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yet ANOTHER DIY Unity, and a spreadsheet for figuring the wood cuts

post #1 of 26
Thread Starter 
This seems to be a hot topic these days, with Cowan's and PaulSpencer's, JohnBomb's, (others?), builds. I'm playing with this, too, so this is kind of a "me-too" design. My first test horn has its glue drying in the garage now.

While making my first test build, I made a spreadsheet to figure out the design parameters and all the awful cutting angles needed for a dual-expansion conical horn (normal, or "offset" Unity style). Thought this might help any others who are thinking of also going off the deep end and building some of these beasts.

The spreadsheet, and some more discussion can be found at
DIY Unity build and Xcel Spreadsheet
post #2 of 26
Very cool. This is something I eventually want to try myself. I am an applied mathematician by background, so I should be able to figure it out.
post #3 of 26
You are the man! I was dreaming of this yesterday and here it is. Thank You. Looking forward to seeing some great results. What mids are you using?
post #4 of 26
Thread Starter 
I'm trying this with these really expensive drivers:
http://www.parts-express.com/pe/show...number=289-127
I think Marlin P Jones has some of these, as well. They were all over the surplus market a few years ago.

They need to have their backs sealed leaving some volume back there, I'm going to try 2" mailing tubes.
post #5 of 26
Oh man, you are going to break me A inexpensive DIY CD and this could be the budget buy of the century.
post #6 of 26
bwaslo, iirc much of the 'magic' in the synergy horn is in the crossover and getting the phase right, whatever 'right' means in this context. cowan tried a number of different crossover networks, but chose the one provided by danley. any thoughts on why the danley network was preferred?
post #7 of 26
Thread Starter 
No idea, but I don't know what Danley's crossover is. He has had more time to work on them though.
For delay variation, though, a MiniDsp can do that really easily.
post #8 of 26
Thanks for contributing that spreadsheet, bwaslo, that's a real treat for us all! I hope your build goes well- looking forward to it.

John
post #9 of 26
Thread Starter 
Tonight I slapped the midrange drivers on, put the back cups on them, wired them up and made a quick measurement:

Not too bad, surprisingly smooth (that's an unsmoothed graph), goes lower than I expected, but not as high as modeled. I think I need to cut frustrums into the ports, will try that to see if I can approach 3kHz.. even if not, plenty usable as-is.

This was a trial build (see see how well it matches HornResponse and to debug my calculations -- the build I did had some errors I had to patch, which are corrected in the posted spreadsheet). The HornResponse prediction isn't too far off other than at the high frequencies (and the response is much smoother than predicted, which showed stronger passband ripples).

Here are some photos of the build process. As you can see, I didn't spend much effort on cosmetics for this first one. The next I plan to make prettier.





post #10 of 26
Cool, Bill. I like the tandem driver mount. I'm guessing 1 hole per driver? How big are the holes?

John
post #11 of 26
Thread Starter 
half inch, slightly tapered. Next I'm getting out the dremel and making much wider bevels
post #12 of 26
"No idea, but I don't know what Danley's crossover is."

iirc cowan posted the final design on his site. dug it up...attached. passive crossover networks are like hieroglyphics to me. just by looking at the crossover, i couldn't tell if it is phase linear, power response linear, or any other kind of linear. :-) all i know is that cowan experimented with a number of different designs including at least one by mckinney, yet he settled on the attached.

maybe you or someone else have a perspective on why it seems "to work"?
LL
post #13 of 26
LTD, it had to do with the XO iterations Danley himself was working on. When the Unity first came out the XO still needed some adjustment and the version that Cowan used is the final iteration to ensure optimal phase and time alignment for that combination of drivers.
post #14 of 26
First of all, nice work on the spreadsheet!

Now I see a couple of errors on the angles at which edges have been cut off. Just wondering if those errors were done in construction, or whether they are in the spreadsheet?

On the second horizontal flares, the edges look at if they got cut off the wrong way.

The mids seem to typically have less extension than simulated, so it's a good idea to aim for a bit more than you actually need. Bit of a pest if you hope for 1k and you get 900 Hz!

Also see that famililar hump at the bottom end.

One tricky aspect of the angles is that I don't actually end up with the angles I intended. I might start with say 80 degrees initially, but then I start working with the throat flaring and modifying the mouth slightly and what results might be 77.4 degrees.

You also might want to consider attempting to mitre the edges rather than doing butt joins. I did butt joins on the first two and found they were a pain in the butt.

It helps with painting. If you do butt joins then the ports for the mids end up going through edges of sheets, which is awkward and you have problems with getting the insides of the ports smooth.
post #15 of 26
Thread Starter 
the butt joints allow the top/bottom to extend, making more room for driver mounting. Also cuts down on the number of angle cuts. These plans are all about minimizing the work, all effort is on the inside of the horn, none on the appearance of the ouside (I'd have that enclosed, anyway).

There were some errors in the v1 of the spreadsheet (never posted), which I had to trim these for. The outer edges of the bell I rough trimmed by hand, since this was just a test horn. For real horns, I'll use guides for that (the plans leave a flat normal to the horn axis at the ends of all panels, making for a pretty wide surface given the angle of the last expansion).
post #16 of 26
Thread Starter 
Update -- I used some wood putty to fill in the front chamber a little and also scooped out the port taper some. Increased the length of the tube behind the drivers to increase the volume. This is now much closer to what I modeled (I had forgotten to include the volume of the magnet behind the drivers, before, and also the volume within the cone itself). And the results fit the model reasonably well now:

Still not quite as strong at HF as modeled, but more than enough to reach the HF driver response I want to use.

I think I'm ready to make some "real" ones next. These are quite fun to work with. Kind of like the speaker building equivalent of a ship-in-a-bottle.
post #17 of 26
Looks really good Bill.

To prop up your high end you might try a little infill between the area under the cone. Makes quite a difference. More trapped air acts like a high frequency filter. Less air will push up your top end.
post #18 of 26
Thread Starter 
mwmkravchenko,

Thanks for the suggestion. My thoughts were rather running that way. I was even thinking of sacrificing one of the little drivers to use as a mold for some wood putty to do it with. If you think it will make that much difference, I'll probably give it a try.
post #19 of 26
Sacrifices to the driver gods!

Think plastic wrap and your driver lives to woof another day. With the cone mold short enough to allow decent excursion you will get closer to your goal.

Mark
post #20 of 26
Thread Starter 
yeah, a $2 driver would be a huge sacrifice!
post #21 of 26
You might find that bondo or something similar may wor better.

Most wood fillers that I can think of will crack and kind of split when they are laid up in any useful thickness.

An automotive filler is fast and happy as a pig in mud when it comes to a heavier plug type of setting.

Just some fuud 4 thot.

Mark
post #22 of 26
Nice stuff Bill! Even if the plug idea doesn't buy you too much more, you still seem to be comfortably at a 2k xover which opens up some options.

It's hard to tell from the photos - what are the dimensions of your horn? guessing 16"x10" or thereabouts?

Are you entertaining thoughts of trying some woofers on the flare for a 3-way Unity, or are you thinking of just augmenting with a conventional woofer?
post #23 of 26
Thread Starter 
24x14

Yeah, the plan is to put 2 or 4 of the Aura 6" buyouts on there, too.
post #24 of 26
These Unity builds are great!

Keep it up... thanks for sharing.
post #25 of 26
Thread Starter 
Another update -- I started making my "real" DIY Unity (Synergy?) horns. First, I revised the design spreadsheet for a much better arrangement at the mouth. If anyone has plans to use the spreadsheet for making your own horn, get the new spreadsheet first, it makes a lot better use of the size and will look better too.

Spreadsheet and some build photos at:
http://www.diysoundgroup.com/forum/i....msg179#msg179

Some teasers:

post #26 of 26
There is a trade-off involved here with making the chambers smaller - you tend to get less acoustic filtering, hence higher distortion. If you look at the original Unity kit, it had very low distortion. For home use with capable compression drivers, I question what is achieved in pushing up the crossover point. I'm aiming to go a little higher, around 1.2 - 1.5k whilst keeping the acoustic filtering for low distortion. In so doing, that's pushing things just a little bit further than my S2, aiming for a bit more headroom.
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