DIY Open Baffle Full Range Speakers from Wal-Mart . . .

[Scottmoose]

He's probably correct, but I'm guessing.

Re the open-baffle isobaric, well, I suppose you could mount them like that, but I'm not sure what you're hoping to achieve by doing it?

[TomekZ]

A narrow baffle with wings works well. Haven't tried the slopping roof, though--just a little awning above the driver. Presently, I've the Fostex 8 inch F200A on a 14 inch wide baffle, 30 inches tall, and wings about 12 and 10 inches deep. Good bass.

[gilbodavid]

Scottmoose, he waas pretty clear it wasnt an isobaric, but an open baffle design, with all the advantages, and without the disadvantage of two huge smooth plates facing you. Among the advantages he listed were that they could go nearer the corner without resultant loss of sound quality and that the sound was warmer. He'd been building OB designs for two years in Coasta Rica. His explainations are quite technical. The latter part of the dark star thread, with a picture of his speakers is the best bet. I'm afraid I'm very new to this, and mainly trying to deside if i should go ahead or not, as the benifits cited for OB sound to me very much like the benifits of my Quad ESL57's, repannelled by One Thing Audio, which are as stunning to me as the OB's seem to be tto those who make them. I hope this clarifies a bit

[gilbodavid]

his name is JohninCR and he said:
"Dmason,

I'll submit that the sonic difference you hear with acrylic is primarily due to reflections off of that big flat surface directed at the listening position with acrylic being more reflective than wood. Try draping a blacket over the front of the baffle left and right of the driver. While you are doing so, also listen for an improvement in imaging.

At the risk of being repetitive, I want to make 2 points from my experience:

1. The complaint of most who are used to high detail boxed speakers with magical imaging is that OB's don't image as well. I believe this is due in large part to the big hard flat reflective surface pointed right at your listening position and often it will be the most reflective surface in the entire room. It also blocks rear wall reflection for that same area, preventing the disappearing act. The same way a computer monitor acts like a black hole in your audio image with speakers at your computer, I believe big baffles have a similar effect. Folding the baffles solves the problems of overall size and reflections off of the baffle.

eg Having a 10" front, one 7" wing and one 8" wing swept back at about 60 degrees results in an effective baffle width for bass purposes equal to about a 38" wide flat baffle. In a 12" wide by 8" deep footprint you are talking about small box speaker size, so which is going to have better WAF?

While there is a slight change away from a pure dipole radiation pattern, I believe it is sonically superior because you do away with a large reflective front and a large blockage of rear wave reflections. This allows much more freedom in placement without losing the open natural sound of OB. In addition it gives you structural support and a place to hide exposed drivers, XO's, etc. With a grill cloth across the back it will look like a box speaker with an interesting shape.

2. I used to be a proponent of adjustable wings, using some type of hinging. After playing around with it, I am now firmly against adjustable wings. This is because significant forces act on those wings and they vibrate. Not only are fixed wings important, but they need liberal cross bracing as well."

The page its on is http://www.audiocircle.com/circles/v...=asc&start=390

I hope me reproducing his post is Kosher. if not the link will take you tyherre and explain it better than I can. Regards, David

[gilbodavid]

Oops. Just reread the thread and I'm no longer sure you were talking to me re isobarics, which is rather cool cos I havent much of a clue as to what they are. A little bit of knowledge is an interesting thing, in a banana skin kind of way..

[Scottmoose]

it was in reference to the post at the top of the last page. ;-)Believe me, I know the feeling though!

For your interest, picture a normal, box enclosure, with a driver mounted on the front baffle. Now picture another, identical driver, completely inside the box, mounded directly behind the first, usually facing in th dame direction. That's the most common type of isobaric design (there are others of course). It has a few advantages; bass performance is usually outstanding for the size of enclosure. It's not often used commercially though. Linn were the most famous exponents with the Sara 2 way, and the infamous Isobarik [sic] 3 way that had amplifiers the world over cowering in fear.

Cheers
Scott

[el`Ol]

Originally posted by gilbodavid
:

1. The complaint of most who are used to high detail boxed speakers with magical imaging is that OB's don't image as well.

I also experienced a clear plus in imaging when I mounted the extra walls. I guess because there is less reflection at the wall between the speakers. If that`s true, a "monobrane" concept will also do the job, but I didn`t test.

[Jezz-the-Fezz]

Re the open-baffle isobaric, well, I suppose you could mount them like that, but I'm not sure what you're hoping to achieve by doing it?

Thanks for the reply Scottmoose! (sorry about the confusion GilboDavid!) - The Isobaric/Baffle idea is one I came up with ages ago. In actuality, it uses the isobaric principle in reverse to solve one of the issues concerning baffle arrangements whilst retaining the mechanical distortion cancellation features of the isobaric layout.

One potential problem associated with a "free-air" driven unit not designed for free baffle mounting is it's (forgive my misnomenclature) increased "slewing" owing to a complete lack of mechanical damping such as the air-pressure/resistance employed in an IB or BR enclosure.

In standard format, the isobaric layout is typically engaged with the drivers working at an equal power level (using the same drivers face-face/back-back if the distortion effect is to be utilised) from the same amplifier source; principally to relieve the frontal driver of some of the pressure of an undersized enclosure.

My idea uses the rear driver at a dissimilar level of amplitude to effectively pressurise the frontal driver, improving transients and improving overall clarity through some elements of the distortion cancelling effect. Just to throw a little more perplexity into the equation, eq could be added to the rear driver in order to counter linearity difficulties at frequencies above roll-off. I was thinking of doing something along these lines using an SE amp for the frontal unit & a Gainclone to power the rear.

Any thoughts?

Cheers - Jezz

[loudandclear]

Well, I decided to take my "experiment" to the next level (thanks to Ed "adason")

I ordered another pair of B200's and mounted them in the corkys below the original B200s. I mounted them in reverse as per Ed's Lowther setup - in effect a mechanical XO with the magnet cutting off the HF. I still thought I could hear some comb-filtering so I attached a piece of felt cloth over to cover most of the bottom B200's. This really made things come together!

All I have to say is WOW! The added LF response sure completed the picture. This may be just the right amount of bass for our apartment setup. The mids and highs are better balanced now. I can honestly say these are one of, if not the best sounding speakers (LF limited) I have heard anywhere, at any price. Not too shabby for under 700 clams.

The additional dipole bass is truly something to behold and must be experienced. I can see what all the buzz is about now.

I made the mistake of wiring the drivers in series (out of phase) to start with. There were some distortion artifacts. Parallel definitely was the way to go. Such clean sound and I still have lots of volume to play with on the preamp. For 96db speakers, the B200's will eat quite a bit of juice.

The corkboards are probably the weakpoint (flex?) now and some more solid baffles are in the works. Also, I had to pull the speakers another 2 feet away from the back wall as the bass was gettting a touch boomy in the original position.

The picture below shows the felt cloth lifted over the left speaker so you can see the bottom driver.

Thanks again everyone. These drivers are a-mazing.

[johninCR]

Jezz,

You'll damage your drivers with unequal output and negate the distortion reduction benefit anyway, since the push and pull wouldn't be equal.

I was on the isobaric trail a couple of years ago and as I understand it's only useful for low frequencies. In the higher frequencies where the distance between the 2 cones is significant in comparison to the wavelength, the operation of the drivers will interfere with each other not complement each other.

Regarding drivers not designed for free air operation, most of time they need boxes to make bass because their Qts is too low. They don't flap around in free air operation, it's just the opposite and isobaric alignment won't help. Super cheapie woofers are an exception.

Isobaric halves the Vas and that's about it, so it reduces the required box size by half. One other time I've found them useful is with cheapie woofers with very high Vas. Their suspension is so loose that they bottom out too easily. Clamshelling them improves their performance.