Offset drivers have become the norm in TL, since 20 years. I am intrigued by the OP's design and hope he can get it to work.
That is true. But it represents a further juggling with resonances. Tricky to accomplish successfully and possibly inappropriate for sound quality where diminishing resonances is the goal.
Ultimately, better to aim for a labyrinth rather than a BR.
B.
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Uhm, yes. But that's not exactly what you've built. See, in the simulation, the way of the sound is the length of the line + the length on the outside, which is the same. That means, the travel distance in the simulation is 182 + 182, your tml is internally from the driver to the exit 182, but from the exit back to the driver it's just ~145cm because it's folded 90° which makes the way back to the driver shorter. That means, the (wanted) cancelation which should have flattened the peak at ~43Hz now happens a few Hz further up, where it's not wanted.
The downfire mount of the driver isn't ideal. The driver got a high Mms of 146g, that means, the resting position isn't where it should be, it's pulled down and the driver got a higher stiffness outwards than inwards, the magnet field is also off and it will leave the linear excursion outwards much earlier than inwards, which results in high non-harmonic distortion. The ear isn't very sensitive to distortion in the bass but it's still wasted performance. Since you can't flip the driver position every half year (because of the construction of the enclosure), over time the driver will sag more and it gets worse.
Of course it can and standing waves [eigenmodes] are the proper terms, but this appears to be a phase issue where the diagonal acoustic path due to the terminus being forward of the driver is a notch rather than damping a peak lower down, so wondering if just tilting the speaker backwards will solve the problem at least at the listening position.
GM
Today I measured everything again, I managed to get the best results when the port was on the ground or the box was on the side
it is also embarrassing because as you can see there are no more problems at 55 that this thread was all about, there must have been some factor when I took the outside measurement the last time that affected this
I also took an impedance measurement that perfectly matches the sim
but I am ditching this design because the plot is still off, the port has to be on the ground, also probably I should have taken into consideration what ICG said about the weight of the cone and in my room the freq plot becomes completely horrible
With great respect , I thank you all for helping me demystify the situation and help me make a decision and I am sorry for being a douche and not taking several more measurements before making a thread but at least we could exchange ideas and maybe erase some illusions.
it is also embarrassing because as you can see there are no more problems at 55 that this thread was all about, there must have been some factor when I took the outside measurement the last time that affected this
I also took an impedance measurement that perfectly matches the sim
but I am ditching this design because the plot is still off, the port has to be on the ground, also probably I should have taken into consideration what ICG said about the weight of the cone and in my room the freq plot becomes completely horrible
With great respect , I thank you all for helping me demystify the situation and help me make a decision and I am sorry for being a douche and not taking several more measurements before making a thread but at least we could exchange ideas and maybe erase some illusions.
This is my idea of a useful thread...and thanks for the sim. I have a Lab 12 driver needing an enclosure.
Well, it takes a dive at ..well.. between 31 and 63Hz, which is.. 55Hz? No matter how you turn it, it isn't anything like the simulation. Either the simulation is founded on wrong data or your enclosure does not match the simulation.
The room response will likely be much better if you'd chose a slow slope from ~70Hz on (just a presumption). Folded TMLs often divert from the simulation because of internal reflections and shifted air pressure/velocity points because of that.
Thank you for following my arguments. The downfire got a lot more of different disadvantages, the close floor poses an air chamber and the contained air adds to the moving mass, thus increasing the Qt and influencing the fs, which is also why your simulation is probably off. Downfire is quite complicated and got a lot of disadvantages as heavy room dependency and changing parameters (because of the compilance, floor absorption and flexibility). It can be done, tailored to the room/circumstances but without driver flipping it does not lead to a satisfactory result, unfortunately.
I like to help. The problem is, not every solution or simulation leads to the desired result. The room is a key element to the sound in the bass and is vastly underrated by most of hifi listeners. You have to take compromises because of your room and your favorite speaker principle may not work great in your situation. BR (with its vast of possible varieties) or sealed enclosures may serve you better. TML ist still an option but probably with a lot different parameters. Try to calculate the roomgain first and then decide what's best for you.
Thanks 🙂
I chose this enclosure because it offered a few more db and a little smaller enclosure than a BR design. I am happy to contribute
Thanks, ICG, for me as a new speaker builder, every bit of info is gold
Thank you for giving me that credit - but the actual physics (i.e. room dimensions etc.) weight a lot more than just my opinion. It would help a lot if you'd post the dimensions of your listening room or a measurement of it. My assumptions my apply but they are probably off. Without actual facts it's still just guessing.
I love to help, if I can, I will. I cannot precict any outcome and neither do I (or others) got a universal answer to the problems but I try to suggest solutions to your (or other users) problems. Some problems might not be solved correctly but that is mostly because of unknown factors (room, other speakers, amps and eqipment etc) but that does not mean the ppl posting don't know anything about PA, it just means they don't know enough about your use of the PA.
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