redoing my 3, 12inch subwoofers, this time trying(harder) to get it right 😉
they will handle almost everything below 100hz as my satelittes dies pretty fast below that.
as i want to keep the port speed below 10m/s, i would like to use two 4.33inch ports, which with the chosen tuning would need a port lenghts of 26 inches 😱
would this port lenght give me noise(pipe resonance?) when blending the woofers with the satelittes from 150hz to handeling almost everything from 100hz and below?
Please educate me 🙂
best regards
panduro
they will handle almost everything below 100hz as my satelittes dies pretty fast below that.
as i want to keep the port speed below 10m/s, i would like to use two 4.33inch ports, which with the chosen tuning would need a port lenghts of 26 inches 😱
would this port lenght give me noise(pipe resonance?) when blending the woofers with the satelittes from 150hz to handeling almost everything from 100hz and below?
Please educate me 🙂
best regards
panduro
Flairs will reduce port length as well as allow slightly smaller diameter without chuffing.
I have never had a problem with corners in my ports. Only done a few as I usually do sealed low Q subs.
If you are trying to cross over at 100 to 150, I sure hope your subs are two cabinets used as main speaker stands, or you will have way too much sub localization. 80 Hz at LR4 is about as high as one can get away with. 65 is much better, but above many small bookshelf speakers. It is a bad service that THX set 80 Hz third order as a standard, as it just does not work well enough. 80 at LR6 is almost bearable.
I have never had a problem with corners in my ports. Only done a few as I usually do sealed low Q subs.
If you are trying to cross over at 100 to 150, I sure hope your subs are two cabinets used as main speaker stands, or you will have way too much sub localization. 80 Hz at LR4 is about as high as one can get away with. 65 is much better, but above many small bookshelf speakers. It is a bad service that THX set 80 Hz third order as a standard, as it just does not work well enough. 80 at LR6 is almost bearable.
specs ?
maybe you have tuned too low
with a 4" port ? my length limit would be 12"
I see now you want two 4" ports
one 4" port each woofer should be ok, if not too long
or are all 3 in the same box ?
DrDyna: thanks, it works 😀
AndrewT: please explain how buying a new computer would be cheaper 😛
Tvrgeek: flaring the port will reduce port lenghts? i thought it was the other way around as the flaring "doesnt" count in the tuning.
best regards
panduro
AndrewT: please explain how buying a new computer would be cheaper 😛
Tvrgeek: flaring the port will reduce port lenghts? i thought it was the other way around as the flaring "doesnt" count in the tuning.
best regards
panduro
3 enclosures with one woofer in each enclosure, all placed between the main speakers.
jbl le120h1 no ts published, im told im suppose to model it as a jbl 128h.
jbl 128H fs 20, qts .024, qms 7, qes 0.24, vas 280.4, pe 100, xmax 7.87, re 5.7, le 0.6, sd 0.053, bl 16, mms 90.
jbl recommend 2,5ft3(71L) with a 30hz tuning.
winisd
71L
30hz
one 4.33inch port- 13.8" long- port velocity 16m/s
two 4.33 inch ports- 32" long- port velocity 8m/s
100L
30hz
one 4.33" port- 8.66" long - port velocity 20m/s
two 4.33" ports- 21" long - port velocity 10m/s
i really dont want port chuffing, is 2 x 4.33" ports per 12" woofer overkill? how long can a port be before it damages the sound?
best regards
panduro
jbl le120h1 no ts published, im told im suppose to model it as a jbl 128h.
jbl 128H fs 20, qts .024, qms 7, qes 0.24, vas 280.4, pe 100, xmax 7.87, re 5.7, le 0.6, sd 0.053, bl 16, mms 90.
jbl recommend 2,5ft3(71L) with a 30hz tuning.
winisd
71L
30hz
one 4.33inch port- 13.8" long- port velocity 16m/s
two 4.33 inch ports- 32" long- port velocity 8m/s
100L
30hz
one 4.33" port- 8.66" long - port velocity 20m/s
two 4.33" ports- 21" long - port velocity 10m/s
i really dont want port chuffing, is 2 x 4.33" ports per 12" woofer overkill? how long can a port be before it damages the sound?
best regards
panduro
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A straight pipe with a sharp edge has the effect of causing a restriction at the exit ( of course, both ends are exits. ) The best description of this I read was in a David Vizzards book on tuning A series BMC engines as it relates to velocity stacks. Fluid dynamics does not know if it is a speaker or car. Anyway, play with a sim program and see what the change in port terminus does. WinISD ( there we go again) can do that.
Example, random driver, let WinISD do a box.
same tuning. 2 flange ends, 19.19 inch, one flange end 19.66 inch, 2 flange ends, 20.14 inch.
same tuning. 2 flange ends, 19.19 inch, one flange end 19.66 inch, 2 flange ends, 20.14 inch.
At what velocities does a stable boundary layer form? What the Reynolds Number? Is there tangential follow creating 3rd harmonic distortion....AHHH...
Either I will break through this fluid dynamical wall or my head will explode.
With more complex port geometries the air velocity can exceed 30m/s with out port compression or turbulence noise. But actually working out the math ain't a walk in the park (Damn you Vanderkooy for making it look easy). I'm in the midst of trying to work this stuff out.
This is some of what I did today:
An externally hosted image should be here but it was not working when we last tested it.
More to the point, WinISD is a great tool and the write up on ports in the help menu is excellent.
Search for "Maximizing Performance from Loudspeaker Ports." if you want to start down the rabbit hole.
-Matt
http://www.diyaudio.com/forums/subw...iy-speaker-mini-bass-array-module-teaser.html
Well, I have seen dimpled surfaces on ports so somebody thinks it is an issue. ( or looked cool, you never know) I am no where near prepared to do the math as it has been way too long and my intro to fluids was just enough to tell me it is really hard. Instead, I use the practical engineering approach: Make it obviously big enough, then cut it down until it breaks. Then make one a little bigger.
If you understand the basic science, let the simulators do their thing. I only caution users to be very careful with simulation if they don't know what they are actually simulating. Like elementary school kids using a calculator and not knowing what multiplication actually is. Only after they learn interpolation and logs should they be allowed to use calculators. Learn the math (or science) then use the easy tools.
So, is the protective fluid around your brain a non-Newtonian fluid? This could matter if you are banging your head against a wall. 🙄
If you understand the basic science, let the simulators do their thing. I only caution users to be very careful with simulation if they don't know what they are actually simulating. Like elementary school kids using a calculator and not knowing what multiplication actually is. Only after they learn interpolation and logs should they be allowed to use calculators. Learn the math (or science) then use the easy tools.
So, is the protective fluid around your brain a non-Newtonian fluid? This could matter if you are banging your head against a wall. 🙄
Hi guys ... good place for me to ask. How would I calculate length if I use two different diameter ports (one 4" and one 3") in the same box. I suspect it's just the total Sv that counts, but one never knows. Yes, I have a good reason for doing so.
Thanks, Zene
Thanks, Zene
again thanks for the replies,
Matt: your mini Bassrig looks very nice, thats craftsmanship. is that the complex ports your are talking about?
complex for me would be to try and flange the plastic drainpipe with a heatgun and some kind of mold. just dont know how to make the mold
proberly wont be pretty...
how "big" should i try to make the flange?
now that ive read the info on the winids program, more makes sense, and i get the end correction part 😉
the winisd text states that to avoid pipe resonans one should keep port lenght below 1/10 to 1/20 of the frequency range the speaker is going to produce.
so is that my box tuning of 30 hz or the highest frequency its going to produce?
344m/s 30hz =1150cm 1/20=57,5cm port lenght kept below 57,5cm.
344m/s 150hz= 229cm 1/20=11.45cm porty lenght kept below 11,5cm.
how much sound will exit though the port at higher frequencies than the box tuning?
sorry if this sounds like random rampling, trying to get my head though the port😀
best regards
panduro
Matt: your mini Bassrig looks very nice, thats craftsmanship. is that the complex ports your are talking about?
complex for me would be to try and flange the plastic drainpipe with a heatgun and some kind of mold. just dont know how to make the mold
proberly wont be pretty...how "big" should i try to make the flange?
now that ive read the info on the winids program, more makes sense, and i get the end correction part 😉
the winisd text states that to avoid pipe resonans one should keep port lenght below 1/10 to 1/20 of the frequency range the speaker is going to produce.
so is that my box tuning of 30 hz or the highest frequency its going to produce?
344m/s 30hz =1150cm 1/20=57,5cm port lenght kept below 57,5cm.
344m/s 150hz= 229cm 1/20=11.45cm porty lenght kept below 11,5cm.
how much sound will exit though the port at higher frequencies than the box tuning?
sorry if this sounds like random rampling, trying to get my head though the port😀
best regards
panduro
complex for me would be to try and flange the plastic drainpipe with a heatgun and some kind of mold. just dont know how to make the mold
Best mold ever, you get to drink it before you use it.
Attachments
Properly stated, flared ports reduce the "effective" length of a port slightly as seen by the slight shift upwards in tuning frequency.
You can calculate the 1/4 wavelength resonance of any standard port quite easily. But to see the magnitude of the peak, yes much easier with a program. Do yourself a favor and get that windows emulator or whatever will allow you to run windows based programs. You ask us to educate you. We're doing just that; give a man a fish you feed him for a day----teach a man how to fish you feed him for a lifetime.
You can calculate the 1/4 wavelength resonance of any standard port quite easily. But to see the magnitude of the peak, yes much easier with a program. Do yourself a favor and get that windows emulator or whatever will allow you to run windows based programs. You ask us to educate you. We're doing just that; give a man a fish you feed him for a day----teach a man how to fish you feed him for a lifetime.
Complex ports
Thank you, and yes. I just posted some new pics of the version two port, or at least the 1/4 section I'm working on. Check them out.
For a flare it's best to have one where the curve is a similar radius to the port. If your design will be used at low spl levels a bigger flare would be beneficial but if high SPL is your target then a slightly smaller radius or exponential curve would be best. Flareing on the inside as well as the outside reduces even order harmonic distortion.
-Matt
http://www.diyaudio.com/forums/subw...iy-speaker-mini-bass-array-module-teaser.html
Thank you, and yes. I just posted some new pics of the version two port, or at least the 1/4 section I'm working on. Check them out.
For a flare it's best to have one where the curve is a similar radius to the port. If your design will be used at low spl levels a bigger flare would be beneficial but if high SPL is your target then a slightly smaller radius or exponential curve would be best. Flareing on the inside as well as the outside reduces even order harmonic distortion.
-Matt
http://www.diyaudio.com/forums/subw...iy-speaker-mini-bass-array-module-teaser.html
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