Definition of Terms
Maximum SPL
Help for each menu item
Driver Parameter
Box
Sealed
Vented
4th order Bandpass
6th order Bandpass
Isobarik
Tools
Port Calculator
Box Calculator
Calculate T/S Parameters
Options
Frequency Range
Amplitude (db/div)
Driver The raw speaker without the enclosure. Also called woofer or subwoofer.
Fs Free air resonance of driver - The frequency at which the driver resonates or naturally vibrates in free air. This number is measured in Herz (Hz).
Qts This is the total strength of the driver resonance. It is a combination of electrical Q (Qes) and mechanical Q (Qms). A speaker with high Qts will have a very stiff suspension.
Vas volume of air having the same compliance as the driver suspension. The compliance, or stiffness, of the driver suspension is determined by the surround and the spider. This parameter is measured in cubic feet.
Qtc This indicates strength of resonance for the speaker system (driver in an enclosure). A high Q system (greater than 1.0) would have powerful, boomy bass. A lower Q system (around 0.8) would have a tight, quick response.
Cone Diameter advertised diameter of the driver cone i.e. 8, 10, 12, 15”
Xmax Peak linear travel
of the cone, measured in inches. In other words, the maximum
movement in one direction. If the manufacturer specifies +/- 0.25in
the value for Xmax is 0.25in. If they specify a total (peak to peak)
value then you must divide by 2 to get Xmax.
Efficiency driver efficiency rated in dB with 1 Watt input and 1 meter. This is sometimes called SPL, or sensitivity as well.
SPL sound pressure level, measured
in dB
For Sealed and Vented enclosures the maximum acoustic power can be calculated based on the driver working within its linear operating range. The acoustic power is then used to derive max SPL. The electrical power required to reach this SPL is also reported. If the required input power is greater than the power rating on the driver you will not be able to reach the maximum SPL.
Make sure you never exceed the manufacturer’s recommended
input power!
The first three parameters, Fs, Qts, and Vas, must be filled in to generate the frequency response for your enclosure.
The optional parameters, diameter, xmax, and effiency, are used for port diameter and max SPL calculations.
All units are English i.e. feet, inches, cubic feet, etc.
Sealed boxes are the easiest to design and generally result in the smallest volume box.
Vented enclosures can usually play deeper with the same driver but result in a larger box. Drivers with a Qts < 0.5 will work well in a vented box.
Bandpass enclosures are becoming popular for automotive
applications. Since all the sound energy comes through the ports,
the enclosure can be constructed in the trunk or bed of a truck while the
energy is transported into the cab via tuned ports. Like the name
suggests, the frequency response of a bandpass enclosure rolls off at high
frequency so an electronic crossover is not required.
The only variable in a sealed box design is box volume. Volume affects Qtc and f3, the point at which frequency response drops below –3db. The smaller the box, the higher Qtc and the higher f3.
A Qtc of 0.7 will result in a wide flat frequency response and very tight accurate bass. However, the bass will be a little weak compared to an enclosure with a higher Qtc. This is the choice often made for home speakers.
A Qtc of 1.1 will yield maximum power handling and efficiency from the speaker. The frequency response is not as wide but the bass will be more powerful and booming. This design is used most often for automotive applications as it yields the most bass response in the smallest enclosure.
To run a sealed box simulation, enter the driver parameters, then enter box volume into the input box titled V1 in the main window (All the other boxes will be grayed out). Hit the Plot button or type ENTER and the frequency response will be displayed on the graph. Qtc is displayed in the upper right corner of the main window.
To calculate the internal box dimensions open the Box
Calculator dialog.
To run a vented box simulation, enter the driver parameters, enter box volume into the input box titled V1 in the main window, then enter tuning frequency into the input box titled F1 (the other boxes will be grayed out). Hit the Plot button or type ENTER and the frequency response will be displayed on the graph.
Once the graph shape is the way you want it, open the Port Calculator dialog and calculate the length and diameter of port to achieve the selected tuning frequency.
To calculate the internal box dimensions open the Box
Calculator dialog.
Bandpass enclosures are much more difficult to design and to build. . As youll notice during simulation, small changes in volume and tuning frequency make big changes in response. So dont forget to account for volume consumed by the driver, bracing, ports, etc.
The ideal response shape is symetrical and flat at the top, it should look something like this
----
To achieve symmetry, set the front enclosure tuning frequency equal to the resonant frquency of the sealed rear chamber (shown in the greyed out box for F2)
The volume of the front enclosure (V1) affects the gain of the enclosure. As V1 increases, gain increases. This will result in more more SPL for a given input power.
The volume of the rear sealed enclosure (V2) tends to move the response in the frequency domain. As V2 increase, the response will shift lower in frequency, dont forget to reset F1 to match the new F2.
To run the bandpass box simulation, enter the driver parameters. Enter box volume for the enclosure in front of the driver into the input box titled V1, enter tuning frequency into the input box titled F1. Then enter box volume for the enclosure behind the driver in input box V2. Hit the Plot button or type ENTER and the frequency response will be displayed on the graph.
Once the graph shape is the way you want it, open the
Port Calculator dialog and calculate the length and diameter of port to
achieve the selected tuning frequency.
The 6th order bandpass enclosure is the most difficult (of the enclosure included here) to design and very sensitive to construction methods. As youll notice during simulation, small changes in volume and tuning frequency make big changes in response. So dont forget to account for volume consumed by the driver, bracing, ports, etc.
The ideal response shape is symetrical and flat at the top, it should look something like this
----
Tuning is similar to the 4th order enclosure except now you have direct control of resonant frequency of both the front and rear enclosures.
The front box frequency F1 affects the lower knee is illustrated in the drawing above. As F1 is set lower, the knee moves lower. The rear box frequency F2 affects the upper knee. A good place to start for a subwoofer design is with F1 set about 30Hz and F2 set about 60Hz. If one knee is starting to peak up higher than the other then move the tuning frequency closer to center.
The box volumes V1 and V2 interact with tuning frequency to move the location as well as the amplitude of the knees.
To run the bandpass box simulation, enter the driver parameters. Enter box volume for the enclosure in front of the driver into the input box titled V1, enter tuning frequency into the input box titled F1. Then enter box volume for the enclosure behind the driver in input box V2, enter the tuning frequency into input box F2. Hit the Plot button or type ENTER and the frequency response will be displayed on the graph.
Once the graph shape is the way you want it, open the Port Calculator dialog and calculate the length and diameter of port to achieve the selected tuning frequency.
To calculate the internal box dimensions open the Box
Calculator dialog.
Multiple woofers in the same enclosure can be wired out of phase such that the net volume and pressure between them is constant. Two woofers in this arrangement act like one woofer with an equivalent Vas equal to half the Vas of a single woofer. Since Vas directly affects box size, this means that the required box volume decreases by a factor of two. For this reason Isobarik designs are common in car audio applications where small size is highly desirable.
The downside to the isobarik configuration is increased cost (2 drivers) and increased weight.
The Isobarik option is available for all for enclosure
types: sealed, vented, 4th and 6th order bandpass. First specify
an even number of drivers and then select Isobarik from the Box menu.
As long as Isobarik is selected each pair of drivers will be treated as
one driver with half the Vas.
The port calculator dialog calculates length of cylindrical ports to achieve the desired tuning frequency. Multiple ports can be used to decrease individual port length.
The minimum diameter is a guide to avoid distortion due
to power compression at the resonant box frequency. Try to keep the
effective diameter value close to or greater than the minimum diameter.
Enclosure Dimension Calculator
The box calculator is a handy tool for determining internal
box dimensions to avoid internal reflections. Three different ratios
are selectable. Don’t forget to add the thickness of your material
to get outside dimensions.
Calculate Thiele/Small Parameters
This tool guides you through a series of electrical measurements to determine the Thiele/Small parameters for an unknown driver. This is even useful if you know the parameters but wish to fine tune the design of your enclosure to use the actual measured parameters for your driver.
Fs Measure free air resonance of driver. Hold the driver in mid air at least 3 feet from any object.
UNDER CONSTRUCTION
Frequency Range opens a dialog box that allows you to specify the lower and upper frequency for the frequency response plot.
Amplitude dB/div Pop up menu that allows the user
to select 1, 2, 5, or 10 dB/div for the vertical axis of the frequency
Last Modified
3/16/99