Kick Bin Design Idea B&C 15ndl76

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   The second to last drawing looks like a better profile, throat chamber includes any negative expansion after the cone, the area at the exit of the chamber will work as a resonant system forming a second order lowpass filter, small chamber with an expansion will minimise that effect so larger throat and smaller chamber will result in a higher cutoff frequency. A non expansion could act as a lumped mass ie like a port tube also adding to the effect of the lowpass filter, not in a good way.Wish I had your drawing skills in Inventor, plan for today is to put some time aside and hopefully not jut look at it with a glazed look as usual, been pulling my hair out trying to get to grips with it.
With regards to ports in the mouth, I don't think you will see any real effect as so close to the mouth though David did include the ability to model it in HR some time ago, I tried to model a box that had the port at the throat, that didn't show any useful results, very different to the measured response, since he added that feature I have managed to lose all my measured data of frequency response and  impedance plots, it could well be that I have just misused HR though - more likely than not.

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fatfreddiescat Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1083	Post Options Post Reply Quote fatfreddiescat Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 8:34am
	The second to last drawing looks like a better profile, throat chamber includes any negative expansion after the cone, the area at the exit of the chamber will work as a resonant system forming a second order lowpass filter, small chamber with an expansion will minimise that effect so larger throat and smaller chamber will result in a higher cutoff frequency. A non expansion could act as a lumped mass ie like a port tube also adding to the effect of the lowpass filter, not in a good way. Wish I had your drawing skills in Inventor, plan for today is to put some time aside and hopefully not jut look at it with a glazed look as usual, been pulling my hair out trying to get to grips with it. With regards to ports in the mouth, I don't think you will see any real effect as so close to the mouth though David did include the ability to model it in HR some time ago, I tried to model a box that had the port at the throat, that didn't show any useful results, very different to the measured response, since he added that feature I have managed to lose all my measured data of frequency response and impedance plots, it could well be that I have just misused HR though - more likely than not.

smitske96 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 February 2016 Location: The Netherlands Status: Offline Points: 1092	Post Options Post Reply Quote smitske96 Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 9:49am
	Did you take in account the volume that's occupied by the driver itself? For the ndl76 it's 3,5 L.

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 11:02am
	The second to last drawing looks like a better profile, throat chamber includes any negative expansion after the cone, the area at the exit of the chamber will work as a resonant system forming a second order lowpass filter, small chamber with an expansion will minimise that effect so larger throat and smaller chamber will result in a higher cutoff frequency. A non expansion could act as a lumped mass ie like a port tube also adding to the effect of the lowpass filter, not in a good way. This matches up perfectly to what I have encountered this morning, if I model the throat chamber as a negative expansion section I end up with a big dip in response between 100-250hz. I can remove this by shortening the first section of the horn to 58mm from 197mm, unfortunately this is difficult to implement in the cad file. I'm not even sure it will be possible. BIG Wish I had your drawing skills in Inventor Never actually spent any time on Inventor, looks like a very nice bit of software. I mostly use Solidworks, Rhino, Autocad and Grasshopper. plan for today is to put some time aside and hopefully not jut look at it with a glazed look as usual, been pulling my hair out trying to get to grips with it. With regards to ports in the mouth, I don't think you will see any real effect as so close to the mouth though David did include the ability to model it in HR some time ago, I tried to model a box that had the port at the throat, that didn't show any useful results, very different to the measured response, since he added that feature I have managed to lose all my measured data of frequency response and impedance plots, it could well be that I have just misused HR though - more likely than not. Thanks for the help info on the port I was hoping that was the case. Edited by luthier - 01 February 2019 at 11:03am

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 11:12am
	Did you take in account the volume that's occupied by the driver itself? For the ndl76 it's 3,5 L. Not sure where you got 3.5L from, when I modelled the driver (from the tech drawing and actual driver) I measured 9.281L of displacement in the VRC. The way I reached that measurement was by creating a solid cube around the driver and intersecting the two components. This removes all the space occupied by the driver basket cone and magnet. It's a very accurate and reliable method. The volume of the cube without the driver was 31.59L and the volume minus driver from cube was 22.3519 L, this leaves me to conclude that the drivers total displacement in it's current orientation is 9.2813L. Edited by luthier - 01 February 2019 at 11:13am

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 11:24am
	SO at the moment I need to shorten the throat length to a maximum of 58mm, at moment is currently sitting at 208.7mm. I also need to keep the VRC chamber as small as possible. Unfortunately I can't move the driver any closer to the s1 as it is already as low as close as it can get.

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 11:42am
	If I remove the volume reducing section of the throat chamber I can get a good result, provided the area up to the S1 act's as the VRC and not a negative expansion horn segment. Here's what happens when the volume of the VRC is reduced (grey is 15L red is (9.4L) If I increase the size to it's current size with no volume reduction in any way it is 18.8L when the 9.281L of driver displacement has been removed. Maybe if I stick a big ferrite driver in there I can loose some more volume! (grey 15L, Red 18.8L)

smitske96 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 16 February 2016 Location: The Netherlands Status: Offline Points: 1092	Post Options Post Reply Quote smitske96 Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 11:49am
	It's in the specsheet of the nld76 under "occupied volume by driver".

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 12:02pm
	In my measurements the driver itself is 3.7L, but the displcment in the chamber is much larger.

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 12:04pm


luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 12:27pm
	Okay so I did it again just to make sure, here's the results: First picture is the volume of the shape with nothing subtracted/intersected. Second is after intersection. Looks like you were right! Think this means I need to start check my late night CAD modeling when I'm a litttle more rested! Also apart from feeling a bit stupid I'm quite happy, I was only 9ml ! over what the manufacturers claimed displacment! Thank you for spotting my error!

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 12:35pm
	Now i've got to remove 7L without creating another horn segment/throat! It's royally cocked up my sim!

luthier Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 21 July 2013 Location: UK - London Status: Offline Points: 271	Post Options Post Reply Quote luthier Report Post Thanks(0) Quote Reply Posted: 01 February 2019 at 1:54pm
	Hoping to be able to conisder all of the blue section as my VRC and not yet part of my horn path.