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Old 20th May 2005, 03:00 PM   #1
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Default 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.
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Old 20th May 2005, 03:14 PM   #2
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Take a look at what Fostex have to say on the matter:

http://www.fostexinternational.com/d...erview_1.shtml

Best
Scott
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Old 20th May 2005, 04:41 PM   #3
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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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Old 21st May 2005, 12:21 AM   #4
AJinFLA is offline AJinFLA  United States
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Default Open Baffle

Quote:
Is a box speaker with the back removed equivalent to an open baffle speaker?
Yes, sort of. But not a good idea. The bible on all such things.
http://www.linkwitzlab.com/
Enter and begin your journey into a whole new world.

Cheers

AJ
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Old 21st May 2005, 01:40 AM   #5
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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.
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Old 21st May 2005, 07:36 AM   #6
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John's points are very good... you can use a folded baffle to achieve a wider effective baffle than is presented by the front, but you have to work to minimize the cavity resonance the walls produce.

dave
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Old 21st May 2005, 01:57 PM   #7
dmason is offline dmason  United States
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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.
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Old 21st May 2005, 02:25 PM   #8
soongsc is offline soongsc  Taiwan
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Quote:
Originally posted by dmason
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.
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Old 21st May 2005, 02:56 PM   #9
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Default 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.
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Old 21st May 2005, 03:07 PM   #10
dmason is offline dmason  United States
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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.
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