Subwoofer with Transducers in omnidirectional Arrangement - Polarity-Rules wanted - diyAudio
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Old 10th November 2011, 02:27 PM   #1
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Default Subwoofer with Transducers in omnidirectional Arrangement - Polarity-Rules wanted

Subwoofer with transducers in omnidirectional arrangement - polarity-rules and theoretic background wanted

Here some examples for subwoofer chambers, where the design is in an omnidirectional arrangement:

Infinite Baffle Subwoofer
Page Title

I am looking arround to the right usual english terms/keywords for this kind of design, because I want to find the associated papers about the theoretical background and the rules of polarity

Last edited by tiefbassuebertr; 10th November 2011 at 02:30 PM.
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Old 10th November 2011, 03:53 PM   #2
tb46 is offline tb46  United States
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Hi,

I found this to be a good resource: "Cult of the Infinitely Baffled"Hear The Bass, Not The Box The definitive online resource for Infinite Baffle subwoofer designEstablished 1999 - Home

Regards,
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Old 11th November 2011, 05:13 PM   #3
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Quote:
Originally Posted by tiefbassuebertr View Post
Subwoofer with transducers in omnidirectional arrangement - polarity-rules and theoretic background wanted

Here some examples for subwoofer chambers, where the design is in an omnidirectional arrangement:

Infinite Baffle Subwoofer
Page Title

I am looking arround to the right usual english terms/keywords for this kind of design, because I want to find the associated papers about the theoretical background and the rules of polarity
"Omnidirectional" in English audio generally refers to the radiation pattern, and at low frequencies, subwoofers are essentially omnidirectional, regardless of the design.

The designs you are looking at incorporate a plenum, also known as a manifold, for multiple drivers.
The plenum eliminates (or largely reduces) the structural vibration problems of woofers mounted directly on a flat baffle. The moving weight of multiple cones is quite a lot, by opposing the cones, vibration of the exit surface is minimized without requiring extensive bracing. The plenum also functions as an acoustical low pass filter. In addition, it reduces the exit area to an easily concealed size.
The drivers all are wired in polarity, positive voltage moves all the cones into the plenum. Series or parallel or series-parallel wiring schemes may be used to arrive at a suitable impedance for the amplification channels used.

A variation of the same idea would have half of the drivers mounted backwards (magnet in)in the plenum, wired in reverse polarity, known as push-pull (PP).

All the cones are still in acoustic positive polarity in a PP set up, positive voltage still pressurizes the plenum.

PP loading reduces even order harmonic distortion. Lack of even order distortion with the presence of odd order distortion subjectively may sound worse at high drive levels, so is not always preferable. Back vented drivers also produce "chuffing", or wind noise from the vent, which may be objectionable when introduced to the plenum.

Although the designs you are looking at are infinite baffle, plenums/manifolds are also used in sealed, ported and horn loaded cabinets.

Art Welter
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Old 11th November 2011, 05:35 PM   #4
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Thank you very much for this detailled explanations. About the google keyword
"manifold subwoofer" (image search)
there is a lot of additional informations and inspirations of new projects.
However, the term "plenum" I don't understand in this respect despite reading the follow wiki explanations:
1) Plenum - Wikipedia, the free encyclopedia
2) Plenum ? Wikipedia
Perhaps you mean a chamber, enclosure, cabinet or boxvolume (the english language have sometimes a wide range of terms for the same meaning) ??

Last edited by tiefbassuebertr; 11th November 2011 at 05:39 PM.
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Old 11th November 2011, 05:56 PM   #5
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Quote:
Originally Posted by tiefbassuebertr View Post
Thank you very much for this detailled explanations. About the google keyword
"manifold subwoofer" (image search)
there is a lot of additional informations and inspirations of new projects.
However, the term "plenum" I don't understand in this respect despite reading the follow wiki explanations:
1) Plenum - Wikipedia, the free encyclopedia
2) Plenum ? Wikipedia
Perhaps you mean a chamber, enclosure, cabinet or boxvolume (the english language have sometimes a wide range of terms for the same meaning) ??
Plenum is the usual name for an air duct used to move hot or cold air around buildings.
They are usually made of thin sheet metal, obviously sheet metal would not be a good choice for high volume subwoofers.

A plenum, as Wikipedia states, is a chamber intended to contain air, gas, or liquid at positive pressure.

That is exactly what the chambers in your OP links are, though the speakers push and pull air pressure in and out of the plenum.

“Manifold” is used more often in the sound (and auto) industry because it sounds cooler .
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Old 12th November 2011, 04:25 PM   #6
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t., what do you want to do?

I think you should describe your goals. I dealt with many non-English speakers for business and I my instinct says your links may be misleading us.

Subwoofers are almost always omnidirectional because they are smaller than the frequencies they radiate. This is true even for horn subwoofers. Rare exceptions might be large concert sound arrays, and unbaffled subwoofers.

Note that the phrase "infinite baffle" is often perverted/twisted. A big flat piece of wood is NOT an "infinite baffle." It might approximate an "infinite baffle" at higher frequencies, but at low frequencies there is just cancellation. A true "infinite baffle" would be like if you cut a hole in your roof: the subwoofer does not see a box, but the rear and front waves cannot mix.

Some companies make speakers with drivers on many sides, to make "omnidirectional" sound. And some companies make subwoofers where the drivers are on opposite sides of the cabinet, or even on multiple side like the Paradigm Sub2. But the purposes are very different. For the subwoofers, the reason is not "omnidirectional." It is to cancel the rocking force caused by a big heavy cone rocking back and forth.

A plenum is, for example, the heating/cooling duct in an office. This is almost always rectangle in cross-section and long. Sometimes subwoofers are designed with the woofer firing into a similar shaped restriction. You can look up "slot loaded" which is another term. This loads the woofer a little more compared to free air, but I have never seen it proven to have a big effect. It can have some negative effect due to resonance of the slot/plenum itself.


By the way, have you started winter there? It looks like you are in a very nice part of Germany. How far are you from Frankfurt and Stuttgart?

Last edited by head_unit; 12th November 2011 at 04:29 PM.
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Old 12th November 2011, 05:26 PM   #7
tb46 is offline tb46  United States
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Hi head_unit,

You may have missed his last thread: New Approach for an Outline from a DIY Subwoofer - Precision Devices PD2150 inside.

Bye the way, I have seen the term plenum translated into German as Druckplenum, or as Druckkammer.

Regards,
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Old 15th November 2011, 07:19 AM   #8
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Quote:
Originally Posted by head_unit View Post
t., what do you want to do?

I think you should describe your goals.
I follow no specific targets in this respect. The only reason to start this thread was the fact, to find out more details (e. g. pro and cons therefore so as the polarity rules) about subwoofer concepts, as you can see on the images about
Page Title
I don't intend to realize a specific subwoofer project in this manner.

Right now I don't know even the most used colloquial english keywords/terms for such a construction.

The term "Infinite Baffle" also may be wrong therefore, but I found by google the most constructions in that kind.
In the headline I call it "Subwoofer with Transducers in omnidirectional Arrangement" but only in that sense, that all bass transducers (bassdrivers) are mounted on all baffles around - except one buffle showed to the floor (that the radiation character in such frequency aera in general is omnidirectional, isn't new for me).
Please note, that my english is bad (english isn't my native language).
Thus it always comes to misinterpretations/misunderstandings - not only by this thread here - sorry therefore.
Nevertheless I've already received here a lot of informations arround that approach to make bass transmission systems.

Quote:
Originally Posted by head_unit View Post
By the way, have you started winter there? It looks like you are in a very nice part of Germany. How far are you from Frankfurt and Stuttgart?
I live near the airbase Hahn, only about 90 km west of Frankfurt - go to
http://www.hahn-airport.de/Default.a...visitors&cc=en
and
http://de.wikipedia.org/wiki/Flughafen_Frankfurt-Hahn

Despite the season, we have since 3 weeks lovely weather, but sometimes whole day fog.
Winter weather is still far away.

Last edited by tiefbassuebertr; 15th November 2011 at 07:41 AM.
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Old 15th November 2011, 09:25 AM   #9
Ile is offline Ile  Finland
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Those manifolds in your first post aren't best examples, because manifolds have 2-3 row of elements. Elements will have phase difference because different distance to manifold opening. Long thin manifold could also cause pipe resonances in some cases.

It's better that all elements have same distance to manifold opening, so cubic manifold are better. Cubic manifold will also be stiffer than that kind long version.

These days there is long excursion (30-36 mm) 18-22" drivers available, so 4 elements in cubic manifold should be enough for most users.

If not, then it's better to use many of those 4 element manifolds. Multible positions will also work better against room modes.
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