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Old 20th December 2012, 03:41 PM   #121
kctess5 is offline kctess5  United States
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I'm totally doing this. I still have a pair of Tang Band W3-881si (the buyout from parts express) left laying around. I've been to broke to take on a full sized project recently so this should tide me over for a while!
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Old 20th December 2012, 03:55 PM   #122
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Originally Posted by xrk971 View Post
Poke holes thru paper with sharp object and transfer points to connect. Don't you have master design on paper already or did you do direct draw onto back first time?
Still on my first one. It's going to be a while anyway because I need help cutting holes for the drivers into the plywood. I'm going to order the drivers and everything next week so it will still be a while before I've got one up and running. By the way, I'm thinking of the TB W3-1053SC instead of the vifa for this first go-around.
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Old 20th December 2012, 04:10 PM   #123
xrk971 is online now xrk971  United States
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The w3-1053sc is smaller than vifa so channel depth is different, but will probably work fine. Vifa has larger xmax and a little more zing on top end. Either will work though.
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Old 20th December 2012, 04:13 PM   #124
xrk971 is online now xrk971  United States
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Originally Posted by kctess5 View Post
I'm totally doing this. I still have a pair of Tang Band W3-881si (the buyout from parts express) left laying around. I've been to broke to take on a full sized project recently so this should tide me over for a while!
Kctess,
Glad to see you joining in, it's a blast and very easy. If you have the drivers already, it won't cost hardly anything. $6 for foam core and $2 for glue.
Good luck.
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Old 20th December 2012, 04:25 PM   #125
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Originally Posted by xrk971 View Post
The w3-1053sc is smaller than vifa so channel depth is different, but will probably work fine. Vifa has larger xmax and a little more zing on top end. Either will work though.
One of the things I'm looking at is the difference in Qts: the vifa is about .9, the TB is "only" around .6. According to MJK, high Qts will result in midbass bloat in a rearloaded horn, so the TB might have more balanced bass response in the cornu. (Probably a Qts of .3-.4 is ideal for this project.)
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Old 20th December 2012, 04:34 PM   #126
xrk971 is online now xrk971  United States
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Good point about the Qts and mid bass, looking forward to hear how yours work out. For $10 more, the w3-315e has lower Qts at 0.52 even. I may try this one next.
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Old 20th December 2012, 07:29 PM   #127
xrk971 is online now xrk971  United States
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George,
Your estimates of phase cancellation/boost assume the waves combine at the mouths of the horn? Doesn't this all change when the sound from each horn actually traverses the room and reflects off walls before combining with direct driver emission? The horns are side firing so really most of the output, I would expect, is indirect from walls, floors, ceilings. This was why I asked Pano to try the measurements farther back. But he said are we measuring the speaker or the room? True, but this speaker is critically dependent on room placement.

In case you may wonder, the spectral output of each horn is different, markedly because of the variations in length. I placed a mic at each mouth and fed pink noise into the driver. Just listening to the recorded sound replayed, you can tell one was mid bass and the other lower bass. It is very apparent to the ear even. Since these are hand built jobs, there are variations in the horn, so even the left and right horns are different slightly, same with up and down.

I am trying to get equipment to do a rough measurement of the spectrum. Pano suggested a great free software that I am trying to get working with my mic and computer. Not having a calibrated mic will only give a rough sense though.

Last edited by xrk971; 20th December 2012 at 07:31 PM.
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Old 21st December 2012, 09:57 AM   #128
xrk971 is online now xrk971  United States
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Originally Posted by Pano View Post
OK, here are 3 plots of impedance. I hope it's legible.
  • Magenta trace = no stuffing in rear chamber
  • Blue Trace = as much pillow stuffing as will fit
  • Green Trace= 1 car polishing rag about 8"x11". A tight fit in the camber.
All were with the beginnings of the spirals medium stuffed with pillow fiber.
I'm new at this, help me out in interpreting it please. I think having more than the single peak at the driver's fs means that the two different horn tuning lengths do indeed have an effect on the back horn loading of the driver correct? The 70 something Hz freq matches what I calculated as the lowest freq based on the longest path. The 200 something Hz peak matches the shorter horn length from the split to the mouth.
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Old 21st December 2012, 01:44 PM   #129
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I think so, too. But will wait for those with better knowledge to chime in.
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Old 21st December 2012, 02:45 PM   #130
xrk971 is online now xrk971  United States
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Hi,
i made these drawings to ease scaling and printing.. first one is sebastian's original drawing and the other has more spiral shape. but i don't know if it has any advantages over the original, does it?
i have a pair of 3" full-ranges, may i use them for 70 cm panel or should i scale-down the layout to (3/4) 52.5 cm?
i also hope these pdfs helps to further builders..
xrk971, thanks for the bring us this project..
Endia,
Thanks for making the drawings - it will be useful for folks wishing to try a more rounded horn. I noticed that your version is smoother and more rounded - that will sound different but it is good to try different things. In fact, for my 14 inch (35.6 cm) cornu, I made it very round like yours and I like the sound it makes. FYI, Planet10 (and others) have made scalable pdf drawings too. I think it is on post 23 of the foam core thread. My guess is that the rounded horn will let more upper bass through, and mids and may be very good for people who listen to a lot of jazz, horns, woodwinds, and vocals. A 3 inch full range driver may be a little small for a full size 74 cm cornu. I did a 50 cm with a 3.5 inch driver, but a 3 inch driver could probably work up to ~60 cm size. It's really all new so who knows? If you try the 74 cm with a 3 inch driver and it doesn't work, you can always put in a 4 inch driver. Although when sizing the channel depth, you may want to pick a depth that in between the two drivers you plan on using. We are seeing depths ranging anywhere from 2.5 inch to 4.5 inch.
Good luck!
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