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Old 2nd December 2012, 10:32 PM   #291
xrk971 is online now xrk971  United States
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Quote:
Originally Posted by planet10 View Post
Sd should have nothing to do with it. It has been historically used forTLs & horns, andunfortunately because of that Martin used it as a unit of area inhis model which confuses things more.

dave
If not Sd, what should we scale the horn channel depth and throat opening with, Vas? If you make throat area smaller than Sd, you would be constricting pressure and increasing velocity of air due to mass conservation. Wouldn't this reduce the horn's efficiency?
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Old 2nd December 2012, 11:11 PM   #292
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There is a relation between Vas, Q, volume of the air cavity, and the throat area that determine the low pass function. Youdon't want too much HF coming out the horn mouth

Further. the difference in path length between the direct radiation and that from the back of the driver to your ear should be an odd number of half wavelengths of the nominal f3 of the acoustic LP of the throat/air cavity.

Efficiency (horn gain) is not high on the list of parameters to design for -- more of interest in front horns. Cal's build ilustrate that as long as you have enuff or more than you need horn gain can be adjusted with stuffing. You want the fall-off of the driver & baffle-step losses to be compensated for by the gain of the horn. With no baffle steptodeal with this horn needs less gain, the big bonuses coming from the ability to get lower bass out of asmall driver, and reduction in excursion at those frequencies.

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Old 2nd December 2012, 11:24 PM   #293
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Originally Posted by 6L6 View Post
Cal - What is the height of your spiral? 4 1/2" ?
Yes.
Also, how much room do you have between the back panel and the magnet's felt?[/QUOTE]
I didn't measure but you can easily look it up. I would guess a couple inches plus.
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Old 2nd December 2012, 11:26 PM   #294
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Originally Posted by planet10 View Post
Top is not as extended as FF125
Hold on there Billy, guys like me find the top end rather restricted. The up side is the lack of listening fatigue. I could listen to these at a decent volume all night.
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Old 2nd December 2012, 11:32 PM   #295
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OK, so I added a little stuffing to the throats and that really helped with the bass horny hump above 100 Hz. I also placed them 12" away from the wall and that was another plus. I am thinking that further stuffing of the throats and returning them closer to the wall will be the cat's meow. I'll find out another day as I have to wrap it up but the improvements were huge, heck even SWMBO took an interest which is almost unheard of. I listened to my regular test tunes and then I put on Jimmy...

That's where I've been for the last couple hours.

I don't know what to say, I'm near speechless. For those who know me that's something they wouldn't believe for a second.

Cheers.
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Old 2nd December 2012, 11:49 PM   #296
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Originally Posted by Cal Weldon View Post
I'm not sure the extra stiffness is necessary when you look at the walls. Except for where the horn exits, is there any difference in SPL on either side of any channel? Why does it need to do any more than it is?

Yeah I see that, at least when the length of adjacent horns are the same. Need to see if that's true for the horn's full length.. Some sticks across the unbraced mouth area would be a good refinement later.

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Originally Posted by xrk971 View Post
I agree that internal walls shall remain foam core as it is stiff enough and may even provide some acoustic damping of higher frequencies, but major selling point is that it makes the build of the curved spirals pretty easy - pretty much the crux of the problem why more folks haven't tried the Cornu spiral before. I was just thinking of the door skins for nice looking facing kind of like veneer to apply to the foam core covers. I am still sticking with foam core for the major structure to the extent possible as I don't have a workshop or power tools other than drill and jigsaw.
The 1/2" foam core, and the door skin suggestions were for the fronts and backs, instead of the 1/4" ply Cal used. They would be lighter, and I was thinking the 1/4" is maybe more than needed. I believe that the door skins are 2 ply 1/8" ply in effect, and as mentioned, appearance was part of it. I've worked with coroplast and it's not stiff at all, I think a lot less stiff than 1/4" foam core, so I wouldn't suggest it for anything!

Um the double thick version with center divider could just have higher, deeper (taller?) walls right, except they would be less stiff, so if we use a stiffer material the center wall might not be necessary, OR if Cal is right and the forces on each side aren't necessary then they don't have to be stiffer..

Last edited by Variac; 2nd December 2012 at 11:56 PM.
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Old 3rd December 2012, 12:02 AM   #297
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crap
i can't seem to find foamcore in my area and after reading that last post i'm not sure i want to start cutting the coroplast i have.
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Old 3rd December 2012, 12:05 AM   #298
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Originally Posted by Variac View Post
Some sticks across the unbraced mouth area would be a good refinement later.
I am considering using a paper and glue laminate to stiffen the outside of the mouth where it runs parallel to the facers. I am wondering if that will dampen the potential resonance better? Could be wrong but...
Quote:
I've worked with coroplast and it's not stiff at all, I think a lot less stiff than 1/4" foam core, so I wouldn't suggest it for anything!
Sorry Mark, I have to disagree. I too, am familiar with the Coroplast and I think once you work with the foam core you will understand. You can't really score and bend it the same way. I thought it was strange when xrk suggested inside scoring but all makes sense when you do some experimenting. Try both and see what you think.
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Old 3rd December 2012, 12:09 AM   #299
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Originally Posted by turk 182 View Post
crap
i can't seem to find foamcore in my area and after reading that last post i'm not sure i want to start cutting the coroplast i have.
Too bad you don't live closer. I seem to have extra.
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Old 3rd December 2012, 01:00 AM   #300
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Originally Posted by turk 182 View Post
crap
i can't seem to find foamcore in my area and after reading that last post i'm not sure i want to start cutting the coroplast i have.
You don't have any dollarama or other dollar stores there? I found "poster" foam board at $1.25 a sheet 20x30 in.
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