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21" Ported Horn design idea - Have I missed something?
21" Ported Horn design idea - Have I missed something?
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Old 27th June 2018, 01:05 PM   #1
kevinmcdonough is offline kevinmcdonough
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Default 21" Ported Horn design idea - Have I missed something?

hey all

I had been vaguely aware of the Othorn, but never really spent too much time looking into it in detail. After reading about it in detail one bored afternoon and learning much more about it, I was rather more impressed! :-) I played about with a few different drivers in the Hornresp sim and fantasised about having a nice big stack of them lol

However as well as tapped horns, I've also always been a fan of ported horns and decided to have a mess about, see what would happen if I took the same drivers and tried them in that design instead, aiming for a box about the same size. I was just curious really to see if it would have any advantages over a tapped design given roughly the same volume of box.

After messing about with the same drivers I had tried in the Othorn (mostly 21sw115 and 21NLW9601 and its carbon cone'd brother) I began to get results that looked pretty usable. Hitting the same low corner at the same SPL, with a bit more sensitivity through the mid range. Thought I was dong pretty well lol......

Then, just for the sake of it, decided to try the 21DS115 in the ported horn box, something I hadn't tried in any other designs.

New design is in black, the HornResp sim of the Othorn in grey....

Click the image to open in full size.
Click the image to open in full size.
Click the image to open in full size.

Definitely caused a little raised eyebrow moment!

Not only does it seem to be more sensitive through the upper bass, it seems to be so right across the board, in some places significantly more so, while still maintaining the same low corner. And this in a box that is about 50 odd litres smaller (the Othorn comes out at about 420 in the sim). There's also a little less strain on the cone, a ratio of 3.7 is still pretty high, but the Othorn was up over 4.

Now I realise the sim of the Othorn was an early one, and it was refined and made more accurate in Akabak after it was built and measured. And I realise these are both 2.83v into a 4 ohm driver so don't represent 1w/1m sensitivities. And I also realise lol that this is just as sim, and it actually has to be folded/made into a real life design that works and then tested. But it seems like a very interesting start at the least.

However, it feels SO interesting that I can't help thinking that it can't be that easy lol, and I must have missed something!

Anyone spot any obvious mistakes or anything in the HR input above?


Last edited by kevinmcdonough; 15th July 2018 at 05:38 PM.
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Old 27th June 2018, 02:56 PM   #2
chris661 is offline chris661  United Kingdom
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My first instinct is you're going to need a bigger port. Ramp up the power and see what the air velocity is - I bet it's well over 30m/s.
For a high-power 21" driver, I'd be looking at 1/3rd Sd minimum for port area.

Have you compared both at Xmax?

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Old 27th June 2018, 08:40 PM   #3
snappyturtle is offline snappyturtle  United States
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Have a look through the SKHorn threads. Essentially what you are creating here.
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Old 27th June 2018, 09:53 PM   #4
Rademakers is offline Rademakers  Netherlands
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Having higher output (near 80 - 100 Hz) as a tapped horn, is typical for a front loaded horn even for relatively small sized ones.

Now for the low end, one design has a port with a relatively very small cross sectional area, whereas the tapped horn average cross sectional area is way bigger. So I would suspect that if you account for the losses at high power, the ported horn doesn't look as good any more, while the tapped horn still does.

Impossibilities we do immediatly, miracles take slightly longer.
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Old 27th June 2018, 09:58 PM   #5
freddi is offline freddi  United States
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21" Ported Horn design idea - Have I missed something?
might the lossy LE option produce the more accurate sim with that driver ? hornresp and a fudge says it would make a pretty good little Karlson box with 216 liters airspace (but would be working much harder at 60Hz so the horn wins)

Click the image to open in full size.

Last edited by freddi; 27th June 2018 at 10:24 PM.
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Old 15th July 2018, 06:23 PM   #6
kevinmcdonough is offline kevinmcdonough
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hey guys,

Sorry was on holiday for a couple of weeks there, thank you for your replies.

And of course you're correct. While I had chosen the port sizes for tuning just to get the response, I hadn't actually considered if it'd work in real life, and as everyone says it's far to small.

Enlarging it to around 600cm2 works much better. It does mean it has to be 85cm long to keep the tuning, so it'll have to have a fold, and the overall box size is then back to being about the same as the Othorn, but keeps the same output plot and the much higher sensitivity.

In the real world this won't give much of a higher SPL, they'll both be limited by the excursion of the driver, but it'll get there with much less amp power, and should have a little more upper bass/kick which might make it a little better for live music.

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