Beyond the Ariel

[MJK]

I thought what ScottG said made a lot of sense.

I think he was referring to the filler driver(s) as the woofer and the super tweeter that fill in where the full range driver is reaching the limits of its capability. Crossovers very low and very high. This is the path I took with my Lowther OB system and I am very happy with the results. I am also taking this path with a new smaller OB design.

To me this option seems significantly more forgiving when compared to a crossover between a large diameter woofer (probably beaming) and a coax compression driver in the 1 to 3 kHz frequency range.

[BudP]

Hi All,

Go and take a quick look at the frequency plots at the tail end of the white paper on EnABL Specifically the initial curve trace of untreated Vs treated cone tweeter.

http://www.positive-feedback.com/Iss...ndingwaves.htm

That sort of "smoothing" up in the harsh top end of cone drivers is very typical of treated cones. So you may be able to have less than perfect cone activity here and not suffer from it. I suspect that a Mamboni process also applied to the cone driver bottom back cone skirt will help smooth things out, as these frequencies, at the top of a drivers range are where the worst sounding of the offending standing waves are created.

Bud

[ScottG]

Originally posted by Lynn Olson
Returning to the 18Sound discussion, the performance of the previously-mentioned 12" drivers and the top-of-the-line 18Sound horn/driver sets is almost making me re-think the whole coax thing. Simple crossovers combined with inherently smooth driver response is a rare virtue in the high-end biz, and even more rare in the high-efficiency world.

An 18Sound top end, combined with 2 or 4 Alnico & Ceramic Tone Tubby's supporting the bass module, could make a stunningly good 99 dB/metre efficient dipole loudspeaker. I'll throw it out to you guys - of all the 18Sound horn/CD combos, which are the best? (Most advanced CD, most advanced horn with the smoothest response, you get the idea.)

..there isn't a single horn there I'd recommend. Horizontal dispersion just isn't enough, and the cut-off freq.s are too high even with a steep crossover. (i.e. you would "hear" the horn.)

DDS had some horns that might "cut it" but they were all about 20 inches in width and not inexpensive. Who knows, maybe assistance audio has some in stock? Purchase one and use it to form a silicone mold for a cement horn?

It would also be MUCH better if there were 2 drivers/horns per loudspeaker operated as a dipole. (..don't remember if that was discussed or not.) Again, another reason to make a silicone mold.

Beyond that would be a custom horn, either radial or bipolar to "graft" radial dispersion.

As to the compression drivers.. Radian (after a good deal of "break in"). (..unless you like ultra clean and "pin point" in which case I'd say BMS.)

[ScottG]

Originally posted by MJK
I thought what ScottG said made a lot of sense.

I think he was referring to the filler driver(s) as the woofer and the super tweeter that fill in where the full range driver is reaching the limits of its capability. Crossovers very low and very high. This is the path I took with my Lowther OB system and I am very happy with the results. I am also taking this path with a new smaller OB design.

To me this option seems significantly more forgiving when compared to a crossover between a large diameter woofer (probably beaming) and a coax compression driver in the 1 to 3 kHz frequency range.

I was also referencing that.. but most of what was written was specifically directed at the B&O filler driver approach that Lynn "shot down".

BTW, I've done this also, Madison Knight 10's (16 ohm) in parallel for the open baffle midbass, fostex 166 esr for the mid, variety of tweeters, monopole sub, etc.. It IS a good solution.

[Salas]

Originally posted by Lynn Olson


I completely agree. From the looks of some of these drivers, there will be a 2nd-order network followed by a shelving network so the energy at 4 kHz and 16 kHz are reasonably level - and then followed by an L-Pad (for development purposes) or an auto/transformer. Not having to use a notch filter would be a big plus in terms of network complexity.

I have seen JBL wedge monitors with 3! LCR antiresonance series traps one after the other! Gruesome complexity for a high pass.
And don't forget the damping factor sacrifice when using big series resistors to pad down the CD. A good traffo is way more elegant.

[planet10]

Originally posted by Lynn Olson
The trouble region for all of these coaxes is obviously in the 1 to 5 kHz region...

Can coaxes be made that are smooth in the critical midrance region? Well, the 12 and 15-inch paper-cone Tannoys succeeded.

(not-simple) Cross-over at 1kHz... the 10 was always my favorite.

dave

[planet10]

Originally posted by MJK
I think he was referring to the filler driver(s) as the woofer and the super tweeter that fill in where the full range driver is reaching the limits of its capability. Crossovers very low and very high.

This is the approach i've been takking for 25+ years... now that i'm on a frugal-phile(tm) budget i'm making do with the filler driver

dave

[Lynn Olson]

Originally posted by MJK
I thought what ScottG said made a lot of sense.

I think he was referring to the filler driver(s) as the woofer and the super tweeter that fill in where the full range driver is reaching the limits of its capability. Crossovers very low and very high. This is the path I took with my Lowther OB system and I am very happy with the results. I am also taking this path with a new smaller OB design.

To me this option seems significantly more forgiving when compared to a crossover between a large diameter woofer (probably beaming) and a coax compression driver in the 1 to 3 kHz frequency range.

Gosh, this embarassing, we're all in agreement! Hello, little trollie, where are you? We need a little fireworks. (Shhh, I didn't mean that, nobody heard it, right?)

Yes, what I'm aiming for is the opposite of the B&O approach - a near-fullrange driver that operates in parallel with bass augmentation, and is "helped out" by a tweeter with a high crossover. If the coax is abandoned, the 12" driver can be run out to its full range, perhaps with a modest series inductor (and Zobel compensation) to offset the rising midrange that is typical of large-diaphragm drivers. Despite what the Polar-Pattern Police say, I can tell you the Bastanis sounds really good (in the MBL class) in terms of dimensionality and imaging with its 12" driver running freely out beyond 5 kHz. As mentioned earlier, I think part of the real secret of dipoles isn't so much the polar pattern, but the complete lack of box coloration.

I am partial concurrence with the dipole tweeter discussion. Rather than have the backwards-facing tweeter assembly sticking out of the front baffle above the woofer, I think a better location for the rear tweeter is below the fullrange driver, maybe even at the base of baffle assembly, pointing up and facing the rear wall and ceiling. The purpose of the rear tweeter is to "light up" the back wall and ceiling reflections, bringing the total room-energy spectrum more in line with the direct-arrival spectrum. It doesn't need to be in phase synchronization with the front tweeter to do this - in fact, there's no way to do this unless you're using a prosound ribbon and remove the back plate (a very possible option).

[jeff mai]

Originally posted by ScottG
..there isn't a single horn there I'd recommend.

Make your own. Although I'm sure Dr Geddes would disagree, there is precious little difference between one of his constant directivity waveguides and a conical horn with a "quadratic" throat detail. I calculated this out and the max deviation between the two profiles is only a few mm.

I was going to build something like this before deciding to buy my Azurahorns. I was also going to do a rolled back edge treatment to reduce diffraction. The edge was going to use a 6 inch PVC pipe split in half lengthwise and attached to the plywood horn sides to form the roll. See the rendering.

The BIG problem with doing a constant directivity horn of any profile is finding a compression driver that doesn't screw up the directivity in the HF. The throat detail on the compression driver itself is usually a small exponential horn which causes beaming in the extreme HF no matter what the horn profile does later. You really need one with a conical throat expansion. As of a few years ago, I don't think anyone made anything suitable.

The next biggest problem is finding a good sounding compression driver. Most don't sound very good, trading away smooth response for impressive -3db HF figures. You're going to need a HP shelving circuit when using a constant directivity horn no matter how great the HF response reads in the specs. Better to get an earlier but controlled rolloff.

[swak]

Jeff,

that is a point (exit of the CD driver) that has been underlined over and over again at the AA board. Maybe the B&C compression driver Geddes is using has an appropriate profile.

How about designing a ribbon with the magnets/steel front structure (and maybe back, if dipole) and flange(s) profiled as a waveguide to control and maybe match the directivity (horizontally) of the 10" or 12" wide-range mid? Linesource, a member of this forum knows ribbon design very well and might be willing to help. he has already posted here lots of interesting material. When I played with the idea of building a ribbon I had the feeling it was nor over-complicated and not expensive. And maybe, instead of a impedance matching transformer for the ribbon one could use a nice small transimpedance amplifier...

I would vote for the DIY ribbon solution, specially as the project now stands as not going for off the shelf components (i.e. designing and constructing a horn for the compression driver, which would be about as complicated as designing and building the ribbon).