Very interesting, Boris. I downloaded MathCad Explorer and MJK's Sample_Problem.mcd to check it out...
However I can't afford the time to pursue this now. I'm interested though how simplified your metod is?
Bjohannesen, I liked that Martin J King for Dummies link in PDF document... added in bookmarks
What TB 4" have you used?
However I can't afford the time to pursue this now. I'm interested though how simplified your metod is?
Bjohannesen, I liked that Martin J King for Dummies link in PDF document... added in bookmarks
What TB 4" have you used?
Vann, the most important point of the transmission line is the length of the line. Quarter wave transmission line means the line length is 1/4 of the wave length, so with some easy maths, you'll end up with 1/4 (330/Fs) as the wave length in meter. The flare rate is not so important in a TL as long as the mouth is smaller than the beginning of the TL. This is just a brief and inaccurate method to guess the length.
That works for untapered lines, but Fo is a function of both length and taper. A reverse-taper line applies a degree of mass-loading on the pipe, how much being dependant on the amount of taper applied, ergo physical length for a given acoustic fundamental resonance can vary dramatically, as demonstrated by Augspurger and King, and many others in non-audio fields. Take a gander at Martin's alignment tables: http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
Line Fo will also depend on whether an untapered pipe or horn (expanding pipe) has any mass-loading applied with a constriction of the terminus cross section, while the pipe will need to be physically large enough to provide suitable gain, especially when damped.
Line Fo will also depend on whether an untapered pipe or horn (expanding pipe) has any mass-loading applied with a constriction of the terminus cross section, while the pipe will need to be physically large enough to provide suitable gain, especially when damped.
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Hi Boris, the genius thing (just pure luck) is that you do not have to change the lengt of the line. The cabinet tuning frequency is 55 Hz, which is lower than Fs of both the 3" and the 4". It works with 3" because the Qes is very high.
And (I am not trying to play "smart") stuffing does not change the tuning of the cabinet, you can not use stuffing to make the driver think the line is longer than it is. Only the shape and physical length of the cabinet determines the tuning frequency. Not the stuffing.
And (I am not trying to play "smart") stuffing does not change the tuning of the cabinet, you can not use stuffing to make the driver think the line is longer than it is. Only the shape and physical length of the cabinet determines the tuning frequency. Not the stuffing.
Hi Scottmose, your comment is very clear !
If you play around with MJK models, you will get a good idea of how shape can change the result. I found that the type of enclosure used in my TABAQ is a very good starting point for any fulle range or sub speaker.
Please take a look at my sub, which is a result of many pleasant hours with MJK models:
http://www.audioxpress.com/magsdirx/ax/addenda/media/johannesen2835.pdf
Hi form
Bjorn Johannesen
If you play around with MJK models, you will get a good idea of how shape can change the result. I found that the type of enclosure used in my TABAQ is a very good starting point for any fulle range or sub speaker.
Please take a look at my sub, which is a result of many pleasant hours with MJK models:
http://www.audioxpress.com/magsdirx/ax/addenda/media/johannesen2835.pdf
Hi form
Bjorn Johannesen
Tnx Bjohannesen, btw the TB W4-930SF has Qes=0.53 and Fs=70Hz... do you think it will do ok in your TABAQ?
Looks to me that you should be OK with that. As a rule be wary about tuning below about 0.707Fs. Dynamic headroom on most small wideband units is bad enough without completely crippling it by pushing them so hard excursion goes through the roof under a constant load with nothing left to handle a dynamic peak on the programme material.
Vann -if you want to investigate how lines work, & you don't have the time to get yourself up to speed on the underlying physics, then I echo Bjorn's suggestion to have a play around in Martin's worksheets, although reading through his alignment table paper first will let you know what to expect.
Vann -if you want to investigate how lines work, & you don't have the time to get yourself up to speed on the underlying physics, then I echo Bjorn's suggestion to have a play around in Martin's worksheets, although reading through his alignment table paper first will let you know what to expect.
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Bjorn, I do not doubt your results as I haven't auditioned them personally, but I suggest stuffing would increase the density of the pipe just like you increase the optical density of a lens, as with higher optical density the wave seems to travel for a longer length, the stuffing seems to make the path longer. If there's little stuffing, you're 100% right as the pipe resonance is due to the length of the pipe and the stuffing merely absorbs some of the energy, but what if the pipe is more densely stuffed? I think PMC played around with that to make their ATL. BTW, by having foldings, you can reduce the midrange output from the mouth of the transmission line. I am not a PhD in physics so that may not be actually correct, just some simplified and inaccurate method for you to begin your project with without messing around with a lot of maths.
Bradbury postulated something similar back in the '70s, & came up with a theory based on modified aerodyamic drag equations that heavy damping would dramatically lower the SoS, and thus increase the apparant line length. Problem is, he was wrong. There is actually a mild reduction in c' when passing through a fibrous tangle due to the vicous damping & non-adiabatic processes, but not to the extent often believed. I suggest you read this: http://www.quarter-wave.com/TLs/Test_Line_Results.pdf I'm afraid your simplified & inaccurate method for begining a project without messing around with a lot of maths could potentially lead someone right up the garden path. Experimentation is good, but knowing the basic principles involved is also good, as it can save both time and money in the long run, which is useful if you don't have much of either to spare.
Different damping materials may require different stuffing densities due to their varying effects of course; Shultz's Alpha TLs are a good example of this. Also, if the line is not deliberately designed as a high-gain device in the first place to offset high stuffing densities, you will supress the fundamental; if your object is a 'pure' critically damped TL, then fair enough (although high stuffing densities may acoustically mass-load the diaphram & thus supress output above the upper midband, so that needs to be kept in mind too), but if your object is to support the LF then you've just shot yourself in the foot.
Different damping materials may require different stuffing densities due to their varying effects of course; Shultz's Alpha TLs are a good example of this. Also, if the line is not deliberately designed as a high-gain device in the first place to offset high stuffing densities, you will supress the fundamental; if your object is a 'pure' critically damped TL, then fair enough (although high stuffing densities may acoustically mass-load the diaphram & thus supress output above the upper midband, so that needs to be kept in mind too), but if your object is to support the LF then you've just shot yourself in the foot.
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Scottmoose, but MJK also suggested that the speed of sound decreases when more stuffing is used, so maybe the apparent length increased but by a very small extend. And also, it depends on the type of stuffing used as the density and stiffness varies. Open cell foams come in different density and hence stiffness and the degree of the effect may be different from wool and may differ from that of glass fiber.
But you are right, if I stuff that much, it's losing the point of having a TL.
Maybe the best way is to mass-load the TL or increase the length...
But you are right, if I stuff that much, it's losing the point of having a TL.
Maybe the best way is to mass-load the TL or increase the length...
Er, is there an echo here? I seem to recall writing
Actually, you don't 'loose the point' by having a TL with reasonably heavy damping per se. Whether you loose the point depends on exactly what it is you're hoping to achieve. Indeed, technically, that's exactly what a TL is: a line stuffed to ~aperiodic levels with the object of providing the flattest possible impedance, gain being neither here nor there. The electrical TL is where the name came from. However, TL has become a catch-all term to refer to resonant & semi-resonant lines as well, and the strict definition is rarely applied. It wasn't even in the first box that was described under the TL moniker.
Whatever, if you want to lower line Fo, then yes, you're better off either physically lengthening it, or acoustically lengthening it by mass loading the pipe with a reverse taper or choked down terminus.
I seem to recall writingand
in my post above...
Actually, you don't 'loose the point' by having a TL with reasonably heavy damping per se. Whether you loose the point depends on exactly what it is you're hoping to achieve. Indeed, technically, that's exactly what a TL is: a line stuffed to ~aperiodic levels with the object of providing the flattest possible impedance, gain being neither here nor there. The electrical TL is where the name came from. However, TL has become a catch-all term to refer to resonant & semi-resonant lines as well, and the strict definition is rarely applied. It wasn't even in the first box that was described under the TL moniker.
Whatever, if you want to lower line Fo, then yes, you're better off either physically lengthening it, or acoustically lengthening it by mass loading the pipe with a reverse taper or choked down terminus.
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Aha, thanks for reminding me that, Bjorn... I feel like a complete jackass.
As Scottmoose had mentioned before, the assumption is not totally wrong, but effect is just too small, so MJK called it negligible. As the length increases, the story will be a bit different, in case you wanna build a straight line subwoofer or what, but that's out of the topic.
As Scottmoose had mentioned before, the assumption is not totally wrong, but effect is just too small, so MJK called it negligible. As the length increases, the story will be a bit different, in case you wanna build a straight line subwoofer or what, but that's out of the topic.
I want to use the W4-930SF as a Midrange driver from 200hz up to some point crossing over to a Vifa XT25SC90-04 ring tweeter above 3khz at some point.
How small can i make the rear chamber for the TB if i am crossing over at 200hz?
I have very limited depth behind the driver and more width then depth.
I know the 6ohm TB and the 4 ohm vifa aren't an ideal match but the high sensitivity of the TB makes it very attractive.
How small can i make the rear chamber for the TB if i am crossing over at 200hz?
I have very limited depth behind the driver and more width then depth.
I know the 6ohm TB and the 4 ohm vifa aren't an ideal match but the high sensitivity of the TB makes it very attractive.
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