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Seeking help with low frequency cabinets: Unfolding a folded horn?


Endo

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Hello, All

I am building an existing design for the Eminence LAB 12 Professional (aka: tapped horn for LAB 12; Claude J1 calls it his "coffee table sub").

 

QUESTION: Can I "unfold" this design without altering the performance? In other words, if I am careful about maintaining fundamentals like: overall horn length; internal volume; sectional areas at throat, mouth and points between... can I take one of the folds out without hindering performance? The only thing I can think of--is the internal pressure might change due to a 'straighter' run (?) and that the driver might behave differently as a result?

 

Pictures of the original plan and also what I'm suggesting:

 

 

 

tapped-horn-for-lab-12-driver.jpg

Screen Shot 2020-06-04 at 1.07.14 PM.png

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You should be able to but it'll be very long.  The driver positioning is critical in a tapped horn so be sure you get that right.  Pay close attention to the flare rate as well.

 

 

When you design one of these in hornrsp it comes out as a long sub like you propose but it's folded to make the size more manageable.

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As long as the wavelengths are significantly longer than the height and width dimensions of the internal path, the sound does not even "see" the folds, so it also won't notice that they're not there. Where you get into problems is when the path lengths between the folds are about the same as half-wavelengths -- that causes standing waves. That said, see http://www.audioheritage.org/vbulletin/showthread.php?31499-Jensen-s-own-Transflex.

 

Edit: Also see http://www.cowanaudio.com/images/air_coupler.jpg.

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Thanks to all for the responses. Ordinarily, I set a very high threshold for modifying a proven design---this is something I typically avoid. In this case, I have been living without a horn loaded, low-frequency cabinet because of the needed space. My wife and I share an 800 sq. ft home. Bring anything through the door and a game of Tetris immediately begins, followed by several OSHA violations.

 

I played around with different locations for the coffee-table-sub, before I gave up and thought about un-folding the cabinet. If I can pull this off, the speaker will sit against the long wall of a room, under a window, and will be built like a bench to match the surrounding cabinets. Its part of a larger remodel project.

 

Thanks, again for all the input.

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37 minutes ago, Schu said:

is there any advantage to using a radius flare?

 

According to Kolbrek & Dunker, section 26.4, there is some advantage to radiused bends at low frequencies. According to Bruce Edgar (no relation), there is some advantage to full 45° reflectors at high frequencies. You're probably not going to encounter high frequencies, so a bit of corner radiusing might help.

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3 hours ago, Edgar said:
3 hours ago, Schu said:

is there any advantage to using a radius flare?

 

According to Kolbrek & Dunker, section 26.4, there is some advantage to radiused bends at low frequencies. According to Bruce Edgar (no relation), there is some advantage to full 45° reflectors at high frequencies. You're probably not going to encounter high frequencies, so a bit of corner radiusing might help.

I could do something like the picture here, gluing stacks of MDF curves to fit the corners...

 

don't know about flare at the mouth.

after posting this thread, I was reading about the development of the LAB12 when I ran across the Danley DTS20 for the first time... Its roughly, similar in overall dimension and when you look at this photo of the mouth, it doesn't look flat-bottomed... looks like there is a curve or inclined surface just inside the mouth (?)

 

Screen Shot 2020-06-09 at 1.55.04 PM.png

Screen Shot 2020-06-09 at 2.02.50 PM.png

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49 minutes ago, Endo said:

I could do something like the picture here, gluing stacks of MDF curves to fit the corners...

 

According to Kolbrek & Dunker, if you can't also radius the inner part of the fold at least half the height of the duct, then it doesn't much matter whether the outer part is fully radiused, like your drawing, or just uses a flat diagonal plate. They're all pretty much the same.

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I'm looking into this...

With trepidation, I feel like I'm venturing into the unknown... right before I step into an unrecoverable abyss...

[Leaning back, now, toward my original position of not deviating from a proven, successful design--not meddling with the hard-won efforts of other, more capable people]

 

Reckless behavior can (sometimes) be fun--if you're all by yourself in some kind of parallel universe (or, if you are Bill Gates). But, not me. Not here.

 

The "tapped-horn for LAB 12 driver" works; and not by accident. I will attempt a version that fits my circumstance with minimal alterations. It won't be difficult to improve on what I have now--which is nothing.

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33 minutes ago, Endo said:

I'm looking into this...

With trepidation, I feel like I'm venturing into the unknown... right before I step into an unrecoverable abyss...

 

I suspect that there is greater danger in folding an unfolded horn than in unfolding a folded horn. The original tapped horns (Jensen TransFlex and JBL Air Coupler) were similar to what you have proposed, so perhaps you can take solace in the fact that it's been done before.

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10 minutes ago, Edgar said:

The original tapped horns (Jensen TransFlex and JBL Air Coupler) were similar to what you have proposed

^ thank you, for that. I'm working within limits. Attempting to get this done. I'd rather try and fail, than... well, the other...

worst-case-scenario: the driver is used for something else.

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Now I'm contemplating Fitzmaurice's 'Tuba HT' - low profile version...

 

I'm not a guy who can modify, test,  and tweak a speaker design... Reading through posts on this forum, I happened on to a link to Bill F's website. Turns out he's got a design that uses the same driver that ALREADY approximates the dimensions of my 'unfolded' horn and fits my available space). Hmmm.

 

Here's my question: Does anyone here have opinions about the Tuba HT coupled with a single LAB12? Comparisons?

  • The LAB12 has already shipped, so that's a given

  • also ordered: Lepai with TPA3118  (PE currently has it marked down, for those interested)

 

I'm not finding data on the Tuba HT with a LAB12 (as apposed the 15" driver). Would love to hear from those who've been down this path before?

Thanks in advance.

 

 

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14 minutes ago, Endo said:

I'm not finding data on the Tuba HT with a LAB12 (as apposed the 15" driver). Would love to hear from those who've been down this path before?

 

The Tuba HT specifies a Dayton RSS390 HF4 15" driver. Substituting drivers in a tapped horn is likely much riskier than unfolding a folded horn.

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