Hi all. I wanted to start a thread to hopefully start a discussion around the finer points of Dipole design since a number of us in this forum are starting to build some. Some background links that I've found invaluable:
Now a couple questions:
1) What are the major resonances that limit how high a U frame can go? Linkwitz mentions there will be a resonance at a frequency F where the distance from the cone to the rear opening is a quarter wavelength of F. Is this the major resonance?
2) Using Boxnotes I wondered if this resonance could be shown. I think "Driver to rear wall" is it, but it's not exactly the same value, perhaps because of the way it calculates the cone position with the cone depth value. Now because there is still an impedance change at the rear opening, there still be a reflection. So I'm thinking that all the resonances in boxnotes are still valid to take into account. What do you guys think?
3) Floor reflection. There is some info on this at John Kreskovsky site. Apparently the dipole roll off is not as bad as theory says (which assumes free space) and the floor will cause the woofer to radiate in to 2pi space progressively as the frequency lowers. John mentions generally where this change occurs according to woofer placement, but no info on magnitude. I found one post at another forum that said where the distance from the woofer to the floor is 1/2 wavelength of a frequency F, the critical frequency, the amplitude will be up 3dB over freespace calculation, and 6dB up one octave below that. So if the distance from woofer (center?) to floor is 20" then the response is up 3dB at 337hz and 6dB up at 168.5hz. What do you guys think? Granted we could say the same thing about any typical box speaker, so all things being equal, the dipole may still sound bass shy relative to the box speaker.
4)Mid/woofer crossover point considering baffle width. This mystifies me more than it probably should, and will probably be clearer after I do some real measurements, but what advice can some one give on this? How do you deal with the dipole peak? Do you keep the crossover above the baffle step? AND the dipole peak (tough to do that one)?
5)Power response. John K has some excellent info on this at his site. Basically just because a dipole can offer an even polar response, does not mean that power response will be even. Lots to dig into on this one.
6)Good sim programs?
-Edge is cool, but can't do U frames or angled, folded back wings without screwing up the baffle step. I suppose if you only look at bass response you could model fairly well with it. Doesn't include teh floor.
-John K has a cool program in his ABCDipole guide that considers driver Q and Fs, does H, U, and flat baffle, and directivity, but nothing on sensitivity or baffle diffraction.
-Soundeasy does just H or U, no flat baffle. Can do sensitivity, directivity, and baffle diffraction. The results don't agree real close with John K's so I don't know what to think. And I can't reduce a U baffle to a flat baffle correctly, so I'm thinking Bohdan needs to look at this model.
-I tried xlbaffle but I'm just not seeing where this an improvement over any of the others.
7)Linkwitz mentions that the U baffle will operate *I believe* lower that predicted, due to end correction like you see of a port in a vented box.
I hope all of you find this baffle and we can get some of these "details" put in to one thread for future use.
Now a couple questions:
1) What are the major resonances that limit how high a U frame can go? Linkwitz mentions there will be a resonance at a frequency F where the distance from the cone to the rear opening is a quarter wavelength of F. Is this the major resonance?
2) Using Boxnotes I wondered if this resonance could be shown. I think "Driver to rear wall" is it, but it's not exactly the same value, perhaps because of the way it calculates the cone position with the cone depth value. Now because there is still an impedance change at the rear opening, there still be a reflection. So I'm thinking that all the resonances in boxnotes are still valid to take into account. What do you guys think?
3) Floor reflection. There is some info on this at John Kreskovsky site. Apparently the dipole roll off is not as bad as theory says (which assumes free space) and the floor will cause the woofer to radiate in to 2pi space progressively as the frequency lowers. John mentions generally where this change occurs according to woofer placement, but no info on magnitude. I found one post at another forum that said where the distance from the woofer to the floor is 1/2 wavelength of a frequency F, the critical frequency, the amplitude will be up 3dB over freespace calculation, and 6dB up one octave below that. So if the distance from woofer (center?) to floor is 20" then the response is up 3dB at 337hz and 6dB up at 168.5hz. What do you guys think? Granted we could say the same thing about any typical box speaker, so all things being equal, the dipole may still sound bass shy relative to the box speaker.
4)Mid/woofer crossover point considering baffle width. This mystifies me more than it probably should, and will probably be clearer after I do some real measurements, but what advice can some one give on this? How do you deal with the dipole peak? Do you keep the crossover above the baffle step? AND the dipole peak (tough to do that one)?
5)Power response. John K has some excellent info on this at his site. Basically just because a dipole can offer an even polar response, does not mean that power response will be even. Lots to dig into on this one.
6)Good sim programs?
-Edge is cool, but can't do U frames or angled, folded back wings without screwing up the baffle step. I suppose if you only look at bass response you could model fairly well with it. Doesn't include teh floor.
-John K has a cool program in his ABCDipole guide that considers driver Q and Fs, does H, U, and flat baffle, and directivity, but nothing on sensitivity or baffle diffraction.
-Soundeasy does just H or U, no flat baffle. Can do sensitivity, directivity, and baffle diffraction. The results don't agree real close with John K's so I don't know what to think. And I can't reduce a U baffle to a flat baffle correctly, so I'm thinking Bohdan needs to look at this model.
-I tried xlbaffle but I'm just not seeing where this an improvement over any of the others.
7)Linkwitz mentions that the U baffle will operate *I believe* lower that predicted, due to end correction like you see of a port in a vented box.
I hope all of you find this baffle and we can get some of these "details" put in to one thread for future use.
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