fullrange dipole with Qts 0.25

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Hello all!

My task was to build something that sounds like an open baffle but doesn`t need that much space. And now I managed to build a dipole from a Qts 0.25 driver standing directly in front of the wall. Pictures of my design will follow soon, but first I want to know whether there is anybody else who managed to get bass out of a Qts 0.25 driver in a dipole.

Greets, Oliver
 

AJinFLA

Banned
2005-02-09 4:35 am
Tampa
Hi Oliver,
there seems to be a common misperception regarding the Qts of a driver when used for Open Baffle. A lower Qts (0.25) only means that you will require more eq than a high Qts driver to maintain a flat response. It has absolutely nothing to do with "how much" bass can be produced. That is determined by other factors, such as the drivers Sd, xmax and the path length difference for your acoustic short circuit. You made no mention of these for your driver.
Another common issue for those who want OB (dipole) but lack the space to do so, is control of your rear wave. One possibility is to heavily treat the area behind the speaker, if it is to be relatively close to the rear wall. This can be effective for upper frequencies, but less effective for the lowest. You could try an OB that does not extend too low in frequency, then use a sub for the lowest.
Another alternative is a cardioid. Using a u-shaped baffle and acoustic absorbers to reduce the resulting resonance peak. Gradient uses this method in their speakers. John K uses a cardioid sub for his NaO design.
Good luck and please post some pics of what you have done.

Cheers,

AJ
 
el`Ol said:
I want to know whether there is anybody else who managed to get bass out of a Qts 0.25 driver in a dipole.

Hi Oliver,

My personal record holder is Timo alias "tiki", who built a W-frame dipole sub with two Isophon PSL 385/400. Qts=0,17

Timo has documented his dipole here (sorry, its all German :D ):
http://www.hifi-forum.de/index.php?action=browseT&forum_id=104&thread=2582&back=&sort=&z=2

Another guy putting his OBs against the wall is another Timo, who presents his "SOS" in the Visaton forum (again German spoken only):
http://www.visaton.de/vb/showthread.php?s=&threadid=10090

So it seems your approach is a very "teutonic" one ;)
 
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The speakers are attached to the wall. Angle is 30°. Drivers are FE126E. They sound like OB, not like BR or TL. The 2/3 tube forms some kind of horn. Bass is ok, I don`t find a sub necessary. Unfortunately the treble is far behind my Ciares, I would try the Supravox 135LB instead of the Fostexes next time.
 

AJinFLA

Banned
2005-02-09 4:35 am
Tampa
Wow, that close to the wall! That setup looks more like some sort of TL ,venting at the top, I can't see OB there. Is the cylinder solid? The only scenario I can think of in that situation would be a flat panel baffle with your driver and lots of acoustic absorbtion on the wall behind. The frequency range of that tiny driver won't extend too low, where the absorbers have the least effect. Good luck!

Cheers,

AJ
 
The tube is attached to the enclosure via a hinge, so the horn throat can be adjusted. I was doing philosophy about my design yesterday: The horn is very short, so it is a hybrid between horn and BR. The compression chamber is open at bottom and top, so it is also a TL. The open design to three directions is like an OB. And the enclosure material (OSB) makes it a resonating enclosure. So it works according to all speaker principles I know. Listening to Stravinsky I found the bass is a bit tiny. I will build the recomended BLH design for the FE126E for comparison. I am no longer so shure that such a bit horn loading is a reason to use a Qts 0.25 driver. An alternative would be the the FE127E, the Ciare HX132, or the Supravox 165LB.
The Fostexes are not as bad as I thought. My glycerol threatment has showed results in the wet weather the last days. The cone has sucked up a lot of water and the treble is a lot softer now.
 
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