Speaker Parameters, Pt. 3
August 8, 2007
DIY cabinet design.
Last month, we discussed how various speaker parameters relate to designing guitar cabinets with modeling software (specifically Eminence Design Software, designed by Harris Technologies). We examined a cone displacement graph, and are now ready to practice designing a cabinet using custom amplitude response.
For the purpose of our discussion, the speaker I’m modeling is a 12” with a Qts parameter suitable for closed, vented or open back designs. The first model I’m showing is an open back design. I can simulate an open back cab using an infinite baffle design – something like a sealed enclosure design, 10,000 cu. ft. Of course, that won’t provide an optimal size, but it is useful for determining output and response shape below 200Hz (fig 1).
Next, I’ll model the speaker in a vented cab (fig 4). This is where it can get tricky!
What the software predicts as optimal may be abusive to the speaker. Remember, we’re dealing with lightweight, full paper cones and very little Xmax. We may want some distortion, but we don’t want mechanical abuse. The software’s only mechanical concern is Xmax. There is no consideration for cone response or the nuances associated with typical guitar cones. The lightweight, full paper cones are used to achieve efficiency, detail, and harmonic content.
It seems that a lot of players today are using drop tunings or seven-string guitars that demand tons of low-end response, and sometimes these goals are unrealistic for a conventional guitar speaker. What looks good on paper may sound like crap and potentially destroy your speaker. I can’t stress enough how important it is to include trial and error. Some of this will be very obvious by simply knowing which frequencies the guitar produces.
For example, if I want the software to model a high fidelity enclosure, the suggested tuning is 58Hz. I’m pretty sure that’s going to be too low for my guitar application, and very abusive on the speaker. My other concern with a vented enclosure for guitar is where to tune versus what I want to hear, and what’s safe for the speaker. This is where it becomes an art; you can only decide through trial and error. One way you can determine what you like is by varying the vent sizes—however, when comparing multiple speakers, your opinion on an optimal tuning frequency will likely change with each speaker.
In summary, if you want to use software as a tool for designing an optimal guitar cabinet, you have to consider your past experiences, tests through trial and error, and use good judgment. Remember, designing guitar cabs is as much an art as it is a science. Software is useful, but there is no substitute for trial and error and lots of experimentation.
I certainly welcome your comments or any experiences you’ve had in designing the ultimate guitar cab. Please feel free to email me.
Anthony “Big Tony” Lucas
is a guitarist and Senior Lab Technician at Eminence Speaker LLC, where he specializes in guitar-speaker design and customer support. Big Tony has been with Eminence for over 10 years and is responsible for many well-known guitar speaker designs.