[jeenie67]

....I'm in the process of designing a dipole system using Altec Lancing 12" drivers and a rather large JBL horn lens. I recently read an interesting article in Stereo Review on a "Jamo" speaker and this has the qualities I'm seeking.....spacious sound staging.
I realize these types of systems rely heavily on room acoustics...this is one area I've been playing with for quite some time now as I have no tone or EQ controls at all in either of my two systems. I adjust the sonic signature with the room reflection, absorption, and reflection.
    I work at a university proctoring Construction Management classes and have the time and resources to build two prototypes. I would like the drivers to achieve a single point source, modifying the baskets and positioning of the LF drivers with the lens close between them.
These baffles are to be poured from high density concrete approx 60" high by 40" wide and 6" thick with a slight curvature rolling off at the edges.
As soon as I figure out how to attach a picture I will be able to send some sketches and diagrams.
What do ya' think? 

[Bob in St. Louis]

Hey Jeenie,
There's a thread about how to post an image somewhere around here but I can't find it. 
I'm very interested in your project... Keep plugging away, it's sounds pretty neat.

Bob

[gainphile2]

That would be an interesting baffle ! 

To be a point-source the drivers need to operate at 1/2 wavelength, otherwise it will beam. so for 12" driver it would be around 500Hz I think.

[markC]

Who's going to carry them into the listening room? 

[jeenie67]

 Hi, Thanks for the input. As far as carrying anything, it will be bags of children's sifted sand box sand, a few gallon containers of additives, and a special dry mix from Thruway Builders Supply near me whom I've already contacted with specifications of what I require.
At university I have complete access to formulas, specifications, and testing apparatus (hardness, density etc.) to monitor the mix and test the final slabs.
Constructing the forms is the most labor and time consuming part. Forms will be made from framing lumber( used lengths of 2x6's recycled by me) and used 1/2" plywood. These I'll have to shluck into the living room....yeah! that's where it all goes down! Maybe about 20 lbs.each. From there it's a matter of mixing the stuff on a large tarp and pouring by the 5 gallon bucket. I've done stuff like this before installing shower bases and pouring small kitchen pads earlier in my constructo days before going back to college.
 Before the crete has fully hardened the speaker baskets (dummies) will be installed so the crete forms around them. All holes etc. to be cut in then too.
After the crete has hardened fully, a coating of clear poly resin to all surfaces; ClearCast it's called. Then installation of the real speaker baskets which are two rings of Ash hardwood separated by aluminum dowels.
I really need to scan my prints and show you all. How the hell do you add attachments here? At Lancing Heritage everything is nicely laid out and some other audio forums I visit. Clicking those icons does nothing. Oh well.....someones sure to give me a hand....I really don't have too much time ...This is my "relief" from writing projects and lesson plans!  I'll be back Tuesday. Aye!  Everyone have a fine week and Tanx!  Jeenie.
 

[Mr Content]

Well they should be very inert anyway. I like that. Looking forward to seeing how your project pans out.

Mr C aa

[jeenie67]

  Good Morning, just before I leave for classes.....!   I read in an old vintage book, Hi-Fi, copyrighted 1953, the properties of materials and how there physical shapes effect sound waves. A concrete tube was number one on the list of, as you've mentioned, as being inert and least intrusive to the natural transference of the sonic wave although it's properties shaped the sound wave and directed it.. This data has always stayed in my memory banks. I've seen examples of this (pics) on other forums as some have constructed large tubes of various materials and dimension. The tubes nice. Then there's the infinite baffle. Not very efficient, but  number one on the list of natural wave form. Now I do have 800 watts to play with...and my Altec M-14's and 15's are extremely efficient in their bass reflex environment, but....
....I do not like the boxiness and lower register accentuation that these cabinets exhibit. Back in the sixties there were marketing and consumer demands to be met....how to be competitive at the expense of purer design qualities and what the general public was seeking. Back then too, they didn't have the amplification that we enjoy now.   ....so... the infinite baffle?   I have to go.....B  Back!  Jeenie

[Bob in St. Louis]

I really need to scan my prints and show you all. How the hell do you add attachments here?

I found the thread, but it's been tucked away to a restricted place for facilitators. 
Here's a quick copy and paste:

===============================
1.  Upload your pics to your Gallery (create one, it's free, if you don't have one already here at AudioCircle)

2.  Go to that picture (in your AC Gallery) and (left) click on it.  It will open up as a larger picture.

3.  Right click that picture

4.  Go to 'Properties' and open it with a left click

5.  You will see either a .jpg or .gif address.....highlight it (by dragging your left clicker over the address) and then right click and choose 'Copy'

6.  Take that and 'Paste' in between the Insert Image icon (the second from the left on the bottom row of buttons available to you)
================================

Hope that helps Jeenie,
Bob

[Bob in St. Louis]

Um...  ...Maybe it's not restricted, try clinking > HERE < for the full thread Jeenie.

Bob

[guest4954]

Fun experiment!
6" thick I would hardly call a baffle, "sounds" like a wall to me.
In the 80's I have casted the satelites of the Linkwitz active speakers with succes. Wall thicknes was less than 1".
(front baffle was different layer of plywood and tar paper)

Is there a scientific or engineering reason why you cast that thick?

Regards,


Michiel

[jeenie67]

Hi. This is the total of the outside dimension of the form. When the final slab is released, it should be about 4" thick. This has the structural integrity it will need to sustain 130db excursions, especially in the lower register. I like my music (some of the time) played at the levels it was recorded at (live Pink Floyd to Diana Krall). (See the Gallery for the sketch) I've had enough of this wireless sh__! Every time I try to transfer an image it gets lost in cyberspace.
I have massive RFI where I live....a microwave tower a few hundred yards from me and the N.Y.State Thruway toll booth and cloverleaf a couple hundred feet from my office.
I haven't finalized a plan yet....I would like some feedback.   Have to go....Jeenie.     

[mcgsxr]

Here is your image for folks to check out.

[jeenie67]

     Hola senor'. Muchos gracias. Soy hasta mucha problema con me computadora! Yo neccesidad tiempo a descubro a solucion'.    I thank you sir (for transferring the image). I'm still having trouble with my wireless laptop and in time will solve this minor problem.
    Tomorrow I plan to study in depth, the waveform emanated by a single 12" driver; it's properties relevant to the environment I shall place it in. Then I need to layer this data to accommodate the second driver, insert similar data of the HF driver element, and finally calculate all dimensions of driver placement. From their I calculate (as stated in an earlier reply) crossover frequencies.
This will be fun!   I've been highly successful designing box type cabinetry, folded horns, bass reflexes, and line transformer arrays.  My two 16" Altec 422-8z's enjoy a folded horn "W" enclosure for high db studio monitoring and sound reinforcement duties. Although cumbersome for a little guy like me, the efficiency and sonic qualities achieved with a "guitar speaker" are commendable. They do the job!
This summer I shall look into tube amp design as I wish to have all my drivers in "happy homes" and singing clean!   Tanx!
     
     

[Angaria]

Depends on your definition of beaming, but I'd say 1kHz is a better upper estimate.

That would be an interesting baffle ! 

To be a point-source the drivers need to operate at 1/2 wavelength, otherwise it will beam. so for 12" driver it would be around 500Hz I think.

[jeenie67]

Hola compadres.  Achieving a true one point source is only possible with one driver. Getting as close to this quality is an item I'd like to take a whack at! This is the reasoning behind trimming the speaker baskets to reduce their diameter bringing them closer together. Squeezing the HF horn in between them takes some study. What matters here I think is a seamless as possible flow of "waves". The angle (Y axis) of the LF drivers is critical also. I'm thinking of trying a nano second delay here; in the two LF drivers signal. I have to try....experiment....backed with available data and proven designs.
Dr. Bose and the crew that developed the original Advent loudspeakers up north did a lot of wacky experimentation. Take Henry's air suspension and play with it. He did! Look what became of it. And all those tubes and horns....!      Like I said, I'm thinking, designing, drawing, dreaming, and applying know fact to an experiment. All I have now is a strong hypothesis.... an idea. I know this design works. Now I want to make it work with what I have.
This weekend I plan to construct a couple of rough prototypes out of used plywood...just to see the effects in my living room.  Aye...16 screws is all it takes. Tanx again!

[jeenie67]

                                    ...Hasta mucho tiempo no hablamos...Si?  ...No?   
                 Much discussion on the x-over frequency. I do have active crossovers, variable to any frequency. With a SPL meter, mike stand, signal generator, and frequency analyzer (all available to me on loan from the Electronics Department on campus), it will take some time...outdoors...to dial these babies in. Prototypes in the process....I've procured some used plywood and 2x6's, made some initial cuts, and will bring it all home Friday after classes. 
                The weekend is made for Michelobe...well..I prefer Arizona Iced Tea and French Bread. I'll be outside this weekend in the ever changing Buffalo weather..makes some want to drink...supposed to be nice...supposed to be. The weathermen here couldn't predict 6:00pm at 5:00pm!  Too much interference from the Great Lakes..which in turn affects the jet stream. They do get better...now with millions in satellite gear at least they can track it.

[jeenie67]

.....Boy! I started this project and the first beautiful day in Buffalo I ran an obstacle course with a quasi parachute jump and shattered my entire right foot heel.  OOOWWWWWCCCHHHH! Everything's on hold for at least two months. It will be a month before I'm normal again after surgery. I just wanted you to know that I haven't given up, or gone off to France or something! I'm so aggravated....I can't do this kind of stuff no more...I must be gettin' old. They won't let me play hockey anymore (I'm a liability regardless of waivers)! In a few weeks I plan to really dealve into the physical properties of the Altec drivers I will use and gather all the data to compute this and that..! Well time for a pill...Thanks to everyone for your input.  Jeenie.