This may be a dumb question, but when building a transmission line enclosure I'm assuming the net box volume is essentially the line volume?
Which means the recommended box volume for the woofer should match the total line volume of the box?
If that is correct are the volumes equal or do you need to modify your calculations to adjust for the transmission line. So for e.g.. should the total volume be slightly lower or higher than the recommended volume for the woofer?
Phew, hope that all makes sense!
Which means the recommended box volume for the woofer should match the total line volume of the box?
If that is correct are the volumes equal or do you need to modify your calculations to adjust for the transmission line. So for e.g.. should the total volume be slightly lower or higher than the recommended volume for the woofer?
Phew, hope that all makes sense!
It is impossible to provide you with some meaningful answers.
There are many variations possible: Qt of the driver, line length, line geometry to name but a few. They will determine the final dimensions/volume.
I suggest to read a bit into the subject; check Martin King's papers for a first and good theoretical basis.
There are many variations possible: Qt of the driver, line length, line geometry to name but a few. They will determine the final dimensions/volume.
I suggest to read a bit into the subject; check Martin King's papers for a first and good theoretical basis.
When designing (modeling, actually) a TL, the first thing you must do is determine what system tuning frequency is optimum for the woofer, based on its fS and Qts. Once you've found that, then the volume in the line will determine what the bass response is, like f3. If the line is long with a constant area, or it's shorter and has a negative taper of its area, the 1/4-wavelength resonant frequency of the line will be the sole tuning mechanism. It the line is mass-loaded, whether having a constant area or positive taper, the system tuning will have two contributors, the line's 1/4-wavelength resonant frequency and the dimensions of the mass-loading port. How much volume is "needed" in the line depends on how low you want to reach in the bass while not readily exceeding the woofer's abilities.
Paul
Paul
What I understand about TL is that they are not a volume that loads the driver but a resonant structure whose main parameter is the length (and additional design option the placement of the driver in that tube).
f3 is determined by the length of the tube and the size of the tube (volume) is determined by the size of the diaphragm. You want the tube to start with a cross section similar to the Sd of the driver and even if it shrinks to become a slit at the other end, that has to be done gradually. In simple words, the actual volume is not a part of the modeling parameters.
The actual volume needs to be stuffed amply to tame the resonances of the air inside the transmission line,
f3 is determined by the length of the tube and the size of the tube (volume) is determined by the size of the diaphragm. You want the tube to start with a cross section similar to the Sd of the driver and even if it shrinks to become a slit at the other end, that has to be done gradually. In simple words, the actual volume is not a part of the modeling parameters.
The actual volume needs to be stuffed amply to tame the resonances of the air inside the transmission line,
This is reasonably close to how I've been viewing it. Note that you need to put the driver in side-on to the tube to get the starting cross-section to match Sd. I've tried a number of tapering tubes, starting at around 120cm and settling on 106cm with an SB12PFC and NRX (Sd = 50 cm^2) and then tried a 10% change in line CSA (starting at 77cm^2 and going to 88 cm^2) at the start.
Increasing CSA gave me more boost at the line resonant frequency, with the 10% increase good for 3dB. See http://www.diyaudio.com/forums/full...ng-40-hz-compact-enclosure-3.html#post5128543.
Vas and [effective system] Qt'. The idea that is has any direct functional relationship to driver Sd is twaddle that needs to be stamped out before it leads anyone else up the garden path. Which it's been doing for decades and is probably responsible for more poorly performing QW designs than anything else.
Hear, hear to the replies from planet10 and Scottmoose. The optimum tuning frequency from a TL is based on the driver's fS and Qts, and once that's determined the bass reach is determined by the volume in the line. You can use any starting cross-sectional area you want (appropriate to the driver's size, of course) as long as the resulting modeling gives acceptable results, the driver is not pushed beyond its abilities, and air velocity in the terminus (or port if mass-loaded) does not cause audible noise.
Paul
Paul
Ok so perhaps I'm a bit more confused than when I started. I'm just learning all of this and the more I figure out, the more I learn, the more I realize I don't have a clue what I'm doing!
Soooo, that said, how do I determine the size length and volume of the T-Line?
Also I've read a few statements about stuffing the line. One said it absolutely must be stuffed, the other stated that it wasn't necessary but could help you tune the box.
Thanks everyone for your help!!!
Soooo, that said, how do I determine the size length and volume of the T-Line?
Also I've read a few statements about stuffing the line. One said it absolutely must be stuffed, the other stated that it wasn't necessary but could help you tune the box.
Thanks everyone for your help!!!
You determine the size by using a modeller. Unfortunatly choices have shrunk recently. Or get someone to model it for you.
The terminus of the TL acts as a low pass filter. The design of a line determines how much stuffing is needed to complete that function. Most TLs need stuffing but some people like some designs with only lining, usually ML-Voigts like the Metronome & some ML-TLs (we have found stuffing needed in all the ML-TLs we have built). Less stuffing usually leads to more bass fundemental but also more ripple from the unwanted harmonics.
dave
The terminus of the TL acts as a low pass filter. The design of a line determines how much stuffing is needed to complete that function. Most TLs need stuffing but some people like some designs with only lining, usually ML-Voigts like the Metronome & some ML-TLs (we have found stuffing needed in all the ML-TLs we have built). Less stuffing usually leads to more bass fundemental but also more ripple from the unwanted harmonics.
dave
For a start, you determine what your design goals are. A TL / QW enclosure is not exempt from basic physical reality: unless all you're interested in doing is slapping a few bits of material together and saying 'that'll do', you first need to decide what it is you want to achieve.
You then decide what general enclosure type will provide the optimum set of compromises for your given set of requirements. If that is a TL / QW variation you are then in a position to start making other choices: what sub-type
With those settled, you are then able to move to more specific matters of design: tuning, and the physical dimensions required to achieve this (assuming it is feasible). You can attempt to reinvent the wheel by building things at random & hoping for the best, or you can use proven data to help design it. Martin King's papers & alignment tables will give you suitable dimensions for a line tuned to Fs (not necessarily the best option but in the interests of brevity you have to pick something) for a variety of tapers. Transmission Line Theory There is a simple-to-use spreadsheet there too. Augspurger's tables & articles provide different variations on the theme and work equally well according to their own particular goals. These are for traditional lines rather than MLTLs, ML-horns etc.
Not all TLs / QW boxes are the same. There are a wide variety of different types and objects. A 'pure' TL is an enclosure designed to provide the flattest possible impedance without any other considerations at all, and uses heavy stuffing in order to achieve this. Very few are so extreme (the uses for such enclosures are rather limited) so attempt to use the fundamental line resonance to provide some output while using a lesser amount of damping, along with driver offset etc. to suppress the unwanted harmonic modes of the line that otherwise cause significant ripple in the response. The optimum amount and location vary depending on the design.
Assuming you have a practical basic alignment (tuning frequency & internal volume), line length is a function of both the axial length & any taper present; see King's papers / alignment tables for examples. An expanding line (horn) is physically longer than an untapered pipe for a given tuning; a reverse taper (contracting) pipe is inherently mass-loaded & shorter than an untapered pipe for a given tuning. Each will exhibit harmonic resonances to different degrees and at different frequencies due to the geometry of the pipe. Some of these can be attenuated by offsetting the driver a certain distance along the line; the optmimum varies depending on the line geometry -again, see King's tables for guidelines / examples.
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