Paul C
Super Member
Boxplot How To Guide
You may download Boxplot here:
http://www.pispeakers.com/BoxPlot_Install.exe
(This download is courtesy of www.pispeakers.com who make some really hip speakers, both built and kits.)
To begin a project:
Open Boxplot, wait for the "gripe box" and then maximize the generic plot in the Boxplot window.
Immediately Save As, and name your project. Since I get most of my woofers from Parts Express, I usually save as using the Parts Express number as the file name. Or I may use Delta12, Gamma15, etc.
Next, enter woofer parameters. Click the red/yellow woofer button in the toolbar. This opens the Speaker Parameters dialog box.
I like to give more info in the Speaker Model box, the Mfg and model. "Eminence Delta 15"
Simply fill in the blanks. Do not fill in Qts. When you fill in Qms and Qes it will calculate Qts.
Occasionally you will have T/S parameters given in metric. Check in the Units section Metric.
NOTE that Xmax, in metric, is CENTIMETERS, not MM's as is usually given. So, move your decimal accordingly. 4.3 mm's is entered as .43 cm. THIS IS IMPORTANT for proper graphing of the power limits.
Also, if Vas is given in liters, check Metric. You can always check English afterwards, and those Metric parameters will be converted to English.
Box Parameters
Access Box Parameters by clicking the black/white speaker box button just to the right of the red/yellow speaker parameters button.
First, in Box Type chose Closed or Vented.
Select the number of drivers in Speaker Config.. Normally it should be 1, but you may configure for 2 or more woofers.
EQ Type. This is usually set to None, but you may use a 1st or 2nd order high pass (subsonic) filter. If you don't know what this is, set None.
Now, back to the Box Type section. If you have chosen Vented, press the Align button. This will provide the flattest, optimum port tuning and box size. And very likely, it may be unacceptable.
Notice down on the bottom right of the main window, you will have Fs=xxx and Vb=xxx. This is the port tuning frequency and the box volume as determined by the Alpha and H figures.
LEAVE Q1 as 7, as this is a typical box Q for ported speakers.
Adjust Alpha in Box Parameters to vary Vb as seen on the bottom edge of the Boxplot window.
THEN adjust H to try to flatten the response curve as best as you can.
Whereas the Align button, like the standard T/S alignments, gives only one optimum, in the real world some ripple is acceptable. In fact, accepting a ripple of even +/- 1 db will give you a wide range of box volumes to choose from. Accepting a very practical +/- 2 db will give an even wider range of box sizes.
Manipulate Alpha and H to arrive at an acceptable box volume and port tuning. Or switch to Sealed and see if that is better.
The box size, Vb, can be chosen because of a limited amount of floor or shelf area to use, or the desire to use a preexisting cabinet. The speaker builder can see how a particular woofer will perform in a particular cabinet.
It is relatively easy to change a port for most designs if a tube is used. If a slotted port, then it may take more work to change the port. Don't let the port stop you. You can change it, or even plug it up entirely.
Now, reading the graph. Notice that the vertical lines, frequency, are not evenly spaced. Well, they are, but by OCTAVE. A doubling of frequency is an increase of one octave.
The black line is the frequency response with one watt of input. It is read and compared to the black db figures on the left side of the graph.
The -3 db dashed line is the "f3", or -3db rolloff. This is considered to be the lowest practical range for the the chosen woofer and box design.
The green line, read with the green numbers on the far right, is the maximum power input vs frequency. The green line will max out at the power rating you entered in the Speaker Parameter dialog box, and is the thermal limit given by the manufacture as the watt rating. But on the low end, the power limit is also affected by the amount of cone excursion (Xmax) vs power vs frequency. Xmax is the limiting factor at low frequencies.
The red line is the maximum SPL that may be produced at various frequencies. It takes into account the power that may be applied without damaging the woofer by burning it up or exceeding Xmax.
The red and green lines may be taken off the graph by clicking (at the top) Edit > Preferences and unchecking Plot Displacement Limit, Plot Power Limit. Then close that dialog box, and click View > Re-plot graph.
Now you may plan your box dimensions by opening the dialog box:
Finally, in the Vent Design dialog box port dimensions will be seen. You can adjust for round or rectangular port, port size, single or multiple ports, etc.
You can make a printed report, with graph, all the box size, port size, etc, but usually the numbers are squished together, the plot not well done. I usually skip printing. If you do print, you may want to experiment with printing as Landscape, rather than Portrait, for a better presentation.
Macaltec, this is for you, guy! :thmbsp:
You may download Boxplot here:
http://www.pispeakers.com/BoxPlot_Install.exe
(This download is courtesy of www.pispeakers.com who make some really hip speakers, both built and kits.)
To begin a project:
Open Boxplot, wait for the "gripe box" and then maximize the generic plot in the Boxplot window.
Immediately Save As, and name your project. Since I get most of my woofers from Parts Express, I usually save as using the Parts Express number as the file name. Or I may use Delta12, Gamma15, etc.
Next, enter woofer parameters. Click the red/yellow woofer button in the toolbar. This opens the Speaker Parameters dialog box.
I like to give more info in the Speaker Model box, the Mfg and model. "Eminence Delta 15"
Simply fill in the blanks. Do not fill in Qts. When you fill in Qms and Qes it will calculate Qts.
Occasionally you will have T/S parameters given in metric. Check in the Units section Metric.
NOTE that Xmax, in metric, is CENTIMETERS, not MM's as is usually given. So, move your decimal accordingly. 4.3 mm's is entered as .43 cm. THIS IS IMPORTANT for proper graphing of the power limits.
Also, if Vas is given in liters, check Metric. You can always check English afterwards, and those Metric parameters will be converted to English.
Box Parameters
Access Box Parameters by clicking the black/white speaker box button just to the right of the red/yellow speaker parameters button.
First, in Box Type chose Closed or Vented.
Select the number of drivers in Speaker Config.. Normally it should be 1, but you may configure for 2 or more woofers.
EQ Type. This is usually set to None, but you may use a 1st or 2nd order high pass (subsonic) filter. If you don't know what this is, set None.
Now, back to the Box Type section. If you have chosen Vented, press the Align button. This will provide the flattest, optimum port tuning and box size. And very likely, it may be unacceptable.
Notice down on the bottom right of the main window, you will have Fs=xxx and Vb=xxx. This is the port tuning frequency and the box volume as determined by the Alpha and H figures.
LEAVE Q1 as 7, as this is a typical box Q for ported speakers.
Adjust Alpha in Box Parameters to vary Vb as seen on the bottom edge of the Boxplot window.
THEN adjust H to try to flatten the response curve as best as you can.
Whereas the Align button, like the standard T/S alignments, gives only one optimum, in the real world some ripple is acceptable. In fact, accepting a ripple of even +/- 1 db will give you a wide range of box volumes to choose from. Accepting a very practical +/- 2 db will give an even wider range of box sizes.
Manipulate Alpha and H to arrive at an acceptable box volume and port tuning. Or switch to Sealed and see if that is better.
The box size, Vb, can be chosen because of a limited amount of floor or shelf area to use, or the desire to use a preexisting cabinet. The speaker builder can see how a particular woofer will perform in a particular cabinet.
It is relatively easy to change a port for most designs if a tube is used. If a slotted port, then it may take more work to change the port. Don't let the port stop you. You can change it, or even plug it up entirely.
Now, reading the graph. Notice that the vertical lines, frequency, are not evenly spaced. Well, they are, but by OCTAVE. A doubling of frequency is an increase of one octave.
The black line is the frequency response with one watt of input. It is read and compared to the black db figures on the left side of the graph.
The -3 db dashed line is the "f3", or -3db rolloff. This is considered to be the lowest practical range for the the chosen woofer and box design.
The green line, read with the green numbers on the far right, is the maximum power input vs frequency. The green line will max out at the power rating you entered in the Speaker Parameter dialog box, and is the thermal limit given by the manufacture as the watt rating. But on the low end, the power limit is also affected by the amount of cone excursion (Xmax) vs power vs frequency. Xmax is the limiting factor at low frequencies.
The red line is the maximum SPL that may be produced at various frequencies. It takes into account the power that may be applied without damaging the woofer by burning it up or exceeding Xmax.
The red and green lines may be taken off the graph by clicking (at the top) Edit > Preferences and unchecking Plot Displacement Limit, Plot Power Limit. Then close that dialog box, and click View > Re-plot graph.
Now you may plan your box dimensions by opening the dialog box:
Finally, in the Vent Design dialog box port dimensions will be seen. You can adjust for round or rectangular port, port size, single or multiple ports, etc.
You can make a printed report, with graph, all the box size, port size, etc, but usually the numbers are squished together, the plot not well done. I usually skip printing. If you do print, you may want to experiment with printing as Landscape, rather than Portrait, for a better presentation.
Macaltec, this is for you, guy! :thmbsp:
