kelticwizard, I forgot to ask if it matters when I put stuffing between the driver and the port? Because some people claim that the driver should 'see' the port, and no damping should be placed between them...
thank you for this advice, I'll take it into account when building a TL.
best regards
Erwin
el`Ol said:
thank you for this advice, I'll take it into account when building a TL.
best regards
Erwin
For full reflex action, the stuffing should be mostly along the walls, and the center of the box and the port should be completely unobstructed.
Some designers do lightly stuff the box, and even the port. There are some advantages to this-smoother impedance curve, for instance. But you begin to lose some of the advantages of full reflex action.
Remember that a ported box packed up with stuffing, at some point, will be no different than a closed box packed up with stuffing. But before hitting that extreme, some people find some nice compromises.
My advice wold be to build it so that the center of the box and port are clear and unobstructed, then have some fun experimenting for awhile.
Some designers do lightly stuff the box, and even the port. There are some advantages to this-smoother impedance curve, for instance. But you begin to lose some of the advantages of full reflex action.
Remember that a ported box packed up with stuffing, at some point, will be no different than a closed box packed up with stuffing. But before hitting that extreme, some people find some nice compromises.
My advice wold be to build it so that the center of the box and port are clear and unobstructed, then have some fun experimenting for awhile.
e-side said:
Hi,
reading this thread no-one has pointed out that 50L is a massive
box for a 165mm driver, commercially 10L/15L is much more likely.
If you tried reflexing the driver in a 15L box you'd agree
that for this box size the drivers should be used sealed.
For a 50L box optimum deep bass needs IMO a 250mm driver
with Vas ~ 75L and Qts around 0.4 or something similar.
A single 165mm driver is going to have powerhandling problems
compared to a larger driver optimised for 50L reflex use.
/sreten.Sreten:
You have some good points, but this is not a case where Esides decided to build a 50 L box and decided to choose a good woofer for it. This is a case where he had these speakers and wanted a box that could deliver some decent bass.
The reflex numbers don't work in WinISD or any of the conventional programs. That is because this is not a reflex, nor a Transmission Line, but a Mass Loaded Transmission Line.
That is an enclosure where, ideally, you put a speaker in a box which is too big for a reflex, then make the height equal to a quarter wavelength of a frequency an octave or so above the port tuning frequency. So Esides box is port tuned to 42 Hz, but quarter wave Transmission Line action is enhancing output at 86.5 Hz, which fills in the response nicely.
Just by happenstance, Esides had built a box which was suited to be used as a Mass Loaded Transmission Line-a tall, thin box with a height equal to a quarter wavelength of 86 Hz.
Martin J King has some nice Mass Loaded Transmission Line projects using the Fostex 206 and 207 at his website. they are going into boxes seemingly too large, but people are apparently satisfied with them.
At 7.2 inches, these speakers are just a bit smaller than an 8, and I have seen enclosures of 1.5 cu ft for 8 inchers, so the size is not so far off.
What can Esides do with these if he wants some bass output? If he puts them into a sealed box, he better make it around 50 L or else his Qtc will be very high. In a 50 L box, his F3 will be around 60 Hz-kind of high for a box that size. If he puts it into a smaller sealed box, his Qtc goes up even higher, and so will his F3.
His Qts is higher than I would like, but I knew the enclosure he used-a tall, skinny tower-might prove useful for a Mass Loaded Transmission Line, so I ran the simulations and things turned out surprisingly decent.
His excursion in the box is pretty well taken care of down to 42 Hz, the tuning frequency. At 42 Hz, his cone movement is 20 dB less than his SPL output. At 50 Hz, it is 11 dB better, and at 60 Hz, it is 7 dB better. Lesser excursion benefits extend up past 100 Hz. I include a graph to illustrate. The step response sim looked okay compared to other Mass Loaded Transmission Line projects.
So he is better off excursion wise and SPL output wise using a 50 L Mass Loaded Transmission Line than a 50 L sealed box, or any other enclosure, that I can see.
You have some good points, but this is not a case where Esides decided to build a 50 L box and decided to choose a good woofer for it. This is a case where he had these speakers and wanted a box that could deliver some decent bass.
The reflex numbers don't work in WinISD or any of the conventional programs. That is because this is not a reflex, nor a Transmission Line, but a Mass Loaded Transmission Line.
That is an enclosure where, ideally, you put a speaker in a box which is too big for a reflex, then make the height equal to a quarter wavelength of a frequency an octave or so above the port tuning frequency. So Esides box is port tuned to 42 Hz, but quarter wave Transmission Line action is enhancing output at 86.5 Hz, which fills in the response nicely.
Just by happenstance, Esides had built a box which was suited to be used as a Mass Loaded Transmission Line-a tall, thin box with a height equal to a quarter wavelength of 86 Hz.
Martin J King has some nice Mass Loaded Transmission Line projects using the Fostex 206 and 207 at his website. they are going into boxes seemingly too large, but people are apparently satisfied with them.
At 7.2 inches, these speakers are just a bit smaller than an 8, and I have seen enclosures of 1.5 cu ft for 8 inchers, so the size is not so far off.
What can Esides do with these if he wants some bass output? If he puts them into a sealed box, he better make it around 50 L or else his Qtc will be very high. In a 50 L box, his F3 will be around 60 Hz-kind of high for a box that size. If he puts it into a smaller sealed box, his Qtc goes up even higher, and so will his F3.
His Qts is higher than I would like, but I knew the enclosure he used-a tall, skinny tower-might prove useful for a Mass Loaded Transmission Line, so I ran the simulations and things turned out surprisingly decent.
His excursion in the box is pretty well taken care of down to 42 Hz, the tuning frequency. At 42 Hz, his cone movement is 20 dB less than his SPL output. At 50 Hz, it is 11 dB better, and at 60 Hz, it is 7 dB better. Lesser excursion benefits extend up past 100 Hz. I include a graph to illustrate. The step response sim looked okay compared to other Mass Loaded Transmission Line projects.
So he is better off excursion wise and SPL output wise using a 50 L Mass Loaded Transmission Line than a 50 L sealed box, or any other enclosure, that I can see.
Attachments
kelticwizard said:
Hi KC,
I was just trying to add some insight into the original
question, not trying to denigrate the use of a 50L box.
I lump these sort of alignments into "oversize", that is
not useful commercially - as there are always better
choices, but does extract maximum bass from the driver.
Any enclosure significantly larger than the Vas of the driver
I regard as "oversize" and for this case its certainly true.
/sreten.kelticwizard said:
That's very interesting and useful! An enclosure with different dimensions (decreased height) apparently won't sound the same, and this explains that it's not only the port which causes the extra bass.
I should take a closer look to Mass Loaded Transmission Lines...
BTW Should drivers suitable for transmission lines have a low EBP? And are these requirements the same for a mass loaded TL?
Erwin
Erwin:
Truthfully, I have not yet built a straight Transmission Line, nor a Mass Loaded TL either. I have simulated them only.
I have built sealed and ported boxes. I just got used to Martin J King's simulation software recently for Transmission Lines. However, those who have built Transmission Lines according to his software have indeed measured, and it checks out.
My impression of straight Transmission Lines is that the drivers should be somewhat similar to bass reflex drivers, but this is just an impression.
So I would be glad to simulate any driver you have in a Transmission Line, but would not go so far as to say "This is the best type of driver to use" without at least having built one of the things.
I believe that Martin J. King's site, www.quarter-wave.com can give you some info on driver selection, etc.
Truthfully, I have not yet built a straight Transmission Line, nor a Mass Loaded TL either. I have simulated them only.
I have built sealed and ported boxes. I just got used to Martin J King's simulation software recently for Transmission Lines. However, those who have built Transmission Lines according to his software have indeed measured, and it checks out.
My impression of straight Transmission Lines is that the drivers should be somewhat similar to bass reflex drivers, but this is just an impression.
So I would be glad to simulate any driver you have in a Transmission Line, but would not go so far as to say "This is the best type of driver to use" without at least having built one of the things.
I believe that Martin J. King's site, www.quarter-wave.com can give you some info on driver selection, etc.
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