Dipole woofers, H-frame and U-frame: Why bother to begin with ?

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FlorianO

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Well, I have my ignorance as an excuse, but -- with the risk of being burned at the cross -- let me ask it:

Why do we bother with dipole woofers, H-frames and U-frames to begin with ?

Maybe I'm missing smth big (and there's a big chance for that...) but as I see it a dipole setup with two woofers achieves +6 dB of a _single_ (sealed) driver at only one frequency. The rest is under Fequal and a PITA to deal with:  Sloped at  +6 dB/octabe (below Fequal), comb filtered above, etc, etc.

The only advantage I see on dipoles is due to the figure-of-eight radiation pattern /  resp. cardioid  (damped U-frame) -- less room interaction, side radiation, etc.

So, the question is again: Why bother and not simply put a big woofer in a sealed or ported box or smth   :scratch:?

So: "Gentlemen, start your flamethrowers".


Regards,

Florian
« Last Edit: 10 Apr 2007, 06:02 pm by FlorianO »

mcgsxr

I cannot answer for the masses, and I have no measurements to back my experience - let's get that on the table right off.

For me, in the 2 different rooms I have experienced it, open baffle bass is entrancing when you get it right.

I am a basshead - let's clear the air on that too!

So, for me, it is really tough to get it right.  I have posted many threads around this, and continue to be open, during my system experimentation, and development.

I built a ported sub a few years ago.  Nakamichi driver, 23Hz tuning, 3.5 cubic feet, ran it with my BASH 300w amp.  Deep bass, strong HT value - hits hard, hits low.  Not fast, and lumbers along under the b200 ob speakers I built.  Did not do it for me.

I also have a sealed sub that I built.  Rockford Fosgate 12 inch driver.  1.5 foot box, ran that with my BASH 300w amp.  Faster, more tuneful, but not efficient, and still did not integrate well.  Better, but still did not do it for me.

Then I built that same sub into a quick and dirty H baffle, using only 1 of the VC to double the effective QTS.  Ran it with my BASH 300w amp.  Better again - complete lack of coloration on what bass there was.  Not terribly efficient.

Then I bought the 2 Mach5Audio 12 inches, and built them into the main baffles.  Ran them with 1 VC each, and with the venerable BASH 300w amp.  Much improved bass.  Quick, resonance free, good stuff.  Not enough.

I miss the impact of bass.  Not sure I can achieve it with OB, but suspect I will get a lot closer with more subs, perhaps of larger diameter.

Would I be better off with a single 15 sealed?  Maybe, but for me, it has always been about exploration, so I will continue to mine away in search of the bass quality I have found with OB, but with more of the impact I recall of sealed boxes in cars...

Rudolf

For me the advantage of OB bass indeed boils down to less room interaction - and that is enough reason to stick with it:

It seems there are less modes resonating in the room - although the first room modes along the listening axis are still excited "very well". Since dipoles need to be kept off the walls anyway, I have found myself more willing to push the speakers around to find the best location than I was at my CB/BR times.

Since there is no room gain I enjoy deep and dark bass in a very transparent manner. Lately I have left a slightly profuse bass lift in my H-frames untouched, because there is such an enticing "underworld" of delicate bass to discover in my CDs.

Last benefit is the "caged-in-the-room-bass". Time after time I am amazed what little of some embarrasing bass level in my listening room gets through to the adjacent rooms.

Sensitised by dipole bass I have since then critically listened to every "punchy" bass that was "offered" to me at concerts, parties or in the car. And I believe most of that impact was combined with a good dose of one-note-bass. Although I have to admit that my 15" drivers convey a bass drum more realistic than my old paired 10" drivers could.

jeffreybehr

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My DIY system is high-efficiency and open-baffle including the bass.  I use two Sonic Craft SCC300 drivers per channel, in parallel, driven by 2 channels of an Outlaw 770.  They're filtered with a dbx DriveRack PA, 60Hz lo-pass, 4th order. 


Here's an early pic of the rear; I added more bracing later.


The bass it generates is tuneful, well extended (being near flat to c. 25Hz!), powerful, etc.  Its overall sound matches well with the dipole bass/midrange of the main system.

When I build the 3rd version of the systems which will be the 1st good-looking version...  aa ...it too will include a dipole bass system.  This time the wings will be shorter, the bassbase (cute name, huh?   :wink: ) will be topcapped, and I might use 3 of those drivers (I'll start with 2), still in parallel.

Maybe I too am a basshead, but probably not the way mcgsxr means.  I want plenty of bass energy, but it needs to be VERY high-quality.  I'm getting that from my open-baffle systems.

BTW I think these open-baffle bass systems do not have a dipole radiation pattern in spite of their physical designs; the wavelengths of bass are too long to have radiation lobes.  Of course I may be wrong about this.

mcgsxr

Sounds to me like you are my kind of basshead jeffreybehr - has to be there, has to be clean, has to be quality.  I stray a little further down the path, to include - has to amaze me with how it CAN be if I want it to, but if it does not blend well with the rest of the system forget it.  That is why the ported 12 was "fired", and the sealed 12 did not cut it either.

The bass quality OB can sound really good to me, in my room, but playing around with the configurations (still not making anything visually attractive yet either!) has led me to understand that there is a lot to learn, but the good sound keeps me motivated to pursue it.

If I could achieve the air movement capacity, I would likely be set.  I will probably have to rationalize selling off the 12's, and buying 15's to get there, in OB, for me.

Wish I could audition it first though, rather than be my own test case!

JohninCR

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To me it sounds better (more natural and clear with better separation between notes and instruments), even though you give up some of the physical impact compared to boxes.  I'm with Rudolf, that the reason boils down to room interaction and much more than just stimulating room modes less.  Boxed bass expands in all directions and what we hear includes many many reflections.  To me it's intuitive that with boxed bass we hear a jumbled mess in comparison to open alignments where the output is concentrated on axis.  My room is primarily concrete, so I am especially sensitive to the difference and could never go back to boxes, despite over 300sqft of panel bass traps built into my room's construction.

Outdoors they are more comparable in sound (no reflections), but for me the edge still goes to OB, and I think that is because the drivers are operating freely instead of against the air spring of a box.

Another important consideration, at least for me, is how much better OB bass stays in room.  I listen mostly late at night, and I can listen much much louder without disturbing others.  In that respect, boxed bass should be outlawed.  eg  I was listening to some little RLH's I made one night.  They didn't have much in the way of LF extension, and I was listening only at moderate levels, yet my wife complained quickly that the kids couldn't sleep.  She's never complained when I use my OB's, and I often play them much louder.

scorpion

The reason for dipole bass is the same as for mid dipole: no sound of a box.

So, you are right FLORIANO, why bother ?  :scratch:

/Erling

FlorianO

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All,

Many thanks for your replies.

To be very honest, my question was if there was smth _theoretically_ better (that I was missing) about dipole woofers that make them attractive -- except that dipole radiation. Well, it seems that alone is enough to live with the drawbacks :)

The second reason was trying to understand why "pro" OBs -- like the Bastani Prometheus, Dick Olsher Basszilla -- box the woofer.

OTOH in my mind dipole woofers and dipole mids are different things (has to do with baffle width / wavelength ratio for flat rectangular OBs).

Thanks,

Florian


JohninCR

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The second reason was trying to understand why "pro" OBs -- like the Bastani Prometheus, Dick Olsher Basszilla -- box the woofer.

Shortcutting cheats with inherently inferior results as far as I'm concerned.

Paul W

Florian,
Building a "perfect" box is necessary, but nearly impossible.  By perfect, I mean one with zero wall vibration, one that reflects no energy back to the driver, etc...humm, Infinite Baffle.

I listen in a very large room, so only limited benefit from the radiation pattern.  For my situation, Erling is absolutely on target.  If you have the room for it, OB woofers with IB subs is a super combination.
Paul

Rudolf

The reason for dipole bass is the same as for mid dipole: no sound of a box.
IMHO: As long as
  • the structure of the box is sufficiently rigid
  • the wavelength is much larger than the dimension of the box
  • the driver is not driven into compression
I don´t see how the box should be responsible for a special "sound".
You can´t simply assign the virtues of mid dipole to dipole bass - for me those are quite different pairs of shoes. :scratch:

Rudolf

scorpion

I was only comparing OBs to Boxes scientifically.  :wink:
If there is such a thing as an easily constructed ideal subwoofer-box the world must be full of them by now.

/Erling
« Last Edit: 11 Apr 2007, 07:34 pm by scorpion »