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Old 24th January 2011, 03:14 AM   #91
jbell is offline jbell  United States
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If you are obviously this passionate about proving you are right.... go buy the plywood and prove it. There are easy ways to set up an airtight cabinet for testing.

There is no substitute for doing.
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Old 24th January 2011, 03:23 AM   #92
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Originally Posted by jbell View Post
I gave you 2 examples.... I have more.... and not just from me.

I also played with reflectors on my big cabinet, and the cube... so I can give you #4, and #5 as well. and guess what fraction of a wave they all line up on?
I can give you one example from the man who actually came up with the TH idea, Tom Danley - the TH-SPUD. He released the plans to the 'net - a search for "TH-SPUD clone" should bring up a few hits.

Please point out to me where he's used "reflectors" in that design. For a sub that wide and high that's designed to do 19Hz to 125 Hz, you'd think he'd have at least one reflector in there, right?
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Old 24th January 2011, 03:25 AM   #93
Djim is offline Djim  Netherlands
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Brian, I’m still working on finding the right theories about this subject so I’m not sure yet if its only possible between driver and walls, walls & walls or any other options.



However, other peoples findings seems to prove its possible anywhere within the horn.
My theory: Cause it interrupts the signal and mirrors it in 180 degrees at ľ of wavelength. So wherever the signal is interrupted it’s always returns backwards into the horn with a perfect shift of 180 degrees in my view…

Jbell, thanks for the sharing, oh and Brian you can use your tube you already build, seems a perfect candidate…
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Old 24th January 2011, 03:32 AM   #94
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There is no substitute for doing.
I don't do unless I'm sure that current theory backs up what I'm doing. As a result, few times I've ever built something that doesn't measure like I expected it to, and if it doesn't, it's usually a mistake on my part rather than a problem with the theory. Stuff costs a lot more here than there, I have a lot less time on my hands than I used to, and pushing pixels is a lot easier than joining wood .
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Old 24th January 2011, 03:40 AM   #95
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However, other peoples findings seems to prove its possible anywhere within the horn.
Any links to before/after measurements?


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Jbell, thanks for the sharing, oh and Brian you can use your tube you already build, seems a perfect candidate…
Good idea. I have access to all sections of that TP, as the side panels are screwed on, not glued together. Give me some hints about where to put "reflectors", and I'll do some before and after measurements to see what difference they actually make. Better than building an entirely new horn just to test this .
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Old 24th January 2011, 04:03 AM   #96
Djim is offline Djim  Netherlands
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Ask Jbell and Anders, they might have measurements results. Especially Jbells open field measurements seem to be a good guideline without the influence of room acoustics, you have any Jbell?

Use my tham suggestion as a guideline. Look at the grey lines from where the reflectors should start. About the steepness: Don’t make it to high cause it narrows the path. Don’t make it low cause it looses its efficiency. If two reflectors see each other it gives the maximum effect. But to many of them can make everything worse…



If you have detailed drawings it would be easier to show a suggestion.
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Old 24th January 2011, 04:34 AM   #97
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Ask Jbell and Anders, they might have measurements results. Especially Jbells open field measurements seem to be a good guideline without the influence of room acoustics, you have any Jbell?
JBell's measurements were done at 28.3V, if I remember correctly. That's way outside what could be considered "small-signal", and as a result may or may not match the HornResp predictions.

To make this as unbiased (by me) as possible, I'll need your specific suggestions re reflector size, angle, location and dimensions. I don't have detailed drawings, but the box is basically consists of four components with internal dimensions of 6"x7.75"x19.5" built out of 3/4 ply, so it shouldn't be too difficult to work it out.

Note: any "reflectors" placed near the driver end of the line are likely to significantly change the response - and this response change can be predicted by HornResp (narrowing the line before S1).
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Old 24th January 2011, 04:53 AM   #98
Djim is offline Djim  Netherlands
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I am a real disaster when it comes to computer drawings so I need some time for that.
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Old 24th January 2011, 05:27 AM   #99
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I'll try to post a picture of the computerscreen during the testing, it may be dificult to work out, but the results where constant over a series of messurements on the two MKII's and the two originals.

Ill try to describe it, the 170 dip is the result of what seems to be several small notch cancelations, on the original there is one narrow deep dip, on the MKII there is a peak in the middle of the same dip, look at it like this, it has gone from a "V" to a "W" and the width of the dip remains the same between the two proposals.

So to my mind the reflectors seems to have had a positive impact, although being of an alomst academic nature, the results remained the same over several mesusrements wich tells me that this is not a matter of erorr in messurement.

Intresstingly enough, when messuring the MKII while running the the testsignal through the original approx one metre to the side of it, the response wha simmillar, this tells me that the reflections in the MKII are different then that of the original, even i messured passivly,t his was an intressting error in messurement though.

I do have messurement data, in file format, but i need the program (REW from hometheatrechack" to get the graphs up on my screen and make pictures of them, and being out of internet at home i can not provide them just yet, sorry.

It seems to me that the reflectors make a differance, that much is clear, but how to tune their impact seems to be a matter of emperic nature, to build and analyze, and when we get (IF we get) to see the best result we can simply back engineer from that and see how it lines up with theory.

Since I lack the deeper understanding of the theory and how to translate that into the THAM15 in form of reflector anfgles and positions testing it out seems to be the way to go, for me at last, but as i said before, my recourses are very limited at the moment.

If anyone is in the process of starting a THAM15 build and feels a bit experimental about it please let us know and perhaps we can provide a proposal of what we collectivly think is the best way to combat the dip using reflectors, when we later take part of the messurements we can see if out thinking was "correct" and perhaps learn abit in the process.

I'll try to sum up all the different proposals we have sofar.
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Old 24th January 2011, 07:05 AM   #100
Djim is offline Djim  Netherlands
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Thanks Anders for sharing again your info and findings so far. It will be interesting to see what your plots are going to show us.

Brian, before I ‘m going to share my reflector picture I want to make sure it’s still a suggestion (although based on improvement for room acoustics).
Any comments or ideas are welcome...


In the left part you’ll see a reflector suggestion for each 90 degree corner. The angle should be maximum 40 degrees for maximal efficiency and no less then 15 degrees for minimum efficiency.

On the right Reflector 2 and 3 have an angle of minimal 7,5 degrees and maximum 40 degrees each.

Try not to pass the blue line to much because the reflector will start to narrow the horn path from that point. Make sure that all reflectors totally cover the parallel wall. This is not possible with 45 degree corners without narrowing the horn path!
The overlaping area means where the reflector is crossing the ideal outline of the hornpath.

The reflectors hopefully work in two ways;
1.) lowering the expansion factor as result of the increased volume in a corner.
2.) minimising the reflection of 1/4 waveforms -out of fase - signals




Click the image to open in full size.

Last edited by Djim; 24th January 2011 at 07:26 AM.
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