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Learning horn resp, need some advice.

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Topic: Learning horn resp, need some advice.
Posted By: SouthwestCNC
Subject: Learning horn resp, need some advice.
Date Posted: 14 January 2017 at 1:06pm
Hi there, I thought it's about time I start learning how to simulate horn response. Getting on quite well with it and now like to understand how using the ported throats works geometry wise. If the port vents into a horn throat does the length of the port include the remaining length to front of the horn its vented into or not. Or in that scenario does the port then become a tapered port?

TIA



Replies:
Posted By: odc04r
Date Posted: 14 January 2017 at 1:18pm
Good plan, always fun to learn something new.

Sound like a slightly odd design though, ports usually tend to end in a chamber as they combine with its volume to make a resonance. You'll have to be careful to avoid taking up throat area if you terminate them there else which is quite a critical design parameter for a horn. Are you trying to make a tapped horn of some decription?

But generally no, you would not include the rest of a horns length in a port wherever it terminated. The port resonance is defined by the mass of air in it, its compliance, and the same for the chamber it is in. If you terminate a port in odd ways and odd places, then you need to consider end correction for it to get accurate results too.

Maybe post up a diagram for some comment.


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 1:24pm
That's great advice thanks. There's no plan I just saw the function available in horn resp and was wondering how that worked. I'll try drawing something up as to what I'd imagine that function is used for, might even be missunderstanding it. Thanks.


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 1:37pm


Posted By: bitSmasher
Date Posted: 14 January 2017 at 2:14pm
Can't advise directly, but there's a huge amount of info on DIYAudio subwoofer forum - Mr McBean posts on there

-------------
https://www.instagram.com/batteryacidsoundsystem/


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 2:16pm
Didn't know that. Thank you!


Posted By: odc04r
Date Posted: 14 January 2017 at 5:11pm
Looks like you're trying to port the rear chamber of a front loaded horn into the horn path at some point. Not a common design! Trying to recombine the rearward wave of the driver with the horn loaded forward will be tricky. I am not sure if horn response will necessarily let you do that either. It has the capability for tapped horns but I am not sure if you can port a rear chamber to a horn node.

Akabak will very much let you do this and simulate it, but need windows xp or earlier and requires scripting to get a sim running.


Posted By: corell
Date Posted: 14 January 2017 at 5:11pm


Posted By: gen0me
Date Posted: 14 January 2017 at 5:55pm
Originally posted by corell corell wrote:

????? Not in hornresp.
https://postimg.org/image/6mhi98j43/" rel="nofollow">


Is that what you mean in 1st post: Ap or Ap1.
https://postimg.org/image/8vjzrz84j/" rel="nofollow">


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 6:40pm
Thanks odc04r I'm learning, really I'm just trying to understand the function of selecting throat ported under the option rear vented. But sounds like it means something other than what I'd imagined.



Posted By: fatfreddiescat
Date Posted: 14 January 2017 at 6:41pm
Newer version of horn response has the option to port into the throat of the horn, not had much luck with it so far, tried modeling my boxes but not had any result from hornresponse that comes close to my measured results. I will give it another go when I get time.


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 6:44pm
Useful info Corell. Thank you.


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 6:46pm
Ahh ok maybe this is the confusion as it's new version I have. So then my understanding of that function may be correct.

In which case how does hornresp know what segment of the horn the port terminates, surely it's going to have an effect.


Posted By: gen0me
Date Posted: 14 January 2017 at 6:55pm
Ap1 into segment S2 for offset driver OD  https://s29.postimg.org/z3v4hcs87/1st_post.png" rel="nofollow - https://s29.postimg.org/z3v4hcs87/1st_post.png
For Nd into S1.
Rear Ap where is S5. Later in SPL (acoustical power) you can specify distance(tools>>combined response) between S5 and end of a port. It may changed in new version though


Posted By: SouthwestCNC
Date Posted: 14 January 2017 at 7:49pm
Oh ok. So with that you are able to simulate a port from driver to s1/s2 but at the same time loose the option to sim a vent in the rear chamber. That doesn't make a lot of sense to me. I'd have thought that kind of port into the throat could be simmed using vtc/atc to the same effect.


Posted By: odc04r
Date Posted: 15 January 2017 at 9:47am
Must confess I am not very good at keeping up with the newest version and features of HR. Didn't know this option was in it now. Impressive updating.


Posted By: fatfreddiescat
Date Posted: 15 January 2017 at 10:57am

' |Horn-Loaded Vented-Box Enclosure With Port Exit Located Inside Horn Mouth
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Select the tapped horn option and set Vrc, Lrc, Ap and Lpt > 0.
 
 Set L12 = 0.01 cm if the driver is not offset.'

Here I have adjusted one of my attempts to hopefully make it clearer, I'm not getting accurate simmed results compared to measured results but I think this is the way that David intended it to be done.

I first used the wizard in the drop down 'help' menu and chose tapped horn with rear chamber and 3 segments.



Posted By: SouthwestCNC
Date Posted: 15 January 2017 at 12:59pm
Originally posted by fatfreddiescat fatfreddiescat wrote:


' |Horn-Loaded Vented-Box Enclosure With Port Exit Located Inside Horn Mouth
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 Select the tapped horn option and set Vrc, Lrc, Ap and Lpt > 0.
 
 Set L12 = 0.01 cm if the driver is not offset.'

Here I have adjusted one of my attempts to hopefully make it clearer, I'm not getting accurate simmed results compared to measured results but I think this is the way that David intended it to be done.

I first used the wizard in the drop down 'help' menu and chose tapped horn with rear chamber and 3 segments.




Great info. Thanks. Be interesting to hear if anyone gets any results with it.


Posted By: gen0me
Date Posted: 15 January 2017 at 2:11pm
Thats newEmbarrassed Remember the old one argueing in that setup that its wrong data Tongue

https://postimg.org/image/o146hcl83/" rel="nofollow">


Posted By: fatfreddiescat
Date Posted: 15 January 2017 at 2:58pm
Could you post a link?


Posted By: gen0me
Date Posted: 15 January 2017 at 3:04pm
https://s29.postimg.org/82vgr7r07/temp.jpg


Posted By: fatfreddiescat
Date Posted: 15 January 2017 at 3:18pm
Not sure what you mean about the wrong data, is that a pic from another thread?


Posted By: fatfreddiescat
Date Posted: 15 January 2017 at 3:24pm
Originally posted by SouthwestCNC SouthwestCNC wrote:

Hi there, I thought it's about time I start learning how to simulate horn response. Getting on quite well with it and now like to understand how using the ported throats works geometry wise. If the port vents into a horn throat does the length of the port include the remaining length to front of the horn its vented into or not. Or in that scenario does the port then become a tapered port?

TIA

My cabs are ported at the throat, sims suggest the port length and area would be at 65Hz if it was a traditional reflex cab, but with having the full length of the horn attached, the tuning drops to 32Hz.
On my cabs the port area is smaller than the throat area and is a hole cut in 18mm plywood.
The problem with the hornresponse sims is that if I model the cab, it still gives a tuning as though the horn is not acting as a duct.



Posted By: gen0me
Date Posted: 15 January 2017 at 3:31pm
Originally posted by fatfreddiescat fatfreddiescat wrote:

Not sure what you mean about the wrong data, is that a pic from another thread?

Wrong data was on old versions of hornresp when Vrc was >0

The pic shows how to make ports at front and rear chamber in tapped horn.



Posted By: fatfreddiescat
Date Posted: 15 January 2017 at 3:51pm
Ah ok thanks.


Posted By: SouthwestCNC
Date Posted: 16 January 2017 at 10:20am
Originally posted by fatfreddiescat fatfreddiescat wrote:

Originally posted by SouthwestCNC SouthwestCNC wrote:

Hi there, I thought it's about time I start learning how to simulate horn response. Getting on quite well with it and now like to understand how using the ported throats works geometry wise. If the port vents into a horn throat does the length of the port include the remaining length to front of the horn its vented into or not. Or in that scenario does the port then become a tapered port?

TIA


My cabs are ported at the throat, sims suggest the port length and area would be at 65Hz if it was a traditional reflex cab, but with having the full length of the horn attached, the tuning drops to 32Hz.
On my cabs the port area is smaller than the throat area and is a hole cut in 18mm plywood.
The problem with the hornresponse sims is that if I model the cab, it still gives a tuning as though the horn is not acting as a duct.






And this goes for the new version of hornresp? How did you manage to identify the port tuning required was that of a 65hz wavelength to achieve an overall tuning of 35hz taking into account the horn is acting as a duct? Trial and error?


Posted By: fatfreddiescat
Date Posted: 16 January 2017 at 12:57pm
Very much trial and error, I built various test boxes that I could change panels to convert between 4th/6th order bandpass and reflex, using bricks and waste pipe to adjust tuning, followed the same method for the horn with blanking plates to change from internal / external vents and sealed rear chamber. First box was built approx 18 years ago.


Posted By: odc04r
Date Posted: 16 January 2017 at 1:22pm
It's an odd one, I could easily see how in this case simulation would struggle to match reality. If the port doesn't terminate one end in essentially infinite space and the other in a chamber far enough from any walls, you need to start making end corrections. But worse than just end corrections is when they terminate into a region of the horn where acoustic velocity and pressure is far from normal. I guess the electronic analog would be boot strapping.


Posted By: SouthwestCNC
Date Posted: 16 January 2017 at 2:30pm
Might be a ridiculous idea but Could the port not be simmed as two seperate horns, as if the rear chamber became the front chamber with a throat port only applying a rear chamber that simulates the remaining volume in the horn. Then sim the correct chamber orientation of driver and combine the results?

 Quite tempted to build one with a port tuning of 65hz to begin with and do the same. If only these could be 3d printed in miniature and tested. 


Posted By: fatfreddiescat
Date Posted: 16 January 2017 at 10:32pm
There are various ways to try and fudge aspects of it HR although probably just as quick to just build a test setup- straight horn with one expanding surface and a reflex box with adjustable port that can be clamped to the horn profile. Model as for a standard ported horn for a starting point.
I also tried modeling it with Akabak but didn't get anything useful although that could have been my understanding of the software.
I will try and get some test results to upload but may be a few weeks before I get to do that, can't find any at the mo so will have to re test , all the old ones were not in ideal test conditions.


Posted By: SouthwestCNC
Date Posted: 23 January 2017 at 11:04pm
Id be interested to see. Ive been going exactly as I mentioned and fudging it in horn resp by simulating the port as s1/s2 then leading to the horn and it seems to narrow the possible frequency tuning range of the port and the horn takes over, Could need three tunings ie two different length ports to compensate. All rather complicated.


Posted By: fatfreddiescat
Date Posted: 24 January 2017 at 8:00am
Using multiple ports is one way to change the tuning, another would be to tune the rear chamber om the high side and then blank off part of the port to lower it.

As and when I get around to working on another version I will make a straight horn expanding from zero in one plane and adjust the position of the rear chamber / driver along the axis of the horn.
I would also aim to have the port tuning half an octave or more below the horn cutoff frequency.


Posted By: jaya000
Date Posted: 29 June 2017 at 12:55pm
Originally posted by corell corell wrote:



How to get high resolution image of yoiur post?


Posted By: DMorison
Date Posted: 29 June 2017 at 2:24pm
Originally posted by jaya000 jaya000 wrote:


How to get high resolution image of yoiur post?

Right click & save the images, or pop them open in new tabs - they're not much bigger that way, but it is enough difference that you can read them.


Posted By: SouthwestCNC
Date Posted: 01 November 2017 at 12:17pm
Originally posted by fatfreddiescat fatfreddiescat wrote:

There are various ways to try and fudge aspects of it HR although probably just as quick to just build a test setup- straight horn with one expanding surface and a reflex box with adjustable port that can be clamped to the horn profile. Model as for a standard ported horn for a starting point.
I also tried modeling it with Akabak but didn't get anything useful although that could have been my understanding of the software.
I will try and get some test results to upload but may be a few weeks before I get to do that, can't find any at the mo so will have to re test , all the old ones were not in ideal test conditions.

Any revelations FreddiesCat? With 0 volume on the rear chamber 0 atc vtc  and no port you are effectively simulating a tapped horn with horn flare extension on the front are you not?. Im thinking i have a tham 12 here, I should sim it as is, measure. Then sim with a horn flare extension and build the flare and stick it on the tham12 and re measure. Will at least give me an idea how accurate horn resp can sim this arrangement initially before trying any porting. 


Posted By: SouthwestCNC
Date Posted: 01 November 2017 at 1:34pm
Just had a go at it and on second thought its probably a futile exersize, Can get some lovely improvements to response but group delay goes through the roof and and more worrying is even with a short horn extension it introduces sharp changes in phase inside operating range so just be measuring distortions thats unlikely to tell me much. 




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