I know there's a few guys on the forum with transmission line experience, I know they can be a bitch to build correctly, but also know they can sound amazing when implemented correctly.
Can people comment on the suitability of a vifa M25WP for transmission line loading, and what length/tuning I would need to go for?
I'm currently guessing I should tune to the free air resonant frequency (28Hz) which would mean a TL length of 2.4m?
Can people comment on the suitability of a vifa M25WP for transmission line loading, and what length/tuning I would need to go for?
I'm currently guessing I should tune to the free air resonant frequency (28Hz) which would mean a TL length of 2.4m?
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Use this rule-of-thumb and it won't be optimum and more often that not it will be way off as is the case with this driver, which is ill suited for an Fs tuning since it has such a low Qts unless some form of EQ is used to artificially raise it and accounted for in the design.
Correctly calculating this without lots of higher math combined with a good understanding of TL design theory use to be a tedious trial and error endeavor, but thanks to MJK, we now have his Classic TL alignment Tables plus at least one spreadsheet to auto calculate it without working through the doc's math, selection tables, which for many is pretty confusing.
Loads of knowledge available on his site for the DIYer: Quarter Wavelength Loudspeaker Design
Transmission Line Theory
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
http://www.quarter-wave.com/TLs/Alignment_Tables_Calculator_3_3_09.xls
GM
Correctly calculating this without lots of higher math combined with a good understanding of TL design theory use to be a tedious trial and error endeavor, but thanks to MJK, we now have his Classic TL alignment Tables plus at least one spreadsheet to auto calculate it without working through the doc's math, selection tables, which for many is pretty confusing.
Loads of knowledge available on his site for the DIYer: Quarter Wavelength Loudspeaker Design
Transmission Line Theory
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
http://www.quarter-wave.com/TLs/Alignment_Tables_Calculator_3_3_09.xls
GM
Qts is not the only parameter of interest when picking the box type to be used.But Qts is an important one so to give some rule of thumb (that works most of the time but may have some few exeptions)
The classical Qts for bass reflex drivers are 0.35 so drivers in the 0.3 to 0.4 work well with classical bass reflex tuning. They also work well in pipe resonanators such as TLS and Voigt pipes. With higher Q than 0.4 bass refex boxes need to be larger fraction of Vas so exept for drivers with small Vas the drivers in the 0.4 to 0.6 range tends to be used in closed boxes.
With Q above 0.6 the drivers either is used in a box with a bass peak (there are ways to tame this) or in open baffles.
Well below a Q of 0.3 say 0.15 then the drivers are used as horn drivers or midbass drivers well above the Fr.
The Vifa drivers Qts of 0.29 will be nudged slighty higher by the serial resistance of the coil(s) of the crossover.
Below is the response of a low Q driver in a TLS. black is pipe output of a pipe with no damping material. Red is the driver at 35 Hz there is driver response dip, minimal output and pipe peak (black). A bass reflex has a similar thing with driver dip and port peak output. The trick is trying to keep the 35 Hz peak that is wanted and at the same time reduce the harmonics at 150, 270, 350 Hz by smart use of folds and placement of damping material.
The classical Qts for bass reflex drivers are 0.35 so drivers in the 0.3 to 0.4 work well with classical bass reflex tuning. They also work well in pipe resonanators such as TLS and Voigt pipes. With higher Q than 0.4 bass refex boxes need to be larger fraction of Vas so exept for drivers with small Vas the drivers in the 0.4 to 0.6 range tends to be used in closed boxes.
With Q above 0.6 the drivers either is used in a box with a bass peak (there are ways to tame this) or in open baffles.
Well below a Q of 0.3 say 0.15 then the drivers are used as horn drivers or midbass drivers well above the Fr.
The Vifa drivers Qts of 0.29 will be nudged slighty higher by the serial resistance of the coil(s) of the crossover.
Below is the response of a low Q driver in a TLS. black is pipe output of a pipe with no damping material. Red is the driver at 35 Hz there is driver response dip, minimal output and pipe peak (black). A bass reflex has a similar thing with driver dip and port peak output. The trick is trying to keep the 35 Hz peak that is wanted and at the same time reduce the harmonics at 150, 270, 350 Hz by smart use of folds and placement of damping material.
Guys,
Thanks for the responses, they've been very helpful. I need to put my hands up and admit that I'm haven't got my head fully around how speaker allignment tables/vas etc interact with each other from a design perspective as I haven't had to do it yet.
I'm keen on the theory of transmission lines and would like to implement one, but obviously I'm nervous about how it can go wrong, reading both that 'transmission lines are hard to get right' and 'Qts Below .3 can be hard to control' doesn't fill me with confidence.
On the bonus side, it would be very easy to convert the cabinet into a transmission line similar to a PMC IB1 (2.4m line, same as a quarter wave of this speakers Frs, which I like)...
I could do this by hacking up and re-building the existing cabinet, which means I'd save myself a lot of woodwork. Would it be incredibly bad practice to attempt to do this and then 'manually tune' the TL until it sounds right (i.e. by ear) => am I setting myself up for a lot of frustration and a ruined speaker?
The current speaker is a very large reflex design, sounds OK but a little bit boomy and loose. THat said there's no stuffing in there at the moment, so sure it could be improved, but I do like the idea of an IB1 clone, i think they're good looking speakers...
Thanks for the responses, they've been very helpful. I need to put my hands up and admit that I'm haven't got my head fully around how speaker allignment tables/vas etc interact with each other from a design perspective as I haven't had to do it yet.
I'm keen on the theory of transmission lines and would like to implement one, but obviously I'm nervous about how it can go wrong, reading both that 'transmission lines are hard to get right' and 'Qts Below .3 can be hard to control' doesn't fill me with confidence.
On the bonus side, it would be very easy to convert the cabinet into a transmission line similar to a PMC IB1 (2.4m line, same as a quarter wave of this speakers Frs, which I like)...
I could do this by hacking up and re-building the existing cabinet, which means I'd save myself a lot of woodwork. Would it be incredibly bad practice to attempt to do this and then 'manually tune' the TL until it sounds right (i.e. by ear) => am I setting myself up for a lot of frustration and a ruined speaker?
The current speaker is a very large reflex design, sounds OK but a little bit boomy and loose. THat said there's no stuffing in there at the moment, so sure it could be improved, but I do like the idea of an IB1 clone, i think they're good looking speakers...
Drivers with a Qts < 0.3 aren't difficult to control as far as LF alignment is concerned: they're inherently well-damped, so very tightly controlled might be a better descriptor.
Assuming no response shaping has been done to the driver & it follows its bald mathematical T/S curve as far as IB LF response goes, then it's the mass-corner that counts rather than the Q alone. A low Q unit in any form of resonant enclosure, including most quarter-waves, is fine, providing Fs is low -basically, the lower the Q, the lower Fs ideally needs to be if you want to get some useful LF output. As GM notes, using 1/4 wave at Fs (assuming that's what you actually do since the resonant frequency of a pipe is a function of both its axial length and taper) with this unit will result in quite a damped LF output (i.e. not very much).
Assuming no response shaping has been done to the driver & it follows its bald mathematical T/S curve as far as IB LF response goes, then it's the mass-corner that counts rather than the Q alone. A low Q unit in any form of resonant enclosure, including most quarter-waves, is fine, providing Fs is low -basically, the lower the Q, the lower Fs ideally needs to be if you want to get some useful LF output. As GM notes, using 1/4 wave at Fs (assuming that's what you actually do since the resonant frequency of a pipe is a function of both its axial length and taper) with this unit will result in quite a damped LF output (i.e. not very much).
Scott,
thanks again for the informative reply,
working from what you've said, does that mean there'll be 'little' bass at all, or just less? The speakers are if anything bass heavy at the moment, I wouldn't mind loosing a little if it tightens things up - that's the goal, and the attraction of the TL for me, in saying that, I do like that these speakers 'go low' - it's amazing how much the last few Hz seem to convey in actual music, a lot more than I realised, and for some reason having bass from these two 10" woofer floor standers is way more than from my current 2.1 set up with an active 8" sub... but that shouldn't surprise me I guess!
thanks again for the informative reply,
working from what you've said, does that mean there'll be 'little' bass at all, or just less? The speakers are if anything bass heavy at the moment, I wouldn't mind loosing a little if it tightens things up - that's the goal, and the attraction of the TL for me, in saying that, I do like that these speakers 'go low' - it's amazing how much the last few Hz seem to convey in actual music, a lot more than I realised, and for some reason having bass from these two 10" woofer floor standers is way more than from my current 2.1 set up with an active 8" sub... but that shouldn't surprise me I guess!
It means it will be highly (probably over) damped, like a very low Q sealed box albeit with an easier impedance load. In other words, they'll be tuned low, but they probably won't have a great deal of output. A decent amount of LF damping is generally advisable for practical in-room conditions, and well designed TLs are good at this, but there's a difference between well damped and excessively so.
You didn't say what the volume & tuning of your current reflex boxes are, but it may be a case of them being misaligned with a peak at Fb or excessive room-gain from an under-damped or flat alignment. If you let us know, we can check that easily enough.
Well, with about 700cm^2 of cone area from a pair of 10in drivers as against about 29% of that from a single 8in cone, you're certainly going to be moving more air. Again though, as far as the bottom end is concerned, room modes &c. aside, this can also be alignment dependent -if you've got some peaking in the 10in units, this is also going to give more -potentially excessively so.
You didn't say what the volume & tuning of your current reflex boxes are, but it may be a case of them being misaligned with a peak at Fb or excessive room-gain from an under-damped or flat alignment. If you let us know, we can check that easily enough.
Well, with about 700cm^2 of cone area from a pair of 10in drivers as against about 29% of that from a single 8in cone, you're certainly going to be moving more air. Again though, as far as the bottom end is concerned, room modes &c. aside, this can also be alignment dependent -if you've got some peaking in the 10in units, this is also going to give more -potentially excessively so.
TL's seem interesting, i don't intend to kidnap the thread but I hope you don't mind if I sneak a question in.
Would a TD15M be a fair candidate for a TL? (Xo 1050'ish Hz) I'm snowed in and can't run the models myself at the moment. Wrong side of the Atlantic.
Looks like an excellent candidate for TL
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Certainly looks interesting, hard to read it properly at the moment as my wife is on the computer, using my dumb-phone. Is there a modelled combined response there? (Driver+line)
Am I right in reading the box volume as 62litres? That would be impressive but folding thebline may be tricky into that size.... the current box is about 88 litres, the design I was considering was closer to 100with a 2.4m line... but looks like that'd be way too long?
Am I right in reading the box volume as 62litres? That would be impressive but folding thebline may be tricky into that size.... the current box is about 88 litres, the design I was considering was closer to 100with a 2.4m line... but looks like that'd be way too long?
Hi,
The driver models to a classic alignment of 50L tuned to 40Hz.
I like the look of 50L tuned to 33Hz more, also 60L tuned to 30Hz.
The bass drivers have good excursion so would need decent sized ports.
If the current boxes are 88L they need tuning low, 28Hz
IMO, and will exhibit a nicely tapered roll-off that should
sound very tight, very deep and not at all excessive.
Tuned too high will tend towards excessive "one note bass".
Port should be 4" dia and 10.5" long.
You should get an excellent result from the correctly
tuned boxes with this particular driver in your boxes.
(simple WinISD modelling, cross check in another sim like Unibox.)
Read MJK's stuff regarding a TL alignment. Its tricky stuff to get
right, nevermind fold into an existing box shape and work with
a given volume. What are the box dimensions ?
rgds, sreten.
The driver models to a classic alignment of 50L tuned to 40Hz.
I like the look of 50L tuned to 33Hz more, also 60L tuned to 30Hz.
The bass drivers have good excursion so would need decent sized ports.
If the current boxes are 88L they need tuning low, 28Hz
IMO, and will exhibit a nicely tapered roll-off that should
sound very tight, very deep and not at all excessive.
Tuned too high will tend towards excessive "one note bass".
Port should be 4" dia and 10.5" long.
You should get an excellent result from the correctly
tuned boxes with this particular driver in your boxes.
(simple WinISD modelling, cross check in another sim like Unibox.)
Read MJK's stuff regarding a TL alignment. Its tricky stuff to get
right, nevermind fold into an existing box shape and work with
a given volume. What are the box dimensions ?
rgds, sreten.
Oh man, wrote a long reply but it didn't post!!! Aghh!!!
Short version:
The current speakers measure 320 (w) 380 (D) 940 (H)
Port = 185 (L) 75(dia)
All measurements in mm.
The cabinet could be converted to a PMC IB1 clone pretty easily (almost the exact same dimensions as the PMC - slightly wider and more depth, 470mm depth as opposed to PMC's 465, The TL would have been 2.4m, with a constant cross section of about 284*75mm, giving a volume of 51.12L, not sure how that would effect the modelling, especially as their would be padding on the walls of the TL that could effectively reduce the CSA... It's certainly looking very tempting now.
sreten, as you've done your winISD model could you check it against the existing box? I'll see if I can dig out some sims myself, but as I said I don't sim with the most confidence when it comes to box design!
Short version:
The current speakers measure 320 (w) 380 (D) 940 (H)
Port = 185 (L) 75(dia)
All measurements in mm.
The cabinet could be converted to a PMC IB1 clone pretty easily (almost the exact same dimensions as the PMC - slightly wider and more depth, 470mm depth as opposed to PMC's 465, The TL would have been 2.4m, with a constant cross section of about 284*75mm, giving a volume of 51.12L, not sure how that would effect the modelling, especially as their would be padding on the walls of the TL that could effectively reduce the CSA... It's certainly looking very tempting now.
sreten, as you've done your winISD model could you check it against the existing box? I'll see if I can dig out some sims myself, but as I said I don't sim with the most confidence when it comes to box design!
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