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Old 29th January 2013, 12:01 AM   #81
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Quote:
Originally Posted by Brian Steele View Post
If going with the THAM 12, I suggest paying a lot of attention to the bracing in the first fold. Don't do like what I did with my THAM12 lookalike and think you can get away with making the external panel removable and mount the driver through the hole. Two layers of 3/4 ply AND metal bracing inside and that panel STILL vibrates, enough to toss one of my tops off of it when I turned the bass up during the last "war volume" test.
So I'm not exactly following which panel that you're talking about, do you have pictures?

Quote:
Which reminds me of another advantage to THs that don't show up in the sims - all that wonderful free side-panel bracing that comes as a result of folding a horn into a box .
Yes, I alluded to that earlier. My impression is that's part of the construction advantage of TH designs.

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I wonder why MLTLs are not being considered?
I don't know anything about them.
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Old 29th January 2013, 12:39 AM   #82
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Originally Posted by ghettosynth View Post
So I'm not exactly following which panel that you're talking about, do you have pictures?
It's the external panel that the driver faces.

You can see pictures of my POC TH at this link: The Subwoofer DIY Page v1.1 - Projects : "Proof of Concept #2"

If I was doing this again, that top panel would not be removable - it would be cross-braced to the panel that's holding the driver.

MLTLs are basically TLs that are terminated by a vent. You can model them (raw response) in HornResp.
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Old 29th January 2013, 02:07 AM   #83
tb46 is offline tb46  United States
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Hi ghettosynth,

One form of the bracing Brian is talking about can be seen in the picture on Anders Martinsson's Blog: Martinsson's Blog - THAM12

By the way, if you want to reinforce this area, the cone correction talked about in the Xoc1 TH-18 thread would be applicable, or you could bifurcate the section to the first right angle corner (fold the duct back on itself).

Regards,
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Old 29th January 2013, 05:21 AM   #84
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Originally Posted by ghettosynth View Post
Out of context my comment probably appears to make no sense, of course hornresp designs consider the dimensions of the cabinet, however, only as a consequence of the dimensions of the unfolded horn. In other words, the cabinet dimensions proper that are not a function of the unfolded horn dimensions are of no concern to the model. Please see my comment a few pages ago regarding the THAM12 design. If one increases the height of the cabinet, holding all other areas constant, then one only changes a single variable in the hornresp design. Experimenting with this it seems that I gain some low end extension by increasing cabinet height allowing for a longer horn, but get diminishing returns beyond 3 to 4 inches. My question was not whether or not this is true, it is, rather, it's whether or not I was overlooking anything else. In other words, it appears to me that my modification would adapt the design more to my liking without compromising any aspect of the fold.
Hi ghettosynth,

Many thanks for the detailed explanation - now I understand :-).

Kind regards,

David
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Old 29th January 2013, 11:18 AM   #85
Chaps is offline Chaps  Denmark
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I'm actually in the making of a couple of THAM12s at the moment.

Click the image to open in full size.
(i know .. MDF .. but i am trying to achieve some kind of cheap boxes and ply is rather expensive where i live)

Hopefully i will have both done and tested in the weekend. Will post my findings.
I have also build four SS15s, but they got too big for my needs, so now i'm trying these small 12" boxes. My choice was also between MTH30 and THAM12, so i'm very excited to hear how they perform. They will be loaded with PD 12SB30.

Last edited by Chaps; 29th January 2013 at 11:20 AM.
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Old 29th January 2013, 02:09 PM   #86
djlivex is offline djlivex  United States
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The Faital Pro 12HP1030 any good in the MTH30? 12.45 mm Xmax whew!
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Old 29th January 2013, 09:22 PM   #87
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Quote:
Originally Posted by Brian Steele View Post
It's the external panel that the driver faces.

You can see pictures of my POC TH at this link: The Subwoofer DIY Page v1.1 - Projects : "Proof of Concept #2"

If I was doing this again, that top panel would not be removable - it would be cross-braced to the panel that's holding the driver.
Great, tnx for the link. After I posted, I guessed what you meant, but the pictures were very informative. In particular, other than the first section of the horn, your horn tapers are stepped, yet, your sim is in good agreement with your measured response, suggesting that horn taper isn't that critical either.

Does anyone have any insight from this from the theory?
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Old 29th January 2013, 09:56 PM   #88
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Quote:
Originally Posted by ghettosynth View Post
In particular, other than the first section of the horn, your horn tapers are stepped, yet, your sim is in good agreement with your measured response, suggesting that horn taper isn't that critical either.

Does anyone have any insight from this from the theory?
At the frequencies the TH is working at, a stepped taper compared to a smooth taper makes little difference.

A 100 Hz wave is 11.3 feet long, a 50 Hz wave 22.6 feet, small changes in the shape have little effect, while restricting cross section may have fairly large effects.

Also of note is floppy panels reduce upper bass more than low frequencies, stiffness is needed for punch, and the throat area is the place where pressure minimum and maximum is greatest, a loose panel there makes more difference than any other part of the cabinet.

Last edited by weltersys; 29th January 2013 at 10:01 PM.
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Old 29th January 2013, 10:00 PM   #89
Xoc1 is offline Xoc1  United Kingdom
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The Tham 12 is tiny.
On Martinsons blog the Tham12 is shown with a sim of over 88 litres
This is despite the actual internal volume being 74.3 litres without any bracing or driver!
The path length is also shorter than shown on the blog.
With the PD 12SB 30 I would expect 98db at 75hz in a 2pi sim
Have not unfolded the MTH30 yet!
Regards
Xoc1
Attached Images
File Type: jpg Tham12.jpg (28.9 KB, 110 views)
File Type: jpg Tham12 hr1.jpg (52.3 KB, 109 views)
File Type: jpg Tham12 hr2.jpg (42.8 KB, 108 views)
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Old 30th January 2013, 12:10 AM   #90
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Originally Posted by weltersys View Post
Also of note is floppy panels reduce upper bass more than low frequencies, stiffness is needed for punch, and the throat area is the place where pressure minimum and maximum is greatest, a loose panel there makes more difference than any other part of the cabinet.
Yep. In fact, if I was building the THAM12 at this point, I'd be using two braces rather than one in the first section, just to ensure that section is as stiff as possible.

A comparison of the impedance vs. frequency measurement on the built sub should show if it's built stiff enough (if it's not, the upper impedance peaks will be degraded and maybe even non-existant). See The Subwoofer DIY Page v1.1 - Projects : Using Impedance Graphs
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