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Old 25th November 2012, 02:12 PM   #691
GM is offline GM  United States
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While I'm comfortable using fractions because it's what I grew up with, once I learned about the decimal system it became my preferred unit of measure, so can understand why metric would be preferred over fractions.

Unfortunately though, many of us have Imperial units so mentally ingrained in us that while converting to decimals is no problem, converting them to metric with what amounts to odd fractions/decimals is tough, so can sympathize with those raised on metrics trying to convert to fractions.

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Old 25th November 2012, 02:22 PM   #692
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Yeah, strait Banana's, standardised Carrots, Potato's, Tomato's, Onions, Lamb and Pork chops.
297mm x 210mm sheet of paper = A4.......... come get me Euro cops.
Makes you wonder how retailers get away with selling me a 38inch lcd tv?
Tis a good job the Euro nannies dont visit my shaping bay, custom surfboards are discussed in Imperial, laid out in Metric and once shaped, the dimensions are written on the shape before glassing in Imperial. One shaper started to write the dimensions in metric and his sales fell - surfers didn't know what size boards they were buying!

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I've been playing with Horn Response for a while - maybe 18 months or so and still cant make head nor tail of it
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Old 25th November 2012, 02:42 PM   #693
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OK, here are the horn cell dimensions of the 1005 as best I could measure.
Going from the mouth back to the throat at 20mm intervals. It was not easy to be exact, as the walls are coated in a rough aquaplas, with bumps and dimples.
You'll see 3 columns, the right most is the measured outside minus 3mm. That's about the difference I measured at the mouth between inside and outside. With aquaplas and lip, it could be 3-5mm difference inside to outside. Take it with grain of salt.

350mm is where the horn goes into the flange, I could not measure beyond that.

If you can get Hornresp going, you might be able to find the actual profile numbers that match this curve. Have fun!
Attached Files
File Type: pdf 1005-cell-dims.pdf (25.5 KB, 49 views)
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Old 25th November 2012, 02:45 PM   #694
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Quote:
Originally Posted by GM View Post
Unfortunately though, many of us have Imperial units so mentally ingrained in us.....

GM
I know my height in feet & inches. It just doesn't sound the same in cm. On the other hand Mrs JRKO like to measure her weight in Kg's as she's no idea what it means

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I've been playing with Horn Response for a while - maybe 18 months or so and still cant make head nor tail of it
Another one who doesn't get HR!! Maybe its one of those jokes where those in on it know it doesn't work but recommend it for a laugh?
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Old 25th November 2012, 03:24 PM   #695
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Come on fellows, all you need to know to convert back and forth from inches to mm is the number 25.4 the conversion factor. As far as measuring an old Altec multi-cell to get the dimensions is a fools folly. I bet no two Altec multi-cells measure exactly the same, they were hand made. All you need are a few numbers to figure this all out. The initial cross sectional area at the start of the horn and the mouth size that you want for cutoff. As far as the length goes that is a little more complicated as you can for-shorten or extend the length without affecting the cutoff frequency in a significant way. First of all design the horn lens for a multi-cell as a single horn lens. After you have that basic sizing calculated just divide the total surface area at any distance along the axis by the number of cells you require. The basic equation that you need to know is
So=Si*e^mx Learn this simple algebraic equation and you are on your way to being a horn designer. It would be easier to help here if I knew all the hidden keys for mathematics. The basic numbers are as simple as taking the number of the speed of sound in air at standard conditions which is 13,548 inches. Take that value and divide by the frequency that you want for cutoff and divide by that value. Then divide by 4 as that is 1/4 wavelength the magic number for a useful cutoff frequency. This can also be used as the length of the horn lens at 1/4 wavelength the common method of design here.

I forgot who asked the question what I would make a horn lens out of. My original design work with horn lenses was to develop a mathematically correct shape that could be inexpensively produced and that material was polyurethane foam materials. I hold a now very old and open source patent for that design. I actually had the first patented design using foamed plastics to produced any horn shape. I could have made more money suing others for that reason than making lenses themselves but never did that. As far as making a paper horn lens I don't see why not if that is what you really want to do. I would probably just cut out the shapes from mat board and glue the sections together with Cyanoacrylate adhesive. Then you could easily wrap that with fiberglass material or just coat the paper with epoxy resins. After that you can fill the open space between sections with some filler material.
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Old 25th November 2012, 03:32 PM   #696
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Quote:
Originally Posted by Kindhornman View Post
As far as measuring an old Altec multi-cell to get the dimensions is a fools folly.
Call me a fool, then. (See my post above). FWIW, the cells on mine all measure pretty much the same, within a mm - considering the coating. I guess the metal parts were cut from a template.

As to how critical it all is, I would guess it's not too.
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Old 25th November 2012, 03:40 PM   #697
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I'm not all that familiar with all of HR's options, especially with all its more recent upgrades, but the basics are simple enough once you know its 'ground rules' listed in the HELP doc.

To generate a single segment horn profile, all you need do is follow the HELP's instructions for Horn Parameters S1, S2, L12, T. All the other fieldís values are irrelevant!

Click Calculate.

F12 displays Fc.

AT displays the throatís half angle in degrees if you want to know how it lines up with a driverís exit angle.

Cir displays the percentage of mouth area to a full size horn based on the local boundary loading specified in the Ang field.

Click Window/Schematic Diagram in the taskbar.

Click File/Export/horn data in the taskbar to pop up the Export Horn Data window. Scroll down to this section of HELP if you have any problem figuring it out.

Once any changes are done [if any], clicking OK pops up a window to save it as a txt or csv file [you choose], which can then be opened in an appropriate program to view all the hornís dimensions at whatever expansion distance specified and/or generate a drawing to print out templates.

HTH,

GM
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Old 25th November 2012, 03:56 PM   #698
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I see that I have an old version and so what you say above just isn't working at all for me.
Will try a newer version
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Old 25th November 2012, 04:11 PM   #699
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Quote:
Originally Posted by Kindhornman View Post
The basic equation that you need to know is
So=Si*e^mx - Learn this simple algebraic equation and you are on your way to being a horn designer
But I'm no further along until I know what the designations So, Si,e & mx relate to. I'm guessing sos & wavelength/freq. are in there somewhere

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To generate a single segment horn profile, all you need do is follow the HELP's instructions for Horn Parameters S1, S2, L12, T. All the other field’s values are irrelevant!
Do I enter 0.0 for the other cells?


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Originally Posted by GM View Post
Once any changes are done [if any], clicking OK pops up a window to save it as a txt or csv file [you choose], which can then be opened in an appropriate program to view all the horn’s dimensions at whatever expansion distance specified and/or generate a drawing to print out templates.

GM
Thanks GM. Is the txt file the list of distance, radius, area etc I've seen on the exponential calc? What are the 'appropriate programs' to send the info too?

I'm going to use the measurements Pano kindly provided to build a proof of concept cell or two. By the time I've narrowed down the particulars of build method I hope to look at replicating using HR for exact plots.
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Last edited by JRKO; 25th November 2012 at 04:33 PM.
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Old 25th November 2012, 04:19 PM   #700
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Seems like a good way to proceed. If I figure out the profile in HR, I'll let you know
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