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Class D Switching Power Amplifiers and Power D/A conversion

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Old 15th April 2011, 08:47 AM   #1101
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Quote:
Originally Posted by Phaedras View Post
Hmm, but with the changed tuning freq wouldn't the port have to be longer? I calculate it to be 7.1cm with a square port of 10,4x4,8cm.. Maybe im wrong?
No, I reverse engineered the new tuning frequency from the original port size which is 34cm2* (or 6.58cm) and 36mm length. Which means I plotted in the size and then adjusted tuning frequency until it matched the port.

*Maybe I should note that the port is 3x12cm but with 3cm rounding in both ends, so the resulting calculation is 3cm area plus 9x3cm, or 7,07cm2 + 27cm2 = 34cm2

Quote:
Originally Posted by ThokN View Post
Just want to say for those thinking about buying the tweeters from eBay, that I got a mail saying they have sold out and will get some more in a couple of weeks :s
That was fast. I didn't even order mine (and Wilcken's) yet.

Last edited by Saturnus; 15th April 2011 at 09:01 AM.
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Old 15th April 2011, 08:57 AM   #1102
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Originally Posted by ThokN View Post
Just want to say for those thinking about buying the tweeters from eBay, that I got a mail saying they have sold out and will get some more in a couple of weeks :s
Wow, that was fast.. I'm glad I ordered immediately when Saturnus posted that they had come up.. My tracking says they are somewhere over the atlantic!

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Originally Posted by Saturnus View Post
No, I reverse engineered the new tuning frequency from the original port size which is 34cm2 (or 6.58cm) and 36mm length. Which means I plotted in the size and then adjusted tuning frequency until it matched the port.
Ahh okay, i'm going with my current calculations.. Don't want to recalculate it again
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Old 15th April 2011, 08:59 AM   #1103
ThokN is offline ThokN  Denmark
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Yes I'm a bit surprised too, since they were listed as "more than 10 available" until yesterday. But maybe it's a good idea to order them anyway so you are first in line.
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Old 15th April 2011, 09:07 AM   #1104
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Originally Posted by Phaedras View Post
Ahh okay, i'm going with my current calculations.. Don't want to recalculate it again
Exactly. Just blind luck I guess but if the cabinet size and the port size is identical to the original then the resulting response graph is pretty much identical as well. So no need to change anything.
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Old 15th April 2011, 10:01 AM   #1105
rubennn is offline rubennn  Denmark
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Aah! I think I'm getting a hang of WinISD now.

Meanwhile I've been looking at some ports online and found a really cheap one 7,5 cm (cross area 44,2 cm2). I put this WinISD and it calculates 5,63 cm port length. There should be no problem in using this instead, right? It's still the same tuning 69,8 hz. I'll just have to cut the port exactly 5,63 cm

I'm building half a boominator for another camp and they are on a tight budget, so this port is appealing.
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Old 15th April 2011, 12:27 PM   #1106
Nahaz is offline Nahaz  Sweden
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I made these cutting instructions for my local hardware store to minimize the risk of something going wrong due to a missunderstanding.
Maybe someone else will find it useful.

In total there are 19 cuts, some stores in Sweden charge by the cut (instead of for time). This means that the cuts would be 190:- at some places (10:-/cut) and 380:- at others (20:-/cut). Some cash to be saved for us cost aware builders ; )
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Old 15th April 2011, 12:47 PM   #1107
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Quote:
Originally Posted by Nahaz View Post
I made these cutting instructions for my local hardware store to minimize the risk of something going wrong due to a missunderstanding.
Maybe someone else will find it useful.

In total there are 19 cuts, some stores in Sweden charge by the cut (instead of for time). This means that the cuts would be 190:- at some places (10:-/cut) and 380:- at others (20:-/cut). Some cash to be saved for us cost aware builders ; )
Neat. Though you should note that it's not the most effective cutting you have described. Generally vertical cuts are done first (on a vertical saw). So you should change cutting 2 and 3 around so that no resetting is needed as some places charge but for cuts and saw resettings.

Also a board is 1220x2440mm.

I used to work as a CNC programmer in the woodworking industry btw.
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Old 15th April 2011, 01:11 PM   #1108
Nahaz is offline Nahaz  Sweden
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Updated the order of the cuts and removed the size of the board, Ive seen different sizes from different stores, 1200x2400, 1200x2500, 1220x2440. It really doesnt matter which size, the cuts will work on any of these sizes.

Suitable scale when printing on a A4 is 30%.
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Last edited by Nahaz; 15th April 2011 at 01:25 PM.
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Old 18th April 2011, 06:48 AM   #1109
Nahaz is offline Nahaz  Sweden
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I also got a reply from the ebay seller stating that the tweeters were sould out and it would take several weeks to get new ones. He asked if I wanted a refund or wanted to wait.

I replied that I could wait, but I never got an answer from him.
My main concern is not receiving the tweeters in time to finish the boominator before this years Roskildefestival.
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Old 18th April 2011, 07:13 AM   #1110
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Btw, I forgot to mention. While at the saw, if you can get the left over 900mm bit cut into a few pieces of 132mm length then you can use those for guides to mount the centerbrace. Width of these aren't really important, anything down to about 30mm will work just fine.
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