SpiralHorn damping.

[FranciscoPerez]

Hi!!

I'm building a pair of wall mounted spiral-horns. They are quite similar as to the "Kompaktes spiralhorns" found at cornu.de

I'm about to glue the front and back baffles but before closing the cabinet I would like to make sure everything's right, as it would be impossible to reopen the cabinet afterwards.

After reading about these enclosures and watching internal images of some of them,I assume that no internal damping materials are needed with this speaker design, but I'm still concerned.

I searched the forum, but did not find any info regarding this.
Does someone know if damping materials are used in this kind of spiral-horns?

You can see some images of my speakers under construction at my blog 22 nanofarads | Audio & Electronics Blog
I'll be posting some updates soon, in case someone is interested!
Do not hesitate to drop a line, I will welcome any feedback!!

Thank you very much!!
Regards,

Fran

 

[gafhenderson]

I was under the impression all 'horns' needed damping to reduce pipe harmonics and it also goes a long way to reducing the high frequencies the horn emits?

 

[FranciscoPerez]

Thanks for the reply!

I thought that the squared form of the spirals towards the centre helped filtering the high frequencies going out of the horns.

I mean, this:
http://fperezroig.files.wordpress.com/2013/03/dsc05435.jpg

However, I'm not sure if that's enough, or maybe there is some other reason why damping materials would be worth here.

 

[Cal Weldon]

It's hit and miss. The spiral horn is used for many different drivers and each requires a unique approach. We have been doing a lot of research into this recently. There is lots of trials with both throat and mouth damping. It' comes down to preference when you get right to it. Damping is hugely critical in the spiral. Try here:

http://www.diyaudio.com/forums/full...k-building-cornu-spiral-horn-now-you-can.html

 

[Cal Weldon]

You will find that if you use a hook tool you can adjust the damping in the throat by removing the driver and it's easy to do at the mouth by hand.

 

[xrk971]

Definitely put some stuffing in the driver chamber to help reduce back reflections and smooth out the response. You can try both ways but we have always seen that it is better with stuffing.

 

[FranciscoPerez]

Thank you!!
That's a big thread, I'm starting to read it right now!
I will be probably using a pair of fostex fe108ez, do you think it's a good match?

Thank you all for your advice, I'm gluing all cabinet and will try different amount of damping afterwards. Any specific damping material that would suit better?

Kind regards,
Fran

 

[Cal Weldon]

I have found that rockwool tends to give you the best bang for the buck. That also means you have to be careful how much you use. It makes a huge difference. Too little and it's terribly boomy. Too much and you suck the life right out of them so be patient and do your testing over many days to make sure you have it right before tightening the screws for the final time.

 

[xrk971]

Thank you!!
That's a big thread, I'm starting to read it right now!
I will be probably using a pair of fostex fe108ez, do you think it's a good match?

Thank you all for your advice, I'm gluing all cabinet and will try different amount of damping afterwards. Any specific damping material that would suit better?

Kind regards,
Fran

Fran,
Glad to see you are doing this. If you wouldn't mind following up with posts of pictures to the cornu thread. The Fe108ez was the original driver specified for this design by Cornu speakers. Jim Shearer has tested this with this driver and results posted in Cornu thread. From what I recall, it works very well. What is your construction technique? I assume you are not using foam core because you did not know about the cornu thread? There is also the foam core thread where a lot of good info can be found. Although that thread is huge and will take a long time to go through. A lot of people use cheap polyfill stuffing you can find inside your pillow. Natural wool fiber works too.
X

 

[FranciscoPerez]

Thanks Cal and xrk971!

There's a post in my blog 22 nanofarads | Audio & Electronics Blog with pictures and a general description of the build.
The front, back and middle plates are 11mm baltic birch plywood, and the material used for the spirals is 4mm okume plywood, 150 mm strips.
I CNC'd the middle plate with an 8mm drill and started inserting the okume strips. It bent quite good, but not good enough to finish each spiral, so had to cut several small pieces of okume to finish the spirals towards the centre.

For gluing, I'm using something called Pattex "no more nails".
To CNC the middle plate I built an Autocad file from a JPG I found somewhere containing the spiral layout. I could share the file if someone is interested!!

I'm posting some pictures in the cornu thread, thanks for the tip xrk971!!