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Old 5th January 2013, 08:35 PM   #11
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Oh, and by the way, I took a shot at Autocad... not my kind of program . I'm ok with Photoshop, but autocad...

And Sketchup doesn't seem to be able to do any sort of complicated calculations.

Of course what I'd really like to be able to do, is set up a design and let the program determine the optimal horn layout . But that's not gonna happen .
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Old 5th January 2013, 08:59 PM   #12
epa is offline epa  Netherlands
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hi thijs
i'm not an akabak guru,but is see some flaws.
vtc should be about 6000 and atc 600,from L45 on,all segments are labeled "4"
but somehow the graph seems right.
i think in reality the low knee is giong to be closer to 40hz.

there seems to be a horn spreadsheet floating around on this forum.
but there's always a human brain drawing program interface needed
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Old 5th January 2013, 09:34 PM   #13
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Oops, forgot to correct the labels (you can see which part I copy-pasted ).

vtc 6000? Isn't this 18mm (baffle thickness) x Sd?

And atc isn't equal to Sd? So the baffle cutout should be smaller than Sd? I thought both values were supposed to be the same as I put them in hornresp? What am I missing?

I've found that horn spreadsheet and fiddled around with it. This is as far as I've gotten with it (see zip).
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File Type: zip Beyma 18P80Nd.zip (44.4 KB, 14 views)
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Old 6th January 2013, 08:27 AM   #14
epa is offline epa  Netherlands
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hr see's a driver as it were a flat piston,if this was the case your inputs were correct.

Volume Throat Chamber of an 18"(volume of the cone)=aprox 6 ltrs(6000cm<3)
Averidge Throat Chamber is about 600 ,so the lenght Throat Chamber wil be about 10 cm.

vtc/atc=ltc


you use lpt1/ap1 for bafle opening wright,i normaly ad the volume of the bafle to the vtc.

so vtc of 8000 and atc 700 comes closest to realety,without the ap1/lpt1 inputs.

it wont make a difference in the spl graph
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Last edited by epa; 6th January 2013 at 08:30 AM.
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Old 6th January 2013, 09:24 AM   #15
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Quote:
Originally Posted by epa View Post
Volume Throat Chamber of an 18"(volume of the cone)=aprox 6 ltrs(6000cm<3)
Averidge Throat Chamber is about 600 ,so the lenght Throat Chamber wil be about 10 cm.

vtc/atc=ltc

you use lpt1/ap1 for bafle opening wright,i normaly ad the volume of the bafle to the vtc.

so vtc of 8000 and atc 700 comes closest to realety,without the ap1/lpt1 inputs.
Ok, thanks. Got it

So this would be correct? :

Ap1 = 1225.00e-4; |Throat chamber port cross-sectional area (sq m)
Lpt = 1.80e-2; |Throat chamber port tube length (m)

Vtc = 6000.00e-6; |Throat chamber volume (cubic m)
Atc = 600.00e-4; |Throat chamber cross-sectional area (sq m)

That's with the use of Ap1&Lpt .

I have to admit I don't like it that the sensitivity now is down from about 104dB to just over 100dB per watt . And there's a 3dB dip at 108 Hz. The T48's (of which I own two) claim to do the same and even more starting from 50 Hz in a lot less space using a 15"... Back to the drawing board .
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Old 6th January 2013, 10:47 AM   #16
epa is offline epa  Netherlands
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you got it

Quote:
I have to admit I don't like it that the sensitivity now is down from about 104dB to just over 100dB per watt
Wel hofmans law says pick any 2 of the 3 low,loud and small.
in you sim it extends down to 35 hz,shortening the horn/bigger mouth wil tune the boxer higher ,resulting in a higher efficientie.
changing layout wil not give you more eff.
however whe could try to decrease the dip.
edit/if you would inverse the driver dip gets smaller.eg make s2 ~550 and take away the throat chamber and port
decrease s3 ,s4 and s5 -250
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Last edited by epa; 6th January 2013 at 11:14 AM.
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Old 6th January 2013, 11:20 AM   #17
epa is offline epa  Netherlands
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increase the mouth to 6000
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Old 6th January 2013, 01:23 PM   #18
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Quote:
Originally Posted by epa View Post
increase the mouth to 6000
Already did that. I also reduced S2-S5 (easy to do by modifying the angle of the baffle). The blue graph represents the latest alterations, the bottom black graph is the starting point.

Still a quick & dirty sim, I haven't recalculated the lenghts of the horn segments...
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File Type: png Beyma 18P80Nd Tapped 10 akabak.png (53.0 KB, 171 views)

Last edited by Thijs666; 6th January 2013 at 01:25 PM.
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Old 9th June 2013, 12:07 PM   #19
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Quote:
Originally Posted by epa View Post
here is a scetch
simple design.
easy tuneable by cutting off the front bafle (red)eg mouth gets bigger and the hornpath shorter.
Click the image to open in full size.
Hi Eric,

Since the summer has finally arrive here in holland, I'd like to start building. I have to work outdoors, so my progress will depend strongly on the weather.
I think your design above is the best possible with this driver and the available space I have, so I'd like to build it. Since it's not a particular difficult design, I hope to be able to finish it quite quickly .
I can (and will probably will) take SPL measurements afterwards, but for now, I still need to translate the design into real world wooden panels, which is something I could use some help with .

What I've got so far:
Inner height of the horn = 50 cm
S1=252 -> width of horn (woh) = 252/50 = 5 cm (speaker baffle starts 5cm+thickness of panel from the right side)
Speaker is mounted with center 30cm from the front, measured along the baffle.
S2=835 -> woh = 16.7 cm (woh at center of baffle = 16.7 cm)
Baffle panel is xx(?)cm long. help very much appreciated
S3=1765 -> woh = 35.3cm ('center' panel ends at 35.3 cm from the back panel and about 40cm from the left side panel. that 40 cm is my best guestimate...
Experimenting with the front panel for best performance is needed.

Would you be able to help me a little with the measurements?
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Old 9th June 2013, 01:19 PM   #20
epa is offline epa  Netherlands
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hi thijs
ill put some measurements in the drawing.
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