Here is a picture collaged together from Martin's ANSYS simulation of a BR vrs his 1st ML-TQWT which clearly shows the different characteristics caused by a stretching the box... both have the same driver, volume & port -- the only difference is shape. The image is still not finished -- it got back-burnered when my emplyment situation deteriorated shortly after Martin 1st published this -- it is part of an unwritten commentary on TL design for my site. (i did get an Intro finely written & up.
dave
dave
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You just have to make an initial assumption and try something. Start with the driver near the closed end and the port near the bottom. Vary the diameter and length of the port to get the tuning you want from the enclosure. Keep adjusting one variable at a time until you get a response that you like. Then start moving the driver and port up and down in the enclosure to see if things improve. After a while you get a feel for what works and it goes a lot quicker. There is no magic answer or hard rules to guide you, you just have to spend time optimizing the desing by hand. Bob's site has some excellent studies of the impact of some of the parameters on a quarter wave enclosure's response.
I have thought about this but have not acted. I have too many other things to work on at the moment.
That's what GM said about it:
http://f18.parsimony.net/forum31999/messages/65544.htm
And it seems to work good. At least on sims
But that's for the box volume and section, what about the length? From what I've seen, ML-TLs are much shorter than a classical TL. (for 35Hz, a straigth TL would need ~94in, a ML-TL needs about the half)
Is there a rule of thumb for that? 1/8WL?
http://f18.parsimony.net/forum31999/messages/65544.htm
And it seems to work good. At least on sims
But that's for the box volume and section, what about the length? From what I've seen, ML-TLs are much shorter than a classical TL. (for 35Hz, a straigth TL would need ~94in, a ML-TL needs about the half)
Is there a rule of thumb for that? 1/8WL?
The actual "correct" positions of the driver and port are pretty much cut-and-try. Fortunately you can do this in simulation instead of wood. If you are designing a TQWT, then use a driver position ratio of 0.5, if a straight MLTL, then use 0.2. This will get you into the the ballpark. Now start moving the driver until the discontinuity in the terminus output goes away. Even 1cm is important.
As far as the port position, look at the group of harmonics starting around 500Hz. Position the port so that the middle spike in this group is minimum. Start at 10cm.
Bob
No rule of thumb that I know of. The more mass you add to the end of the TL, the shorter it gets for the required tuning frequency. You know it can't be any longer then the length from the alignment tables, so start with the same alignment table area and 2/3 of the length and a port of some convenient diameter. Start changing the length of the port, the diameter of the port, or the length of the enclosure and work towards the tuning frequency you want to achieve. Watch the system SPL response and see how different changes move you towards a desired response or away from a desired response.
Don't think too much, just try it and practice. You might find several different combinations that yield good responses and then you need to decide which one to build. If you think to much you end up with "analysis paralysis". I know all about "analysis paralysis".
I think I understood my problem with the ML-TL and it's design/simulation.
Bob precised that a BR works as a Helmholtz resonator, and the ML-TL as a quarter wave resonator. And that's the point: I don't know how to differientiate one from the other.
How can I see, on the mathcad graphs, if the enclosure is acting as the first one or as the second one?
Bob precised that a BR works as a Helmholtz resonator, and the ML-TL as a quarter wave resonator. And that's the point: I don't know how to differientiate one from the other.
How can I see, on the mathcad graphs, if the enclosure is acting as the first one or as the second one?
If, by the quarter wave harmonic series, you mean the dips at n*Fp, yes I see what it looks like.
The BR is ruler flat, no or minimal peaking at Fp
Do you mean that a ML-TL is somewhere between the 2? Acting a little like a BR and a little like a TL?
Except from the dips at n*Fp (that can be damped with more stuffing), I don't see much difference on the other graphs.
The BR is ruler flat, no or minimal peaking at Fp
Do you mean that a ML-TL is somewhere between the 2? Acting a little like a BR and a little like a TL?
Except from the dips at n*Fp (that can be damped with more stuffing), I don't see much difference on the other graphs.
No, No! Being a quarter-wave pipe is like being a little bit pregnant. It either is or it isn't. The quarter-wave harmonics may start out weak, but they are either there or they are not.
Personally, I've never investigated the transition point. All of my designs are either floor standing MLTL's or stand mounted BR's.
Bob
Personally, I've never investigated the transition point. All of my designs are either floor standing MLTL's or stand mounted BR's.
Bob
Bob Brines said:
I am confused over this ML TL/BR thing, as I am currently building a pair of speakers with the 7W4411 woofer by Focal, and Orca (parent company of Focal) recommends a 1.728 ft^3 ported box with a 3"d x 8.5" port. If I make a ML TL of the same volume, 8.5" x 10" x 35", it works great with a 3"d x 4" port, and medium stuffing in the top half.
What do I call this enclosure, does it go from a BR to a ML TL by just adding stuffing, and decreasing the port length?
How do I find if my speaker cabinet is pregnant?
--
Brian
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