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Quote from: Rudolf on 28 Oct 2006, 08:59 amWith your range decision I'm looking for the two octave range 70-280 Hz.Quoteyou are effectively ruling out the most convenient dipole configurations aka H- and W-frame...To reach 70 Hz would necessitate a really large flat baffle or something like two octaves of 6 db/oct EQ for a 50 cm wide OB.OK, this is what I like, hard numbers. 20" wide baffle & 12 dB of EQ over my two octaves. So...let's say you have a closed box w/ 89 dB senstivity & 400WRMS power handling @ 4-Ohms (reasonable, easy to accomplish). For an OB design w/ a similar 89 dB sensitivity to equal the output of the above system would require a SIX-THOUSAND FOUR HUNDRED WRMS POWER AMP & THE SAME POWER HANDLING IN THE DRIVERS!!!!!!!!!!!! That is an astounding fact. If accurate this certainly demonstrates well the shortcomings of OB design & fully explains their general neglect in the marketplace. This is not meant as an attack or claim that the design is inferior overall or anything else. It is not an attack on anyone who loves these designs. It's just an interesting point. QuoteSo many people would recommend a W- or H-frame here (which could happily support 40 Hz too). I sure don't see how any OB design could support 40 Hz based on your numbers above, at least not for the SPL I'm interested in.QuoteAt the opposite end of your range, 280 Hz would be VERY near to the typical first manifold resonance of those W- and H-frames. You would need a 24 dB/oct. LP at least to subdue that resonance effectively."At least" scares me.QuoteWithout necessity you are pushing yourself into the situation you don´t want: the need of much EQ at the lower or upper end of the passband. If you could move that band to 40-160 Hz (two octaves too) you could happily get away with some proven W- or H-frame solution, demanding much less EQ. QuoteMy goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound. Funny, that you intend to stop with the OB just were the bouncing really starts (280 Hz). I'm actually not "pushing" myself into anything. I'm interested in the theoretical question whether or not an OB design could practically replace a box system for the range of 70-280 Hz. This is the range, period. Not higher, not lower. The range above 280 Hz is not in question. I'm not open to changing it or to even thinking about changing anything else in this system. To suggest otherwise would be like me stating here that an OB design is far inferior to what I've employed. If OB proponents wish readers to get the impression that OB designs are difficult to isolate to reproduce this two octave range, that is the exact impression I'm getting.
With your range decision
you are effectively ruling out the most convenient dipole configurations aka H- and W-frame...To reach 70 Hz would necessitate a really large flat baffle or something like two octaves of 6 db/oct EQ for a 50 cm wide OB.
So many people would recommend a W- or H-frame here (which could happily support 40 Hz too).
At the opposite end of your range, 280 Hz would be VERY near to the typical first manifold resonance of those W- and H-frames. You would need a 24 dB/oct. LP at least to subdue that resonance effectively.
Without necessity you are pushing yourself into the situation you don´t want: the need of much EQ at the lower or upper end of the passband. If you could move that band to 40-160 Hz (two octaves too) you could happily get away with some proven W- or H-frame solution, demanding much less EQ. QuoteMy goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound. Funny, that you intend to stop with the OB just were the bouncing really starts (280 Hz).
My goal is to minimize the rear wave bouncing against the cone's back side, muddying the sound.
Jim,70hz is a piece of cake. If you want to set spl/frequency goals for OByou need to use Linkwitz's free DipoleSPLmax spreadsheet. To match your sealed box example, the minimum cab would be the same driver as your sealed box in a 16" deep U-Baffle, and that could easily be smaller than your sealed box. From 70hz, response would rise by 6db to a peak at about 210hz followed by a deep null at about 410hz, which you could use judiciously as part of your low pass filter.To answer your driver question, for running up into the hundreds of hz, use a mid Q pro type woofer. A perfect candidate was in one of these threads recently for $40/pr in a scratch and dent sale. For a heavy duty 15" that can play way down low and have no problems up to several hundred hz with a low order XO, then the Hawthorne Augie is what you need.I need exact performance goals and size and $ budget to be of more assistance.
I'm not sure what you mean by minimum polar dispersion. A dipole has narrow dispersion in the bass region (a figure 8 pattern front and back) with virtually zero bass at the sides. A pure U baffle has a cardioid dispersion pattern with a wider prime area in front, but at the sides output is significantly reduced and the area of greatest null is at the back.Another potential snag in your idea is combining an array panel with a point source. If your panel is functioning as a line source for anysignificant distance, you're combining apples and oranges and the tonality of the speaker will change with listening distance. This is because a line source's spl decreases by 3db for each doubling of distance and a point source decreases by 6db each time you double the distance. Add into the equation that lower frequencies need longer array lengths, but larger driver spacing is ok, then you're looking at a whole can of worms that needs addressing.
I still don't understand the need for OB speaker operating only in the 70-280hz range. What is this for?
Is the array panel OB too?
Do you really need 114db at 1m?
