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Open Baffle Design / Source help

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  • Open Baffle Design / Source help

    I like building HiFi speakers. Recently I became enthralled with the concept of open baffle. Where can I find concise information on what specifications I should be looking for with regards to a 10" or 12" full range or coaxial driver? Any recommendations for drivers around $150 each? Are there any online DIY plans or websites I should be looking at? Thanks in advance!

  • #2
    This guy knew a few things.


  • #3
    I am not sure about full range, but I have wanted to try the SB Audience Bianco 120B150- 12" Open Baffle Woofer or the 15" version. You could add a 3" or 4" full range and make it a 2 way. There is the
    Fast, fun, Inexpensive OB project thread on diyaudio that does something similar. It seems like a fun project to try open baffle.


    • #4
      Not much to look for in the way of OB specific specs. A Qt of roughly .7 will give you a controlled roll off on the low end but even with that your low end will be practically determined by baffle width more than anything. I'd model excursion in whatever driver you're interested in and apply filters to get something workable. I"d concentrate on using low end filters at or above whatever your baffle will support.


      • #5
        I look for drivers that have around 0.5 Qts, that is a critically damped system and will have very tight bass response. You could go with a higher Qts, your bass resonance will be louder but still largely cancelled out by the open baffle so not too noticeable. Bass resonant frequency (fs) around 40 to 50 hertz seems to work well for me. I've used Eminence Alpha8 and Alpha10 along with the ASD1001 HF driver with good results. The Beta12CX is a coaxial with similar specs, I expect it could work well also.


        • #6

          Originally posted by SL
          Q34 - What is the optimum Qts for the drivers of a dipole woofer?

          A34 - The low frequency roll-off of a woofer and its associated group delay are optimal, from what I have observed, when they follow the response of a 2nd order highpass filter with Q = 0.5. When a driver is mounted in a dipole W-frame or H-frame its mechanical resonance frequency Fs decreases to Fd, due to air mass loading, and Qts increases by a similar percentage to Qtd.
          For example, a driver with very strong motor, Fs = 18 Hz and Qts = 0.2 might have Fd = 16 Hz and Qtd = 0.22 as determined from an impedance measurement of the baffle mounted driver. With Qtd < 0.5 the low frequency behavior of the woofer is characterized in the complex s-plane by real axis poles at -69 Hz and -3.7 Hz and by 3 zeros at the origin. One of these zeros is due to the front-to-back dipole cancellation with its 6 dB/oct low frequency roll-off. The frequency response of this 3rd order acoustic highpass filter must be equalized to obtain a flat response. A suitable target response could be Fd = 20 Hz and Qtb = 0.5. It is easily realized with two shelving lowpass filters. The first filter with a pole at 20 Hz and a zero at 69 Hz corrects for the low Qts of the driver. The second filter with a pole at 20 Hz and a zero at 400 Hz compensates the 6 dB/oct roll-off due to dipole cancellation. The 3.7 Hz pole is low enough in frequency so that the response is dominated by the 2nd order roll-off below 20 Hz. An advantage of a low Qts driver is the ease with which it can be equalized for an optimum response with Q = 0.5.
          A driver with a smaller motor might give Qtd = 0.7 and Fd = 20 Hz, which leads to a pair of complex poles in the s-plane. This can be readily changed to a 3rd order Bessel highpass response by using a shelving lowpass filter with a pole at 20 Hz for the necessary dipole roll-off compensation.
          Likewise, if Qtd = 1 and Fd = 20 Hz, then an additional pole at 20 Hz, from the dipole equalization, leads to a 3rd order Butterworth acoustic highpass response. Third order filters introduce more group delay than 2nd order ones. It is therefore advantageous to use Qts < 0.5 drivers, even when they require driver roll-off equalization in addition to the normal 6 dB/oct dipole correction.
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          • aarond
            aarond commented
            Editing a comment
            Definitely worth considering but I'm not sure how applicable that info is for a single full range driver in an open baffle that will likely be limited to well above 100Hz