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-   -   Height issues for Dayton CSS AC 3way (http://www.diyaudio.com/forums/multi-way/51358-height-issues-dayton-css-ac-3way.html)

dunderchief 11th February 2005 07:47 AM

Height issues for Dayton CSS AC 3way
 
Hi there,

So I'm a big sissy and I copped out on the TL design for my RS225, WR125, AC G2si 3ways. The box geometry just got too crazy, and I couldn't get a decent tapered line to work out. Regardless, I'm going to go with a simple ported 75L box tuned to 24hz. This seems to give plenty of extension, and lets me use the precut 3" port from PE. Okay, right, I'm rambling.


The box I've design comes out to be 42 inches tall, that makes the mid around 46" high, and the ribbon tweet about 50" high.

These numbers are getting really tall and it kind of worries me. I've heard a ton of things about the vertical dispersion of ribbons being bad, and if I'm sitting down, 50" is way above ear level. I generally sit about 15'-20' from the speakers.

So I see it as three options.

One, leave them how they are and live with a tall box.

Two, increase the width of the baffle (currently 12") to decrease the height of the box. This pushes the baffle step point down (right)? but the mid seems to be able to handle that fine. Also the system will be fully active, so compensation won't be a problem.

Third, angle the tweet to be pointed more toward ear level. I don't like the sound of this since it would only correct for one general area.

Well, thanks in advance and sorry I can seem to put a post into less than about a page of writing. I just wanted to opinions before I start cutting wood tomorrow.

Jim85IROC 11th February 2005 02:47 PM

What enclosure volume did you choose? I modeled the 225 with a 2.25 cubic foot enclosure tuned to 28hz. With an internal baffle width of 10.5" (12" external assuming 3/4" MDF), an internal depth of 12", I come up with an internal height of 31.25". Add spikes and wood thickness, and you're only at 34" maximum. I would think that even with a separate chamber for the mid and tweeter, that if you mount the tweeter below the mid, your height shouldn't be an issue.

Luke (Uof Iowa) 11th February 2005 04:00 PM

What about simply increasing the depth?

- Luke

tiroth 11th February 2005 04:36 PM

Well, the VBA is likely negative anyway, which solves part of the problem. You'll need to at least mock up and test with your intended xover to determine the exact angle.

I have a design with G2 and PR170M0 that places the midpoint of the tweeter about 1" above seated ear height. I had to tip the baffle back 5 degrees to get zero VBA. Alternatively, I could have done the math and made the tweeter higher, but as you point out it can only be optimized for one listening distance. I encourage you to do the math though, because depending on the angle and width of the lobe you may well have good results over a broad set of distances.

I think you also left out the option of MTW, which would place the tweeter lower.

tiroth 11th February 2005 05:15 PM

Sorry Jim, I missed seeing you had already suggested MTW

GM 11th February 2005 06:15 PM

Quote:

The box geometry just got too crazy, and I couldn't get a decent tapered line to work out.
Oh really?! Using PE's measured specs I got a nice ~flat half space FR down to 30Hz with either a positive or reverse tapered ML-TL pipe. Proper folding will allow optimum mid/HF driver location.

With a 42" i.d. straight pipe, driver down 16.43" with a 2" radius x 11.5" long vent looks good for a max flat with a 0.25lbs/ft^3 stuffing density. Assuming 3/4" material thickness, this puts the driver at 26.32" so there's plenty of space for the mids/HF above it, though some thought is required as to how to insert the mid's rear chamber without disrupting pipe action too much. One option is to fold the pipe so that a separate mid/HF cab sets on top of it. This has the advantage of the divider also being a strong brace and any cavity left over can be filled with kitty litter, sterile sand, or similar to mass load it.

WRT ribbon placement, they have limited vertical off axis response so need to be at seated face height or somewhat above depending on the slope of the XO.

GM

dunderchief 11th February 2005 07:28 PM

thanks for the thoughts guys.

I guess I should have explained a little more.

The internal structure of a box is a triangle with a depth of 21". I would really like to keep it at that since it's already pretty deep.

The final boxes will come out looking A LOT like the B&W 801. I'm already working on the fiberglass that will sit on top of the cab to house the mid and tweet. As much as I hate to admit it, I would like to keep the visual flow of the speakers right, so I'd like to keep the tweet about the mid.

I was trying to model a tapered line in this enclosure, but the transition from Trapezoid to triangle was really tripping me up. I had a nice even taper, and then a big change, and then another nice even taper. A straight pipe would be much easier, and a 42" line also would be a lot better. I haven't done any work with a straight pipe though. Would you mind letting me know what you used for the area behind the driver? I'm gonna go play with Mathcad now and see if I can work something out.

any more help is of course greatly appreciated.

dunderchief 11th February 2005 08:30 PM

2 Attachment(s)
Ok, so I've just done some playing with MJK sheets and while I don't fully grasp everything that they do, here's what I figure I've got.

I modeled a 55" straight line with 1.8Sd for the area. with a 1.5"x11.5" port I seem to get a pretty decent line.

It's about 3db down at 30hz and seems good below that.

With the materials on hand I can easily go with a longer line, but I can't go with much more area. I've already gone over budget about 20 times on the project so I'd like to not buy anything more.

I've attatched a pictures of my graphs with both a 55" line and a 65" line.

Roughly speaking a 55" line puts my mid at about 34" midline and my tweet 40" mid line.

The 65" line puts the mid about 38" and the tweet 44"

Thanks for letting me ramble to someone beside myself. It helps. At this point I'm thinking that I'll probably end up just building the line whereever between 55" and 65" is easiest to cut with what I've got. Also, I'll definately look into tipping the baffle on the mid and tweet to get everything just right.

Thanks again
-Steve


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