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Old 20th December 2012, 12:09 AM   #111
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by Soldermizer View Post
if you have something resembling a conventional box on the floor and an unknowing person tries to sit their big butt upon it and ... crush.

Good thing the cornu-copy-a is a wall-mount

If you must have it on the floor perhaps hot glue a bunch of pointy-end-up thumb tacks and other sharp objects atop it
Once assembled it is surprisingly strong - could probably sit on it fine. kind of like honeycomb panels used in aerospace.
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Old 20th December 2012, 12:23 AM   #112
xrk971 is online now xrk971  United States
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Originally Posted by Pano View Post
I dunno. Can't measure until tomorrow evening. Will let you know before the world ends, if I can.

As for pink noise, yes, you could do that. You have to take into account the mic curve, but you can get a general idea. If you have a mic and a soundcard, use HOLMImpulse or ARTA for your measurement. Easy to get very good results.
Thanks for the tip on Holimpulse. Exactly what I was looking or. I was using the spectrum tool in Audacity sound mastering software.
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Old 20th December 2012, 12:48 AM   #113
ruerose is offline ruerose  Canada
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Your building scaled off the Planet10 pdf Pano?

If so, I'm also really interested in seeing that RTA to see if it has that null from the combined output.

...have to figure out where that's coming from before I go cutting.
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Old 20th December 2012, 01:38 AM   #114
xrk971 is online now xrk971  United States
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Has anyone tried this maple veneer plywood at HD? The 24 inch x 48 inch size is perfect for one 24 inch Cornu with a 3.5 to 4 inch driver. Looks like the perfect facer material.
1/4 in. x 2 ft. x 4 ft. Maple Plywood-1789 at The Home Depot
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Old 20th December 2012, 05:55 AM   #115
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I purchased a small panel of birch plywood very similar to that, but just a little bit cheaper. At my home depot it was the most attractive choice available.

I've also had a thought, inspired by an earlier post if the foam board thread: assuming you make a cornu with 3" or 4" wide foam board strips, why not buy thin sheets of balsa and use it as a veneer? It might look really good!

balsa wood
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Old 20th December 2012, 06:00 AM   #116
xrk971 is online now xrk971  United States
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I agree, you mean apply balsa veneer to exposed channels?
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Old 20th December 2012, 06:16 AM   #117
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For anyone looking at a 24 inch Cornu with a 3.5 in deep channel, the Tang Band W3-315E with magnesium driver cone looks like a perfect driver with the correct Sd to match 3.5 inch depth and it has a hot high end from 12k to 20k Hz witha Vas that is bigger than Vifa. The appeal of the 24 inch size comes from fact that birch and maple plywood in 1/4 in thickness is readily available from HD for less than $10 per speaker in 2 x 4 ft sheets. I am considering this driver for next build in plywood.
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Old 20th December 2012, 06:56 AM   #118
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Quote:
Originally Posted by xrk971 View Post
I agree, you mean apply balsa veneer to exposed channels?
Right, in other words veneer the visible foam board with the balsa. It's a job that could presumably be done even after the speaker is all glued up, provided there is not too much glue runoff. As always, my signature applies to the contents of this post.


My next task, apart from cutting driver holes, is to get copies made of the design. After that, should I just trace the design with a marker that will bleed through onto the wood?
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Old 20th December 2012, 11:07 AM   #119
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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?
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Old 20th December 2012, 04:22 PM   #120
gpapag is offline gpapag  Greece
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In my previous post I wrote about some calculations but I didn’t provide enough tabulated data. Here it is

Baffle 200mmx200mm:---su=14.3mm
Front path length = 114mm. Horn length= 571mm. Delay= 1.33ms
Comb. Boost freq=376 Hz Comb. Notch freq=753 Hz

Baffle 300mmx300mm:---su=21.4mm
Front path length = 171mm. Horn length= 857mm. Delay= 1.99ms
Comb. Boost freq=251 Hz Comb. Notch freq=502 Hz

Baffle 400mmx400mm:---su=28.6mm
Front path length = 229mm. Horn length=1143 mm. Delay=2.66 ms
Comb. Boost freq=188 Hz Comb. Notch freq=376 Hz

Baffle 500mmx500mm:---su=35.7mm
Front path length = 286mm. Horn length= 1429mm. Delay= 3.32ms
Comb. Boost freq=151 Hz Comb. Notch freq=301 Hz

Baffle 600mmx600mm:---su=42.9mm
Front path length = 343mm. Horn length= 1714mm. Delay= 3.99ms
Comb. Boost freq=125 Hz Comb. Notch freq=251 Hz

Baffle 700mmx700mm:---su=50.0mm
Front path length = 400mm. Horn length= 2000mm. Delay= 4.56ms
Comb. Boost freq=108 Hz Comb. Notch freq=215 Hz

Baffle 800mmx800mm:---su=57.1mm
Front path length = 457mm. Horn length= 2286mm. Delay= 5.32ms
Comb. Boost freq=94 Hz Comb. Notch freq=188 Hz

Baffle 900mmx900mm:---su=64.3mm
Front path length = 514mm. Horn length= 2571mm. Delay= 5.98ms
Comb. Boost freq =84Hz Comb. Notch freq=167 Hz

Baffle 1000mmx1000mm:-su=71.4mm
Front path length = 571mm. Horn length= 2857mm. Delay= 6.64ms
Comb. Boost freq =75Hz Comb. Notch freq=151Hz

These are results of “time of flight” calculations, based on drawing of Dave’s pdf.

In practice, expect a variation of +/-10% from tabulated frequencies

The amount of boost and cancellation will depend on the relation btn the front and rear acoustic intensities at these frequencies.

George
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