Some design ideas for Dipole/OB needed?

[Mayhem13]

Well after playing around with OB midwoofer and 1" domes on scrap MDF, i can honsetly say that i prefer the boxless sound.......profoundly i might add. So with much reserve and not enough $$$, i'm gonna do it anyways!:D

But before i begin, i'd like to have some opinions on the room and placement as even though the junk/test boards gave a very pleasant and spacious presentation, a properly designed point source may be more practical.

I have about 18" of space behind the baffle as free space and the same to the outer walls. Seperation would be about 9ft center to center with an average listening distance of 14ft.

High dynamic range and high efficiency are primary design factors so.......

For bass duties, i simply don't have the space for dipole/OB 15" woofers.....and my room does pretty well with sub 100hz content. First compromise/tradeoff already identified and accepted!

I'd like to use some stuff i already have....namely a pair of RSS315HFs ready for repurposing......as an active bottom end to a 2way OB/dipole top end. Plenty of power on tap for these by way of an NHT B-20 subwoofer amp which currently gives really flat smooth output on the RSS's to the mid twenties. The second order filter goes as high as 240hz need be......in true stereo of course. Figuring on sealed boxes on the bottom and detached from the OB baffle top, i figure on 2.25 cuft volume....Bass response models very well and the current 2cuft sealed arrangement is very smooth in the current position so no worries there.

That being said, for the top end, i'm thinling along the lines of the Deluxe Econowave H0's.....only OB for the 3012HO. Take a look at the open basket on these babies.....


So this is as far as my knowledge of dipoles can take me. Measurements of the 3012 show that we can push it to 1.5kz or so without a problem, but i'm inexperienced on how it will behave OB and just how low it'll go or how low i should take it.

Now the QSC/B&C 250 combo seems like a no brainer here and offsetting the horn for matching the AC to the woofer is a piece of cake. But my biggest concern is the possible 'disconnect' in soundtage from the dipole midbass to the high directivity horn......but maybe with the right slopes and XO point it might just be what i'm looking for.

For Pete S, hopefully this isn't bearing too much resemblance to your steriod powered Orion idea, which BTW is exactly what's fueling this project. You and Zilch have to take some of the blame here with all of the great work done in the Ewave variations.

As does Paul Carmody whose Aethers have been an aching thorn in my side from the first time i saw them......HYbrid is a great thing and will probobly be a large part of the design criteria here as the side panels obviously help with bass extension.

So..please....all of those with knowledge in this area kindly share your thoughts and design philosophies if you wouldn;t mind. Too bad AJINFLA is banned as he certainly has a wealth of knowledge on the subject....and the appropriate amount of sarcasm to share as well.

As always thanx in advance!

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

Everything you need to know is at http://www.linkwitzlab.com/ , , , read especially through the Phoenix design section and the "issues in loudspeaker design" and "conclusions" sections.

The problem with transitioning from a sealed woofer to a dipole mid is that around crossover the front waves add and the rear waves cancel. Sounds weird when that happens at 150 Hz and up. Not quite so bad lower, where the room shifts into pressurization mode, but dipole bass sounds better. "H" and "W" frames work fine, and fit better in the room than a stack of 15"ers.

The transition from dipole midrange to a uni-directional horn tweeter also raises issues. It just doesn't sound right, and really messes up the sense of "space". Adding the rear tweeter to ORION made/makes a substantial difference. Maintaining something close to a uniform polar response matters . . . a speaker that transitions from omni bass to dipole mids to uni-directional highs just compromises too much . . . there's a lot more to gain from going dipole than just getting the mids "out of the box" (although that's certainly a good thing too).

18" from the walls is really too close . . . it will sound better to move them out and closer together.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Good points......and realizations of most of my fears unfortunately. I've read the same from other designers in regards to the mid/high transition. I think i could like with the omni bass though and could get the XO point low enough without sacrificing power handling of the mid. The horn tweeter is going to take some thinking. Adding a second rear firing HF device is out of the question...for size, space and budget reasons of course.

Somehow the Emerald Physics designs seem to overcome this issue.....possibly through extensive DSP from the active crossover?......i don't see how though. Directivity is directivity.

The god thing is experimenting here isn't going to be that labor intensive as baffles are pretty easy to construct as opposed to conventional enclosures.
Thanx for the help Deward!

[natediggidy]

Re: Some design ideas for Dipole/OB needed?

Some things I've learned from having Maggies is room treatments and speaker positioning are as important as the speakers themselves.

As far as room treatments, you want absorbtion at the sidewall first reflection points and diffusion on the wall behind the speakers. Boxless sound can be great, but if the room you're in is working against you, you might as well be listening to Bo$e.

Positioning is key too. Give your test speakers a good listen, then move them twice as far from the side and front walls as they are now. See how the sound changed. Probably by alot. Dipole/OB react with the room very differently than regular box seakers.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

And i always thought that OB/Dipole speakers were influenced LESS by the room than a conventional speaker, not differently. I really liked the way the throw together OB's imaged but they are a far cry from what i'm proposing.

Question: Will a box speaker with a very narrow baffle share some of the imaging characteristics of an OB/Dipole. My living room system has a Pair of Athena towers whose baffle is only 4" and imaging is fantastic-----tonality and distortion are terrible but....the imaging makes them usable and even somewhat enjoyable at lower levels when used with a sub.

[Deward Hastings]

Re: Some design ideas for Dipole/OB needed?

baffle is only 4" and imaging is fantastic-----

That's because the very narrow baffle moves baffle step up in frequency (making the speaker omnidirectional well up into the midrange). It's that "constant directivity" thing again. See, for example, Linkwitz's comments comparing ORION and PLUTO . . .

[natediggidy]

Re: Some design ideas for Dipole/OB needed?

And i always thought that OB/Dipole speakers were influenced LESS by the room than a conventional speaker, not differently.

Imagine a diagram of your room with your speakers on it. The speakers, being dipolar, radiate sound to the rear as well as the front. The rear soundwave has more surfaces to reflect off of and each of those surfaces will change the sound a bit before it reaches your ears. Do the "twice as far from the walls" thing and see what results you get. The good news is that room treatments can be DIY'ed inexpensively.

[Flint]

Re: Some design ideas for Dipole/OB needed?

If you put the RSS315s into H-baffles, the deep bass would be limited but you'd get that OB bass character and the dipole radiation pattern. The H-baffle would be usable up to around 150 Hz. It should be fine for moderate listening levels. Active EQ would be necessary.

If you did use boxes for the bass, you could simplify the Orion concept by going 3-way for the system. Basically omit the H-baffle bass section and transition directly from midrange to subs. The 3012HO might get you down to 80 Hz or so. This would be a very wide ranging mid, from 80 Hz to 1500 Hz or so, handing over the highs to a...? It would be a dramatic change in radiation pattern to use a horn above an OB midrange. But there are fans of that arrangement.

There's also the Manzanita project, which used a Peerless SLS 12" and a SEAS tweeter (27TDF?) in a 2-way open baffle. Your version could substitute the Eminence 12". Dome tweeters could be mounted back to back. Having rear tweeters would make it more crucial to have space behind the speakers. Of course if these are 2-way open baffles with a single 12", they wouldn't be particularly large, and it would be easy enough to pull them out for listening.

Another thought: for the price of the 3012HO you could get a SEAS L26, kind of an oversized version of Orion's mid. Cross at 1.2 kHz to a waveguided tweeter (RS28F). This would work best crossing above 120 Hz to an H-baffle woofer.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

I Do have a pair of 27tdfc's as well as a pair of modded MCM 6.5" waveguides and other waveguides i've been foolin with....but i fear the 1.5khz XO for the dome is too much to ask and i'd have to pad the 3012HO to meet it.....exacly what i don't want from this design.

My biggest concern is the different radiation patterns between the mids and highs BUT...what makes the constant directivity of the horn different from the radiation pattern of the orions single forward tweeter om a flat baffle? The single tweeter model is a very highly regarded speaker as i understand it. I havent' had a chance to read through all of SL's papers on dipole theory but i'll certainly tackle this tonight.

On another note, if the type of open, spacious sound i'm looking for can be obtained from a very narrow baffled enclosed speaker, i'd gladly persue that option over OB/Dipole. I can get the efficiency out of 4 6.5" midwoofers and an SB29 WG mounted. Thoughts?

[gvimhoof]

Re: Some design ideas for Dipole/OB needed?

Another good source of info in OB is the "Open Baffle Theory Articles" by MJK.

I made that same recommendation today to some one else... weird. Maybe the stars are in alignment for a rash of OB experimentation? Open Baffle = Open Sound!

[brianpowers27]

Re: Some design ideas for Dipole/OB needed?

If you have the parts on hand go ahead and try it. I think that with some work the mid to horn integration can be successful.

The rear tweeter in the orion adds ambience but due to the wide baffle it likely doesn't contribute to the overall tweeter directivity.

If this build requires extra cash, I would strongly suggest considering the possibility of a dipole 3 way + sub. This would greatly improve your sound since the woofer wouldn't be forced to cover ultra low frequencies.

1. If your sub amp has an adjustable lowpass, try rolling the 15" off around 50-100hz and place the woofer in a simple OB configuration.
2. See if you can find a polar response chart for the horn at the intended xo point. Use this to attempt to match the polar response of the mid.
3. The polar response through the xo region can be adjusted by means of xo slopes and ac alignment.

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

Thanx Brian......i need some encouragement here as i'm starting to head back inside the box so to speak. It's quite possible that my listening room/theater is not OB/Dipole friendly and after reading SL's placement recommendations or should i say 'limitations' for dipole speakers i'm even more concerned.

I've been searching a long time for that acoustic magic moment....the one that lead most of us to this hobby in the first place. For me, it was 'Time' from Dark side of the Moon in the Hayden Planetarium on a custom installed Advent system......between the reverberent roto-toms in the intro to the amazingly spacious first and second solo's......nothing i've heard comes close to date. I've attributed it to the dome ceiling as the diffuse soundfield..and the dynamics of course. Not one of my either commercial or DIY projects have captured this.....nor have they been OB/Dipoles.

Obviously a project of this magnatude is gonna involve a significant investment of both $$$ and time....of which i have little of both:D so i'm asking the question.....Should or Could?

[Mayhem13]

Re: Some design ideas for Dipole/OB needed?

A ray of sunshine......maybe?

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

A dipole mid section with a high directivity HF section.....someone likes the idea!:D

[DoubleTap]

Re: Some design ideas for Dipole/OB needed?

Don't overthink it, and don't let bogus advice like that from Deward deter you. Pulling off a great sounding OB design isn't that hard. 90% of the magic from OB comes from having the vocals OB, don't worry about having only a forward facing tweeter and woofers in a box. Sure they can produce incremental improvements, but clearly aren't mandatory for great results.

I'd think you won't have any problem crossing the TDFC at 1500 if it's in the MCM waveguide. The TDFC can come pretty close to doing 1500 on a flat baffle, and the MCM guide will give you enough gain to do the trick.

As far as what style box comes close to producing OB sound, it's not a narrow baffle ... it's the near infinite-baffle style box that does. Very narrow baffles are almost the exact opposite of OB sound, while the Sonus Faber Stradivari style produces that big diffuse center image with instruments floating in an area - not a pinpoint location. What OB's do better however is front/back image depth.

I've done 4 OB's, have two more in planning ... there aren't any OB 'rules'. And they're easier to pull off than most on the intrawebs would lead you to believe. For what ended up being my best OB design, I honestly didn't sim anything with the OB behavior. I just built it and listened.

[dickwest]

Re: Some design ideas for Dipole/OB needed?

Plow through this rather long thread for some good info, both measured and subjective, on the importance of baffle width:

http://www.audiocircle.com/index.php?topic=64048.0

I built a pair of Aether clones using some superb (now unobtanium) audax drivers, and experimented with one baffle with wings, another baffle with no wings and narrower, and finally an even narrower baffle. Narrow trumps wide and the above thread helps to tell us why.

Good luck