MathCad Computer Models : Upgraded Versions

Last Revised 2/25/08


The MathCad worksheets, that have been available for the past few years, have now been upgraded to include several new features aimed at providing a better calculated estimate of a speaker system's in-room performance. A few small changes have been made in the main body 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.

A second section has been added to the bottom of the upgraded worksheets that accounts for separate driver and open end locations and the enclosure's position in the room. The new calculations simulate the relative positions of the driver and terminus (port or mouth) on the front or rear baffle, the influence of floor reflections, the baffle step response, and the influence of a rear wall located at a defined distance behind the enclosure.

A third section has also been added that 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 new 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 Projects. Also, any time enough design information for a speaker system of interest has been presented on the Internet, or in a magazine review, have run a simulation for comparison and the correlations have been good.

However, this should be considered a work in progress. Most of the older models have been upgraded but a few less popular ones will follow later if time permits. A recent upgrade removed the restriction that the baffle geometries could only be modeled as rectangular shapes. For example, analysis of a ML TQWT design is no longer limited to a rectangular front baffle and it can accurately be simulate with the trapezoidal baffle used in Project #2.

The biggest change in the worksheets is that they are no longer free. I watched numerous individuals use the MathCad worksheets to design, produce, and sell quarter-wave based loudspeaker systems. In the past, with the exception of one individual (Bob Brines) I had not seen a single benefit from any of these commercial offerings. This activity stopped me from releasing upgraded MathCad worksheets over the past several years. So I decided to try this approach and am offering access to some of may latest worksheets for $25/year for a DIY user's personal projects and for $250/year for each individual commercial user. Once I have received the appropriate fee, a User ID and password will be provided allowing the User to enter the Models Vault and download any of the available worksheets and documentation for a one year time period. At the end of the year, the User ID and password will be deleted and the User can decide to renew the arrangement or delete all of the worksheets they have downloaded from their computer system. I will watch the traffic to the Models Vault very carefully and hope people behave honorably. If this system does not work, then this will be the end of my distributing MathCad models. If this system works, I will continue to upgrade current models and make additional models available.


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 a program already resident on the host 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. 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.

Available Worksheets :

  1. Transmission Lines
    • Open End TL Sheet (last revised 2/09/08)
    • Closed End TL Sheet (last revised 2/09/08)
    • Offset Driver TL Sheet (last revised 2/09/08)
    • TL Sections Sheet (last revised 2/09/08)
    • ML TQWT Sheet (last revised 2/09/08)
  2. Closed and Ported Boxes
  3. Double Bass Reflex
  4. Back Loaded Horn
  5. Open Baffle and Dipole
  6. Ported Box Bipole

Worksheets Under Development :

  1. Addition of Toe-In of Speaker Relative to Rear Wall, Side Wall Reflection, and Corner Loading.


What do you get for the fee :

  1. Access to the models and documentation for a 12 month period.
  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. Please recognize, I don't have all the answers. I make every effort possible to respond to all e-mail 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. 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.


Correlation Example


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 the worksheets but not save any results. A second source of MathCad is eBay where you can buy a legal copy of an earlier version at a deep discount. This is my first choice of upgrade path. If you go this route, I would recommend getting either MathCad 2000 or 11. Avoid MathCad 12, it is full of bugs and crashes frequently. Earlier versions of MathCad (versions 6, 7, and 8) required numerous patches and are no longer supported by MathSoft. Or as a last resort, you can always order the latest version from MathSoft Inc.
  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 is locked so you cannot alter any of the input parameters.
  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 3.0 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 specific User ID and password will be e-mailed that will allow access to all of the MathCad worksheets and documentation contained within the Models Vault. This User ID and password will be active for 12 months. Then follow the path below to the Models Vault.

    -Terms and Conditions-
    -Models Vault-

    -Home Page-