Driver/baffle arrangement? CTC spacing?

[emilime75]

It's always been my understanding that individual drivers on a baffle should be placed in line vertically, or close to it, in order to avoid comb filtering and undesirable polar patterns. Looking at many of JBL's highly regarded designs, like the 4xxx line, it looks more like they're just thrown on a baffle, almost haphazardly. Looking at the Synthesis line, things get better in that regard, but still not quite there on some models.

As for driver center to center(CTC) spacing, it's also been my understanding that having them as close as can be, or within 1/4(some say 1/2, some say 1...) wavelength at the crossover, is the way to go. This also doesn't appear to happen in many of JBL's systems, unless we assume that up to a full wavelength is OK. Large horns/waveguides don't allow close CTC spacing, especially when both the HF and MF drivers are horn loaded.

For instance, within the Synthesis line, all but the Everest are inline vertically and I can only assume that the crossover frequencies are low enough between individual drivers that their CTC spacing is within the desired length...but what about the Everest? Is it actually a 3.5 way, where one of the woofers is low passed lower than the other? If so, are they designated left and right, as in, if only one of the woofers is crossed at the mid's high pass, and those 2 drivers being offset to each other on the baffle, does this steer the polar a certain direction...meaning the left speaker would need to be a mirror image of the right...I hope I'm making sense here.

Or, does the waveguide width negate the offset placement, since it is as wide as the 2 woofers? I would still think that having both woofers, side by side, and both playing up into the midrange's highpass would result in some negative effects in that region.

Help me understand this better.

[pos]

The larger the CTC spacing compared to the crossover wavelength the smaller the lobe of correct summation, meaning that you will have nulls on smaller vertical angles.
Larger CTC also means that the apparent size of the source will be larger for a given distance.

The closer the spacing the better, but as always in sound reproduction it is all a matter of compromises.
The array 1400 for example has a very large CTC spacing, but on the other hand the horn has full vertical directivity control at the crossover point thanks to its big vertical dimensions, which is also important for vertical behavior at the crossover point.

[emilime75]

Yes, that was my general understanding of it...which leads me to ask again, as an example in a 2 way with a horn loaded HF driver, are we still measuring CTC of woofer to HF driver, or woofer to the mouth edge of the horn? Also, just how important is the vertical polar for a home setting? I would think not very, since we are almost always seated at the same height, like on a couch, so as long as there aren't any nulls at or near sitting/ear height???

I also found an answer to one of my questions from the original post, and that is that the Everest is, indeed, a 3.5 way. One of the woofers is low passed at 150Hz, while the other runs up to 800Hz. So, being that the woofers aren't lined up vertically with the center of the horn/HF driver, how does that steer the polar response.

I'm asking these questions because I am generally curious, plus I am in the design stage of a set of monitors for my personal use and want to know how offsetting drivers from a straight vertical line will alter the response.

[hsosdrum]

The Everest DD65000 and DD67000 have shorting bars that determine which woofer receives the LF-only signal and which receives the full-bandwidth signal, allowing the user to designate either speaker as the left or right speaker. Once the speakers are installed in the listening room the user sets the shorting bars accordingly, placing the full-bandwidth woofer on the inside (closer to the other speaker).

FYI, I wrote the user manual for the DD65000 and DD67000. I'd attach it here, but the PDF is over 16MB. When the Synthesis website is back online it should be available there.

BTW, the crossover between the full-bandwidth woofer and the horn is at 750Hz in the DD65000 and at 850Hz in the DD67000.

[bubbleboy76]

BTW, the crossover between the full-bandwidth woofer and the horn is at 750Hz in the DD65000 and at 850Hz in the DD67000.

Do you know why it was changed from 750 to 850Hz?

[hsosdrum]

Although I can't be sure, I assume that Greg Timbers chose 850Hz for the DD67000 because that crossover point better matched the directivity characteristics of the 1501AL-2 woofer (which is not the same woofer as is used in the DD66000) to those of the midrange horn and 476Be driver.

[emilime75]

The Everest DD65000 and DD67000 have shorting bars that determine which woofer receives the LF-only signal and which receives the full-bandwidth signal, allowing the user to designate either speaker as the left or right speaker. Once the speakers are installed in the listening room the user sets the shorting bars accordingly, placing the full-bandwidth woofer on the inside (closer to the other speaker).


Ahhhh, yes, now it makes sense. Thank you for that. The question that remains is the CTC distance, and primarily, the vertical offset between the center of the inner/lower midrange and the center of the waveguided upper midrange.

If anyone is interested, I am planning on a cheap man's version resembling the DD6x000. The plan is a 2226H, with a 10" mid next to it and a Cinema series 2374 waveguide above them. The 2374 is 30" wide and should allow a crossover in the 650-800Hz range, but I don't think I want to push things that low. Currently on the 2374 waveguides are 2425H CDs, which I may, or may not, replace.

Or, keep everything inline vertically, that would still put the center of the HF at about 36" from the floor. The other option is dual 2226H woofers side by side, 10" mid centered above them and then the 2374.

It'll be fully active with DSP, just trying to determine what arrangement I want to go with before I start cutting wood.

[hsosdrum]

If you're going full digital with DSP to each driver, the CTC distances really don't matter much, since you can apply delay in the DSP that will align the arrival times of all the drivers to any single point in space. Of course, this can only work for one speaker and one ear, and only if you keep that ear perfectly still in that exact spot (one of many reasons why stereophonic reproduction has such difficulty producing a truly lifelike analog of real sound), but that's a whole other kettle of fish. Using DSP and driver delay will get you closer to "real" than you can get without it.

I would go with whichever driver arrangement produces speakers that physically integrate better into your listening area. YMMV.

[1audiohack]

Although I can't be sure, I assume that Greg Timbers chose 850Hz for the DD67000 because that crossover point better matched the directivity characteristics of the 1501AL-2 woofer (which is not the same woofer as is used in the DD66000) to those of the midrange horn and 476Be driver.

Also if I correctly recall the DD6500 uses the 476Mg driver like the 4365 no?

Barry

[1audiohack]

Ahhhh, yes, now it makes sense. Thank you for that. The question that remains is the CTC distance, and primarily, the vertical offset between the center of the inner/lower midrange and the center of the waveguided upper midrange....

Or, keep everything inline vertically, that would still put the center of the HF at about 36" from the floor. The other option is dual 2226H woofers side by side, 10" mid centered above them and then the 2374...

My vote always goes for two 15"'s and a 10" like the 2123 or 2012, that done right would absolutely rock! I just love the bass presentation of wide baffle boxes like 4350, 4435 and DD6X00's.

The vertical tightly packed arrangement is an ideal, and a good one but it's not always possible. Close together is never a bad thing and something I strive for in design.

This should be fun! I want to see how it turns out.

All the best,
Barry.

[hsosdrum]

Also if I correctly recall the DD6500 uses the 476Mg driver like the 4365 no?

Barry

Yep. In the 65000 both the 476 and the 045 drivers have Magnesium diaphragms; on the 67000 they have Beryllium diaphragms.