Open Baffle vs Box Speaker Question

Is a box speaker with the back removed equivalent to an open baffle speaker ? Is it just a matter of maintaining a certain path length from front to back, or is there something else ? I guess what I am getting at is it possible to make open baffle speakers with smaller frontal areas, (so they can fit in small rooms ), by just using a box, but with no back on it. Rather like old console radios.

thanks.
 
I do exactly that, not because of room considerations but because I don't like the look of big wide baffles. There are some considerations that you must take into account and I highly recommend using test baffles first.

Any time the front and back of your baffle are not identical like with a flat baffle or a uniform H baffle, you no longer have pure dipole radiation. If found the effect to be minimal with only 8-10" depths on the sides. Even though the box is open there are still significant forces acting on the sides and top, so bracing across the back is even more important than with a sealed box because you have no corner strength in the back.

Parallel sides will create cavity resonances. You can damp these out, but that also absorbs a significant amount of the rear output and "closes up the sound" somewhat. Splaying the sides at least 1" for each 6" of depth and using unequal depths for the sides (opposite on each speaker) completely negates cavity resonances. I'm not sure why unequal side depths helps but it does.

These types of cabs can be placed quite close to rear walls and still retain much of the open natural sound, however, a hollow sound usually results and this requires polyfill batting behind the driver to eliminate.

Here's a set that turned out great with a low Qts 8" driver (the Adire HE8.1) plus four cheap 6" TV drivers in a W manifold to help fill in the bass . The pics are before I added 3 cross braces in the back because the 1" hardwood still vibrated without bracing. Note that the maximum width at the bottom is 19" and these work out to the same added rear wave travel distance as a 45" wide flat baffle for bass rolloff purposes. The sonic difference between these and the recommended BR cab are a night and day improvement. Unprompted my 9yro daughter asked why the OB set sounded so much better when I was doing A/B testing.
 

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soongsc

Member
2005-03-26 2:31 pm
Taiwan
Anything is possible, in your situation it would be more an issue of how to integrate it with your room. That's a custom design that is quite complicated.

If you can post some pictures on what you plan to do, it might be possible to get some feedback.

Current commercial speakers already have the front as small (slim) as possible.
 
I have found that piano hinge is your best friend in this regard; it allows you to adjust the baffle, and it provides continuity TO the baffle, effectively stopping any leakage through the joints.

The idea of folding the baffles in this way allows you to experiment with the effect on the room/presentation, in various angle "settings" yet allows for an open, flush baffle.

What I found was that the flush open baffle was a whole other animal, and to me at leastl, represented the optimal presentation. I am sure this dynamic changes from driver to driver.

Folding back the "wings" to 90' reduces the apparent width of the whole thing, and any non-parallel fixing of even one wing over 10' made a noticeable difference.

I am sold on this method, and using folding wings of differing widths for offset is a VERY easy and effective way to do it right. Add vertical round-overs and some veneer, and you have a really nice looking, all-business speaker system.

Subs are easier to integrate than what I had read. Dual, in "H" frames is best.
 

soongsc

Member
2005-03-26 2:31 pm
Taiwan
dmason said:
I have found that piano hinge is your best friend in this regard; it allows you to adjust the baffle, and it provides continuity TO the baffle, effectively stopping any leakage through the joints.

The idea of folding the baffles in this way allows you to experiment with the effect on the room/presentation, in various angle "settings" yet allows for an open, flush baffle.

What I found was that the flush open baffle was a whole other animal, and to me at leastl, represented the optimal presentation. I am sure this dynamic changes from driver to driver.

Folding back the "wings" to 90' reduces the apparent width of the whole thing, and any non-parallel fixing of even one wing over 10' made a noticeable difference.

I am sold on this method, and using folding wings of differing widths for offset is a VERY easy and effective way to do it right. Add vertical round-overs and some veneer, and you have a really nice looking, all-business speaker system.

Subs are easier to integrate than what I had read. Dual, in "H" frames is best.

Their used to be a site that shows this concept, but seems to have disappeared. Some really nice curves and finishes I beleive created by CAD program.
 
the reason I ask

Thanks for all the replies.

to soonqsc, who asked what I plan to do :
Basically I am trying to "use up" some miscellaneous, inexpensive, unknown drivers I have lying around. Some are pulled from old console stereos, some are from ebay, one is 3 way car speaker. The thing they have in common is high Qts, ranging from about 1.8 to 3.4. What I have done in the past with these sort of speaker is just put them into as large a box I have room for and hope for the best. Not very scientific, or audiophile stuff, but then I am not trying to meet some sort of audio objective, just enjoy a diy project.

But then I thought if the old console radios were backless, then what about just making a box the same size as the speaker compartment in the console. I thought this might produce the same effect as open baffle speakers, but with say 16 or 18 inches of width rather than a few feet of width.

When I was fooling around with the baffle calculation spreadsheet I got here, I noticed that high q speakers seemed to work out well, at least on paper.

To dmason who mentioned piano hinge : this sounds interesting. I think what I will try is a sort of universal test stand, ie a skeleton with a empty central area, ay 1 foot by 1 foot, and piano hinge on each of 4 surrounding sides. On each of those I can attach wings, and angle as required. In the central area I would put a filler panel with a cut out in it for one of my several drivers. To change drivers I just change the panel, I dont need to rebuild the whole thing. It makes sense to me, any comments ?

Now, this leads me to another question. Somebody in another thread spoke about using cardboard for the baffle, and then it is easier to experiment with than wood. Can this work ? Will it not have all kinds of funny vibrations etc ? I thought speaker cabinets had to be as stiff and massive as possible.

thanks.
 
Don't bother with cardboard, IMO, do it right; get two sheets of 1/2" MDF, nice and stiff, and start cutting. The universal slot thing for interchanging drivers is fine, if less than optimal. If you find a driver that works ~well, flush mount it on a new panel. It is the flush mounting that is paramount here. Rebates made a huge difference. I eventually used T nuts for a real solid anchor and this made an even greater difference. I talked to someone who, when settled on a particular driver, even machined brass bezels to mass load the driver, a la Fostex Sigma Dragonfly rings. He said this made the biggest difference of all!!

When you identify a driver you like, Qts 5-7 being the theoretical ideal, and pay attention to all these extra efforts, open baffle sound becomes astounding. Many report they can hardly even listen to music coming from boxes after this experience.

Perhaps Planet10- could comment abit on his Visaton B200 experience, as this driver is ~ideal for OB with a Q=7, it is reasonably priced, and we trust Dave's ears with our lives.:clown:
 
dmason said:
could comment abit on his Visaton B200 experience, as this driver is ~ideal for OB with a Q=7, it is reasonably priced

My experiences were very pleasant. Used on a baffle about 1.2 x 1.1 m made from donated plexi from ICBC (saved from the dumpster). I still might get the opportunity to go back to them, but will need to come up with something a bit more room friendly (or get someone to buy me a big flat panel TV of projection screen -- so i can flip my room 180 degrees)

dave
 

AJinFLA

Banned
2005-02-09 4:35 am
Tampa
Actually many car speakers will work quite well for OB applications, since most are intended for IB type scenarios and feature high Qts. I suggested as much in a previous post and was scolded by someone - shall we say - less informed.:whazzat:. Another thing is that cardboard IS a great material to work with for baffle shape. Use a wood baffle just wider than your (mounted) driver, then add cardboard in every shape and direction to get your final shape. Measure away. Then build it in wood.
I'm working on an inexpensive OB/monopole modular speaker that will use computer, car and ceiling speakers. Thats right. Ceiling speakers!:D
I also have plans for a folding wing dipole PA speaker. Literally a fold-up speaker! Ah yes, the fun never ends.

Enjoy

AJ
 

AJinFLA

Banned
2005-02-09 4:35 am
Tampa

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AJ

Ceiling speakers are a many splendored thing; the Radian 508, and Beyma 8agn among others are all "ceiling" speakers. The Radians sound ALOT like Lowthers. (the good parts)

The Ciare CH250 is a "car" speaker. If so, it is the King Of All Car Speakers...

I like your idea about using cardboard to shape a baffle. Sonotube and plywood cylinders also need be mentioned here as one could work that into a very sweet looking curve using a fraction of a half-cut tube.

Which ceiling and computer speakers, inquiring minds wish to know...
 
I have to side with AJ over DMason regarding cardboard for OB testing although the best is the foam filled posterboard used for architect's models (but it's not free). A narrow wooden baffle to mount the drivers, tape, and cardboard and go to town. While almost anything will work as a flat baffle, almost anything not very heavy and/or well braced is going to flap in the wind, so use something easy to work with since bass extension is what you are testing.

Hinges to join the wings to the front baffle give you flexibility, but unless you make them very heavy you will feel vibrations in them if folded. I opt for permanent folded and braced wings.

A compromise never mentioned of big flat baffles is the large reflective surface you create which is directed at your seating position and also blocks reflections from the rear wall. I believe this is a major cause of OB's not imaging as well as a tall narrow boxed speaker. I prefer to sacrifice pure dipole radiation for better imaging.

WRT testing, do it in room from your listening position. Also, very high Qts drivers are a little harder to work with because you have a rising bass response down to Fs. If you get just the right match of dipole bass rolloff due to baffle size with the increasing bass response of the driver then you can create magic, but it's tricky. I stick with Qts's below 1 and usually determine the baffle I want, then test to see what the actual bass extension is and figure out how to improve from there. Then final tuning is simplified with variables of placement, rear wave attentuation, and crossover changes all of which are very quick and easy without a closed box.
 

AJinFLA

Banned
2005-02-09 4:35 am
Tampa
Cheapo dipole

Hi dmason,

I've heard the Radian. I have not heard the Beyma. The Radian was nice sounding, but 1mm Xmax makes not an OB speaker. Too many compromises. Both will cost more than the ENTIRE speaker system I'm building. I'm going to call it the SCAD. Simple Cheap Active Dipole. I'll use them in the rear of my theater and bring them to DIY events. Dipole, well sort off, since dipole bass = $$$. A cheap large dia. woofer and a huge baffle can circumvent this, but defeat the purpose. These will be small (11"x11" footprint). Monopole sub. Dipole on upwards. Logitech Z-2200. Here it is:
http://www.tomshardware.com/consumer/20041111/logitech-02.html#on_the_graph_and_to_the_ear
Same sub, the Z2300 satellites are smaller. $65 with shipping!
The ceiling speakers are these: http://www.jbl.com/home/products/product_detail.asp?ProdId=HTI6C&SerId=HTI&sCatId=IWO
OB off course. I like the 2k XO on the tweeter. Shows good design. Diffuser will be chopped. Aluminum midbass driver too.
I've found them on ebay for just over $100/pr.
Probably $250 for the whole mess (1 sub/ch). That will be version 1.
Believe it or not that's a decent little amp in the Logitech. 200w RMS might be a stretch, but numerous reviews have measured peaks of 110+db from that little TB driver, which can't be more than 90db efficient (if that!). So somethings going on there. I can't beat that for 65 bucks even if I built it myself. Version 2 will use sonotube and .....
Well, we'll see:)

Cheers

AJ
 
A really good car speaker for OB use s the GM/Delco 6x9 whizzer cone driver. Found in 4 ohm & 10 ohm versions. Keep your eyes out at garage sales... invariably somebody has replaced theirs with $100 plus triaxials and the better FR is going for a pittance.

Tannoy ceiling speakers are probably one of the least expensive sources of new dual concentrics.

dave
 

AJinFLA

Banned
2005-02-09 4:35 am
Tampa
That is correct Dave!
You will find suitable OB drivers in the least likely places. I comb ebay lurking for such items. Ceiling speakers by Tannoy, KEF, Paradigm, etc. Car models too. High Qts and decent Xmax wanted. I picked up a pair of brand new Dynaudios about a week ago for about $220 with shipping! These actually
http://www.dynaudio.de/eng/mobile/driver/mw180.htm.
Shhh, don't tell too many people:apathic: . I hate bidding wars:D
I have way too many drivers sitting around right now, so I'll probably stay off ebay for a while now. Unless of course something tasty comes along......

Cheers,

AJ
 
Delco's - you can also get them for a song or smile from your local auto-graveyard.
Ford 5x7 with whizzers sound great too, I've tried them on open baffles and they sounded pretty good. The Ford speakers have a glued on grill though, kind of a pain to remove without wrecking the surround but it's doable. I don't worry about destroying them though, I get as many new ones as I want for free through my work. I use them for experimenting.

Anybody want some?