Are these two speakers of two different types? I have yet to master the alphabet (MLTL TQWT BLH BVR BIB).
WIBAQ https://www.diyaudio.com/forums/full-range/226767-wibaq-tabaq-design-betsy.html
Singularities Speaker Design Works
WIBAQ https://www.diyaudio.com/forums/full-range/226767-wibaq-tabaq-design-betsy.html
Singularities Speaker Design Works
Mass Loaded Transmission Line (MLTL) design is same concept, but design is for specific drivers.
The term "mass loaded" is really a poor name choice, but it stuck. It refers to the analogy that if you add mass to the tip of a tuning fork resonator, the frequency drops. How does that relate to a speaker design?
A transmission line (TL) design is an acoustic resonator with a characteristic low corner frequency. By constricting the output end of the TL (adding a vent tube vs a big open end) lowers the characteristic tuning frequency. There is no "mass" addition per se.
It really should be called constricted exit TL or CETL. In a similar way, a TL that gradually tapers to the exit also has a lower corner freq than a straight cross section TL.
Both the PS220 and Betsy use a secondary cone (whizzer) to achieve higher frequencies. Some may not like this sound - it is kind of diffuse and lacks crispness of timing that a single dome tweeter produces (or even a single 3.5in full range) that can go up to 16kHz to 20kHz without resorting to a whizzer.
You may or may not like the whizzer sound.
There is a very good 5in full range that does not resort to a whizzer to achieve 20khz and that is the Tang Band W5-2143. It has a remarkably high frequency output and sounds very crisp and natural yet superb bass extension. It would make a superior CETL, vs a whizzer cone based one, IMO.
Large full range drivers also "beam" that is, they have a narrow beam of sound since the dispersion angle is inversely proportional to the driver diameters. Hence tweeters are about 1in, and 2in to 3.5in is really about as big as you want to go and still keep a wide even sound field.
Hope that helps.
The term "mass loaded" is really a poor name choice, but it stuck. It refers to the analogy that if you add mass to the tip of a tuning fork resonator, the frequency drops. How does that relate to a speaker design?
A transmission line (TL) design is an acoustic resonator with a characteristic low corner frequency. By constricting the output end of the TL (adding a vent tube vs a big open end) lowers the characteristic tuning frequency. There is no "mass" addition per se.
It really should be called constricted exit TL or CETL. In a similar way, a TL that gradually tapers to the exit also has a lower corner freq than a straight cross section TL.
Both the PS220 and Betsy use a secondary cone (whizzer) to achieve higher frequencies. Some may not like this sound - it is kind of diffuse and lacks crispness of timing that a single dome tweeter produces (or even a single 3.5in full range) that can go up to 16kHz to 20kHz without resorting to a whizzer.
You may or may not like the whizzer sound.
There is a very good 5in full range that does not resort to a whizzer to achieve 20khz and that is the Tang Band W5-2143. It has a remarkably high frequency output and sounds very crisp and natural yet superb bass extension. It would make a superior CETL, vs a whizzer cone based one, IMO.
Large full range drivers also "beam" that is, they have a narrow beam of sound since the dispersion angle is inversely proportional to the driver diameters. Hence tweeters are about 1in, and 2in to 3.5in is really about as big as you want to go and still keep a wide even sound field.
Hope that helps.
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... I'd say that absolutely all drivers "beam" at certain frequencies, but in general, a large membrane driver does so from a lower frequency compared to a smaller membrane driver.
Wizzer drivers are indeed a bit of a mixed bag, but wizzer or no, I've yet to listen to two drivers that sound and behave exactly the same.
It's all in the implementation.
Perhaps it might be easier to make a good small driver, but sometimes I catch myself thinking it's only because they are easier and quicker to design and prototype.
As far as I am aware, its popular origin is from Martin King's 2001 article 'Design and Construction of a Mass Loaded Tapered Quarter Wavelength Tube (ML TQWT) Using the Fostex FE-164 Full Range Driver', pp.9-10
The final detail that plays a major roll in the system response, shown in Figure 5, is the narrow shelf that forms the terminus geometry. The terminus in this design represents a significant restriction at the end the line. The air in the slot becomes an additional mass loading on the quarter wavelength standing waves. If the base of the cabinet was removed, and the terminus area increased to the maximum cross-section, the first mode of the straight TQWT would rise to 73 Hz. By inserting the shelf and creating an air mass in the slot, the first quarter wavelength mode drops from 73 Hz to 38 Hz. In addition, this mass loading also causes the roll-off of the terminus response above 100 Hz to be significantly faster compared to the tapered transmission line and the folded TQWT. These are the reasons that I refer to this design geometry as a mass loaded tapered quarter wavelength tube or expressed in abbreviated format a ML TQWT.
Thanks for the clarification, Scottmoose. I wonder why bass reflex boxes are not called mass loaded Helmholtz resonators (MLHR)? 
Putting large radius round overs to change the pressure loss coefficient from. 0.6 for a sharp edged orifice vs 0.9x for a smooth and rounded inlet/outlet and mass hasn’t changed.
Putting large radius round overs to change the pressure loss coefficient from. 0.6 for a sharp edged orifice vs 0.9x for a smooth and rounded inlet/outlet and mass hasn’t changed.
Well, a vented box based on Small's electrical filter derivations technically isn't a bass reflex either. A bass reflex is an enclosure derived from method predating Small, Thiele and Novak.
It's really just linguistic semantics. There are more important things in life to worry about. Be that as it may, mass-loading as a term is not unreasonable when applied in certain situations for clarity since most are familiar with ducted vent boxes of the more common kinds. If you object to it, perhaps you would prefer Schultz's 'Omega Quarterwave Reflex' which was a specific cookbook alignment of MLTL, or MLQW if you prefer. AFAIK the OQR did not take off; nothing wrong with the math per se, it just wasn't very accessible and the vent dimensions were usually rather small.
A bass reflex is an enclosure derived from method predating Small, Thiele and Novak.It's really just linguistic semantics. There are more important things in life to worry about. Be that as it may, mass-loading as a term is not unreasonable when applied in certain situations for clarity since most are familiar with ducted vent boxes of the more common kinds. If you object to it, perhaps you would prefer Schultz's 'Omega Quarterwave Reflex' which was a specific cookbook alignment of MLTL, or MLQW if you prefer. AFAIK the OQR did not take off; nothing wrong with the math per se, it just wasn't very accessible and the vent dimensions were usually rather small.
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i.e. its upper mass corner frequency [Fhm] where it rolls off from its acceleration to mass controlled BW where T/S theory peters out:
Fhm = 2*Fs/Qts'
Qts' = Qts + any added series resistance [Rs]: HiFi Loudspeaker Design
GM
By quite a wide margin
, Thuras' 1930 patent, granted 1932: US1869178A - Sound translating device - Google Patents
GM
As Scott noted and I just elaborated on; if BW limited to the driver's Fhm, then all else equal, yes at average playback levels as our hearing is falling off below ~800 Hz, requiring ever higher SPL to hear it clearly and don't have any 'clues' from the BW where we can hear subtle differences: https://upload.wikimedia.org/wikipedia/commons/thumb/4/47/Lindos1.svg/600px-Lindos1.svg.png
GM
By quite a wide margin
I forgot it was 1930; I generally remember the 1932 grant but not the submission, which is arguably more important, historically speaking. Thanks for the reminder (and the lesson -I must pay more attention to all the dates).
It's still a formidable piece of work. I was looking over it & his BLH patent a few days ago. Albert &co. were 'a bit good' weren't they.
What happens when you get some great people together and give them the budget.
There is no fixed +/- dB criteria for bandwidth as an overall concept, unless otherwise stated.
Fhm = 2Fs/Qt'. As GM notes, this is the -3dB point where the drive unit transitions from the rising response (acceleration) part of its bandwidth to the mass-controlled (nominally flat) part of its bandwidth. The latter is usually, though not always, much wider.
As GM alluded to, Thiele / Small (T/S) parameters are a mathematical construct based on electrical filter theory that describes the behaviour of a drive unit below its mass corner frequency. They do not, however, tell you much useful about its behavior above that point.
Fhm = 2Fs/Qt'. As GM notes, this is the -3dB point where the drive unit transitions from the rising response (acceleration) part of its bandwidth to the mass-controlled (nominally flat) part of its bandwidth. The latter is usually, though not always, much wider.
As GM alluded to, Thiele / Small (T/S) parameters are a mathematical construct based on electrical filter theory that describes the behaviour of a drive unit below its mass corner frequency. They do not, however, tell you much useful about its behavior above that point.
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