Ever think of building a Cornu Spiral horn? Now you can! - Page 35 - diyAudio
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Old 8th January 2013, 12:38 AM   #341
xrk971 is offline xrk971  United States
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Quote:
Originally Posted by Jim Shearer View Post
Cal & XRK,

I'm getting ready to start a pair of Cornucopya's with the Altec Lansing 405A drivers I have. Near as I can tell, the 405A is close to the same size as the FF125wk, although when I measure the cone, it looks to me like 8.5 cm dia. pistonic size, or an S(d) = 57 cm**2, compared to the FF125wk spec of S(d)= 66.5 cm**2.

When I plotted the spiral (which Cal appears to have used at the start of this thread) for a 27" horn, I find a CC measuring 4.5" x 5" with throats about 17mm wide. If I use a channel depth of 5", this comes out to 43 cm**2 total for the two throats.

How do I get the total throat area up closer to S(d) which IIRC is what you recommend? Shrink the CC a bit?

Thanks, Jim
Jim,
There are several ways to expand the throat area: custom draw the channels to have a wider throat if you want to keep external dimensions the same; increase depth of channel, or grow whole cabinet. Note that some compression is ok, if ratio of throat area to Sd is greater than 75%, it's probably ok. For low Qts, high Bl drivers with low xmax, you might want more compression to load driver and reduce excursion. It should be modeled - a simple model in HornResp with a conical horn for first section to exponential horn near mouth wirh
appropriate dimensions for driver chamber will tell you a lot about excursion of cone.

If you are using the plan from planet10's pdf diagram, I think the the throat width is 0.9 in for the 27.6 in cornu. That is 2.3 cm wide not 17 mm wide. This gives a throat area of about 57 cm^2 for a 5 in deep channel. This about a perfect match for your driver if you wanted no compression. You could probably go as thin as 4 in and be ok.

What are the T/S params for your Altec driver?

Good luck!

Xrk971
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Old 8th January 2013, 12:57 AM   #342
prezden is offline prezden  Canada
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Hey Cal- I was just looking at your speaker projects. What on earth do you do with all that marvelous stuff?
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Old 8th January 2013, 01:27 AM   #343
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Unless you and the others gives us a first name, that's a secret.

I have further listened to to the LG's and I don't know what to say. My wife is in the bath and she asks [honest to Jimmy], are those the new ones?

3" speakers doing that?
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Old 8th January 2013, 01:40 AM   #344
xrk971 is offline xrk971  United States
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What are the LG's?
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Old 8th January 2013, 03:07 AM   #345
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Post 340 tells you what I know. I wish I had more of them, seriously.

What I can say is they sound really nice, they are better than expected.

Jimmy appreciates that.
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Old 8th January 2013, 03:36 AM   #346
xrk971 is offline xrk971  United States
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Cal,
I missed that post somehow. Glad they sound good, do you have any photos? Are these one of those concave aluminum dome drivers? Who is Jimmy? Buffett?
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Old 8th January 2013, 04:44 AM   #347
prezden is offline prezden  Canada
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Closet door stereo
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Old 8th January 2013, 07:48 AM   #348
xrk971 is offline xrk971  United States
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Prezden'
Very nice setup there!
Is that the Sure TPA3110 amp you are using? How do you like it?
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Old 8th January 2013, 09:33 AM   #349
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Quote:
Originally Posted by xrk971 View Post
I was wondering what a Cornu horn would look like if we were to actually use the true Cornu function which is also known as a clothoid. ...
Nice work. Did you notice something something pretty significant? The resulting horns closely follow an exponential length/area law. You can model single-spiral (divided 4 ways) Cornu horns in Hornresp using a single exponential section, and the multi-length horns like the one in your post in AkAbak. I'll modify (simplify) my AkAbak model accordingly.
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Old 8th January 2013, 10:14 AM   #350
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Hello. Has anybody tried this with a different enclosure shape? Aesthetically I was thinking about a circular overall shape rather than square. Good idea? Many thanks for any advice.
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