Hi,
A very nice and helpful member of another audio forum has designed this for me:
It's a sub for home theater use that uses a 70-odd liter ported box (after displacement of driver and brace).
It uses a Infinity 1260W driver (which I haven't bought yet) and I have a BASH 300s amp on the way.
https://s31.postimg.org/bpe769oyz/1260w_sub.jpg
I'd appreciate your opinions on the design (performance wise, nevermind the colors. 🙂).
Thanks.
A very nice and helpful member of another audio forum has designed this for me:
It's a sub for home theater use that uses a 70-odd liter ported box (after displacement of driver and brace).
It uses a Infinity 1260W driver (which I haven't bought yet) and I have a BASH 300s amp on the way.
https://s31.postimg.org/bpe769oyz/1260w_sub.jpg
I'd appreciate your opinions on the design (performance wise, nevermind the colors. 🙂).
Thanks.
Hi,
I'm not a fan of slot ports with 90 degree bends.
It should not be necessary. If you use one run
a couple of spars front to back to reinforce it.
What frequency is it tuned to ?
I reckon it should be 20Hz.
rgds, sreten.
I'm not a fan of slot ports with 90 degree bends.
It should not be necessary. If you use one run
a couple of spars front to back to reinforce it.
What frequency is it tuned to ?
I reckon it should be 20Hz.
rgds, sreten.
Unless it is tuned really low you are going to have too much bass. I'd just put the woofer into 70 litres sealed.
dave
dave
Hi,
70L sealed doesn't look much better than 40L sealed and well stuffed.
Still its much better than tuning it too high, it needs very low tuning.
rgds, sreten.
70L sealed doesn't look much better than 40L sealed and well stuffed.
Still its much better than tuning it too high, it needs very low tuning.
rgds, sreten.
I have one in an offset driver tapped pipe designed by TB46 - have not felt well enough to put it to use much yet it intend to use to augment a couple of little speakers - there is no fill in the pipe - just some carpet felt. I think it might work in some bandpass boxes.
Triticum Audio has a more conventional offset t-line for a similar woofer (JBL gto1214) which may work well with a 1260W - there may be a plan for it within diyaudio (?) AH - check this thread, TheJessMan's comments and post 270 within the thread for the plans - there may be a hornresp model too
here's the plan and hornresp sim with a Lab12 - Jesse used the JBL which I think is similar to a 1260w http://www.diyaudio.com/forums/atta...tl-design-bj-tb46-od-t-tl-design-mod-3-sn.jpg
my tall pipe with 1260W
http://www.diyaudio.com/forums/subw...-transmission-line-od-ml-tl-design-bj-31.html
a round port would probably play a bit louder without chuffing but this will work for the levels I like
Triticum Audio has a more conventional offset t-line for a similar woofer (JBL gto1214) which may work well with a 1260W - there may be a plan for it within diyaudio (?) AH - check this thread, TheJessMan's comments and post 270 within the thread for the plans - there may be a hornresp model too
here's the plan and hornresp sim with a Lab12 - Jesse used the JBL which I think is similar to a 1260w http://www.diyaudio.com/forums/atta...tl-design-bj-tb46-od-t-tl-design-mod-3-sn.jpg
my tall pipe with 1260W
http://www.diyaudio.com/forums/subw...-transmission-line-od-ml-tl-design-bj-31.html
An externally hosted image should be here but it was not working when we last tested it.
a round port would probably play a bit louder without chuffing but this will work for the levels I like
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You can use a bend in a port, but it works better if you make it gradual. Otherwise it will chuff a high volume.
Not sure what making it gradual would look like?
This is how it was designed the first time:
Is this a better way to build the port?
If the rectangular opening on rear of enclosure is for plate amp, I'd recommend a sealed compartment for it. Even better would be to get the amp out of the sub box altogether, but that's not always convenient.
I want the plate amp on the back of the sub for convenience and practicality.
Did you mean I should make a compartment inside the enclosure for the amp only? An enclosure within an enclosure?
I'd prefer we get back to talk about that tuning frequency, is 23.5 not low enough?
Hi YonathanZ,
I made a quick Hornresp simulation using your data:
Infinity 1260W / Port:W34.4cm x H2.5cm x L58cm (86cm^2) / V_net=71L / BR (bass reflex).
I'm attaching the Hornresp Export file, SPL (both vented and closed [set Ap to .01 for closed]) and port velocity graph.
At Xmax the port velocity looks too high. (Because of the long duct w/ a 90° corner it might just choke itself down to act more like a closed box at high volume levels, which may be a good thing.) A recommended maximum is in the 10 - 15 m/sec range.
AT normal listening level this may just not matter.
Regards,
I made a quick Hornresp simulation using your data:
Infinity 1260W / Port:W34.4cm x H2.5cm x L58cm (86cm^2) / V_net=71L / BR (bass reflex).
I'm attaching the Hornresp Export file, SPL (both vented and closed [set Ap to .01 for closed]) and port velocity graph.
At Xmax the port velocity looks too high. (Because of the long duct w/ a 90° corner it might just choke itself down to act more like a closed box at high volume levels, which may be a good thing.) A recommended maximum is in the 10 - 15 m/sec range.
AT normal listening level this may just not matter.
Regards,
Attachments
What do you mean by "act more like a closed box"? What would the difference be between a "ported box sound" and a closed box one?
Hi YonathanZ,
Post #12: "What do you mean by "act more like a closed box"? What would the difference be between a "ported box sound" and a closed box one?"
That's what I get for trying to be descriptive: "...choke itself...". 🙂 Just trying to indicate that the port will not behave at high levels as in the simulated low level design simulation.
Google: port noise, bass reflex port velocity, and similar searches.
As to the second question: to my ears the closed box sounds tighter, but a little thinner than a bass-reflex box, and is my preference. But, that's an awfull generalization, isn't it?
There will be a strong port(duct) resonance in your design, usually people disregard it, as it might be out of the passband; but, it might still affect the crossover design. The BR needs a high-pass filter, you might get away without one in the CB (closed box). Look at frequency response (SPL), impulse response, group delay and phase in Hornresp, maybe that explains it. Even the loading to the driving amplifier is different, see: impedance curve.
Just stuff to think about. Your design is fine (could use a little more bracing), you can always fill the port with a foam plug, and see which way you like better.
Regards,
Post #12: "What do you mean by "act more like a closed box"? What would the difference be between a "ported box sound" and a closed box one?"
That's what I get for trying to be descriptive: "...choke itself...". 🙂 Just trying to indicate that the port will not behave at high levels as in the simulated low level design simulation.
Google: port noise, bass reflex port velocity, and similar searches.
As to the second question: to my ears the closed box sounds tighter, but a little thinner than a bass-reflex box, and is my preference. But, that's an awfull generalization, isn't it?
There will be a strong port(duct) resonance in your design, usually people disregard it, as it might be out of the passband; but, it might still affect the crossover design. The BR needs a high-pass filter, you might get away without one in the CB (closed box). Look at frequency response (SPL), impulse response, group delay and phase in Hornresp, maybe that explains it. Even the loading to the driving amplifier is different, see: impedance curve.
Just stuff to think about. Your design is fine (could use a little more bracing), you can always fill the port with a foam plug, and see which way you like better.
Regards,
Attachments
BR = Bass Reflex?
How do I make a high pass filter for the port itself?
And how would you design the port to make it better?
As for the bracing, can I copy the bracing that exists and do the same at two other heights in the box?
Attached is the SketchUp file of the design. Again, wasn't made by me.
Thanks.
How do I make a high pass filter for the port itself?
And how would you design the port to make it better?
As for the bracing, can I copy the bracing that exists and do the same at two other heights in the box?
Attached is the SketchUp file of the design. Again, wasn't made by me.
Thanks.
Why are you not just using a round vent? Much easier to make and technically superior.
As to the vent choking itself at higher volumes: this can wreck drivers, since at resonance (Fb), the driver is braked by the resonance, which in the enclosure itself is in counter phase. This is the dip you see in the FR between the two peaks; the excursion of the driver is limited by this phenomenon, which leads to less back EMF around resonance. Close the vent, the braking effect collapses and the driver may bump the back plate.
As to the vent choking itself at higher volumes: this can wreck drivers, since at resonance (Fb), the driver is braked by the resonance, which in the enclosure itself is in counter phase. This is the dip you see in the FR between the two peaks; the excursion of the driver is limited by this phenomenon, which leads to less back EMF around resonance. Close the vent, the braking effect collapses and the driver may bump the back plate.
The initial design was based on a round vent, but I checked 4 hardware stores and couldn't find any PVC pipes that are the right diamater (10cm), so it was decided that I'll let the carpenter make the vent too.
Yonathan,
1) Yes.
2) The 90 degree bend does high pass filter the port to some extent. Lining the port with several layers of felt or jute (organic carpet backing material) will knock off more upper frequencies, but the port may have to be made slightly larger diameter to have the same tuning, the addition of damping material in the port will reduce the port diameter slightly, lowering the tuning.
3) "Better" is subjective. A larger cabinet with a larger port would have more SPL (sound pressure level) at a lower power level with less distortion and port chuffing (vent noise caused by too high air velocity.
4) Yes.
It is not possible to have too much bracing, unless the bracing reduces the box volume too much.
Art
What about improving the lower bass extension? How low will this design go, based on simulations?
Hi YonathanZ,
Post #13: "...The BR needs a high-pass filter, you might get away without one in the CB (closed box)...."
Post #15: "...How do I make a high pass filter for the port itself?..."
As Art said in Post #15 bends will high pass filter an acoustic duct element. I have not found, that a single 90° degree bend influences the vent output much. For an expample look at the picture in Post #5: in the internal side view of the OD-MLTL that TheJessman build I designed in a number of bends between the driver and the terminus (port output).
But, as my quote from Post #13 indicates, I was talking about an electronic HP Filter in front of the driving amplifier, e.g. for your sub: 20Hz HP4 (4th order highpass).
My rule of thumb for bracing is: no unsupported span of more than 8"-10"[20-25cm]. You can use side to side round or square dowels at random position, or more braces with holes cut into them.
See Post #11 for low end extension (the closed box line is very faint on my computer).
Regards,
Post #13: "...The BR needs a high-pass filter, you might get away without one in the CB (closed box)...."
Post #15: "...How do I make a high pass filter for the port itself?..."
As Art said in Post #15 bends will high pass filter an acoustic duct element. I have not found, that a single 90° degree bend influences the vent output much. For an expample look at the picture in Post #5: in the internal side view of the OD-MLTL that TheJessman build I designed in a number of bends between the driver and the terminus (port output).
But, as my quote from Post #13 indicates, I was talking about an electronic HP Filter in front of the driving amplifier, e.g. for your sub: 20Hz HP4 (4th order highpass).
My rule of thumb for bracing is: no unsupported span of more than 8"-10"[20-25cm]. You can use side to side round or square dowels at random position, or more braces with holes cut into them.
See Post #11 for low end extension (the closed box line is very faint on my computer).
Regards,
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