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The U- and
H- frame worksheet is a MathCAD worksheet for designing U and H frame woofers.
The worksheet is an adaptation of the Open Ended TL worksheet, developed by
Martin J. King, to U and H-frame woofer systems. A detailed discussion of the
theory upon which the TL analysis is based can be found by going to http://www.quarter-wave.com/
(see the White Papers section of the FRDC). The conceptual development and
adaptation to U and H frame woofers was a joint effort by both authors. The
software was written and modified by the first author.
Version 1.0 Date: April 2004
Download U & H Frame Woofer Worksheet
Mathcad File Size 186 k - Word File Size 107 k - Download Size 180 K
|The H-frame woofer system has the advantage that, since the front and rear of the driver are symmetrically loaded, the SPL radiated from the front and rear openings will also be symmetric. Thus, the H-frame forms a natural dipole. Stuffing can be added to the H-frame to help damp the ¼ wave resonance and provide a smoother response in the region of the resonance, but the stuffing must also be symmetrically added to both front and rear TLs. By contrast, the U-frame woofer system exhibits differences in the SPL radiated from the driver and open end. If left undamped, the U-frame will behave as an H-frame dipole woofer system of the same length at low frequency. At higher frequencies, as the ¼ wave frequency of the U-frame is approached, the behavior of an undamped U-frame departs from that of a dipole due to the asymmetry of the driver and terminus SPL amplitude and phase. Ideally the U-frame would be damped such that the ¼ wave resonance was completely eliminated and the driver and terminus SPL response be identical in amplitude. However, achieving this result is beyond practical limits. Never the less, if the U-frame is correctly damped several interesting features are observed. First, the polar response of the U-frame undergoes a transition from that of a dipole to a near cardioid or hyper-cardiod over a significant portion of its operating range. Second, the on axis response shows a nominal 6dB increase over that of a dipole of the same overall length. Typically a true cardiod response is not obtainable but a reduction in rearward radiated SPL on the order of 10 to 15 dB is obtainable. This is not an insignificant reduction in rearward radiated power. Thus over all the damped U-frame radiates predominately in the front hemisphere and has an on axis sensitivity 6dB greater than an H-frame woofer of the same length.|
This version is Free for personal and DIY use.
The contents of this webpage are intended for personal use and not for any commercial venture or gain. Using the MathCad worksheets to study, design, and build U- and H- frame woofer systems for your own enjoyment is encouraged. Selling these speaker systems, or the designs, for profit is prohibited without a written agreement in place.