TH-18 Flat to 35hz! (Xoc1's design) - Page 92 - diyAudio
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Old 14th September 2012, 10:50 PM   #911
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Hi Xoc1,
Could you give me those dementions or a drawing,I do not know yet how to arrive at them myself ,to determine the plug,I have some others suggestions,but wouldd like yours too!
I lived in Greenville,Sc we had bike rallies every weekend as long as it wasn't raining,Roped off most of downtown,was lots of people ,brewed beer and fun!
I smell like sweat and saw dust,lol. BUT it a good day in Texas,nice and cool,we got rain last night!
Thanks,
NS

Last edited by noSmoking; 14th September 2012 at 10:53 PM.
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Old 14th September 2012, 11:27 PM   #912
Xoc1 is offline Xoc1  United Kingdom
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I then used the calculated area dimensions to plot out a cone compensation plotting line to be used in the horn model.
The compensation line starts at the intersection of the internal baffle face and the baffle cut out.
This imaginary line is then used as one side of the throat cross section.
The other side of the horn is shaped to follow this contour and the desired horn throat areas.
I averaged the compensation line and reduced it to 3 sections. This is to make it practical to build in timber.
This process leads me to a throat shape roughly as attached. Which is as far as I have got. I now need a spare day to fettle the rest of the folding, and to concider what else needs to be done.
It is obvious how the cone compensation bend can be used to increase the internal path length of the TH18 -SS15 fold..
Yes it needs more work and a few more sketch lines, but I see it as a valid way of calculating a TH horn throat in a way that can be understood and applied by the DIY builder
Regards
Martin (Xoc1)
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File Type: jpg TH18 Throat Comp Prelim.jpg (66.9 KB, 365 views)
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Old 14th September 2012, 11:51 PM   #913
Djim is offline Djim  Netherlands
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Hi Martin,

Nice to see you are back in bizz, hope you are doing well. I only want to point out that when the cone moves into the direction towards the mouth, the cone volume increases further. That means the pressure point still ‘travels’ during excursion. If you make the “V” more sharp and closer to the driver-baffle, you can prevent this ‘travel’. Using Xmax or Xvar depends on the type of driver. Xmax for 'less strong' drivers (Low BL, high Vas) and Xvar for 'strong' drivers (High Bl, low Vas).
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Old 14th September 2012, 11:56 PM   #914
Xoc1 is offline Xoc1  United Kingdom
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Hi Nosmoking I'm not trying to ignore you! Just busy cross posting to get the process I am trying to develop on to the forum.
As you can see from the posts I just put up, the compensation profile is there - you could use some of the simple techniques of horn design to come up with a throat shape - this can be as basic as using cut up bits of paper to get a horn contour to follow an profile.
The large S1 area before the S2 point at the centre of the driver seems to give a bit more lower end - reducing S1 extends the top end extension in a Hornresp sim, but not many have found a practical use for an extended top end response.
DJims Stub Looks OK to me and if its is what Crescendo built then it must work! But the compression at S2 looks quite high with DJims stub. It might not be suitable for everyone - it could depend on a decently robust speaker driver.
Must get to bed - Big Day tomorrow - Should be fun 'Making some Good Noise'
Which after all is the point of all of this effort!
Regards
Martin
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Old 15th September 2012, 12:05 AM   #915
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Hi Martin,
Wasn't in a big Hurry, Didn't feel ignored,Thanks for your Ideas and Drawing from you and Djim,
I am going to contour the speaker cone to as close as your cross section and Djims drawing,and finish this cabinet,Thanks for EVERYONE'S Help!
Glad your back to health!
NS
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Old 15th September 2012, 12:08 AM   #916
Xoc1 is offline Xoc1  United Kingdom
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Hi Djim
You can squeeze down S2 to suit whatever driver you desire to use........
I am trying to make this a process that we can understand, and apply, with the tools at our disposal - Surely the at rest position is the average volume as the cone moves up and down.
Cheers
Martin
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Old 15th September 2012, 12:21 AM   #917
Djim is offline Djim  Netherlands
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Hi Martin,

I will try to explain. The cone correction makes it function like the sim, which increase the output at the lowest part of the bandpass.

What makes the driver loosing control over the excursion is the 'travelling' of the high pressure zone as result of the excursion (= changing cone volume) in relation to a 'not moving' cab. To keep the control over the excursion, the "Stub" (or "V" in your case) needs to have the highest compression factor, even when the cone moves away from the stub.

Click the image to open in full size.

Last edited by Djim; 15th September 2012 at 12:43 AM.
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Old 15th September 2012, 12:33 AM   #918
kctess5 is offline kctess5  United States
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Here's an idea I had while looking at how to do cone correction without having to buy more materials...

What if we took the driver cutout and cut smaller coaxial circles out of it at a 45 degree angle with a saber saw or something then stacking them. It seems that one could pretty closely approximate a cone with that method. Then just attach it onto Internal 2. It may not be totally ideal but would it at least be better than nothing?

For a visualization of what I mean think of making onion volcanos by taking it apart and inverting it.

Click the image to open in full size.
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Old 15th September 2012, 12:58 AM   #919
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hi kctess5,
If you took a couple of pieces of that clinkie plastic like suran wrap and put it across the cone and then filled the cone with foam you will have to only figure how far away to mount that perfect replica to optimize the cone,Nice pic,I like steak and chicken hibachi,lol.Plum wine is good with that meal Too!

NS
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Old 15th September 2012, 01:09 AM   #920
Djim is offline Djim  Netherlands
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Follow up for post#917

In order to compensate for the changing cone volume as result of excursion (towards S4) you increase the compression factor at S2 by lowering the "stub" or "V".


In order to compensate for the increasing 'overall' compression when the cone moves into the other direction, you need to decrease the compression by making the base of the "stub" or "V" smaller.


Click the image to open in full size.

(see my ealier post on 'ideal' models)

Last edited by Djim; 15th September 2012 at 01:33 AM.
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