Quarter Wave Box Calculator
Pearls from Martin J King Quarter Wave Design Pearls from Martin J. King Quarter Wave Design An introduction by Bjorn Johannesen, Denmark. 11-december-05 The first time you visit, you might get overwhelmed by the tremendous work done by Martin J. I have with great interest studied the information on the site, and Martin has been very patient answering my questions. When I realised quarter wave design was not that mysterious after all, I decided to write this article, which has been reviewed by Martin. Without the very helpful support from Martin, this article could not have been written.
A history of western music 9th edition pdf free. But it cant be mixed frequecies, like a deck with a 60hz boost, and a amp with 40hz boost, you need to cancel 1 freq out, or level the 2 freq's (there will be cancelation, and the sub will sound like its being pushed to hard-boost for tline have to be close to the quarter wave of the box as possible) This allows you to use a shorter tline.
To fully understand the quarter wave design, download MathCad and the MathCad worksheets. They are available for private non-commercial use.
Quarter Wave Design In a Transmission Line (I use the term TL for all types of quarter wave designs), the goal most often sought after* is to extend the bass by adding a lift to support the driver. The output from the opening is a desired property of the quarter wave design, and the line should be relatively lightly stuffed. *[a TL may also be used to create a highly non-resonant enclosure in which the goal is to completely eliminate the back wave of the speaker (ie a desirable goal if you are working with a midrange or a tweeter), and of course there is a continuous spectrum between these two] Problems with TL A TL is a resonant system. The first (lowest) resonance is the one you want. Unfortunately, there are higher resonances as well.
These higher harmonics are unwanted, because they cause an uneven sound pressure level with peaks and nulls (ripple). This problem can be minimized by one or all of the following: The geometry of the cabinet (tapered pipe), driver offset down the line and stuffing. But every time you solve one problem, you create another. This is the great challenge about quarter wave design. MathCad is a very good and proven tool to find the best compromises. Resonance Systems When you combine a pipe and a driver you are merging two mechanical systems to produce a new mechanical system with its own resonant properties. You need to look at the driver as one system, the pipe as a separate system, and the driver in the pipe as an entirely new combined system.
Figure 1: Transmission Line System and Infinite Baffle Impedance In this example, the driver resonance (F s) is 40 Hz. This is shown by the blue line. The pipe is tuned to 40 Hz as well. Normally you would not set the pipe resonance equal to driver F s. The red line is the combined system with the driver and cabinet, resulting in 2 new resonances. Vcredistx642015x64.
The first resonance (impedance peak) at 30 Hz is a combination of the air of mass in the pipe combining with the moving mass of the driver cone and voice coil oscillating on the driver's suspension. The second resonance peak about 53 Hz is the original cabinet resonance, but with the influence of the driver. At the original 40 Hz tuning frequency of the pipe, there is a dip, where the driver output is at the minimum and the opening output is at the maximum. This is not caused by resonance, but is the middle between the 2 new system resonances.
MathCad is simulation tool — not a magic box -- With the MathCad worksheets, you are able to do what-if-analyses. This helps you to understand the consequences of changing the TL design.
MathCad is not a guaranty your design will be a success; it can only predict accurate results from the input given. Use the alignment tables -- The best document to start with are. This document includes very useful tables that allow you to quickly generate some baseline designs. It is a good starting point, even if you want to do further analysis using the MathCad worksheets. There are a few terms that need some explanation: Effective Length versus Physical Length -- At the opening, there is an acoustic impedance which makes the line behave as if it were slightly longer than the physical line at low frequencies. MathCad includes this impedance so depending on the geometry of your cabinet the actual tuning frequency might be a little lower than you would expect.