ok so im way, way more confused than before.
the new 40hz tuned 20 litre enclosure that looks great in the new winisd (with the "transmision line port model" enabled)
looks terrible in the old winisd (a big knee at 40 hz)
it also looks bad in hornresp ( although im not sure ive input all the data correctly, i just downloaded it)
-it kinda matches the old winisd, but including the resonance peak that the new winisd shows.
without that "transmission line" option enabled, i get the big "knee" in the new winisd too.
so.. which is right?
the new 40hz tuned 20 litre enclosure that looks great in the new winisd (with the "transmision line port model" enabled)
looks terrible in the old winisd (a big knee at 40 hz)
it also looks bad in hornresp ( although im not sure ive input all the data correctly, i just downloaded it)
-it kinda matches the old winisd, but including the resonance peak that the new winisd shows.
without that "transmission line" option enabled, i get the big "knee" in the new winisd too.
so.. which is right?
attached are example graphs.. hornresp (may be missing some needed parameters, i threw what i had in there)
old winisd and new winisd with two graphs, red is with the new transmission line option enabled, blue without.
odd one out is definitely the red line here. i based the design on that result, but it seems there is a problem somewhere.
old winisd and new winisd with two graphs, red is with the new transmission line option enabled, blue without.
odd one out is definitely the red line here. i based the design on that result, but it seems there is a problem somewhere.
Attachments
driver is this one:
Dayton Audio RSS210HO-4 8" Reference HO Subwoofer 4 Ohm
ive done about a dozen design iterations based on the results from the old winisd, new one is telling me something completely different works.
its a slot ported enclosure with 3 ports, each 2cm x9cm (9cm is fixed, 2 can be varied a bit)
Dayton Audio RSS210HO-4 8" Reference HO Subwoofer 4 Ohm
ive done about a dozen design iterations based on the results from the old winisd, new one is telling me something completely different works.
its a slot ported enclosure with 3 ports, each 2cm x9cm (9cm is fixed, 2 can be varied a bit)
OK, i simmed it like this -
300W input
Net Int Vol = 20L
fb = 35Hz
1 rectangular Port H = 40mm x D = 100mm X L = 436mm
Edit - Forgot to list - 24 db LR HPF @ 40Hz
Seems to better ALL round like that
Why did you sim it with 3 ports ? It seems fine with one
300W input
Net Int Vol = 20L
fb = 35Hz
1 rectangular Port H = 40mm x D = 100mm X L = 436mm
Edit - Forgot to list - 24 db LR HPF @ 40Hz
Seems to better ALL round like that
Why did you sim it with 3 ports ? It seems fine with one
Attachments
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Well i had 3 ports because the original design was a slot as tall as the box. Adding a reasonable amount of bracing divided it in 3. A single port of a different height will require a redesign. Fine of course if necessary. However, we seem to be ignoring the issue of massive changes to LF response between old winisd, new winisd and hornresp...? Ive read what i can online, and several commenters have suggested that winisd "transmission line" model is not to be trusted.
hm, your sim does not exhibit such massive changes like mine does. could it be an issue with multiple ports in this new vent model?
i also wonder why you consider your result to be so much better than my efforts. (im a bit of a noob so im not 100% at reading the results yet.)
As far as i can see, you have a different highpass filter, which is chopping off quite a lot of low end extension, but provides reduced cone excursion, group delay and vent speed, allowing higher power handling.
attached are a couple of graphs.
one shows your 30hz tuned proposal (blue) vs my last one (red) , both with transmission line enabled.
yours is running 300w, mine 250.
mine seems better.. to me..? you gain half a db above 50 hz, but mine goes significantly lower.
having said that, the spl graph isnt noticeably higher output and your putting an extra 50watts in.
the second graph shows both solutions with "transmission line" disabled.
in this case, agree, mine looks awful.
question is, why the difference?
i also wonder why you consider your result to be so much better than my efforts. (im a bit of a noob so im not 100% at reading the results yet.)
As far as i can see, you have a different highpass filter, which is chopping off quite a lot of low end extension, but provides reduced cone excursion, group delay and vent speed, allowing higher power handling.
attached are a couple of graphs.
one shows your 30hz tuned proposal (blue) vs my last one (red) , both with transmission line enabled.
yours is running 300w, mine 250.
mine seems better.. to me..? you gain half a db above 50 hz, but mine goes significantly lower.
having said that, the spl graph isnt noticeably higher output and your putting an extra 50watts in.
the second graph shows both solutions with "transmission line" disabled.
in this case, agree, mine looks awful.
question is, why the difference?
Attachments
quote from DIYSPEAKERGUY on the AVS forum ( seems like a knowledgeable guy)
"WinISD is the wrong tool to use if the resonances are anywhere near the passband. The "use transmission line model for port simulation" is laughably inaccurate. There are plenty of very good free tools, please don't use WinISD for this.
As I mentioned before, there's nothing wrong with having low frequency resonances even if they are right inside the passband. They can even be helpful. This is how horns work, a series of resonances spaced apart to prop up the entire bandwidth for up to 3 octaves."
"WinISD is the wrong tool to use if the resonances are anywhere near the passband. The "use transmission line model for port simulation" is laughably inaccurate. There are plenty of very good free tools, please don't use WinISD for this.
As I mentioned before, there's nothing wrong with having low frequency resonances even if they are right inside the passband. They can even be helpful. This is how horns work, a series of resonances spaced apart to prop up the entire bandwidth for up to 3 octaves."
ok so i tested on bassbox pro. it is in agreement with old winisd, and hornresp. my earlier designs work better than the one that looks good in new winisd (with transmission line enabled)
it includes port resonances, as does hornresp.
my conclusion is that the new transmission line function of winisd doesnt work properly.
it includes port resonances, as does hornresp.
my conclusion is that the new transmission line function of winisd doesnt work properly.
Why model it as a transmission line to begin with? (not a reasoned criticism, I just don't understand)
The port model won't be accurate anyway though. You're really going to need to test it if you don't want to risk fudging your shot with the CNC, even if your prototype is a crude cuboid approximation with a trimmed pipe port (I mean, a generic off the shelf pipe port trimmed until you get the sound you're looking for) it'll be a lot better than no prototype imo.
vent tuning
These tests may well not apply to your enclosure but they give an indication of the potential discrepancy between simulations and reality with WinISD's port length estimates, which is well documented.
Edit: Well maybe I'm overstating the risk a bit for a couple of Hz of tuning, but given the behaviour of the sub in your unusually shaped room isn't easy to predict there are lots of benefits of being able to tune the tuning, so to speak.
The port model won't be accurate anyway though. You're really going to need to test it if you don't want to risk fudging your shot with the CNC, even if your prototype is a crude cuboid approximation with a trimmed pipe port (I mean, a generic off the shelf pipe port trimmed until you get the sound you're looking for) it'll be a lot better than no prototype imo.
vent tuning
These tests may well not apply to your enclosure but they give an indication of the potential discrepancy between simulations and reality with WinISD's port length estimates, which is well documented.
Edit: Well maybe I'm overstating the risk a bit for a couple of Hz of tuning, but given the behaviour of the sub in your unusually shaped room isn't easy to predict there are lots of benefits of being able to tune the tuning, so to speak.
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thanks for the useful feedback. i was "modelling it as a transmission line" insofar as i enabled the "transmission line vent model" option in winisd 0.7, as advised, due to it including pipe resonance.
ive no idea personally if this is advised or not, all i know it it produces results which do not correlate with other softwares i have tested.
that study you have done wrt. port lengths is very interesting. im tempted to multiply my port length by 0.8 right off the bat. especially since in my construction the box walls provide quite a bit of extension on one side of the vent after each termination.
even if the simulation is spot on, it just means the response is rather flatter with a sharper falloff than before (closer to my first effort) , but not massively different.
ive no idea personally if this is advised or not, all i know it it produces results which do not correlate with other softwares i have tested.
that study you have done wrt. port lengths is very interesting. im tempted to multiply my port length by 0.8 right off the bat. especially since in my construction the box walls provide quite a bit of extension on one side of the vent after each termination.
even if the simulation is spot on, it just means the response is rather flatter with a sharper falloff than before (closer to my first effort) , but not massively different.
ok its now got a shorter port, and its had a bit of a restyle!
This model has an internal volume of 20.3 litres ( with driver subtracted) and a port length of 66 cm, which is circa 0.8x the simmed vent length of 80cm.
the internal wall thickness has increased to 2cm.
With those massive flares on the ends, and the internal surfaces and braces providing probably rather a lot of port extension, anyones guess as to how long the actual ports are!
in theory i could clamp the whole thing together without glue ( it will have guide pins between layers) , listen to it, and then saw off some of the internal wall to shorten the port if necessary. itll probably not look very neat unless i go mental with the sander, but heck, its not gonna be visible.
This model has an internal volume of 20.3 litres ( with driver subtracted) and a port length of 66 cm, which is circa 0.8x the simmed vent length of 80cm.
the internal wall thickness has increased to 2cm.
With those massive flares on the ends, and the internal surfaces and braces providing probably rather a lot of port extension, anyones guess as to how long the actual ports are!
in theory i could clamp the whole thing together without glue ( it will have guide pins between layers) , listen to it, and then saw off some of the internal wall to shorten the port if necessary. itll probably not look very neat unless i go mental with the sander, but heck, its not gonna be visible.
Attachments
Re - Transmission line option
It is NOT for designing TL's, but Only for estimating port harmonics
From the Help File in WinISD Pro
You don't need to guess Use the End Correction info in WinISD, and/or use this this
Flare-it - Free Speaker Design Software
I simmed it with HR with the same details as my 35Hz design, & the Port & Group Delay Harmonics are at very similar locations. I totally agree that HR is better, but WinISD is not the bogey "some" people say it is
It is NOT for designing TL's, but Only for estimating port harmonics
From the Help File in WinISD Pro
You don't need to guess
Use the End Correction info in WinISD, and/or use this this Flare-it - Free Speaker Design Software
I simmed it with HR with the same details as my 35Hz design, & the Port & Group Delay Harmonics are at very similar locations. I totally agree that HR is better, but WinISD is not the bogey "some" people say it is
Attachments
Just jumping back to an early suggestion about using the centre cutouts to make some satellite speakers.. Anyone care to suggest a driver/s that could potentially sound better than my mission 780 se's but in a tiny 8 litre sealed box? (i could always do small vents, but to be honest i fancy a break from vents.)
Obviously duty below 90 odd hz would be taken care of by the subs.
EDIT: GONNA START A NEW THREAD IN THE APPROPRIATE FORUM
Obviously duty below 90 odd hz would be taken care of by the subs.
EDIT: GONNA START A NEW THREAD IN THE APPROPRIATE FORUM
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I am a bif fan of fullrange drivers (and the missions are not all that hard to surpass), but not many do 90 Hz sealed. Off the top of my head the Mark Audio Alpair 10.2 (10 litre) and SEAS FA22 (much more) can. I’d have to check my sims to see if there are other candidates.
dave
PS: Post link to your new thread.
dave
PS: Post link to your new thread.
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