115Hz Tractrix turned plywood bass horn

[Studio Au]

I'll let the pictures do the talking.

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[Old'n'Cranky]

2.7 meters high.
I want to see a picture of the room their going in.

 

[Inductor]

Nice.

"61, 62... TODAY I'm GOING HOME!"

 

[dukanvadet]

Wich driver will you use?

 

[AndrewT]

What size of lathe can turn that?

How do you support it to turn the inside profile?
How do you support the tool to get into a 1m deep hole?

 

[Studio Au]

The overall height has been reduced to a mere 2.4m.

They are for a client, who I'm sure will chime in.

These are for a Fane 8M, with the midrange being handled by Vitavox S2.

 

[rakeshpoorun]

The overall height has been reduced to a mere 2.4m.

They are for a client, who I'm sure will chime in.

These are for a Fane 8M, with the midrange being handled by Vitavox S2.

Hi Louis,

The way you are building the frames and horns, the height of the entire acoustic system is really a function of the room and the solutions chosen for a given frequency range.

Just as an extreme example, using the (off the top of my head) 168Hz tractrix with the 115hz Upperbass and the Fostex T500 AM Mkii would lead to an overall system height of 180cm.

In my case, in my current room, the maximum height is 2.35cm, the operative word being "maximum." I imagine that given the listening distance of 2.8-3.5m, I might well opt for a system configuration that will cause the overall height not to exceed 1.9m.

Once the Tractrix 115hz and frames are delivered within the next two weeks, I will have a better understanding of what's more likely to work in this room. I guess my initial order is pretty much reflective of what the final system configuration will be in this current room.

In a larger room, with a listening distance of 3.5-4.2m, I imagine that the 167Hz/400Hz Tractrix will be a better combination.

Obviously all the above makes sense only in the context of the compression drivers being used. Now even with the Vitavox S2 and S3 drivers which I will be using initially, chances are that the ideal horns for this system will depend on the diaphragms used as well as the crossover frequencies.

One question that I never mentioned is that there is a school of thought that softer materials (like MDF or pine wood) are better than birch ply for the 400Hz horns. Down the line, I may investigate. For the time being, I am hoping that esthetic considerations and the desire to avoid the use of MDF as working material in a non-industrial setting will not lead to any obvious perceptible sonic artifacts.

Anyway, Louis, I hope that the end of the heat wave we experienced last week will mean I will have the horns in situ fairly soon.

Cheers
Rakesh

 

[atilsley]

Wow, from one builder to another, well done. I love the concept of CNCing. I built a Trio/Cessaro style 4 way using CNC'd stands...but would love to use the ply rings to build the horns. The closest I came was a small tweeter, using CNC'd rings, then turned on a lathe. Andrew

 

[Kay]

One question that I never mentioned is that there is a school of thought that softer materials (like MDF or pine wood) are better than birch ply for the 400Hz horns.

many years ago I do it with paperboard, 2mm thick.
It's possible to cut the rings with a knife
and than clueed together.
The steps of 2mm must be not removed because of wavelength.
Unfortunately I don't have pictures

 

[atilsley]

Reminds me of Romy's mid bass.

GoodSoundClub - Romy the Cat's Audio Site - 10-feeter horn

Another here -

A new midbass horn | Audio Forums

 

[CLS]

The throat looks small for an 8" cone driver.

Will there be any 'phase plug' or the likes?

 

[rakeshpoorun]

I have been meaning to update this thread a couple of months ago when I was supposed to take delivery of the horns.

Well, Louis has explained that the lathe that he recently ordered has a little issue and it will take a while longer to fix the lathe and turn the large horns.

He has suggested that he might be able to build the smaller diameter 160Hz tractrix horns first so at least I do not have to wait another few months before I have something to play with. Having said that, the aluminium profiles for the frames are in the process of being ordered so these should be ready quite soon.

As for the next step, I was thinking of either using some Scanspeak drivers or maybe a pair of tapped horns but really the tractrix horns must be completed first.

But Louis is working on it and I have no doubt I will have something very concrete to post and very soon...

 

[rakeshpoorun]

A pair of 140Hz Tractrix horns sold on ebay and I must say I was sorely tempted to buy them myself.

Stereo-Lab SL140Hz Horn Mit 6" Hals Mitteltonhorn Tractrix Kugelwellenhorn | eBay

In the end, I thought that having waited well over 6 months now, and given that Louis is clearly doing his best to overcome the technical hurdles that have beset him that I should resist temptation. Still, these horns would have been a nice interim solution...

As I said before, Louis has suggested that I give him more time, and also the go-ahead for the smaller 180Hz horns that he wants and promises to build before the 110Hz horns.

So all I need to do is be patient a little while longer. Once Louis supplies me with the 110Hz and 180Hz horns and frames, I will hopefully be able to get something up and running. Maybe before end of October.

Come on Louis...surprise me.

Rgds
Rakesh

 

[rakeshpoorun]

Hi Louis,

Long time, no news.

It would great and very kind of you if you could update this thread with a progress report. I placed this order many months ago and am hoping the first stage will be completed quite soon in spite of the difficulties with the lathe.

Some pictures of the work done thus far would be the icing on the cake!

Keep up the good work.

Thanks

All the best
Rakesh

 

[wesayso]

Maybe a word of warning/caution, I've worked with large stacks of birch ply and eventually suffered from cracks developing. Not on my glue seem but in between the ply laminate itself.
I have since covered my stack with glass fibre reinforced epoxy (and some other tricks) and haven't had any other problems. But it may be wise to be ready to cover them with something as the wood will continue to expand/contract, and with these sizes that can become a problem.
I've seen other examples of stacked enclosures with similar problems (cracks developing) on this site.
The condensed story in pictures:

Stacked birch ply, internal 4x 8mm threaded rods

Painted inside and out with a polyurethane

Crack developed after a sudden weather swing in humidity

covered with matt and epoxy, after first dividing the enclosure into 25 separate parts with foam in between

Finished result in room

Just a heads up...

More info here: http://www.diyaudio.com/forums/full-range/242171-making-two-towers-25-driver-full-range-line-array.html

 

[JLH]

I have plywood and also MDF horns out there that are over 15 years old. None of them have cracked. You have to glue and screw every layer together. I use 12 screws per layer and rotate the next layer 15 degrees so I don't hit the head of the screw in the layer below it. The screws act as the clamp so you can build up the horn in a single setting. There was no need to use hand clamps and wait for each layer to dry. Each horn ended up with a 5 pound box of screws in it.

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[wesayso]

Thanks for adding that JLH, good to know a tested recipe exist. My stack was a bit bigger I guess at 2.25 meter. I had seen a B&W inspired mid enclosure build developing similar cracks, hence the warning.
http://www.diyaudio.com/forums/full-range/167744-fe168e-sigma-teardrop-enclosure-20.html
This size is much closer to a horn build.

So it does make sense to copy a working recipe to build a stable non cracking horn.
It's better to get the advise now than after the horn is finished in a way that might not work in the end. Especially if you're building it for someone else.

 

[rakeshpoorun]

Maybe a word of warning/caution, I've worked with large stacks of birch ply and eventually suffered from cracks developing. Not on my glue seem but in between the ply laminate itself.
I have since covered my stack with glass fibre reinforced epoxy (and some other tricks) and haven't had any other problems. But it may be wise to be ready to cover them with something as the wood will continue to expand/contract, and with these sizes that can become a problem.
I've seen other examples of stacked enclosures with similar problems (cracks developing) on this site.
The condensed story in pictures:

Stacked birch ply, internal 4x 8mm threaded rods

Painted inside and out with a polyurethane

Crack developed after a sudden weather swing in humidity

covered with matt and epoxy, after first dividing the enclosure into 25 separate parts with foam in between

Finished result in room

Just a heads up...

More info here: http://www.diyaudio.com/forums/full-range/242171-making-two-towers-25-driver-full-range-line-array.html

Thanks for the heads up. I think that following John Hasquin's suggested advice will address the issue and I am sure Louis will not mind the advice as this is the first horns of this size that he will have built.

Your project was also very relevant to mine for a couple of other reasons. Firstly, The first finish that you obtained, with a dark stain, is very close to the finish I and Louis are looking for. Louis said he has tried a couple of stains with which he was not happy but would be trying some Liberon sourced stains. May I ask which one you used just out of curiosity?

The second reason I found your project so astonishing is that this is exactly the construction design I had suggested to Louis regarding the bass array with Scanspeak drivers I am planning to have built eventually. I like the fairly random internal structure and varying wall thickness which is achieved (as well as the looks).

Congratulations on your speaker project. It was enlightening (and encouraging to see what can be done).

rgds
Rakesh

 

[rakeshpoorun]

I have plywood and also MDF horns out there that are over 15 years old. None of them have cracked. You have to glue and screw every layer together. I use 12 screws per layer and rotate the next layer 15 degrees so I don't hit the head of the screw in the layer below it. The screws act as the clamp so you can build up the horn in a single setting. There was no need to use hand clamps and wait for each layer to dry. Each horn ended up with a 5 pound box of screws in it.

[IMGDEAD]https://scontent-ord1-1.xx.fbcdn.net/hphotos-frc3/v/t1.0-9/536628_272237769579021_258534377_n.jpg?oh=76b0485820636775ee53946893cb8e7d&oe=56992678[/IMGDEAD]

Hi John,

Thanks for chipping in. With your experience building horns, this sounds like excellent and most sensible advice. I am sure Louis will not mind following it. I certainly would hate for cracks to develop over time.

With regard to finishing the plywood, we are hoping to achieve a dark stain to match the look of american walnut. Any idea with regard to what stain might suit?

rgds
Rakesh

 

[rakeshpoorun]

Hi Louis,

Long time, no news.

It would great and very kind of you if you could update this thread with a progress report. I placed this order many months ago and am hoping the first stage will be completed quite soon in spite of the difficulties with the lathe.

Some pictures of the work done thus far would be the icing on the cake!

Keep up the good work.

Thanks

All the best
Rakesh

Hi Louis,

I am sure things must be very hectic or you have other concerns which pre-empt updating this thread or sending me an e-mail. I have seen you have been online here in the past few days but have not heard from you.

But please be kind enough to send me an update even if there are some issues. I am sure I understand the challenges that you face but would like to know what's happening.

Hope all is well,

regards
Rakesh