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.
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.I found the link where I originally read this info, and there are a couple charts to boot:
http://www.audioroundtable.com/SingleDriverSpeakers/messages/1787.html
http://www.audioroundtable.com/SingleDriverSpeakers/messages/1787.html
drongo said:
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...
Re: Re: MLTL v. ML TQWT
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.
critofur said:
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.
Stuffing tends not to be very effective on the fundamental low frequency standing waves. So a quarter wave enclosure can be designed to supply more bass output compared to a BR. A quarter wave enclosure can have a slower transition to the 24 dB/octave roll-off which will make the bass sound less one note tubby and more natural.
Most of the simple BR freeware design programs, or the formulas used in the original technical papers on BR designs, neglect to account for standing waves. If the enclosure is a squat cube geometry this is a decent assumption. If the enclosure becomes tall enough to support standing waves in the long direction, then the basic BR analysis is no longer producing the correct result. An analysis that handles a ML TL geometry can also handle the BR case, the opposite is not true. There is a large grey area between a classic BR and a ML TL design.
Most of the simple BR freeware design programs, or the formulas used in the original technical papers on BR designs, neglect to account for standing waves. If the enclosure is a squat cube geometry this is a decent assumption. If the enclosure becomes tall enough to support standing waves in the long direction, then the basic BR analysis is no longer producing the correct result. An analysis that handles a ML TL geometry can also handle the BR case, the opposite is not true. There is a large grey area between a classic BR and a ML TL design.
critofur said:
To expand on what Martin said.
If you stuff a box so as to supress all the standing waves (not really possible in a qw design) then you end up with an aperiodic box. The goal of most qw designs is to use the lowest fundemental standing wave for bass augmentation and supress all those above it. Damping, box geometry, and driver offset all play a role to do this.
dave
Hi Martin,
Do you think there is value in having a BR that manages to have "virtually no" standing waves inside? Just the intended Helmholtz resonance?
I am trying to achieve this by using felt-covered 1" dowels glued inside a golden-ratio BR. It looks like a bamboo forest in there. Subjectively, sticking my ear up to the vent, it seems well-damped, i.e. minimal reflections.
Do you think this is an equally valid, or even halfway valid, approach? Thanks in advance for any thoughts.
Do you think there is value in having a BR that manages to have "virtually no" standing waves inside? Just the intended Helmholtz resonance?
I am trying to achieve this by using felt-covered 1" dowels glued inside a golden-ratio BR. It looks like a bamboo forest in there. Subjectively, sticking my ear up to the vent, it seems well-damped, i.e. minimal reflections.
Do you think this is an equally valid, or even halfway valid, approach? Thanks in advance for any thoughts.
planet10 said:
Well, that's not at all what I do - I place a sheet of a special damping material in certain points in the box which breakup the standing wave without being too restrictive to reduce bass output.
So again, I ask, assuming standing waves are not an issue, what other benefits might be had from a TL?
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