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Old 17th December 2008, 09:21 PM   #1
drongo is offline drongo  Australia
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Default MLTL v. ML TQWT

Anyone have any comments about the relative strengths and weaknesses of an MLTL design (like Bob Brines' LT2000 or Martin King's project 4) verses an ML TQWT design like Martin's project 6?

Also , is the stuffing necessary in the ML TQWT, or would lining the cabinets be sufficient?
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Old 18th December 2008, 03:31 AM   #2
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I must be crazy to jump in here, but since no guru has taken this up, here's what I've read Bob say elsewhere (but I'm just repeating what I've read / learned):

The ML TQWT has the driver at ~50% and suppresses the 1st harmonic, but the third harmonic may not be completely suppressed (unless further optimized). In contrast, the Brines MLTL has the driver at ~25% and suppresses the third harmonic, and can end up suppressing the 1st and 5th harmonics too, and thus it may be easier to get a flatter response. It's also more compact (obviously).

The LT-2000 is excellent and don't underestimate the value of driver swappability. It can take several different 8" Fostex, and various Lowther so there's an upgrade path. I have the LT-2000's and have had several different drivers, the best to my ears is the FE208-Sigma but I might be alone in thinking that. You also have future tweakability with the Fostex drivers, e.g. phase plugs etc.
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Old 18th December 2008, 03:56 AM   #3
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I found the link where I originally read this info, and there are a couple charts to boot:

http://www.audioroundtable.com/Singl...ages/1787.html
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Old 18th December 2008, 09:10 AM   #4
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An ML TQWT is actually a mass-loaded conical horn (anything that expands toward the terminus falls under the horn remit). You should be fine by lining one. As for the rest, it'd depend on the driver & design.
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Old 18th December 2008, 12:46 PM   #5
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Quote:
Originally posted by rjbond3rd
I found the link where I originally read this info, and there are a couple charts to boot:

http://www.audioroundtable.com/Singl...ages/1787.html

Wow, did you ever dig for that one!

Bob
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Old 18th December 2008, 01:36 PM   #6
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speaking very tongue in cheek....

from experience I have found that the theoretical distinctions can be large(depending on perspective of course) but the practical differences are near undetectable in a good example of each......

I guess it depends how clinical you want to be

Ed
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Old 18th December 2008, 02:41 PM   #7
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Hi Bob, actually I just read the entire Audio Round Table single-driver forum in reverse chronological order (by clicking on "Previous Posts" at the bottom of the page). It's a goldmine for newbs.
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Old 20th December 2008, 12:47 PM   #8
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Default Re: MLTL v. ML TQWT

Quote:
Originally posted by drongo
...comments about the relative strengths and weaknesses of an MLTL design ... verses an ML TQWT design...
Does "ML" mean different things in MLTL vs ML TQWT - and - what about TQWT without the "ML"? (I'm guessing that the ML in MLTL is the stuffing, and the ML in the "ML TQWT" is the port?)

Also interested in OP's first question there, which none of the replies seem to address?

I heard some TL speakers at the Dayton Audio '08 that I liked, particularly the bass. Unfortunately, I didn't look close enough to notice if the slot was a port, or just the open end of the TL...
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Old 20th December 2008, 04:12 PM   #9
MJK is offline MJK  United States
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Default Re: Re: MLTL v. ML TQWT

Quote:
Originally posted by critofur


Does "ML" mean different things in MLTL vs ML TQWT - and - what about TQWT without the "ML"? (I'm guessing that the ML in MLTL is the stuffing, and the ML in the "ML TQWT" is the port?)

Also interested in OP's first question there, which none of the replies seem to address?

I heard some TL speakers at the Dayton Audio '08 that I liked, particularly the bass. Unfortunately, I didn't look close enough to notice if the slot was a port, or just the open end of the TL...
People like to assign names to different geometries such as TL, TQWT, or horn. Some people have really restrictive definitions of what is meant by these names and will strongly argue forever about what constitutes a TL, TQWT, or a horn. These people tend to be the ones with a limited understanding of the math/physics and they are not flexible enough in their understanding to see the large grey areas between their black and white rigid definitions. But if we recognize that all of these enclosure geometries, one end open and one end closed, can be defined as a quarter wave enclosure and that there are no solid lines between them then things become a lot less confusing. There is a lot of grey areas between what some people define as a TL, TQWT, or a horn. The same basic equation of motion covers all of the geometries.

So a quarter wave enclosure can be defined by a length, an area at the closed end S0, and an area at the open end SL. Assuming that the area varies linearly between S0 and SL (this is a simplification for this discussion, the area could vary exponentially or conically without impacting the explanation) then the resonant frequencies of the 1/4. 3/4, 5/4, .... are defined by these three geometric values. Mass loading refers to an intentional severe restriction placed at the open end that dramatically reduces the area from SL. This restriction can be a round port, a square or rectangular opening, or a narrow slot. The length of the restriction can be just the wall thickness of the enclosure or it can be significantly longer. The mass loading refers to the slug of air in the restriction since it acts like a concentrated moving mass. The benefit of mass loading a quarter wave enclosure is that it can now be made shorter in length for the same tuning frequency and the slug of air that is the mass load tends to reduce the output from the harmonics of the fundamental standing wave that is used to augment the bass output of the system. The fiber damping does not provide any mass load, it just provides damping of the internal standing wave resonances of the air in the enclosure.

Mass loading can be applied to a tapered TL, a straight TL, or a expanding TL which is commonly refered to as a TQWT. It works by the same principle for each geometry. In my opinion one geometry is not better then the other two if the designs are done correctly. Optimum driver position is a finction of the shape of the enclosure and the driver is typically placed at about 0.5 x L for a TQWT and between 1/3 to 1/5 x L for a straight or tapered TL. Depending on the degree of taper or expansion there will be an optimum position for the driver that will minimize the output from the higher harmonics.
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Old 20th December 2008, 04:20 PM   #10
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Ok...

So, assuming I have reduced standing waves in the cabinet to the point where they are no longer an issue, using various stuffing materials to both breakup and damp them, is there any further advantage to "TL" designs over a basic BR design?
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