent length, in addition to Vb and Fb. Each curved line you meet when drawing an horizontal line in the chart corresponds to a vent diameter (available or not in stores) and the further you go to the right the larger the vent diameter will be and the duct also gets longer for constant Fb. My suggestion is to just draw the horizontal line right across the whole chart and then see what your feasible options are in terms of port dia. vs length. Don't forget JBL suggested vent dia. should be at least one-third driver size (e.g. 5" vent for 15" driver), but more recent high-power drivers now requiring even more vent size. The new rule is to use the largest vent that practically fits in the cabinet.

    The important thing with the chart is the line going from Vb, Fb up to the vertical "Lv" line MUST be straight, as well as the one starting from vertical "Lv" and going horizontally inside the chart itself. For true readings the latter must be CORRECTLY horizontal as in the dotted line example shown. Then look or trace straight down the chart to see the corresponding vent length (Lv). For diameter results half-way between two curved lines, for example, you may want to add two adjacent diameters then divide by two to get a middle number (e.g. 102 + 127 mm = 229 divided by 2 = 115 mm), if such vent diameter exists in stores/cardboard or go to the nearest dia. one, preferably on the larger side, that's suitable.

    Recently in another thread, a fellow member had difficulty understanding or making sense of software determined Dv/Lv. I hope getting familiar with this chart from the "old days" will shed some light and help him with the relations between vent dimensions and box size/tuning frequency. Initially, it may look more intimidating than it really is in practice.

    Also, sometimes a commercial box may mention a Vb and not much more useful box details. Or someone wants to clone a box, having Vb, but doesn't know Fb. By simply measuring carefully the vent dimensions of the original box and converting this into a vent surface area (shown on the chart), "reverse engineering" using this chart can help figuring pretty closely what the model boxe's tuning frequency is.

    The example given on the chart is for a 115 liter box, tuned at 35 hz, using a 102 mm dia. vent leading to a 101 mm vent length. The somewhat overly complicated explanation at the top of the JBL chart mentions it is to find Fb. However, having seen the original chart in Small's papers (Vented-box... Part 2, JAES, p. 330; Vented-box... Part 3, JAES, p. 335) and remakes of the chart in JBL's John Eargle Handbooks (Loudspeaker p. 68; Sound system Design p. 109) I can certify the chart's purpose IS, first and foremost, to tune an enclosure (i.e. port dimensioning) as indicated by Small and Eargle. However, with "reverse engineering" it DOES allow to find Fb, knowing box volume and vent dimensions, as explained above.

    BTW Small adds the following important note about vent/chart: "End corrections for one open end and one flanged end are included in the construction of the chart. For intermediate vent areas the chart may be interpolated graphically." (Part 2, p. 330) Like my half-way between two chart diameters mentioned above. Regards,

    Richard

    P.S. I'm posting pictures of the above soon in separate posts since sometimes many in a single post don't turn out to be in the order planned. I guess I must be doing something wrong...

  6. #6
    Senior Member RMC's Avatar
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    Metric converter pictures of both sides


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    JBL box tuning chart previously mentioned, in two copies since one seems better than the other re text above the chart. Will be back later with the Mc Cauley charts.



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    Senior Member RMC's Avatar
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    The Mc Cauley Sound first box tuning chart. One vertically oriented, the other one side ways.



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  9. #9
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    The Mc Cauley Sound SECOND box tuning chart. One vertically oriented, the other one side ways.



    Attachment 82481Attachment 82482

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