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Review BassBox 5.1 Design Software For Loudspeaker Enclosures This comprehensive speaker enclosure design package requires Windows 3.1 & DOS 5.0 or later & allows two design approaches. You can select a speaker & vary the box parameters to suit it or you can ‘pick a box’ & check the performance of various speakers in it. By RICK WALTERS The minimum system requirements to run this package, apart from Windows and DOS, are a 486 processor, 4Mb of RAM and 7.5Mb of hard disc space to accommodate the files. Following the usual procedure of “when all else fails – read the manual”, we in­stalled the software and proceeded to explore its capabilities, without reading the manual. We were able to enter speaker parameters and plot impedance curves 4  Silicon Chip but the subtlety of a picture of a motor car with a check box beside it, which when ticked changed the response curves, had us reading through the manual very carefully. The 112-page manual is quite detailed. The major headings are Getting Started, Running BassBox, Editing the Loudspeaker Database, Testing Loudspeakers, Testing Passive Radiators and Constructing The Box. The first paragraph in “Getting Started” informs us that the product is pronounced as “base barks” (presumably with an American drawl), then goes on to list the main features of the program. These include both small and large signal analyses, plots of amplitude, phase and group delay, multiple onscreen response plots for easy comparisons, acceptance of Thiele-Small or elec­ t romechanical parameters, variable box damping, built-in test procedures for analysing speaker parameters, the ability to select imperial or metric units, with the capability to switch in the middle of a design, and the ability to save and recall designs. When you start BassBox under Windows, you get the familiar bar across the top of the screen together with drop-down menus. As mentioned previously, there are two approaches to using the program, either by selecting a speaker and operating with the box as the variable or starting with an enclosure and testing its performance with various speakers. If you run Windows in 1024 x 768 resolution, the main Bass­Box window normally displays columns for six sets of speaker data, one set of box parameters and one graph, as shown in Fig.1, or it can be switched to the display shown in Fig.2. This only applies to the main screen; no others can be changed. Speaker parameters When you begin a new enclosure design the first step is to enter the speaker parameters. The program accepts Thiele-Small (T-S) or Electro-Mechanical (E-M) parameters. T-S par­ameters are named after Neville Thiele who pioneered the development of small speaker enclosures in 1961 and Richard Small who expanded on vented box loudspeaker systems in 1973. Most speakers nowadays are supplied with Thiele-Small parameters. The electromechanical parameters are much harder to measure and are not often quoted. Only three T-S parameters are necessary for the program to be able to calculate the box size and plot a response curve. These are the speaker free-air resonance Fs, the total Q (both mechanical and electrical) Qts, and the volume of air having a compliance equivalent to the loudspeaker suspension, Vas. A database of loudspeakers listed by manufacturer is acces­sible from within the program. This includes most well known makes from the USA and Europe. Unfortunately though, when Fig.2: this alternative screen can be selected when your video resolution is set to 1024 x 768. The four plots – Amplitude Response, Power Response, Phase Response and Group Delay – are all displayed on the screen. I searched for two Peerless models which are available in this country, they weren’t included in the Peerless database of 33 units. However, you can readily add new speakers, edit existing speaker data or delete existing models. If the response curve is plotted and you wish to vary the box size, the quickest way is to duplicate the data from the optimum column into the custom column and then vary the volume, plotting this response. Both responses then appear on the same graph, giving an immediate indication of the change in performance. The standard vented enclosure only controls the low fre­quency end of the speaker response. By using a double enclosure with two ports, a bandpass vented box is created – see Fig.3. The program allows the design of 4th and 6th order bandpass boxes. BassBox also provides for the design of boxes with passive radiators. These are essentially speakers without voice coils and magnets and are often called drone cones. They effect the response in a manner similar to the port in a vented enclosure. Fig.3: by using a double enclosure with two ports, a bandpass box is created. You can design either 4th or 6th order responses. Fig.1: the opening screen for any video resolution. The other responses shown in Fig.2 are individually selectable using the GRAPH menu. June 1996  5 Fig.4: when you select a vent type the vent picture changes to reflect this. If one of the vent dimensions is entered the other is calculated immediately. There are six different response curves available for each speaker/box combination. These are the normalised response in dB, power response in dBSPL, acoustic power, impedance, phase and group delay. As the box parameters are varied these graphs can be erased and redrawn for the new conditions or superimposed on the previous ones, allowing you to see the effects of the changes. In addition, if the actual response curve of the speaker is available, this information can be entered and will be reflected in the amplitude response plot. It is also possible to enter the room or vehicle response as well, if this is available, to get a more realistic idea of the final system performance. Once the box volume has been optimised, the duct size is calculated. Normally the duct is flush with the front panel and protrudes into the interior of the box but with a bandpass Fig.5: a preview of the printout of a design. If an enclos­ ure has been designed for a client, the graphs could be supplied with the system. system both ends of the duct are flush. BassBox can take these facts into account when calculating the duct length. The calculator (see Fig.4) allows round, square or triangular vents, although round vents, using PVC pipe from your local hardware store, are the easiest to produce. OK, we have the volume and the vent size. We now need to establish the dimensions of the enclosure. The dimension calcula­tors make this easy. A large number of cabinet shapes, such as barrel, cylinders and the usual style of optimum prism, as well as many others including a wedge shape, are avail­able. The calculator lets you compensate for the space taken up by the speaker and internal bracing, by adding these to the required internal volume. Once they are entered, the three box dimensions can be calculated or for example, if the internal height was to be 860mm, Fig.6: the responses for both the 44-litre and 14-litre enclosures are shown here. As you can see the smaller box lifts the bass response slightly but at 67Hz starts dropping off more rapidly. You trade volume for extended bass response. 6  Silicon Chip this dimension can be entered and the other two will be calculated using the ratio of 1.62:1.00:0.62 for height to width to depth. Having completed the design, it can be printed out as shown in Fig.5 and filed or used to compare the performance of various combinations. As mentioned previously, the program comes with a loudspeak­ er database. If the speaker parameters you need are not available or should you wish to verify them for a suspect loudspeaker, a testing procedure is included in this program. It draws a circuit of the setup needed to make the particular measurement and gives you instructions on how to carry it out. As you enter each meas­ured value the program proceeds to the next step, changing the circuit and instructions as necessary. A procedure is also included for measuring the parameters of a passive radiator. The sequence is similar to that detailed above. The final chapter of the manual gives some details on the construction of speaker boxes. Headings are Shape, Materials, Construction and Duct Placement. Proven results All this is very impressive but how well does the program work? In the January 1993 issue of SILICON CHIP we described a 2-way speaker system using a 165mm Peerless woofer type 174WF. This design, which used the T-S parameters to calculate the box de­tails, featured a vented enclosure with an internal volume of 14 litres. YOU CAN AFFORD AN INTERNATIONAL SATELLITE TV SYSTEM SATELLITE ENTHUSIASTS STARTER KIT Fig.7: this response graph for the woofer in a 2-way system was taken from our January 1993 issue and shows excellent correlation with Fig.6. The response curve for the woofer was published in the article. By substituting those parameters in this program we did a comparison to see how closely the results agreed with one another or if they agreed at all. The data was entered into BassBox and it was asked to cal­culate the optimum enclosure. This it did, giving a figure of 44 litres. Upon checking this box response with the previous one we saw that the hump at 100Hz was missing from our new design. The hump in the older design indicates that a smaller enclosure volume was used. After entering a volume of 14 litres into the program, the two graphs were virtually identical. The previous graph shows a peak of +2.26dB at 100Hz while ours shows +2.3dB at 100Hz, an excellent correlation. Our two plots of the optimum and custom values are shown in Fig.6. The previous data is shown in Fig.7. Of course if both programs use T-S parameters and are based on the same calculations, the results should be the same. It becomes a question of whether there has been any “enhancement” of the procedures. In summary, I found this a fascinating and rewarding program to use. Its operation is reasonably intuitive and the handbook is quite detailed. Being able to select a woofer from one of the retailer’s catalogs, enter the T-S parameters and plot the bass response in a matter of seconds is a real boon. Still wondering about the motor car and check box? There is a natural bass rise of about 12dB/octave in most motor vehicles, beginning around 50Hz. Ticking the box adds this boost into the response curve to give a better idea of the speaker’s overall performance in a car. Crossover design too As an added bonus a copy of X.over 2.0, a passive crossover network design program, is included. This lets you design 2-way and 3-way cross­ overs. It can calculate values for many common 1st, 2nd, 3rd and 4th order networks including Butterworth, Bessel, Chebychev and Linkwitz-Riley. And as you would expect, woofer details can be loaded from BassBox files. It also allows you to design LCR networks to compensate for the rise in im­pedance of voice coils at higher frequencies. At its price of $299, I believe Bass­ Box 5.1 with X.over 2.0 is good value for money. The package is available from Earthquake Audio, PO Box 226, Balgowlah, NSW 2093. Phone (02) SC 9948 3771; Fax (02) 9948 8040. YOUR OWN INTERNATIONAL SYSTEM FROM ONLY: FREE RECEPTION FROM Asiasat II, Gorizont, Palapa, Panamsat, Intelsat HERE'S WHAT YOU GET: ● ● ● ● ● ● 400 channel dual input receiver preprogrammed for all viewable satellites 1.8m solid ground mount dish 20°K LNBF 25m coaxial cable easy set up instructions regular customer newsletters BEWARE OF IMITATORS Direct Importer: AV-COMM PTY. LTD. PO BOX 225, Balgowlah NSW 2093 Tel: (02) 9949 7417 / 9948 2667 Fax: (02) 9949 7095 VISIT OUR INTERNET SITE http://www.avcomm.com.au YES GARRY, please send me more information on international band satellite systems. Name: __________________________________ Address: ________________________________ ____________________P'code: __________ Phone: (_______) ________________________ ACN 002 174 478 June 1996  7