Ever think of building a Cornu Spiral horn? Now you can!

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#764
xrk971 said:
Throat area is gap perpendicular to channel flow direction at entrance to channel from driver chamber. For the 20 in scaled plan the gap width is about 0.85 inches multiply by 2 for 2 channels and by depth for total throat area.
Click to expand...


So:

Area Throat = 2(Width Gap x Depth Channel)
Area Throat = Area Driver surface
Area Driver surface = 2(Width Gap x Depth Channel)
Depth Channel = Area Driver surface/2(Width Gap)

Yes?
 
#765
Yes - to first order. Although it is entirely possible to have throat area less than Sd. As small as 50% even (in cases where driver has low Qts (<0.35) with powerful high Bl motor typically used for back loaded horns), and a typical 75% of Sd is no problem for standard drivers. Certainly a little bigger than Sd, say 125% is OK too - quire forgiving. The scaling with Sd is only a rough rule of thumb. To set the throat with precision though, you should model the chamber/driver/throat and typical horn length in HornResp or similar program. The throat affects the high frequency cutoff.
 
#766
My son and I are beginning to build a pair of 24" cornu horns using TANG BAND W3-881SJF 3" drivers. I have read several differing opinions on the use of acoustical stuffing. My questions are:

1. Should stuffing be used at all?
2. If yes, which is best? Fiberglass, fiberfill (polyester), other?
3. If yes, how much and how tightly packed?

Thanks.
 
#767
2bz,
Yes stuffing is needed in the Cornu. You will have to experiment a bit but typically, a moderately packed amount in the driver chamber is necessary. If too much bass, add a small amount loosely packed into the first couple of inches of the entrance of the channels. This can be done with a bent piece of wire from a coat hanger to put it in place. Alternatively, you can add a 4 to 6 in long bundle of stuffing that is glued to a piece of string and pull on the string to adjust position of stuffing to best suit your tastes in real time as speaker is playing music. I have also heard some people putting stuffing in from the mouths of the horns.

I think a 24 in size Cornu may be a bit too big for a 3 in driver like the W3-881. 20 in is more suited for that size driver. I would go with any TB W4-class driver for a 24 in to 27 in Cornu and it will work. Scale the depth of the channel accordingly. I use simple regular stuffing from an old pillow (polyester fiber fill). I have heard rock wool works too. Certainly fiberglass will work but is itchy. One of the best may actually be natural wool fiber if you have access to that or an old sweater that you are going to throw away.

Good luck and keep us posted with pics of course.
 
#768
Hi Guys
While I am plodding away on a new pair of 16" spirals a friend has asked me to make a pair for use with his old Marantz 2240B receiver. It's rated at 40 watts @ 8ohms.
He would like something in the 20-24" size.
Any recommendations would be greatly appreciated 😀
It's great to see how this discussion has progressed and all the great speakers being being made 😎
 
#769
xrk971 said:
2bz,
Yes stuffing is needed in the Cornu. You will have to experiment a bit but typically, a moderately packed amount in the driver chamber is necessary. If too much bass, add a small amount loosely packed into the first couple of inches of the entrance of the channels. This can be done with a bent piece of wire from a coat hanger to put it in place. Alternatively, you can add a 4 to 6 in long bundle of stuffing that is glued to a piece of string and pull on the string to adjust position of stuffing to best suit your tastes in real time as speaker is playing music. I have also heard some people putting stuffing in from the mouths of the horns.

I think a 24 in size Cornu may be a bit too big for a 3 in driver like the W3-881. 20 in is more suited for that size driver. I would go with any TB W4-class driver for a 24 in to 27 in Cornu and it will work. Scale the depth of the channel accordingly. I use simple regular stuffing from an old pillow (polyester fiber fill). I have heard rock wool works too. Certainly fiberglass will work but is itchy. One of the best may actually be natural wool fiber if you have access to that or an old sweater that you are going to throw away.

Good luck and keep us posted with pics of course.
Click to expand...

Thanks for the advise.
 
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