Some design ideas for Dipole/OB needed?

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

Very narrow baffles are almost the exact opposite of OB sound

Between your opinion and SL's observations re. ORION/PLUTO (and I've heard both myself, too) I'll go with SL . . .

[DoubleTap]

Re: Some design ideas for Dipole/OB needed?

Between your opinion and SL's observations re. ORION/PLUTO (and I've heard both myself, too) I'll go with SL . . .

Apparently I'm not the only one who thinks that about wide baffled speakers.

http://www.troelsgravesen.dk/Acapella_WB.htm

Pinpoint imaging isn't what OB's do ... but it is what narrow baffles do (among other things). OB's from my experience almost always have a larger, more diffuse center image.

[dickwest]

Re: Some design ideas for Dipole/OB needed?

Here are some more findings/opinions about baffle width:

http://gainphile.blogspot.com/2008/04/ob-design-mantras.html

- The baffle size should be less than 2.2x effective midrange cone diameter. This way the dipole peak will be pushed higher in the frequency response, ready to be crossed with a tweeter. Using very wide baffle will push down the peak (more bass) but also put the peak-and-dip in tweeter crossover region.

[Flint]

Re: Some design ideas for Dipole/OB needed?

Yeah, this is the current state of the art for dipole design--as you go higher in frequency the baffle needs to get increasingly smaller. The point is that the radiation pattern will remain true to the theoretical figure-8 dipole diagram when the baffle doesn't interfere with cancellation between the front and back. As you go lower the baffle needs to get bigger either to help get more output or just to fit larger drivers. It suggest either a cascade of mini-baffles, a ziggurat or pyramid or another tapering shape, or a frosty the snowman stack, etc. There isn't one width that works from top to bottom.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Lots of conflicting opinions here but some things said smatter with a breath of credibility. To not offend either, i'll keep the rest to myself.;)

That being said, i'm vey greatfull for the links.....excellent reading. The Orion isn't the slimmest, or widest baffle but SL himself says he's astonished at the level of performance of the Pluto when costs compared......that does say something for Dewards point i must admit.

On the other hand, wide baffle designs from Troels such as his PM Straads are very well received by the builders and listeners alike.

I think the build strategy here might be a modular system while under testing/construction. My original plan includes the RSS315HF in a sealed enclosure on the bottom.....that box can be built to optimum volume with a 15"x15" baffle and left as is. The mid and high section can be attached makeshift with simple temporary side rails on the bass bin.

I might just jump in with the purchase of a pair of the Eminence 3012HO' and get em on an opne baffle and see just how they react with the room and more importantly......my ears. Given this, does anyone have an objection to this driver OB given the T/S parameters, Augerpro and Zilch's measurments or the fact that there's a capable sub underneath that can extend in stereo to 200hz beautifully! Whatever HF device is chosen, it can be mounted on multiple baffles of different widths. Maybe even the QSC horn with no baffle at all!

[martin]

Re: Some design ideas for Dipole/OB needed?

Yeah, this is the current state of the art for dipole design--as you go higher in frequency the baffle needs to get increasingly smaller. The point is that the radiation pattern will remain true to the theoretical figure-8 dipole diagram when the baffle doesn't interfere with cancellation between the front and back. As you go lower the baffle needs to get bigger either to help get more output or just to fit larger drivers. It suggest either a cascade of mini-baffles, a ziggurat or pyramid or another tapering shape, or a frosty the snowman stack, etc. There isn't one width that works from top to bottom.

I totally disagree. While the narrow baffle at first seems like a nice concept, it also comes with some drawbacks that are not always discussed up front by supporters.

If you use a narrow baffle so that the driver is operating below the dipole peak, you need to add EQ and additional power to compensate for the 6 dB/octave roll-off inherent with this concept. This most likely means an active EQ/crossover with multiple amps, not a design for a passive crossover or a newbie. If you really want to stay true to the concept, it also means at least a three way and probably a four way or more. In summary, more drivers, more EQ, more amps, more complexity, and more COST.

I prefer a simple approach that uses the dipole peak in the crossover design between a high Qts low cost pro woofer and a midrange or full range driver. This can be done actively or with a passive crossover. This is a simple low cost design that is very flexible. The radiation pattern is still a figure 8 and the baffle does not interfere in any way. Operating the midrange or full range driver above the dipole peak, the main objection from the narrow baffle crowd, can introduce some ripple that is reduced by off-setting the midrange or full range driver from the baffle centerline. The ripple is minor compared to what the room introduces.

I look at the narrow baffle designs as state of the art with respect to complexity and higher cost. I look at the wider baffle designs as state of the art in terms of simplicity and lower cost. Both can sound great. The designer needs to pick the trade-offs.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Excellent point Martin, and i've followed your design Mantras around the high Q drivers (Alpah15's and the like) where the models on an infinite baffle really make sense of what's going on in the sub 100hz range.

If i might ask.....consider your explanation of a midrange/fullrange driver on top.......as a comparator or equivilent would a waveguide loaded dome tweeter that holds directivity to 1khz or so do the job?

I'll reference MarkK's recent experiments with the Dayton RS28F in an 8" waveguide

http://audioheuristics.org/RS225%20dipole%20project/whats_new.htm

Without considering anything other that the measurements and your theories on dipole radiation......whadda you think? Considering my goal of a high sens/high spl/dynamic system certainly a more suitable HF device could be mated to a similiar WG with good results.

And again for Martin, if i'm not mistaken such a design when mounted on a wider baffle 'fixes' the problems associated with the HF device on the wide bafflle and measures as if on no baffle at all due to the radiation pattern of the WG. I'll quote Zaph as it MIGHT pertain to this.....

"Related to the directivity benefit is the fact that a waveguide is not affected by the baffle it's on. Baffle diffraction is a non-issue compared to a standard dome mounted in an enclosure. In a waveguide system, you will not see the lower treble "ripple response" present in typical box systems. Fans of flat baffle dipoles, take note: with no cabinet depth, this is the worst case diffraction ripple. A waveguide is perfect for dipole usage, keeping the lower treble smooth"

Hey John......hopefully i'm not misquoting you here...it's not my intention:D

I'm hoping that the more i read, the closer i might be getting to something really special here!

[DoubleTap]

Re: Some design ideas for Dipole/OB needed?

Just realized you might be thinking I mean to imply that I prefer wider baffles for OB, that's not what I meant. My point only was that for a boxed speakers, wider baffles tend to have a more "OB like" imaging characteristic whereas narrow baffles are more pinpoint imagers.

But the real point in my first post is echoed by Martin, don't sweat it ... there are plenty of ways to get fantastic results. Set some goals, choose drivers and a design appropriately, and get started. Equip yourself with the necessary tools to identify and fix any problems encountered along the way and you'll do fine.

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

There isn't one width that works from top to bottom.

That's where a "H" frame has an advantage . . . in becomes acoustically wide at low frequencies without becoming . . . wide. It makes for a more managable speaker, much less . . . imposing . . . than planars (I used to have MG3s) or giant triangles with a couple 15" drivers at the bottom. With an appropriate width midrange baffle determining overall width you get uniform dipole radiation up to the MT crossover.

How to maintain a dipole pattern above MT is a different problem. It is difficult to get clean side-wave cancellation with back-to-back tweeters, so there can be a polar "bloom" in the lower tweeter range, before the tweeters begin to beam, with . . . unpredictable . . . side wave summing. In many cases a little side-wall absorbtion will take care of things. Absorptive donuts around the tweeters might work (I hear little/no noticable difference in my room, but side-wall absorbers are already in place). Waveguides would be nice, but to be effective may exceed baffle width, and are difficult to nest (front and back). Single (unidirectional) tweeters blow the polar altogether, and "soundstage" with it, while small dipole planars tend to high distortion, and the midrange baffle is too wide for them. There's no perfect solution.

Imaging is precise with properly set up dipoles, while "soundstage" is full and convincingly "realistic" *if the front wall (behind the speakers) is a diffuse reflector*. The front wall should not be "dead", and does not sound as good if it produces pronounced "specular" reflections. To my taste the back wall (behind the listener) should be relatively dead, while the rest of the room can have "normal" small room acoustics (which the brain masks out when listening to the speakers). Not surprisingly my ORION sound best in my room in almost exactly the same location that my Maggies sounded best (5-6 feet from the front wall). Perhaps surprisingly the Thiels that I had (between the Maggies and ORION) sounded best in about the same location, but while quite "clean" never had the soundstage that the dipoles had/have. I'm blessed with a good room . . . a number of speakers I've tried over the years sound good in it. But there's no doubt that full range dipoles sound best . . . and the ORION sound substantially better overall than the Maggies did (even with a subwoofer), especially in the bass.

As I've said a couple times in the past I'm relatively sure that ORION performance could be mimicked or matched at considerably less expense (mostly in drivers) . . . but I wouldn't stray too far from the basic design were I to try.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Deward....i would assume that you suggest that a rear firing tweeter is essential for this type of design? Please say it ain't so? If that's the case i'm s#@t outta luck i think. I will treat the area behind the speakers with DIY panels......maybe tackle this first to get a fresh 'canvas' to work with so to speak.

[brianpowers27]

Re: Some design ideas for Dipole/OB needed?

Deward....i would assume that you suggest that a rear firing tweeter is essential for this type of design? Please say it ain't so? If that's the case i'm s#@t outta luck i think. I will treat the area behind the speakers with DIY panels......maybe tackle this first to get a fresh 'canvas' to work with so to speak.

I think that you wouldn't have much to lose... go ahead and go for it, if it doesn't require the purchase of many parts.

If you have the measuring gear, work this through an iterative process. Post results and I am sure you could find others to help you through.

[ocdSCHACK]

Re: Some design ideas for Dipole/OB needed?

You should build them; I would've never built a single speaker if I listened to the warnings of the masses. Because I built a pair of dipoles, I feel the need to comment though. After building a pair, I now tend to think:

1) For dipole, the mid-range speaker has the largest effect. (In my opinion, bass often has, at least 100Hz and lower, too low a frequency to really make a huge sound difference, and the tweeter radiates plenty on its own.) -I'm only referring to what is most important, not what is perfect.

2) Be sure to use speakers with a decently flat Frequency Response. The response will not be as perfect as your normal box speaker, so simplify everything where you can.

3)If you build a 3 way where all 3 speakers are open baffle, don't assume you will have good low end response. I used two Peerless 10" XXLS per speaker(4 total) and still had a large drop at 100Hz.

Good luck with the build. Don't get scared away from doing it.

For more info on my build, the link is:
http://techtalk.parts-express.com/sh...d.php?t=214732

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

3)If you build a 3 way where all 3 speakers are open baffle, don't assume you will have good low end response. I used two Peerless 10" XXLS per speaker(4 total) and still had a large drop at 100Hz.

Clearly you know that ORION uses two Peerless 10" XLS per speaker, and has no drop in bass . . . they're flat to at least 30 Hz in my room (though they run out of excursion on explosions and dinosaur footfalls). Since your "H" frame has roughly the same dimensions I'd guess the drop you see is an equalization issue, or a room issue.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Nice Job!

I'm waffling all over the place with this now!:eek:

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

Deward....i would assume that you suggest that a rear firing tweeter is essential for this type of design?

Not "essential" . . . ORION originally had a single tweeter, after all. But properly positioned in a good room the addition of the second tweeter makes a significant, obvious improvement . . . not in "clarity", and not in localization (which may or may not be the same as "imaging" to some people), but in the creation of a believable "soundstage" or overall "sonic image". In this my experience agrees completely with SL's comments at the Linkwitzlab site.

I thought ORION were the best speakers I'd ever heard with only one tweeter. Adding the second made them better. I'm not convinced that the rear radiation could not have been filled in with a less expensive driver (after hearing PLUTO I'm not convinced Millennium are needed in front, either), but at this point I have no reason, or desire, to experiment. I'm pretty sure a less expensive driver wouldn't sound *better*, so there's no reason to change.

"Something new" might change that, of course, but I haven't heard it yet . . .

Edited to add that if your front wall is "dead", or the speakers are placed too close (less than four feet) to it, a rear tweeter will add little or nothing to the presentation, and may even detract from the clarity of the sound.