Brandon, I just saw your design thread over at HTG. Here's my observation.
There are some reasons why the LR2 implementation without a delay network worked for your particular design. First, the W5-704D is 5.5" driver with its AC not as behind the baffle as 7" driver's. In the case of 7" drivers, the AC is farther recessed. Second, according to my bunch of simulations of LR2 designs (w/ 2 k to 2.5 kHz xover points), a null due to phase mismatch on a flat baffle usually occurs in the 4.5 kHz to 7 kHz range. Instead of 2 k to 3 kHz, try to draw a polar plot in this range. You'll see much more downward polar patterns. But luckily, a tweeter's diffraction bump in a usual size baffle occurs exactly in this range (around 5-6 kHz)! So, this null can be compensated nicely.
Suppose that you used the HDS 810921 in your design with the W5-704D. This tweeter has a dip around 6 kHz. So, the summed response wouldn't be as nice.
Your choice of DX25 is excellent. A very nice tweeter, indeed. It's a high Qts tweeter like the XT25. LR2 is easier with this type of tweeters due to less stress on their low end.
There are some reasons why the LR2 implementation without a delay network worked for your particular design. First, the W5-704D is 5.5" driver with its AC not as behind the baffle as 7" driver's. In the case of 7" drivers, the AC is farther recessed. Second, according to my bunch of simulations of LR2 designs (w/ 2 k to 2.5 kHz xover points), a null due to phase mismatch on a flat baffle usually occurs in the 4.5 kHz to 7 kHz range. Instead of 2 k to 3 kHz, try to draw a polar plot in this range. You'll see much more downward polar patterns. But luckily, a tweeter's diffraction bump in a usual size baffle occurs exactly in this range (around 5-6 kHz)! So, this null can be compensated nicely.
Suppose that you used the HDS 810921 in your design with the W5-704D. This tweeter has a dip around 6 kHz. So, the summed response wouldn't be as nice.
Your choice of DX25 is excellent. A very nice tweeter, indeed. It's a high Qts tweeter like the XT25. LR2 is easier with this type of tweeters due to less stress on their low end.
Jay_WJ said:
For sure. And who knows, the 704 may even have a shallower AC then other 5.25"ers.
The tilt stayed fairly steady at about -10 degrees up to around 10khz. From 7khz and up the peak to null difference is only around 2.5dB and less. In the 3khz to 5khz area though the difference is much larger- staying fairly on axis to the main lobe is probably a good idea.
It really fit the design needs well. From my limited listening so far it sounds quite good, nothing is obviously poor about it.
augerpro said:
I think your guess is right. I did several LR2 simulations using usual 1" to 1.5" AC offsets for some 5.25" to 7" drivers. My conclusion was that LR2 on a flat baffle wouldn't work without a delay network. Perhaps, the 704's actual AC is not that far behind.
I'd be very interested in seeing your design's polar plots in the 3 kHZ to 6 kHz range.
augerpro said:
Do you have an idea about what frequency range you might be talking about (hearing some deficiency) perhaps?
I was thinking about using some of these: P.E. Buyout Alesis Non-Woven Carbon Fiber 6.5"
to help the W-5 out on the low end.
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critofur said:Hmm ~ I'd like to see what the effect of a small waveguide, like that on the semi-spherical housing, would be without the benefit of 2pi radiation.
I guess changing the size of my semi-sphere + waveguide enclosure design will necessarily shift the crossover frequency, and also the design would contribute to a steeper slope.
Perhaps housing the tweeter in a ~ 5" - 8" sphere could have multiple benefits and may work well in your Duo. You experimented some with the Duevel style waveguide/deflector thingies, have you done any experiments with spheres over the midrange like they do with their "Planets" speakers?
I had experimented briefly with some smaller elliptical/spherical deflectors some years ago trying to get an omni radiation pattern out of a regular dome tweeter without much success.
Since I went ahead and ordered that router bit, I will be trying at least some sorts of waveguide experiments within a week or two (I hope).
I've done a lot of experimenting and testing with dome of curved deflectors and found them to be pretty ineffective and not really worth doing. The concave cone shaped delfectors work much, much better, based on my testing.
Hey Brandon,
This is a bit off topic, but of the 6"-8" pro mid/woofers you have tested, what are the top two you would consider for sealed midrange use in a 3way with these needs:
Sensitivity of 92db or above
Useable Frequency Range of 300-500hz up to 3000-4000hz or so
Fairly flat FR and reasonably low distortion
This is a bit off topic, but of the 6"-8" pro mid/woofers you have tested, what are the top two you would consider for sealed midrange use in a 3way with these needs:
Sensitivity of 92db or above
Useable Frequency Range of 300-500hz up to 3000-4000hz or so
Fairly flat FR and reasonably low distortion
dlneubec said:
This isn't a "pro sound" driver, but, it does have the unusually high 92db sensitivity, and, it's on clearance for $26 at P.E. now:
http://www.partsexpress.com/pe/pshowdetl.cfm?&Partnumber=264-852
Tang Band W6-789
edit: I could bring one to InDIYana on Sat., I bought a couple.
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dlneubec said:
Hi Dan. Keep in mind this is just a "paper" guess, since I've yet to use these:
The B&C 8NDL51 is sweet all around, if using LR4 should probably be crossed around 1.5khz though, maybe higher with a notch. I'll be using this woofer soon.
B&C 6NDL38 is a nice woofer too, can't run much higher than teh 8NDL51 though. Performance in all areas is slightly below the 8NDL51.
Haven't tested a B&C 6MDN44 but it looks very nice, maybe a better fit for your needs, with a rising response and good sensitivity that can accomodate some BSC. Is this for an omni? You're a madman!
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