Hi all
I'm trying to design a 3-way speaker based on mid-range and tweeter I already have (used in a 2 way speaker some years ago).
I decided to add SB26SFCL38-8 to these 2 drivers in bass reflex configuration. The volume for the woofer will be around 88L with a resonant frequency is 27Hz.
I want create a cabinet with hard plywood 19mm with external size WxDxH 38x55x63 (the height is a constraint).
The cabinet will have a "small room" for the mid and tweeter of about 8L.
The port tube will have diameter of 9,2 cm and length of 22,5 cm
I have 2 main doubts now (may be more 🙂)
1. Where put the port tube. I have not enough space below the woofer do I would like to place it upper. Something like this...
I also did a try with 2 port of 6,6 cm and 24,5 cm length below the woofer.
What do you think is the best solution?
2. How many braces, where to place them and how shape them. I'm not so expert about this aspect.
I'm trying to design a 3-way speaker based on mid-range and tweeter I already have (used in a 2 way speaker some years ago).
I decided to add SB26SFCL38-8 to these 2 drivers in bass reflex configuration. The volume for the woofer will be around 88L with a resonant frequency is 27Hz.
I want create a cabinet with hard plywood 19mm with external size WxDxH 38x55x63 (the height is a constraint).
The cabinet will have a "small room" for the mid and tweeter of about 8L.
The port tube will have diameter of 9,2 cm and length of 22,5 cm
I have 2 main doubts now (may be more 🙂)
1. Where put the port tube. I have not enough space below the woofer do I would like to place it upper. Something like this...
I also did a try with 2 port of 6,6 cm and 24,5 cm length below the woofer.
What do you think is the best solution?
2. How many braces, where to place them and how shape them. I'm not so expert about this aspect.
As I mentioned in your other thread placing the port at half length of the longest enclosure dimension is good.
Two ports and placing them near the bottom (pressure peak) will lead to a strong resonance output and increased chuffing.
Have a look here regarding driver and port placement!
I can tell you with absolute certainty that placing the port close to the tweeter in the horizontal plane will negatively effect tweeter FR. The diffraction will be significant at frequencies well in the tweeter's bandwidth. If you're stuck with such a port location, you'll want to treat the surrounding tweeter surface area with foam at least 3/8 inch thick. You'll lose a little lower midrange energy, but the HF linearity gain will be worth it.
I'm confused about the use of "horizontal plane." The OP has shown front mounted ports and I can understand your comment if the port is next to the tweeter. But are you saying that it's also bad to have a rear mounted port directly behind a tweeter on the horizontal plane?
I'm minutes away from putting a port behind a tweeter again.
mmm
interesting!
So it is not a good idea to have it there? Should I prefer the 2 port below the woofer?
Is there a reasonable distance that can avoid the interference of the port with the tweeter?
interesting!
So it is not a good idea to have it there? Should I prefer the 2 port below the woofer?
Is there a reasonable distance that can avoid the interference of the port with the tweeter?
I think it's far enough away from the tweeter. If you placed it much closer, then you would have a problem. It may have some effect on the mid though.
Keep in mind, you can have an elbow in the port. So it might be at the bottom, but the entrance to the port could still be mid box.
Sorry, but now I'm confused...
I understood that positioning the tube in the middle of the baffle can create interference on the tweeter due to the diffraction on the rear of the baffle.
My issue with positioning is not related to internal space but to space on the baffle. So I don't understand how the elbow can help me.
You can have the interal port end at the middle of the enclosure (to cancel enclosure length mode) and the exterior end far from the tweeter to avoid reflections.
I was looking to PVC tubes for hydraulic but they have diameter of 63mm (too small) or 80mm (too big)
What you are suggesting, I guess, are tube in PP (polipropilen) that, as far as i understood (I'm not expert) are less permormant in this use case.
Am I right?
What exactly is meant by "less permormant"?
We call the pipes "HT-Rohr", HT stands for "high temperature". They are quite stable, even pipes with a rather small diameter (example: DN 32 = 32 mm) have a wall thickness of 1.8 mm, larger diameters approach 3 mm wall thickness. And yes: they are made of polypropylene.
I have always built rectangular ports myself, so I have not yet used HT pipes. One disadvantage I have heard of is that special glue is needed to glue PP in place, possibly also a primer applied beforehand. Press-fitting would also be an option.
We call the pipes "HT-Rohr", HT stands for "high temperature". They are quite stable, even pipes with a rather small diameter (example: DN 32 = 32 mm) have a wall thickness of 1.8 mm, larger diameters approach 3 mm wall thickness. And yes: they are made of polypropylene.
I have always built rectangular ports myself, so I have not yet used HT pipes. One disadvantage I have heard of is that special glue is needed to glue PP in place, possibly also a primer applied beforehand. Press-fitting would also be an option.
Ok, thanks. This is important info for me. It means that I can use them...
I will try to arrange a sketch and then I will back here to have feedback
Cool: stuff like this could even be used to realise an internal tube resonator to combat longitudinal resonances in the BR port:
Theoretically, the effective length of the resonator should be 50 % of the effective port length, but in practice you will probably have to feel your way round. The resonator has to be filled very loosely with damping material.
Theoretically, the effective length of the resonator should be 50 % of the effective port length, but in practice you will probably have to feel your way round. The resonator has to be filled very loosely with damping material.
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even if I do not have precise size of the tube and the elbow, I did a sketch of one port (I need 2)
my first impression is that I'm very close to the woofer and I can have space issue.
In addition the second tube should be exactly below the mid room, so probably I will need a different angle for the elbow or I need to change the position/shape of the mid room.
It looks not optimal solution to me... I need to study a bit more.
In the meanwhile, I was thinking to print the tube with 3d printer in ABS. In this way I can have more control on the shape and on the size . As far as I understood it is possible but it is not best practice due to the non-smooth surface.
Any comment on this?
my first impression is that I'm very close to the woofer and I can have space issue.
In addition the second tube should be exactly below the mid room, so probably I will need a different angle for the elbow or I need to change the position/shape of the mid room.
It looks not optimal solution to me... I need to study a bit more.
In the meanwhile, I was thinking to print the tube with 3d printer in ABS. In this way I can have more control on the shape and on the size . As far as I understood it is possible but it is not best practice due to the non-smooth surface.
Any comment on this?
Printing the port opens up all sorts of new possibilities!
I would still consider mounting the port at the side or back of the speaker for easier/optimum placement.
Also, the port you show in the last images seems quite small (diameter).
If I may I would also suggest you try my port geometry optimizer - let me know if you need assistance.
Also have a look at some parametric port models in the same thread, posts 624, 627, 646!
How I make 3d printed ports and smoothen the surface.
Some people just use spray filler to smoothen the surface (see augerpro's post just after the one linked above!).
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