So - why DON'T people go with open baffle?

[spasticteapot]

I've been looking at bodging together some open baffle designs, and was curious what their detractors have to say on the subject. Aside from the enormous cost of the giant woofers involved (which is, to be fair, a definite detractor), OB speakers seem to have their competition licked when it comes to even dispersion and dealing with room acoustics.

That said, some of the math does seem to be a bit fuzzy. Without extremely narrow baffles and some slightly unusual drivers in a 4-way configuration (like a certain dipole speaker sold by a certain forum member), getting even dispersion seems almost impossible. The need for enormous midrange air movement also tends to result in some somewhat odd driver pairings, such as a pair of 8" woofers with a dome tweeter (sans waveguide)!

I've never had a chance to hear OB speakers of any quality personally - aside from endless mediocre Martin-Logans, they're just too darned rare. I have, however, heard quite a lot of very nice conventional monopoles. Can anyone who has had the opportunity to compare and contrast give me their opinions on the subject?

[MSaturn]

Re: So - why DON'T people go with open baffle?

It's just another option in a wide gamut of choices intended to minimize certain properties - room interaction in the bass, box resonance - and maximize others, like euphonic reflection and controlled directivity.

There's solid science behind the 'openness' of dipoles, which has less to do with the actual open nature and more to do with the total elimination of box pressure and internal reflections. A critically damped box system will sound very similar, if not the same.

Dipoles tend to be larger, uglier, and more expensive, and perform much better (in my opinion) when used in an active setup, which adds further cost. I support the idea, but I've discovered it's best to have a full measurement setup and a lot of space if you're going to go OB.

And yes, the overall science and its application are esoteric or little-known fields. Some users have things locked down, like John K. There aren't many like him out there, though - and you'll notice most big OB supporters are those with many years of experience with standard speakers and their science looking to push the envelope (see Linkwitz, for instance, and his recent work with OB and omnidirectional systems).

In the sense of ultimate performance, I believe an OB speaker might be vital. But the cost level we're talking about there is one most users will never reach.

[Saurav]

Re: So - why DON'T people go with open baffle?

Here are some of the potential downsides to OB as I perceive them. Just my experience, in my room...

* As you mentioned, they have the potential for good off-axis response, but that usually requires narrow baffles, specific drivers, and often, complex / active crossovers. I haven't heard / measured any of the wide-baffle designs, so I don't know what their polar response is like.

* Generally speaking, you need to pull them further out into the room. In my case, I have about 3.5' between the baffle and the wall. I've tried it about a foot closer, and the soundstage depth collapses completely. It's been a while since I had box speakers in this room, so maybe a box would do the same thing, I can't say.

* The imaging is more vague / diffuse. Again, just in my room, which is completely untreated. I suspect things would get better if I could put diffusion on the front wall, and if I weren't sitting with the couch up against the back wall. But anyway, that's one of my impressions. This may or may not be a negative. It doesn't bother me, and with some music (mostly classical), I actually like this kind of presentation better. It seems to decouple the image from the speakers better.

* No low bass. I cross to a sub at 80Hz, and I don't listen very loud, so I can get away with a single 12" per side. If you want to go lower and/or louder, you'll need more woofage.

[AMC]

Re: So - why DON'T people go with open baffle?

I think in the end it comes down to that problem of getting any low end response out of the system. Some will supplement with a more conventional driver arrangement for that range to be a fix. Also, there will be some that will tell you the uncontrolled nature (even dispersion) that you tout as a benefit is in fact a problem.

For me, I don't like them because they tend to get very large, complicated, and ugly before you get a speaker that sounds as good as a well designed conventional system, that ends up half the size and cost. There is, however, some cool factor in having something different.

[skatz]

Re: So - why DON'T people go with open baffle?

Where are you located? If nearby you could come listen to my system. Its a two-way with BG 50" Planar dynamics open baffle, and sealed 12" woofer, electronic XO. I'm in west central Ohio.

Steve

[martin]

Re: So - why DON'T people go with open baffle?

It does not have to be expensive.

It does not have to be complex.

You can get bass into the 20 to 30 Hz range with a woofer costing less than $80.

You can use passive crossovers.

You can build a passive OB system for less than $500.

No rocket science is required.

All you need is to design with the right baffle width (a 20" x 40" works well), offset the drivers, and select a complimenting crossover point. In my opinion this huge effort to get some special radiation pattern with a narrow baffle is over rated, put the system in a room with reflections and I am not convinced if it is that important. You can get deep bass and good imaging even in a smallish room. It can be as simple or complex as you like, take of the narrow baffle blinders and pick your trade-offs.

[Saurav]

Re: So - why DON'T people go with open baffle?

See, I would think the opposite - the more reflective the room, the more I would expect the radiation pattern would matter.

But, I'm with you on some of what you say. I too have often wondered just how much some of this stuff really matters. For me, part of the reason for trying a narrow-baffle OB was the complexity / challenge / fun. And I'm quite pleased with my results (I usually am ). But like I said, I haven't built / heard / measured any designs based on the "fullrange + helper woofer on a wide baffle" principle, so I can't compare the two approaches.

[Face]

Re: So - why DON'T people go with open baffle?

* The imaging is more vague / diffuse. Again, just in my room, which is completely untreated. I suspect things would get better if I could put diffusion on the front wall, and if I weren't sitting with the couch up against the back wall. But anyway, that's one of my impressions. This may or may not be a negative. It doesn't bother me, and with some music (mostly classical), I actually like this kind of presentation better. It seems to decouple the image from the speakers better.

That's the nature of the beast. If you prefer large, spacious imaging, OB is the way to go. If you prefer well defined, pinpoint imaging, look elsewhere.

[MSaturn]

Re: So - why DON'T people go with open baffle?

Well, that depends on the room. A well-treated room with dipoles is going to image more correctly, as far as I'm concerned. Omnipolar speakers are the holy grail, but the more complex the reproduction method, the more complex the room must be, also.

[dlr]

Re: So - why DON'T people go with open baffle?

Before I got into DIY, my favorite system was a hybrid ribbon, dipole above 200Hz, closed box below, augmented with a subwoofer later on. I'm now going in the direction of dipoles of my own. This I almost certainly would not be doing were it not for the Ultimate Equalizer (UE) in SoundEasy. I have no desire to build active crossovers or buy them and passive equalization just isn't always suitable as I see it, it depends on the approach. My position on that is that it's more limited. The dipole equalization can be a sticking point. Not so with the UE. Active EQ also works well, of course.

A lot of reasons for/against have been mentioned, I agree with many and disagree with a number of them, some of which come down to preference, not absolutes. They need breathing room, yes. Deep bass is more difficult, but I have a great subwoofer as it is. I though I'd not need it, having two Peerless 10" woofers per side, but the bottom just wasn't there, though with the right setup the potential is there for dipole bass. Image will likely be less precise. To me, the tradeoffs are worth it.

I liked my old CB 3-way fine for a long time, still could be happy with it. The bass section is now deconstructed (a PR setup), but I can still use the M/T section on a 10" CB or my new dual 10' dipole. The difference in sound is surprising. Despite what some claim, I easily hear the difference, primarily in the midrange. The tweeter isn't a dipole, however.

My four woofers were PE buyouts at $35 apiece with the price break at four. So I have very good bass (not deep bass) for $140 in woofers. These cross at 250Hz and are not purely mid-bass drivers. They cross nicely to a 5" midrange. The UE allows me to easily cross LR8, so displacement isn't a big concern.

A large system is not necessarily required. H-frame or U-frame woofers are probably the key to keeping the size down. Those of Linkwitz and John K. show some of the possibilities. They are certainly a lot smaller than my old Apogee hybrid ribbons, if not in floor space, at least they're not 6 feet tall. My new 3-way is a bit smaller than my previous closed box 3-way system. The bass is also better, if not quite as deep, due to better in-room response, it doesn't energize the room modes in the same way. The lack of "one note bass" is actually a surprise and takes a short bit of time to become accustomed to. It's like switching from a sharp, edged system with which you've adjusted to one the is closer to flat. It doesn't make itself obvious, but you realize over time that it sounds a bit more accurate, or whatever you may want to call it.

The image is more diffuse, but part of that has to do with how close one sits. My room is small, I sit more closely, so I still have a relatively well-focused soundstage. Many don't care for that, it's still a preference.

You do need more amplifiers, of course. That was easily one of the bigger stumbling blocks, but with newer electronics available, it's less of an issue. The difficult part is in the measurement side. If you have difficulty with this, you're probably better off with something other than a dipole for DIY, unless you build a kit. I also forked out the cost for a remote controlled multi-channal volume control. Not a requirement, of course, just another possibility.

I also have to disagree with the suggestion that OB (dipole) is inherently dispersive and uncontrolled. Quite the contrary. Just because it's a dipole does not make it uncontrolled. A dipole is, in a way, better controlled than an monopole. A dipole can possibly have more "controlled dispersion" (read directivity) than a monopole (CB, reflex, whatever). I'd go so far as to say that it's easily more controlled than most monopoles. However, there are limits to that control based on dimensions, as it is for diffraction in a monopole, and the design will reflect that. Pick your poison, so-to-speak.

The nature of a dipole is inherently controlling in a way, given the interaction of front with rear radiation. How well or poorly it performs has more to do with the designer than it does the system. This is no different than any other system. Comparing poor to good is a canard. Consider just how many really bad sounding systems you've heard. I would wager that most were probably not dipoles. ;) That probably has more to do with the number of designs of given type than it does type of design.

There are additional difficulties with a dipole. I'm running into some of them now. :( There is one item that I find exceedingly beneficial. I don't have to construct a box. :D

I'm working towards a (quasi-)dipole system in a 3-way. The tweeter is not dipole, though ultimately I'll build a system that has that. As it is, it seems feasible to build a dipole system with relatively good directivity (controlled, not constant, dispersion) and it isn't absolutely necessary to use exotic drivers. I'm using a Scan-Speak as much because I have it on hand. Linkwitz's and John's systems do not use expensive, exotic drivers, either (well, not exceeding expensive for some). In the end, the cost of the drivers may be no more than an equivalent monopole system.

It can be a bit more tricky, for me that's partly because I've chosen the goals, one of which is to maintain true dipole operation across a wider spectrum. As in all things audio, the devil is in the details. Much depends on your set of goals. Just as with any multi-way system, there is wide latitude on what the system may ultimately provide in key areas.

dlr

[dantheman]

Re: So - why DON'T people go with open baffle?

Martin, I've built dipoles similar to yours using your website and their polar pattern was the problem I heard. Believe it or not--your choice. Narrow in the bass + MR bloom = bright/thin sound. Think about what recordings are made on--just the opposite. Linkwitz addresses this with a shelving filter. For some recordings the sound was awesome, but for many it was just too thin and bright. Much like a cone/dome 2-way taken to the extreme with no BBC filter and some added spaciousness.

Here's some recording monitors just to enforce my opinion:

http://dtmblabber.blogspot.com/2011/01/review-of-polar-graphs.html

It might be possible to treat the room well enough to compensate for the the power response issues, but it wouldn't be my method to start with.

Sorry,

Dan

[diy speaker guy]

Re: So - why DON'T people go with open baffle?

I've been looking at bodging together some open baffle designs, and was curious what their detractors have to say on the subject. Aside from the enormous cost of the giant woofers involved (which is, to be fair, a definite detractor), OB speakers seem to have their competition licked when it comes to even dispersion and dealing with room acoustics.

That said, some of the math does seem to be a bit fuzzy. Without extremely narrow baffles and some slightly unusual drivers in a 4-way configuration (like a certain dipole speaker sold by a certain forum member), getting even dispersion seems almost impossible. The need for enormous midrange air movement also tends to result in some somewhat odd driver pairings, such as a pair of 8" woofers with a dome tweeter (sans waveguide)!

I've never had a chance to hear OB speakers of any quality personally - aside from endless mediocre Martin-Logans, they're just too darned rare. I have, however, heard quite a lot of very nice conventional monopoles. Can anyone who has had the opportunity to compare and contrast give me their opinions on the subject?

I agree with everything Martin said (with a couple of exceptions) and have a few comments of my own.

The math is not fuzzy at all, it's extremely well defined, otherwise software wouldn't be able to model OB accurately. It's easy to design extremely narrow OB baffles, and the drivers that "like" narrow baffles are generally very inexpensive. If you choose the right combination of driver and baffle size you don't need active eq and the design process is exactly the same for monopole or OB if you use Bagby's software. If anything, OB design is easier than monopole design because you can very accurately estimate the OB bass response in your head, without the use of a computer.

Car audio drivers generally have a very high qts that is perfect for OB. For example the GM/Delco 6x9's that are in practically every car for the last 30 years are virtually perfect for extremely narrow (8 inch) OB woofers and can be found everywhere for free. Use 4 per side and you have a free, extremely narrow OB bass solution that is easy to cross over passively to your choice of mid. They will only go down to their fs (60 hz) but that's not a huge problem. There's no benefit to using OB bass below the room's modal region.

Mids do not have to displace enormous amounts of air. In fact, the displacement requirements are almost exactly the same as they would be for any other alignment until you get below the step frequency. In fact, I modelled one of the cheap 2 inch tang band "fullrange" drivers, and it could do 104 db at xmax, as long as it was crossed at 600 hz (12 db/oct) on an 8 inch baffle.

To answer your question - I have no idea why people don't go with OB more often. It's extremely easy.

[spasticteapot]

Re: So - why DON'T people go with open baffle?

Where are you located? If nearby you could come listen to my system. Its a two-way with BG 50" Planar dynamics open baffle, and sealed 12" woofer, electronic XO. I'm in west central Ohio.

Steve

Madison, WI. Ten miles from Madisound. Who doesn't have a demo system.

[spasticteapot]

Re: So - why DON'T people go with open baffle?

Here's the quick rundown on my current situation:

1. I have the following drivers:

2x Scanspeak 15Ws
2x Scanspeak 6600s
4x 12" high-Qts AE subwoofers w/ 14mm of excursion and good up to about 350hz.

Also, a DCX2496 and lots of amplification. These drivers were mostly bought because I got very good prices on them :D

2. The speakers will likely be used in a very small apartment, so big SPL isn't entirely necessary. A separate subwoofer is to be avoided if possible, mostly because I can't afford another DCX2496 and amplifier.

3. My three main options appear to be:

A. a traditional box with a critically damped sealed alignment,

B: a "hybrid" OB with open-baffle mids and a boxed woofer,

C: a W-frame arrangement using two woofers per side in a W-frame arrangement (which I'm not entirely sure how to calculate).

There's also the question of how narrow I should make the baffle (wider baffle = less even dispersion, but requires less power and Xmax from mids) and exactly how much less floor-shaking a W-frame will produce due to the opposite movement of the cones (a major bonus).

[Saurav]

Re: So - why DON'T people go with open baffle?

Do you have measurement tools? If so, I think you should be able to try some OB experiments.

I think you'd probably want to start with your mid. Linkwitz has a spreadsheet which will tell you what SPL you can get from any combination of Sd, Xmax, and baffle width. Use that to figure out how low your mid will play on any given baffle width. If you can get it down to the 300-350Hz range (for whatever your desired SPL target is) with a reasonable baffle width, then you should be able to make something work. Note that if 350Hz is the corner frequency of an LR4 crossover, then the 'flat' / bandpass output will be 6dB higher, so keep that in mind.

I don't know anything about H/U/W frame woofers. Martin and John both have tools on their websites that can calculate a lot of this for you, but neither is free. There may be free tools available as well. You'll get to a point where you'll just have to build and measure. But I would think that you should easily be able to get adequate 'apartment bass' with those woofers.

Edit:

> B: a "hybrid" OB with open-baffle mids and a boxed woofer,

Depends on what you want. Painting with a very broad brush here, but with dipole woofers, you'll give up that kick-in-the-chest bass pressurization that you get from monopole woofers, in exchange for better articulation and hearing more 'tone' in the bass guitars, hearing more differences across bass guitars in different songs, stuff like that (as corny as that sounds). I think both are side effects of how the bass interacts with the room differently.