any scientific approach to OB?

Altec Open Baffles, etc.

any scientific approach to OB?

Postby bz » Wed Aug 20, 2008 12:41 pm

I have seen the JE labs design wich came from a japanese design, I have seen thoursten which is slim type, I have seen the old brochures almost looking like an a shape. My question is is there any scientific way of approaching this design?
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Postby Jon Agner » Wed Aug 20, 2008 12:46 pm

From what I recall, the front baffle should be at least 1/4 length of the FR.

Try to google the old articles written by David Weems. I have one of his books but don't have it with me right now.
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Postby obi » Wed Aug 20, 2008 12:53 pm

the OB design might have been based on the old wharfedale sfb-3 and on this project...

http://members.myactv.net/~je245/obriggs.htm
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Postby bz » Wed Aug 20, 2008 7:47 pm

Jon Agner wrote:From what I recall, the front baffle should be at least 1/4 length of the FR.

Try to google the old articles written by David Weems. I have one of his books but don't have it with me right now.


Thanks for the reply. Forgive my lack of knowledge when you say length is that the line that is touching the floor? What do you mean by FR?
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Postby bz » Wed Aug 20, 2008 7:54 pm

obi wrote:the OB design might have been based on the old wharfedale sfb-3 and on this project...

http://members.myactv.net/~je245/obriggs.htm


Obi, thanks for the reply. Sorry, medyo masyadong technical yung binigyan mo. pasensya na. Can you please explain it it laymans term as I am having a hard time decoding them. Hehehe. matanda na kasi eh.
Siguro what I meant by scientific is for the layman. like how to compute the base and the hight of the baffle. What is the location of the driver center ba? All based on the specs of the driver.
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Postby setup1 » Wed Aug 20, 2008 10:37 pm

bz wrote:
http://members.myactv.net/~je245/obriggs.htm

Obi, thanks for the reply. Sorry, medyo masyadong technical yung binigyan mo. pasensya na. Can you please explain it it laymans term as I am having a hard time decoding them.


Hi bz,

The simplest explanation for a flat baffle (OB) is, it acts as a barrier to prevent the back waves from escaping to the front (cancellation). Since lower frequencies have greater ampitude they need greater surface area to act as a barrier to reproduce properly. Ideally the OB should be infinitely large (wide and tall) but this is not feasible in the real world. In my experience the SFB3/Briggs design (very similar dimensions to a Quad ESL57) offers an excellent "real world compromise" (as all else in audio) because the driver is mounted close to the floor and the width in relation to the floor provides enough surface area for preventing cancellation. With this information you should be able to decode the Briggs article linked above.

To fully understand the OB principle try a simple experiment. Mount your chosen driver at the center of an approximately 36" x 32" piece of plywood or even hard cardboard. Find a way to stand it up on the either the 36" or 32" side. Listen which sound you prefer and/or decide whether the OB project is worth pursuing.

Happy listening!

je
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Postby setup1 » Wed Aug 20, 2008 11:22 pm

Image

Here's a vintage chart of baffle length vs. frequency in free field.

Ex: 35" width is good to 90 cycles (or hertz) theoretically in free field. However in room with floor reinforcement I hear significant improvement in low frequency extension.

One can interpolate from the Briggs article as to how his chosen dimensions react with different placement in a room (see the graphs). But this is still theory (measured by tools using pink noise, warble tones and etc.) as opposed to actual practice (music as perceived by human ears) :wink:

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Postby bz » Thu Aug 21, 2008 12:44 am

WOW!!!! That's the way to go!!! You hit the nail exactly to the head. THat's what's all I wanted to know. Thanks
Let's use your example of 35" does that mean you don't get to hear the instruments from the lower frequency or it is just there but not so clear?
Saw those Hawthorne and Bastanis type OB. The fullrange drivers are a little bit higher is that the reason why they added active bass bellow?
Have you tried using 4" driver for OB? The driver used for OB is full range nothing else right? thanks again[/img]
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Postby setup1 » Thu Aug 21, 2008 5:30 am

bz wrote:Let's use your example of 35" does that mean you don't get to hear the instruments from the lower frequency or it is just there but not so clear?


My point was even if theoretically the 35" width is limited to 90hz, in my room I can easily hear music down to an octave below that (45hz) with Altec 755s and even lower with 604/605 duplex. It may not measure flat on a real time analyzer but I'm talking about actual music playback.

bz wrote:Saw those Hawthorne and Bastanis type OB. The fullrange drivers are a little bit higher is that the reason why they added active bass bellow?


If you read and understood the Briggs article and the table I uploaded, a tall/thin OB does not do well in the bass. But to satisfy the aesthetic standards of contemporary high end aficionados the baffle has to be slim so you get another compromise - OB midrange----> highs and active woofer in a box for bass.

bz wrote:Have you tried using 4" driver for OB? The driver used for OB is full range nothing else right? thanks again


The smallest driver I've tried in this OB is the Diatone PM610MB (6") and it played the same amount of bass as it did in the stock bass reflex cabinet. That cabinet was so boomy the lower midrange was affected. In the OB, bass was tighter thus the entire midrange sounded more natural.

You can try any type of driver on an OB some work better than others. My experience is limited to mostly vintage classics like the 8" Altec 755 fullrange and 605 duplex (15" co-ax with a compression horn driver for the high frequencies) for monaural. I have two friends who use Altec 604-8G duplexes in OBs - Ding and Abe (amandarae). Abe's system is posted at the Member's system forum with links to You Tube. Joel (setup2) uses the OB for his 12" Altec 414 woofers with 511/902 horns for the upper frequencies. Go to my OB webpage to see what drivers I've tried through the years.

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Postby bz » Thu Aug 21, 2008 10:12 pm

Pambihira si JEsmilla ka pala. Tama ba Ko? Naalala ko pa nga nung dito ka pa sa pinas nag praktis kayo ng dad (conductor) mo sa U.P. You were playing lead then you kept on comiting mistake then your dad pretended to pull out his belt para paluin ka tapos nagtawanan lahat. I don't know if you still rember that scene you were still very young then. Anyway appreciate everything.
I got hold of a Philips 12" fullrange AD 4200M from some old speaker box. So I don't know where to start that's why I came to this board. The graph showing the frequency vs db seems (from my little knowledge) lack in the bass area. Maybe I'll just experiment it with the board you suggested. It also came with a pioneer tweeter of that era also. I guess this is to augment the HF. Thanks and Thanks again.[/img][/imeem]
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Postby bz » Wed Aug 27, 2008 12:45 am

I can still recall the many times I thought that I let my dad down but all the time this was his way to show how he wanted me to do my best in all things and indeed latter to find out that was his way to show and encourage me. Boy am I glad I had a dad like that. My passion for music is one possitve aspect of what my parents did to me. Hindi lang chopstics sa piano ang alam ko ngayon but did my own variation of chopstics. hehehehe. Now if somebody will be willing to record my variations .....hmmmmmm.
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Postby setup1 » Wed Aug 27, 2008 4:58 am

bz wrote:Pambihira si JEsmilla ka pala.....


If you know me and my dad at UP CMU, then I should know you too...it would be nice to put a face on a handle/name.

Thanks!

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Postby bz » Thu Aug 28, 2008 12:49 am

Nope, didn't realy meet you personally but fortunately I was there when you had your rehersal when I visited. Had my 1 year stint long before you. I did not finish music and shifted to anoother course. Have a close friend though the former Ms. Kleiner who finished magna cumlaude i think. I don't know if she's still teaching there. I guess we came from the same school and same college but destiny does have their own way of leading ones life to different direction. I was close with a certain Conrad, fluitist, back then alam mo yung tipong jamming pagwalang ginagawa. I think he is in Germany now. And also a sax player who became famous jazz player , Tots is his name. Never had the opportunity to see them again. I don't know if Ryan will remember me but I guess it will be fun to get together again. But again they are already up there in the field of music. And here i am asking about OB hahahaha. If I remember right I had Pajaro and Deleon were two of my prof. there. Naabutan mo ba si Deleon? O grade school ka pa? Anyway, you do us proud to be out there playing and representing the Filipinos. Mabuhay ang Pilipino!!!! Do you think there are a lot of musicians who are audiophile also. My impression is parang konti lang.
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Re: any scientific approach to OB?

Postby Octaver » Thu Oct 30, 2008 3:20 pm

Met this Guy who really Fan of Infinite Buffle design speakers. He build his own Speakers. Follow his Link:

http://www.mfk-projects.com/theatre_woofer.htm
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