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35-100hz ported/hybrid horn

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luthier View Drop Down
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    Posted: 25 March 2020 at 4:55pm
Hey all,

Here's a little idea I've been toying with, I'm trying to make a ported/hybrid horn for use between 35-100hz. I'm open to suggestions any of you may have.

The criteria I've set myself are as follows:
  • Usable range of 35-100hz +/-3db
  • Over 100db sensitivity in 2pi
  • Must fit in a 1280 x 850 x 636 enclosure 
  • Must be able to work with cheaper drivers (i.e not just the B&C 21sw152)
  • Must be a simple construction (no intricate mouth or +45 cuts)
There are reason I want a single cab solution between 35-100hz is because I want to use this cab bellow my 3 way mid top I'm currently working on(link here). The idea is to have a 4 way solution allowing to run one 8 core nl8 cable to each stack. 

As a side note the reason for a simple construction is to allow me to either manufacture multiples of these cabs easily myself or release them as a free plan. 

So far the cab is modelled using an rcf lf18n401 although it also works well with a faital pro 18 1600xl.

2pi


Xmax - Currently quite concerning given that it is 10mm over xmax. Although I do understand this is calculated as a sine wave and not a true representation. I would however like to get thoughts on the cone becoming unloaded. 






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Meat View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Meat Quote  Post ReplyReply Direct Link To This Post Posted: 25 March 2020 at 5:53pm
Did you already see the Startec HR118 ported horn? That uses the same RCF driver that you are considering.

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The RCF looks like a good choice, it's used in several similar designs.

Your mouth seems quite small, you might get more gain by opening it up.

Rear chamber seems pretty massive!


Don't test the champignon sound
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luthier View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote luthier Quote  Post ReplyReply Direct Link To This Post Posted: 25 March 2020 at 6:27pm
Originally posted by Meat Meat wrote:

Did you already see the Startec HR118 ported horn? That uses the same RCF driver that you are considering.

Comments

The RCF looks like a good choice, it's used in several similar designs.

Your mouth seems quite small, you might get more gain by opening it up.

Rear chamber seems pretty massive!



Yep, I have played around with the hr118 a fair bit, but I never quite managed to make it work for the response I wanted out of it. 

I played with opening up the mouth but it seems to create a peak around 60hz and cause the response to drop off sharply above 80hz. Maybe worth playing with again though.

Rear chamber is definitely huge! Which to me seems pretty logical considering the low tuning of 32hz. 

Cheers for the comments, food for thought :) 



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luthier View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote luthier Quote  Post ReplyReply Direct Link To This Post Posted: 25 March 2020 at 6:34pm
I should add, I'm happy for the horn to be less efficient in order to keep the bass extension and overall system balanced. I don't want it to be only good for... psytrance

I think the end aim is for the cab to be a compromise between 6th order bandpass enclosure and a short BPH. 
 


Edited by luthier - 25 March 2020 at 10:23pm
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VECTORDJ View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote VECTORDJ Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 1:09am
A+
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Post Options Post Options   Thanks (0) Thanks(0)   Quote VECTORDJ Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 1:17am
Hi, What is the horn response for 4 units?  8 units????  VECTORDJ
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Post Options Post Options   Thanks (0) Thanks(0)   Quote luthier Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 9:16am
Cheers VECTORDJ, here you go:


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Post Options Post Options   Thanks (0) Thanks(0)   Quote luthier Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 9:30am
With a bit of playing around here's the results with a larger mouth, also I seem to have gotten rid of the dip at 80hz.

What I've noticed with the modifications:
 
  • The horn is now outrunning the ported section in singles but of course that is to be expected
  • The horn in 0.5pi is extending and flat to 50hz   
  • the horn sensitivity drops by -3db at 40hz
  • The port output in .5pi @30hz is 4db lower than the horn at 40hz 
  • Combined in .5pi I seem to have a nice response
My worry with the larger mouth and faster flare rate is that I will loose too much space in the ported chamber and won't be able to get the sensitivity I want at my 32hz tuning. 

Here's .5pi (or 4 cabs)



2pi

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Post Options Post Options   Thanks (1) Thanks(1)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 10:25am
My approach that has worked for me when prototyping is to make a box that is as easy as possible to adjust re tuning, for example, build oversize ported cab, use tubes to tune, easy to cut different lengths etc, bricks to reduce internal volume. Make your different flares so as can be bolted to ported box. Doesn't need to be pretty, 'sticks like shit' type gap filling adhesive is great for speeding things up :)
With regards to tuning the reflex part, look at the frequency response without the horn, if you have a big peak then it will ring like a bell, all to often, ported horns are tuned flat, to do this the reflex part is very peaky. Bottom line is that the bit near cut off is reflex only and sets the min sensitivity. 
By building an adjustable prototype, you will soon get a feel for what works and what doesn't. Corner loading can help with it equating to a larger number of boxes.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote luthier Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 1:35pm
Originally posted by fatfreddiescat fatfreddiescat wrote:

My approach that has worked for me when prototyping is to make a box that is as easy as possible to adjust re tuning, for example, build oversize ported cab, use tubes to tune, easy to cut different lengths etc, bricks to reduce internal volume. Make your different flares so as can be bolted to ported box. Doesn't need to be pretty, 'sticks like shit' type gap filling adhesive is great for speeding things up :)
With regards to tuning the reflex part, look at the frequency response without the horn, if you have a big peak then it will ring like a bell, all to often, ported horns are tuned flat, to do this the reflex part is very peaky. Bottom line is that the bit near cut off is reflex only and sets the min sensitivity. 
By building an adjustable prototype, you will soon get a feel for what works and what doesn't. Corner loading can help with it equating to a larger number of boxes.


Thanks once again @fatfreddiescat, some really useful techniques and insights. 

As for the 'sticks like shit' glue I've got a tonne of EVER BUILD 5 MIN LUMBERJACK WOOD ADHESIVE which does exactly that! 

Reflex part is definitely very peaky, thanks for the warning.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 3:21pm

The loudspeaker is the limitation. It is easily shown in the TS Parameters. Because you are using Horn Response which uses parameters that do not show the weakness of a driver when constructing a reflex box, Horn Response does not tell you why you have such a peaky response. The ideal enclosure size for the driver in question is 7 cubic feet. When you take into consideration other drivers that are smaller in diameter that offers similar TS Parameters as the driver in question, it becomes obvious the driver's diameter is the limiting factor why it cannot take advantage of a large enclosure.    

The driver will offer a good response for horn loading and an adequate response for a reflex box. That is the price you pay when aiming for the best of both worlds using one driver than can execute both tasks.

All in all, the driver is at it's limit (37 Hertz) on how low it can go while maintaining a flat response. Because you are tuning the driver lower than it's limitation, you will attain a sharp peak followed by a sharp decline.

The overall frequency response is pretty much standard of a double-tuned band pass box.

 

Best Regards,

 

 



Edited by Elliot Thompson - 26 March 2020 at 3:29pm
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VECTORDJ View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote VECTORDJ Quote  Post ReplyReply Direct Link To This Post Posted: 26 March 2020 at 4:21pm
Now WE have some Bass!!!!!!
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