MathCad Computer Models : Upgraded Versions

Last Revised 1/30/10


The MathCad worksheets, that have been available for the past few years, have now been upgraded once again to include several new features aimed at providing a better estimate of a speaker system's in-room performance. A few small changes have been made in the first section of the worksheets to improve the fiber damping correlation, allow the user to defined input power level, and automatically adjust the Thiele/Small parameters to account for the effects of additional series resistance.

The second section of the worksheets account for the physical geometry of the speaker enclosure and positioning in the room. The newest calculations simulate the relative positions of the driver and terminus (port or mouth) on the front or rear baffle, the influence of room corner reflections, the baffle step response, the angular position of the speaker relative to the corner, and provides two different methods of defining the listening position relative to the speaker system.

The third section once again assists in the sizing of a passive inductor/resistor baffle step correction circuit. The circuit values are then used to correct the calculated SPL response and show the final predicted system SPL response and impedance. These newer worksheets represent the most accurate speaker design simulations that I have been able to formulate and seem to correlate very well with measurements I have made over the past few years on some of my own design projects. Also, any time enough design information for a speaker system of interest has been presented on the Internet, or in a magazine review, I have run a simulation for comparison and the correlations have been very good.

Last November, I suddenly halted distribution of the MathCad worksheets due to continuing problems with commercial users and a general lack of support from the DIY community. Since then I have had a few discussions with long time users of the MathCad worksheets and I have been convinced to try making them available one more time with a slightly different licensing arrangement. Access to the latest worksheets can be obtained for a one time fee of $25 for a DIY user's personal projects and for $250 for each individual commercial user. The license fee is for one User only. The User may download the worksheets and then use any of the worksheets or documentation consistent with the type of license granted (DIY or Commercial) for as long as the worksheets function under future Microsoft Operating Systems. If a newer version of the worksheets is released, the license can be renewed or the User may choose to continue working with the previous version. In summary. the license fee is a one time charge to gain access and download the MathCad worksheets that are available at that point in time.

Once I have received the appropriate fee, a User ID and password will be provided allowing the User to download any of the currently available worksheets and documentation. I will watch the traffic very carefully and hope people behave honorably. If this system works and there is sufficient support, I will continue to upgrade the current models and make additional models available possibly on an annual basis. If this system does not work, then this will be the end of distributing MathCad models. Support from the DIY community is a key factor in my continuing to offer and improve the MathCad worksheets. Reading this page today means they are available now, there is no guarantee about tomorrow.


The Worksheets :

All of the worksheets have been saved in a format that is compatible with the free MathCad Explorer program or any other version of MathCad subsequent to Version 8. The calculations have been locked to prevent tampering with the mathematics and to protect my intellectual property. I have unlocked the plot regions to allow users to rescale the plots and display data in a more convenient format for the analysis being conducted.

In most cases, the input data in each file corresponds to one of the projects shown on this site. The user can edit this input data section to enter a different driver and a specific geometry of interest. With the exception of a decimal point convention and "Script" blocking in older versions of the Norton anti-virus software, I have not experienced many other problems with people downloading and using my MathCad worksheets. However, on one or two occasions a particular computer has not been able to run the MathCad models for some unknown reason. This is most likely a conflict between MathCad and some other program already resident on the user's computer. This situation is very rare.

Note 1 :

A few European countries denote a decimal point using a comma (not a period). This convention is defined in the set-up of the computer in the Windows control panel. If you live in one of these countries, and the MathCad worksheets fail to calculate when opened, please check to make sure that your computer recognizes a period as the decimal point. I have encountered this problem a few times over the past several years and it is easily solved by changing the computer set-up to recognize a period as the decimal point.

Note 2 :

Every once and a while, I get an e-mail describing problems editing some of the inputs in Parts 2 and 3 of the worksheets while using the free MathCad Explorer program. In Part 1 of the worksheet, moving the curser arrow over an input variable and left clicking the mouse opens the region allowing the user to define a new variable value. However, lower in the worksheet moving the curser arrow over an input region changes the curser arrow to a hand and the region cannot be opened using a simple left click of the mouse. The work around is to click the curser near the region to be edited, which places the red plus sign marker, and then using the arrow keys move the red plus sign into the region to be edited. The region will open and the user can then change the value of the input variable. Clicking the mouse curser arrow outside the region closes it again. This seems to be a fairly rare problem with MathCad 8 Explorer and I have no idea what causes it.

Note 3 :

Older versions of the Norton anti-virus program may shut down the MathCad application when you first open one of my worksheets. This seems to be caused by the "Script" protection feature in the Norton anti-virus program not liking something in the algorithm I have programmed in the worksheets. If you disable "Script" protection, everything will function correctly in the MathCad worksheets. I have left this feature disabled in my copy of Norton anti-virus without incident, but you should make your own decision with respect to your personal computer security requirements. This problem seems to have been fixed in Norton anti-virus 2005 and I have not had a problem since with script blocking.


MathCad Worksheets Available for Downloading :

MathCad Transmission Line Worksheet Tutorial

Thiele / Small Parameter Consistency Check Worksheets

Closed End and Ported Transmission Line Worksheets

Open End Transmission Line Worksheets

Bigger Is Better (BIB) Transmission Line Worksheet

Back Loaded Horn Worksheets

Double Mouth Back Loaded Horn Worksheets

Double Bass Reflex Worksheet

Open Baffle and Dipole Worksheets

Ported Box Bipole Worksheet


What do you get for the fee :

  1. Access to the current models and documentation.
  2. Any bugs or problems will be fixed ASAP, although I have checked each worksheet I am not perfect and occasionally something slips by me.
  3. I will try to answer questions about the worksheets, or how to model a particular geometry, promptly and to the best of my ability. Worksheet support can be gained by asking questions on my Yahoo Groups electronic mailing list, please do not e-mail me directly. Also recognize that I don't have all the answers. I will make every effort possible to respond to all questions within 24 to 48 hours.
  4. If we have a common interest, or if your project is something I am actively already working on, then I am open to collaborating if there is an equivalent mutual benefit.


What don't you get for the fee :

  1. I cannot run simulations for you, I just don't have the time to accommodate these requests.
  2. I cannot recommend or assess drivers for your projects. I can comment on drivers I have used but do not know much about the vast number of drivers available to the DIY speaker builder.
  3. I cannot write custom or special versions of the worksheets for an individual. If enough people want a specific feature, or enclosure geometry, I will look into providing a worksheet in the next revision. If you really require a custom worksheet then we need to make a private arrangement, it won't be free.
  4. I cannot design, build, and test an entire speaker system for an individual. I cannot test your driver's Thiele/Small parameters. I will present the projects I have designed and built on this site along with any preliminary driver measurements and finished system performance measurements.
  5. I will not present your work or project on this site beyond a picture in the gallery. With very rare exceptions, I would like to keep this site for just presenting my own work. If you have something significant that you would like to share, it is really not that difficult or expensive to put together your own website. I did it after reading HTML for the World Wide Web by Elizabeth Castro.


How to License the Worksheets :

  1. There are three sources for the MathCad computer program on the Internet. First there is the free version of MathCad Explorer 8 that allows you to run and print the worksheets but not save any results. Download the zipped file to your desktop, run the executable file to install, and use all of the default settings. A second source of MathCad is eBay where you can sometimes buy a legal copy of an earlier version at a discount. If you go this route, I would recommend getting either MathCad 2000 or 11. Earlier versions of MathCad were unstable requiring numerous patches which are no longer supported by Parametric Technology Corporation, the company who bought MathSoft. And third, you can always order the latest version from Parametric Technology Corporation. Whichever option you select to pursue, please recognize that MathCad 8 is the oldest version that will run the worksheets.
  2. Download the sample problem and run it on the computer you plan to use for your speaker design projects. The sample problem is intended to check that the worksheets run, give you a preview of the worksheet features, and provide an idea of the time and effort it takes to run a typical simulation. The worksheet's driver definition is locked so you cannot alter any of those input parameters, but you can alter with the enclosure and room definitions.
  3. Download the worksheet tutorial to review the typical worksheet's inputs and outputs and learn about some of the features and techniques used to model a speaker system in MathCad.
  4. Review the two competing programs for modeling quarter wavelength loudspeaker designs. I consider AJ Horn and TLwrx Version 3.1 to be the two other options for performing these types of calculations.
  5. After reviewing items 1 through 4 above, please review the Terms and Conditions then return to this page.
  6. Finally, to purchase a one year license send the appropriate fee ($25 for a DIYer's single user license or $250 for each single commercial user's license) in US dollars, along with a working e-mail address, using PayPal (MJKing57@aol.com) or by mailing a check to :

    Martin J. King
    40 Dorsman Drive
    Clifton Park, NY 12065
    USA

  7. Once the fee has been received and cleared, a User ID and password will be e-mailed that will allow access to all of the MathCad worksheets and documentation contained within the Back Room. This User ID and password will be remain active until the next revision of the worksheets is released. Then follow the path below to the Back Room.

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    -Back Room-

    -Home Page-