Open Baffles - how they work, and how to use them well

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Rudolf

In many OB projects the relationship between baffle size and driver size doesn't get the attention it deserves. But there are big differences, if you look at two point sources in free air, at small drivers in big baffles or at dipole drivers without any baffle at all.

I have made up a PDF which focuses on the relationship between driver size and baffle size and what it implicates for your next project. You can download it from http://www.dipolplus.de/frameset.htm?/thema11.php. Look for the Download button under the red text.

Actually there is nothing in the PDF, that has not been told before. But to my best knowledge nobody has tried to tell the story as well in laymans terms and visually illustrated as I do. So you better don`t miss it.  :wink:

Rudolf

djn

Re: Open Baffles - how they work, and how to use them well
« Reply #1 on: 13 Aug 2010, 05:49 pm »
Great reading rudolf.  I just skimmed it but printed it out from closer review.  As you know, I just finished an OB Line Array project.  It was just an experiment as I have all the stuff to build them.  I've been a horn guy for my whole audio career (hobby) and think I like the OB better.  For just whipping them together, they sound great.  Very open and big.  Great detail and a wide and deep sound stage.  I am now thinking about building a more serious version and will do a lot of reading before hand.....your link helps.  Cheers.

chlorofille

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  • 8'' MTM with scanspeak 21w8554 & D2904 7100
Re: Open Baffles - how they work, and how to use them well
« Reply #2 on: 13 Aug 2010, 05:59 pm »
Amazing presentation Rudolf !

nunhgrader

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Re: Open Baffles - how they work, and how to use them well
« Reply #3 on: 13 Aug 2010, 06:01 pm »
I'm game - love the presentation and thank you!

scorpion

Re: Open Baffles - how they work, and how to use them well
« Reply #4 on: 13 Aug 2010, 08:13 pm »
Congratulations, Rudolf !

Great write up, there is nothing like it available anywhere. The OB- or better all the HiFi-community is up to date now !  :D

/Erling

Luigi

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  • Busa doing the business
Re: Open Baffles - how they work, and how to use them well
« Reply #5 on: 14 Aug 2010, 12:07 am »
Agreed. Thank-you very much for taking the time. The great thing about this, from a personal view point, is that it addresses questions I have regarding baffles.

What disappoints about the article - and I dont like to be churlish here; it is a great effort - is that there is no list of practical implications and conclusions at the end of the article. Which is why MJK's articles are so enlightening. Meaning I have to sit down and nut these out myself. And for someone with not much in the way of technical background....
Luigi

D OB G

Re: Open Baffles - how they work, and how to use them well
« Reply #6 on: 14 Aug 2010, 06:31 am »
Thanks VERY much Rudolf.

I look forward to maybe seeing some accounts of your latest prototypes?? :wink:

David

mcgsxr

Re: Open Baffles - how they work, and how to use them well
« Reply #7 on: 14 Aug 2010, 12:17 pm »
Thanks for sharing, I found the reading interesting, if a little complex for me.

I know that the entire DIY community benefits from your efforts!

Thanks!

Rudolf

Re: Open Baffles - how they work, and how to use them well
« Reply #8 on: 14 Aug 2010, 06:11 pm »
Thanks everybody for your encouraging words. Much appreciated. But don’t forget: It was rick57 of this forum who gave it the final polish.  :)

From some posts I conclude that some people expect more tangible advice how to build a real dipole speaker. I won’t give that – with intent. There are still many ways to skin the dipole cat. My PDF may sound as if I heavily prefer baffle-less dipoles. But that is only one approach – and the most complicated indeed. So everybody has to find his own solution.

But it is completely justified to ask for my own state of art. Here we go. This is my listening situation:



It took me more than an hour to get that part of my “private” room into a presentable shape. My wife calls me a “messie”, I call it creative organic growth. :wink: So please don’t ask when I will tidy up the cable mess on the front wall.

In the front of the picture you see the back of my listening chair. The dipoles are 2.15 m apart (center-center) and it is 2 m from each tweeter to the corresponding ear. The dipole axes are meeting 20 cm in front of my ears.

Two more perspectives:





What my ears hear, looks like this (right is red, left is green):



I credit much of the congruence of both channels to the symmetry of that room side. You may have noticed how the furniture is mirror imaged.

And this is the way how it is distributed to the drivers:



Crossover from the H frame to the mids is 300 Hz, mid-tweeters is just above 2k.
I will tell more about the drivers and why there is hardly any response below 50 Hz in another post.

Rudolf

Rudolf

Re: Open Baffles - how they work, and how to use them well
« Reply #9 on: 15 Aug 2010, 10:34 am »
Drivers are A&D 15308 http://www.traumboxen.de/ad-audio/15308.htm, Monacor SPH 176 http://www.monacor.de/typo3/index.php?id=75&L=1&act=&act_sub=&artid=4084&spr=EN&typ=u and Monacor DT-25N  http://www.monacor.de/typo3/index.php?id=75&L=1&act=8&act_sub=25&artid=3574&spr=EN&typ=u. Those drivers are nothing special in general. In fact they are low cost, but they give much value for the money. None of them is made for earbleeding SPL levels though.
 
What I really like about the SPH-176 is the small size of the spider, which opens the cavity between cone and basket and IMHO is responsible for the acceptable front-back SPL similarity.




Measured from approx. 0.5 m distance:


 
Measured from listening distance (2 m):




The DT-25N simply were the smallest decent 1 inch tweeters available when I bought them. As I have explained in http://www.diyaudio.com/forums/multi-way/161299-directivity-dipole-tweeters.html I try to have a true dipole response as far up as possible (horizontal polars 0-90° in 15 ° steps, taken at 40 cm distance):



Note how for all of its frequency range the 90° level is at least 25, mostly 30 dB below the on-axis level. In fact it is mostly buried in the noise floor.

hndaaudio

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Re: Open Baffles - how they work, and how to use them well
« Reply #10 on: 16 Aug 2010, 06:04 am »
Rudolf,

Thanks for your info on building open baffles.I could use some advise on using drivers with a lower than ideal QTS,in this case the
 Hammer Dynamics 12" "Fullrange",QTS .38 FS 46.I am wondering what it would take to get flat response over my target range of 120 - 10k,if EQ would be necessary.Thanks to anyone who can offer their knowledge.





scorpion

Re: Open Baffles - how they work, and how to use them well
« Reply #11 on: 16 Aug 2010, 06:00 pm »
One simple baffle to test is the JE Labs variant like here: http://members.myactv.net/~je2a3/open.htm , which is used for a similar purpose.
I think you could reach your goal without EQ at least if the Hammer is a bit like the Eminence Beta 12 LT which the constructor is comparing it with.
It would not cost you much to test.

/Erling

hndaaudio

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Re: Open Baffles - how they work, and how to use them well
« Reply #12 on: 17 Aug 2010, 05:51 am »
Thanks for the link,Scorpion.