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Multi-Way Conventional loudspeakers with crossovers

Seas W22XL in Transmission Line
Seas W22XL in Transmission Line
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Old 2nd August 2018, 02:29 PM   #11
pkitt is offline pkitt  United States
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The driver location in the line is important but if it's within an inch of that modeled, negative effects will be very minor. If you want the performance that I modeled, you need to build it as I modeled, however. Those fillets around the corners are absolutely useless regarding the line's performance. They are the result of old and incorrect theories and all they do is consume some of the line volume. The line's beginning doesn't have to be exactly horizontal but the beginning of the line's length is measured from the middle of that angled member. You can definitely locate the crossover as shown; however, the crossover, the woofer and any braces you add, all consume volume which will affect the bass reach a bit. In order to compensate for consumed volumes, estimate their total amount and calculate what percentage that is of the total line volume, then simply increase the internal (and line) width of the cabinet by the same percentage when you build (the volume for the angled line divider is automatically compensated for in the modeling). For sketch 2, there will be reinforcement from the floor boundary of the terminus' output, which may be "too much of a good thing". You won't have that problem with that shown in sketch 1.
Paul

Quote:
Originally Posted by LJT View Post
So, I went shopping wood for the new cabinets today.
Since this is also a case study before my next set of DIY speakers, I decided to go with the conventional line.
For my next project MLTL is an option due to cabinet shape.

It should be noted that I have decided to deviate somewhat from the original Trym layout. I believe the Trym is an early design and I will eventually attempt an XO redesign. This change of layout has the effect of putting the bass element in a slightly different location compared to pkitt's modelling. I don't think this is as critical for a conventional TL as it is for an MLTL?

Before I start cutting I hope someone verify my understanding of pkitt's modelling.
Attached images show two alternative boxes. I believe box #1 should be very close that proposed by pkitt. Alternative #2 has a slightly longer line, but if necessary, I can shorten it further by lifting the start of the line by making a false bottom.
So my questions before I make final decition towards alternative 1 or 2 are:
- How critical is the line lengths
- How important is the radius fillets, and what do you propose to make them from?
- Do the start of the line have to be level, or is it OK if it is slanted (I.e - do I have to make the cavity for the XO in alternative#2 or is it OK to simply attach the XO to the cabinet at the start of the line?
- Any other comment you may have
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Old 2nd August 2018, 03:53 PM   #12
bentoronto is offline bentoronto  Canada
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Seas W22XL in Transmission Line
Quote:
Originally Posted by pkitt View Post
...They are the result of old and incorrect theories...
I think that cries out for an explanation or just what are the old and the new theories?

BTW, here's my theory:

Long pipe to sequester rear wave

B.
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Old 2nd August 2018, 05:10 PM   #13
pkitt is offline pkitt  United States
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The incorrect theory (probably more accurately called guesses) about using deflectors or fillets in the corners was that those "steered" the sound wave more smoothly around them, but that's not true. The stuffing in a line is an acoustical, low-pass filter, so only the long wavelengths get through, and those wavelength are so long that they don't even "see" the deflectors or fillets.
Paul

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Originally Posted by bentoronto View Post
I think that cries out for an explanation or just what are the old and the new theories?

BTW, here's my theory:

Long pipe to sequester rear wave

B.
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Old 5th August 2018, 04:01 AM   #14
Greebster is offline Greebster  United States
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and... at low frequencies approaching the line's quarterwave resonance it acts like a solid slug of air moving within the line. This is because @ resonace the wave becomes planar. If we do not smooth the corners then the exact same turbulance that occurs in air ducts booger up the smooth flow required to maximized bass output cleanly.

As the old adage goes, there is no replacement for displacement. In a TL to maximize bass output you must maximize flow. Anything below 30hz requires flow, ask Bruce Thigpin.
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Old 5th August 2018, 11:46 AM   #15
bentoronto is offline bentoronto  Canada
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Seas W22XL in Transmission Line
So the general question is how to handle the wrap with respect to the reflection, the hole, and the placement of damping too. While textbook-like precision always appeals to members of this forum, it is heterogeneity and un-tuning that I think works better to avoid having any characteristic "voice" to your sub. You would make an irregular hole and leave the turn square for that goal.

B.
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Old 15th March 2019, 07:30 PM   #16
LJT is offline LJT  Norway
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Default Slow progress

For a variety of reasons things are moving ahead slower than what I'd hoped for. I am planning to close the boxes later today. Before I do that I would like your advice on stuffing.
At the moment I have bitumen on every panel, and some lining on top and bottom of the cabinet, hoping to kill of some standing wave modes.

For stuffing I intend to use long fibre wool from my old Bailys, simply because that is what I have at hand right now.
I have four questions.
- Lining: Should I put more lining than what I already have (see picture)?
- Is recommended amount of line stuffing the same for polyester as for wool (0.75 lb/cu.ft. for the first 2/3 of the line).
- In terms of midrange quality, am I better of with a little less filer behind the mid-woofer or should I keep fill density constant
- Later, when doing impedance sweeps, what should I look for in terms of determining amount of stuffing? Will near-field SPL close to the line terminus be a better measure?
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File Type: jpg Open_box.jpg (70.1 KB, 95 views)
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Old 15th March 2019, 11:35 PM   #17
planet10 is offline planet10  Canada
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Seas W22XL in Transmission Line
Quote:
Originally Posted by LJT View Post
At the moment I have bitumen on every panel, and some lining on top and bottom of the cabinet, hoping to kill of some standing wave modes.
biteminum will do nothing to affect standing waves. It is intended to damp panel resonances (but can often backfire).

Quote:
Is recommended amount of line stuffing the same for polyester as for wool (0.75 lb/cu.ft. for the first 2/3 of the line).
There will be a difference, even between different species of polyfluff. Wool is good for damping but not for stability and is a good moth food. i would mix with some poly to get stability with most of the dampin gof the poly.

dave
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Old 15th March 2019, 11:40 PM   #18
planet10 is offline planet10  Canada
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Seas W22XL in Transmission Line
Quote:
If we do not smooth the corners then the exact same turbulance that occurs in air ducts booger up the smooth flow required to maximized bass output cleanly.
For the very reasons stated, the turbulence does not affect the LF only stuff up higher, the expansion at teh corner acts as an additional LP so one can use a (tiny) buit less damping with a corresponding increase in bass (ie less suppresion of the fundemental from the damping)

dave
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Old 17th March 2019, 03:56 PM   #19
onken69 is offline onken69  Italy
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Following the topic. I realized a TL with w22 in a 3 way with seas w15cy: the intersection between wf and mid it’s a damning mess...it’s caused by the ripple due to the room and the TL. Maybe in a 2 way this could be avoided (the xo point in my system is 400hz) i don’t know. Or maybe that was due to my wrong approach. Anyway i’m waiting for your result.
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