I was asked to build a sealed enclosure for another local DIYMA member. This member thought his current sealed enclosure itself was why he didn't like the sound of his subbass. So, I was going to build a nice sealed enclosure.
After modeling his sub in WinISD, I really didn't like the results. I wanted to know if someone had more sophisticated software that can model a slot ported sub. This is being used for sq purposes.
I got these parameters from WT3 and it is a 12" sub:
ohms - 1.51 (single 2 ohm voice coil)
Fs - 38.36
Qts - .403
Qes - .43
Qms - 6.329
Le - .649
Sd - 481cm^2
Vas - 28.3 L
Now, this is a single 2ohm Fi Q12 and looking at their site, they are currently only selling dual voice coil Q12 subs now. The ported shows 1.8-2.5 at 28-33Hz. I would like to do a ported or bandpass based on which works best and if I do slot ported, what the port width and length would be.
Guessed at 500wrms and 1.5cf tuned to 30.67Hz gave a nice flat response, going up to 2.5cf gave little gain in extension, so for the smaller footprint I'd stick with 1.5cf.
Box dimensions:
14"H x20"W x 10.51" depth
Vent: 12.5"H x1"W x 22.7"L
Give me some constraints for the BP and i'll model some too
Its my sub so I'll chime in a bit with some more info for you.
First of all thank you Jerry for doing all this work for me. Second, I have a PPI P1000.1 so up to 750watts RMS available at 2ohm. The original sealed box was 1.1cuft after sub displacement
PPI Art A600.2, A404.2 & PPI P1000.1, FI X12, Alpine CDA-9887 Dyn Audio Esotar2 650, Dyn Audio Esotec MD130, Arc Audio PS8, JL Audio C5 4"
Akabak model of 1.5 ft^3 tuned to 30Hz. Although if doing a slot port using 3 walls of the enclosure, I would do a 12x1.75in port (or equivalent area), 21" long to tune to 30Hz.
Out of curiosity why do people suggest such high aspect ratios on slot ports? I was under the impression that high aspect ratios produce an aperiodic venting rather than a true helmholtz tuning. Does Akabak take the aspect ratio into account? I assume winisd doesn't.
Out of curiosity why do people suggest such high aspect ratios on slot ports? I was under the impression that high aspect ratios produce an aperiodic venting rather than a true helmholtz tuning. Does Akabak take the aspect ratio into account? I assume winisd doesn't.
I'm sure Akabak can, but I always tend to keep the aspect ratios "decent" so as to not have to worry about those kinds of problems with tuning. In the actual program itself, I specify a 'duct' and it's area, as opposed to HxW of the duct.
Out of curiosity why do people suggest such high aspect ratios on slot ports? I was under the impression that high aspect ratios produce an aperiodic venting rather than a true helmholtz tuning. Does Akabak take the aspect ratio into account? I assume winisd doesn't.
Easier construction, if the slot is the full height of the box you can use it as an internal brace.
I've never used abak, but have heard it can model things like this.
1" width is the lowest I would go, never had a problem with it before.
I'd probably imagine that with higer SPL desires - this is a total acoustic assumption - 1" might become a bit too aperiodic in certain boxes?
It's totally possible to consruct a port that still acts as part of a brace but doesn't use the whole box width. Now we're getting advanced, and like you said, less easy. Slightly more construction materials and time.
Right, Jerry's contacted me with a bit more info with regards to the volume constraints of the enclosure-Height limited to 16" and width to 33" and 3" rake on the angled face of the box
So I've come with the "box" below 1.726cf before displacements. If you're 100% happy the gross width and height of 33" and 16" can be used and still get the box in situ I'll re-model with that.
Unfortunatley I'm having a lot of trouble tuning to the 30Hz mark with this volume of enclosure:
The original design I suggested would produce a lot of port noise with 750wrms.
To combat this I need to give the port more area
To give the port more area I need to lose box volume
Problem is that at a point your increased port volume has such an effect on tuning you cannot get any lower and increasing the port length then starts to tune the box higher!
With the following enclosure dimensions best results I can get is with a 6" port, tuned to 30Hz with a length of 49.69"! Or two 3" ID ports each 24.28" long.
The sub may be a candidate for a TL/Horn enclosure, but my skills there are somewhat limited-I'll have a play none the less
I'd probably imagine that with higer SPL desires - this is a total acoustic assumption - 1" might become a bit too aperiodic in certain boxes?
It's totally possible to consruct a port that still acts as part of a brace but doesn't use the whole box width. Now we're getting advanced, and like you said, less easy. Slightly more construction materials and time.
Yes, you'd be right there, it's a fine balancing act-made much harder by todays "small enclosure" subs!
Thanks for all the help! So, the port would need to be in the side of the box? Or should I put it in the front (where the sub would be) and use a 90 degree elbow? Any one better over the other?
If there's room so the ports and sub can be seen through the ski hatch then put the ports on the front by the sub. If there's no room I'd port up though the shelf.
If the sub wasn't going in a sealed boot then the positioning of the ports would make little difference, if the trunk is sealed then firing the ports into it with the box masking the ski hatch wouldn't make much sense.
Out of curiosity, have you included any allowance for internal volume to be eaten up by bracing, and the driver itself? I know you've accounted for the port volume, but I see no mention of bracing anywhere.
well, Jerry is a smart guy, im sure if he feels the need to add bracing he will take care of that. the displacement of the sub is only 0.06ft^3, im sure he accounted for that too if it was absolutely necessary.
PPI Art A600.2, A404.2 & PPI P1000.1, FI X12, Alpine CDA-9887 Dyn Audio Esotar2 650, Dyn Audio Esotec MD130, Arc Audio PS8, JL Audio C5 4"
Out of curiosity, have you included any allowance for internal volume to be eaten up by bracing, and the driver itself? I know you've accounted for the port volume, but I see no mention of bracing anywhere.
For the 1st box I haven't factored any in, easy enough to do-just wanted to get us in the ball park. Jerry's likely to have some of the ports external, so the space freed up from that can be allocated to braces.
2nd box uses a slot port, which will have a lot of port and I'd lay it out so as to brace the enclosure.
Quote:
Originally Posted by kizz
well, Jerry is a smart guy, im sure if he feels the need to add bracing he will take care of that. the displacement of the sub is only 0.06ft^3, im sure he accounted for that too if it was absolutely necessary.
Ah, I did ask for the driver displacement, will factor that in now
For the 1st box I haven't factored any in, easy enough to do-just wanted to get us in the ball park. Jerry's likely to have some of the ports external, so the space freed up from that can be allocated to braces.
2nd box uses a slot port, which will have a lot of port and I'd lay it out so as to brace the enclosure.
Ah, I did ask for the driver displacement, will factor that in now
Cool, just trying to openly critique your design to be better is all - not trying to say you're doin' anything wrong.
When I build sub boxes I make sure there's at least one brace touching every side, and if it's a large box/surface then multiple braces are placed on those sides. Here's a pic of a slot ported box (someone else made this, not me) that not only utilizes the slot port as a brace without it being the width of the box, but also has a very nicely braced interior. I thought I'd share.
lol-don't worry, we Birts have thick skins, I'm not gonna ask you outside over the internet
That's a nice box
I've deliberately left some play in the designs, the height is 1" below the requested height, likewise the width is 1" less than requested, this allows Jerry to make sure it will fit-and me to add some height/width if he/his client are happy the requested size will defo fit. That extra 1" on the top would allow 0.75" x 7" x 32" of bracing=168ci
lol-don't worry, we Birts have thick skins, I'm not gonna ask you outside over the internet
That's a nice box
I've deliberately left some play in the designs, the height is 1" below the requested height, likewise the width is 1" less than requested, this allows Jerry to make sure it will fit-and me to add some height/width if he/his client are happy the requested size will defo fit. That extra 1" on the top would allow 0.75" x 7" x 32" of bracing=168ci
Cool, good to hear.
Here's that box finished (with grill cover removed) - it's almost more beautiful on the outside than inside:
I would still think that your latest box design installment might verge on aperiodicity at higher SPL, and seeing as the client has 750W to drive it with...
You may also be able to get away with a slightly smaller box if the vent has a more square or circular shape to it as the wood to construct the vent would be less, thus taking up less internal volume. It's also generally best if the vent is away from the box edge by about the width of the vent though I guess that's what makes your design work in that space.
That is a nice finished article-wish my skills were that high!
The vent is 2" wide, so should be fine, the problem with these new style subs is you end up with more vent volume than box volume unless you tune very high.
The vent should be positionable in the face of the box close to the driver so it can vent through the ski hatch too.
With regard to the vent distance from the edge of the box: the one in your pic fails this, as do most sub boxes I have seen/used. For high frequency/Full range enclosures this is something I would consider more important, due to edge diffraction-however with bass frequencies the soundwaves are so long that the edge/location of the port is not as relevant. IMO the "worst" and edge based port could do would be to slightly extend the port length, giving a slightly lower tune-not a bad thing in most cases and a slight bonus in this case if it were to be used.
For this install I'd suggest Jerry measure the opening from the ski hatch and I'll re-design the port to suit the space available.
Here's that box finished (with grill cover removed) - it's almost more beautiful on the outside than inside:
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Hold up, Stop the press....Jerry, I want that box!!! lol beautiful work, what sub is that? And sorry for being a subwoofer novice, but could you please explain to me what you are talking about when you mention aperiodic responses with higher SPL? I figure you are talking about an aperiodic vent but why would it act like that?
PPI Art A600.2, A404.2 & PPI P1000.1, FI X12, Alpine CDA-9887 Dyn Audio Esotar2 650, Dyn Audio Esotec MD130, Arc Audio PS8, JL Audio C5 4"
Hold up, Stop the press....Jerry, I want that box!!! lol beautiful work, what sub is that? And sorry for being a subwoofer novice, but could you please explain to me what you are talking about when you mention aperiodic responses with higher SPL? I figure you are talking about an aperiodic vent but why would it act like that?
At higher SPL the turbulance in the port can effectively make the enclosure act like one with an AP vent as opposed to a port-however I've not had any problems with subs on that power and ports of that size.
If stochastic can link me up to any info I'll happily look into it
Quote:
Originally Posted by Niebur3
^^I want one too....gorgeous box!
lol, join the queue!
Have you had chance to measure the ski hatch hole to see whether I need to re-jig the port dimensions to get it alongside the subwoofer?
Help Designing a slot ported box!
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