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Old 5th January 2013, 09:35 PM   #121
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New Bass Horns

Some playing with Hornresp and it's System Design and using the current Eminence Kappa 15A's (I really like their sound), and I get

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This is interesting as the freq resp is flatter and has only about 66cm mouth diameter and about 92cm in depth including back chamber.

If it works anything like the current conical horn I have it will be a winner + I can drop the overall height of my rig by around 24cm.

As before, I plan to use these crossing at 100Hz and 330Hz.

I will try and use a large flat bed printer I can borrow some time on at work, on which I will print out the curve I need and use that to make a template to guide the inner curve as I machine it.
The size of the throat means I can easily get my small angle grinder with suitable wood cutting disc in to shape it.

Tomorrow I will start planning / making the horn rotation platform and probably start cutting rings to laminate together
This project will not be a plug I can use to make GRP but around 1" thick birch ply one off horns.

Let the fun begin...
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Old 6th January 2013, 03:50 PM   #122
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I made the horn spinner today.

I knew I had a nice big 360 deg castor base with wheel that had a good quality close tolerance bearing, big plate mounting one side and the large rubber wheel the other. Removed the wheel and a little but of birch ply cutting and drill and I had an adjustable angle spinner that can easily take my weight. I think the castor was spec'd at 150Kg each wheel.

I made up a couple of pulleys on the lathe and a simple belt drive from my hand drill was fine for spinning the wife round on - yes, shes a game lass at times.

Then I though the cheap pillar drill I have would actually make a nice platform and provide some mass.

A few bits more birch ply and its all on a stable base that I can stand on. Perhaps some bags of sand or cement on the edges once I am ready.

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So, envisage a spinning roughed out, birch ply, sandwiched horn spinning at just the right speed and gentle application of the cutting disc on an angle grinder - gonna be a piece of cake Famous last words...

Rings are a nice job for the weekday evening - do a few each evening and see how we get on.
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Old 6th January 2013, 08:16 PM   #123
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I admire your creativity... can't wait to see the finished article.
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Old 6th January 2013, 09:50 PM   #124
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Quote:
Originally Posted by Speedysteve7 View Post
I made the horn spinner today.

So, envisage a spinning roughed out, birch ply, sandwiched horn spinning at just the right speed and gentle application of the cutting disc on an angle grinder - gonna be a piece of cake Famous last words...

Rings are a nice job for the weekday evening - do a few each evening and see how we get on.
Steve,

Reminds me of a Leslie I made several years ago.
I don't have a lathe, used a cove bit on a router and spun the rings on a drill press.
It originally used a very long horn, replaced that with 4 x5".

It really spins fast in high gear and high motor speed !

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Old 9th January 2013, 07:30 PM   #125
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That looks interesting. Love the sound.

How fast do you rotate? The web says anything from 40 to 400rpm. The gearing on yours looks pretty high?

I've not had much time for the project in the workshop the last couple of days, but I am measuring up / calculating the number of rings I will need etc.
Then I can start cutting out ring upon ring upon ring...


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Originally Posted by weltersys View Post
Steve,

Reminds me of a Leslie I made several years ago.
I don't have a lathe, used a cove bit on a router and spun the rings on a drill press.
It originally used a very long horn, replaced that with 4 x5".

It really spins fast in high gear and high motor speed !

Art
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Old 9th January 2013, 10:52 PM   #126
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Originally Posted by Speedysteve7 View Post
That looks interesting. Love the sound.

How fast do you rotate? The web says anything from 40 to 400rpm. The gearing on yours looks pretty high?

I've not had much time for the project in the workshop the last couple of days, but I am measuring up / calculating the number of rings I will need etc.
Then I can start cutting out ring upon ring upon ring...
Mine is built for speed. Normal middle pulley Leslie High rotor low speed is 40 RPM, high speed is 400 RPM, I'd guess mine goes from about 200 to 600 rpm.

At the highest speed, the motor (from a 14" fan) is overworked and gets hot pretty fast...
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Old 13th January 2013, 04:50 PM   #127
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Bass horns on the go

After some plotting and working out, I needed 32 rings of 24mm birch ply. This gave 76.8cm - near enough to the 75 horn resp is telling me.

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Jig sawing them out uses much less wood and less mess than a router. The mess comes later
With 3 pieces of ply I could cut all the rings I needed, ever reducing following the Hyperbolic curve.

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I revolved the piece letting the jig saw follow the plot line.

A few rings done

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All rings cut and peering into the ring mass while gluing. Some clamps and weights and plenty of PVA squeezed out.

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The horn lathe was a bit of a disaster. Not really stable enough and hard to get at the right speed.
It would have been fine if I was doing a plug (cutting the outer surface for GRF and had another bearing at the front. Needing to get inside preludes that.
So a really coarse grit on the a big drum sander and lots of power sanding.
So far I've done about half way down the horn on a first pass. Easy enough to get accurate even in coarse mode. I have the throat area to do. Further in but less area to cover. It's best done with the horn standing up. Perhaps another evenings work.
I might use the horn lathe again for light final skim and probably have human helper powering it

Click the image to open in full size.

Brought it in to see how it looks - Tiny at 72cm diameter against the Conical 90cm.
Smaller throat / hyperbol flare, more compression, they model quite a bit better than the conical at any rate.

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Looks fine and true even as rough work from the listening chair.
I'm am going to spray paint them the same as the other pairs for a matched look.
I will be able to lower the rig a fair bit and have them further away from the rear wall if I want to.

Knackered now but proved to myself I can DIY it. Time for a pint.
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Old 13th January 2013, 04:57 PM   #128
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Great work as always Speed. I saw on a TV show about woodworking the guy did the same as you with cutting rings with a jig saw, but he cut on a 45 degree angle as was able to use one sheet of plywood for the blank. The 45 allowed him to stack one cut right onto the next.

P.S., he was making bowls but it was the same principle.
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Old 13th January 2013, 06:00 PM   #129
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Yep good point. I thought about it but my recirculating jig will only do vertical or 45 degrees. Pretty useless really. Should get a new one...
45 would give me very steep cone - still lots of material to remove and more hassle for the saw too.
At it nears the throat the angle reduces quite a bit.
Getting the angles right'ish would save a lot of sanding work and use even less ply I guess.

The smaller diameter curve and no flat surfaces means even less resonance (more dead when you knock on it), than the 12 sided conical. Got to be a good thing. However, I've ever heard the concial solution suffering from resonance when playing though.
A fellow DIY'er did square exponential (I think it was) and ended up with several braces inside. That was on a 12" driver which meant they had to be much longer too.


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Originally Posted by djn View Post
Great work as always Speed. I saw on a TV show about woodworking the guy did the same as you with cutting rings with a jig saw, but he cut on a 45 degree angle as was able to use one sheet of plywood for the blank. The 45 allowed him to stack one cut right onto the next.

P.S., he was making bowls but it was the same principle.
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Old 23rd January 2013, 09:33 PM   #130
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Well, Interesting this large horn building lark.
Many have have said that you can calc and calc but you only really know what you have got until you build and listen.

That is exactly what I have found with this part of the project. Sims and calcs are one thing, nice flat freqs one thing, how they will sound is another altogether.
I build the back box on Saturday and brought the horn in for a listen. I'd started out with a lowish area mouth. 15cm diameter = ~177cmsq. I'd put in a few extra discs of 24mm birch ply to accomplish this so the horn length was greater.

Hmm, dire was the first word that came to mind for the sound. Listening to just the bass horns for prolonged periods is always a challenge but in comparisons with the larger conical, things did not sound good.
The rather lovely rich bass was not there, the top end seemed to sound strained and tinny.
Measuring showed none of the tinniness traits - looked fine in fact, more extended top end if anything but not much really. Lower end was interesting - dip in the slope / a step much earlier than Hornresp predicted it seems.

After a rest I then enlarged the throat to 17cm diameter 227cmsq. This gave a some improvement. Still rather strangled upper freqs compared to the conical with a 20cm / 314cmsq throat, but definitively an improvement. The larger throat gave less of the step in lower bass when measured.

As a last ditch attempt to make something of this horn (other than firewood or a wigwam cat house, with suitable door cut in the side), I then enlarged the throat to the same as the conicals. This shortened the horn length to a little over the original design.

Listening extensively this evening to just the bass and then LH / RH side comparisons things are now pretty good. The bass coming from this horn has regained its pleasant upper freq character and tone - gone are the strangled sounds and it competes on a level field with the conical now in this.
On the sound overall I hear less colouration on the more rigid circular construction smaller horn now than the conical. It's a bit tighter (general over used adjective when considering the sort of boom boxes it is usually associated with in describing), a little punchier and faster than the conical too.
The upper registers seem to integrate better with the tractrix mid horn.

I can't explain why the larger throat works better - driver / horn properties that sims can't figure out?

I have ended up listening to the system with one conical and one Exponential horn for the evening. Quite a pleasing sound overall.

So definitely worth the effort to build a 2nd prototype for a proper listen.

Here's how she looks in situ - just plonked down

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This was a pic with the smallest throat size... As you can see plenty of potential for lowering the other drivers and making the sound more compact - That will have to wait until the 2nd horn is build and the sound liked.

A comparison

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I'll be cutting more rings soon - this time with more suitable angled edges if I can and to the same dims as the first one

Last edited by Speedysteve7; 23rd January 2013 at 09:45 PM.
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