dipole infinite baffle panel question

[zuki]

how much can the baffle panel be bent/folded and still act like a dipole design ?

my thought is sort of a woofer panel folded like a taco shell,standing up.
as if you took a full sheet of material and folded it in the middle and stood it.

thinking full sheet of plexiglass.

if you will with the woofers mounted at the fold


or does the design become something else ?

similiar to the lumen white enclosure fold style

http://www.robinkikaku.co.jp/ces2003/2003_01_11/026.jpg

[Timn8ter]

Leave it to me to get hung up on terminology, but, dipole and infinite baffle are complete opposites in my mind. An infinite baffle doesn't allow the rear wave to meet the front wave (infinite separation) whereas a dipole (or open baffle) is allowing the rear wave to meet the front wave under controlled circumstances. Are you perhaps envisioning something like this?

[zuki]

on the link in the thread above.

the maple wood has been folded/wraped to create an open back enclosure/drivers mounted at fold,
for the lumen white speaker.

i remember in woodshop 20 years ago, they had a large box/steamer for treating/bending wood.

i know the plastic supply house has a large heating element they can fold a sheet of plexi or whatever for a small fee.

making a small /er dipole panel out on an otherwise full huge sheet

the lumen white speaker sounds good.
except the apprx. $50,000 price

[Rudolf]

Here is another example of a "Dipole in disguise":
http://www.auditorium23.de/Speakers/Rondo.html

And someone else, who did a clone of the Rondo with Saba greencone speakers:
http://www.drei-welten.com/
Look for "Rondo". The building process is documented in many pictures. So you need not read german.

The builders of the Rondo point out that the speaker cabinet sides vibrate intentionally - contributing to the overall frequency response.

[zuki]

that looks exactly like what i was thinking.

so a folded panel remains a dipole ?

as long as the back is open ?

[Timn8ter]

To a point. Some real smart person may want to chime in here but, a dipole allows an out-of phase signal to join the primary signal. If the signal from the rear of the driver is controlled to the point where it becomes in phase then it's a bass reflex design.

[zuki]

so i have to watch how closed the back becomes then ?

trying to reduce occupied floor space and allowing the panel to hold itself up were the reasons/ was the reason for the fold

[Rudolf]

Linkwitz arrived at the flat dipole after "unfolding" the H-dipole.
If you are folding back the wings of an open baffle, it more and more becomes sort of a U-Frame as described by Kreskovsky
http://www.geocities.com/kreskovs/NaO-Woofer1.html
and Linkwitz
http://www.linkwitzlab.com/frontiers.htm#L

My personal experience is, that you can fold back some wings to an angle of 45° between them before getting that "boxy" sound again.

[CeramicMan]

Just how big is that opening at the back of those Lumen White speakers? The reviewers at Stereophile seemed to think it was a port in the form of a narrow slot. Those reviewers can drool over the quality sound of Accuton speaker drivers all they like, but frankly I think that the enclosure design is the dumbest I've seen all week, even if it does cost a whopping $50000.

In the measurement section of their review, they found that there were lots of nasty internal reflections due to the lack of damping in the box. The woofers had a high crossover frequency which meant that lots of high-frequency sounds got measured through the port. But worse than that: the high-frequency sounds going through the port are totally unclean, with lots of resonant peaks and nulls...

If you want to avoid a "boxy" sound coming from boxed speakers, then as you're making them you should get (as a rough guide) 2 big bags of stuffing material that:

a) are much bigger than the exterior dimensions of your speaker boxes,
b) are really tightly packed.

When you proceed with the "insert the stuffing" DIY stage, you will somehow manage to squeeze it all in. Ok, maybe that's a bit of an exaggeration , but IMO some people aren't even remotely generous enough with stuffing to get good results with classic boxes. If the design includes a ported woofer, then that woofer should not play at midrange frequencies where stuffing material is required to damp standing waves. PS: attach a square of light curtain fabric behind the speaker to protect it from the fibres that will end up pressing against it.

My rule of thumb is: either make the midrange enclosures drastically big, with plenty of material to absorb standing waves (approx. infinite baffle) ... OR, make the enclosure small enough so that the speaker is "pressure-loaded" throughout its range of frequencies. Anywhere between these two extremes there will be "box breakup" which is kinda like cone breakup except that the cone resonances are caused by resonance in the box.

If you want to make a dipole: don't stuff around with some weird and wonderful hybrid design, just make the panels flat or moderately curved. For better bass response without drastic amounts of EQ the panels just have to be big. This is where the "H" designs can help by reducing the apparent size a lot. I don't see anything wrong with a moderate U or V shape, except if it's overdone then the backwave might have boxy resonances. Brainwave: you could make it a reverse U shape, so that effectively a concave parabola shape would beam the sound at the listener. This would also guarantee much less "boxiness" caused by interactions between the back wall and the baffle.

CM

[Nuuk]

Zuki, it is my practical experience that the sound of a flat baffle and that of a folded baffle are different. The more you make the baffle like a box, ie adding wings at the rear, the more it starts to sound like a box.

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