Hello everyone, this is my first time designing a ported enclosure so I would like to get some feedback on it.
My space available is 13"x31"x15.5" and will be placed in the trunk of my sedan facing rearward.
Single Sundown Audio SA12 running at approx 1000WattRMS at 2ohm.
Specifications SA‐12D4
RE (ohms) 7.07
FS (Hz) 33.96
Vas (L) 24.63
Qes 0.55
Qms 5.15
Qts 0.49
Le (mH) 4.84
BL (NA) 25.67
Mms (Grams) 237
Cms (uM/N) 92.27
Sens (1w/1m) 84.22
Xmax 19mm one-way by 70% BL
Suggested Ported Enclosure: 1.5-2.0 ft^3 @ 35hz
I modeled this in WinISD. I am attaching the WinISD project here as well as pictures of the design.
From WinISD:
BOX:
Volume: 1.85ft^3
Tuning Freq.: 32Hz
VENT:
14"x2"x35.3"
End Correction: 0.732 (IS THIS CORRECT?)
Actual Design:
BOX:
Volume: 1.85ft^3
Vent: 14"x2"x35.25"
3/4" MDF
Double laminated baffle+dowel supports will be added. Port opening edges will be rounded as will the corners within the vent.
I am looking to get some good low end bass for pop music and some hip hop. Tuned it a little low on other peoples suggestions with the SA12. Mostly looking for SQ but I am not an audiophile and I like heavy bass like the rest 🙂. Thanks for any help.
My space available is 13"x31"x15.5" and will be placed in the trunk of my sedan facing rearward.
Single Sundown Audio SA12 running at approx 1000WattRMS at 2ohm.
Specifications SA‐12D4
RE (ohms) 7.07
FS (Hz) 33.96
Vas (L) 24.63
Qes 0.55
Qms 5.15
Qts 0.49
Le (mH) 4.84
BL (NA) 25.67
Mms (Grams) 237
Cms (uM/N) 92.27
Sens (1w/1m) 84.22
Xmax 19mm one-way by 70% BL
Suggested Ported Enclosure: 1.5-2.0 ft^3 @ 35hz
I modeled this in WinISD. I am attaching the WinISD project here as well as pictures of the design.
From WinISD:
BOX:
Volume: 1.85ft^3
Tuning Freq.: 32Hz
VENT:
14"x2"x35.3"
End Correction: 0.732 (IS THIS CORRECT?)
Actual Design:
BOX:
Volume: 1.85ft^3
Vent: 14"x2"x35.25"
3/4" MDF
Double laminated baffle+dowel supports will be added. Port opening edges will be rounded as will the corners within the vent.
I am looking to get some good low end bass for pop music and some hip hop. Tuned it a little low on other peoples suggestions with the SA12. Mostly looking for SQ but I am not an audiophile and I like heavy bass like the rest 🙂. Thanks for any help.
Attachments
Thanks Etocynned,
I am not quite sure what your pictures are telling me, would you mind explaining it?
Also, I took your suggestion and tried to put the vent along the back wall.
Unfortunately when I do this within my size constraints (same total inside box dimensions) I am only able to get a volume of 1.73ft^3 vs 1.85^3 for the previous version.
WINISD suggests that for 26.75"x8"x14" = 1.73 ft^3
Vent = 2"x14"x38.05"
Do you think that the loss in volume is worth it in order to reduce the number of bends in the vent? It seems the back-and-forth vent is more space saving than the along-the-back counterpart.
I am not quite sure what your pictures are telling me, would you mind explaining it?
Also, I took your suggestion and tried to put the vent along the back wall.
Unfortunately when I do this within my size constraints (same total inside box dimensions) I am only able to get a volume of 1.73ft^3 vs 1.85^3 for the previous version.
WINISD suggests that for 26.75"x8"x14" = 1.73 ft^3
Vent = 2"x14"x38.05"
Do you think that the loss in volume is worth it in order to reduce the number of bends in the vent? It seems the back-and-forth vent is more space saving than the along-the-back counterpart.
Attachments
The left pic is the Hornresp input screen...where you add the data about the driver and enclosure.
The right pic is the frequency response graph after Hornresp calculates.
The vent velocity is low enough that the bends shouldnt be a problem at the stated power, ~25m/s. I just prefer fewer bends, tough the smaller size will raise tuning a bit 2-5 hz.
Im pretty sure this sim is correct. Notice that the freq response graph assume the box is in the corner of a living room. You can add a 12db/octave boost below about 80hz to that when its in a car.
The right pic is the frequency response graph after Hornresp calculates.
The vent velocity is low enough that the bends shouldnt be a problem at the stated power, ~25m/s. I just prefer fewer bends, tough the smaller size will raise tuning a bit 2-5 hz.
Im pretty sure this sim is correct. Notice that the freq response graph assume the box is in the corner of a living room. You can add a 12db/octave boost below about 80hz to that when its in a car.
WinISD doesn't use the proper end correction for a 3 common wall slot port like you are wanting to use. Your port should be quite a bit shorter to get the 32 Hz tuning you desire.
I build a LOT of car audio enclosures so I've developed my own method for determining the proper end correction for slot port enclosures. To tune your 2" x 14" port to 32 Hz, with a net volume of 1.85 cu ft, the port should be 30" long when measured down the center line of the port.
Another thing to think about, you need to account for the space the sub takes up in the box when determining your net volume. In the case of your SA-12 that is .14 cu ft. You should have adequate space to get the 1.85 cu ft net you desire with your port shorted to 30". I agree with Etocynned that you should run the port along the back wall of the enclosure to eliminate all those 180 degree bends if possible.
I build a LOT of car audio enclosures so I've developed my own method for determining the proper end correction for slot port enclosures. To tune your 2" x 14" port to 32 Hz, with a net volume of 1.85 cu ft, the port should be 30" long when measured down the center line of the port.
Another thing to think about, you need to account for the space the sub takes up in the box when determining your net volume. In the case of your SA-12 that is .14 cu ft. You should have adequate space to get the 1.85 cu ft net you desire with your port shorted to 30". I agree with Etocynned that you should run the port along the back wall of the enclosure to eliminate all those 180 degree bends if possible.
Thanks Jessman,
Would you mind explaining the methodology? I believe that the recommended volume specs from the Sundown website include the driver displacement. Doesn't winisd account for this when modeling as well? I assumed this is why winisd had me enter the driver displacement.
I am really confused now, I went to the SA website and looked at their recommendations
They have created a box design of the following:
Volume: 2.0ft^3 (before driver displacement, excluding vent volume)
Vent:
14"x2"x37.75" tuned to 35hz
Slot port along two outer walls of the enclosure.
When I model in winisd 2.0ft^3, 35hz, 14"x2" rectangular port i get a recommended length of 26.3"
This is telling me that the manufactures recommendation is a port LONGER than what winisd is saying. This is the opposite of what you have recommended? Just trying to understand why there are so many conflicting enclosure designs. Is there a software that properly models a slot port?
Would it be better for me to simply use a round port due to the higher accuracy of the model?
Thanks again for your help, really want to get this right the first time.
Would you mind explaining the methodology? I believe that the recommended volume specs from the Sundown website include the driver displacement. Doesn't winisd account for this when modeling as well? I assumed this is why winisd had me enter the driver displacement.
I am really confused now, I went to the SA website and looked at their recommendations
They have created a box design of the following:
Volume: 2.0ft^3 (before driver displacement, excluding vent volume)
Vent:
14"x2"x37.75" tuned to 35hz
Slot port along two outer walls of the enclosure.
When I model in winisd 2.0ft^3, 35hz, 14"x2" rectangular port i get a recommended length of 26.3"
This is telling me that the manufactures recommendation is a port LONGER than what winisd is saying. This is the opposite of what you have recommended? Just trying to understand why there are so many conflicting enclosure designs. Is there a software that properly models a slot port?
Would it be better for me to simply use a round port due to the higher accuracy of the model?
Thanks again for your help, really want to get this right the first time.
Sure, so the the problem with WinISD is that it DOES NOT account for driver displacement, and it only has end correction values for flared and non-flared round ports (k values of .614, .732, & .850). For slot ports you need higher k values, depending on how many walls the port has in common with the rest of the box, as shown here:
I tweak those values slightly based on the dimensions of the port to determine what the tuning would be. This seems to get me as close as anything. Please keep in mind that port tuning is never going to be an exact science, since changes in air temperature and pressure can shift the tuning frequency around 1 or 2 Hz anyway.
The design Sundown has on their website for a single 12" sub has 1.98 cu ft of internal volume, you need to subtract the sub displacement from that though to get net volume and net volume is the number that matters. So in your case your SA-12 displaces .14 cu ft, giving us a net volume of 1.84 cu ft. With a 2" x 14" port 37.75" long it's going to tune that box to right around 30 Hz, quite a bit lower than 35 Hz. I don't know why Sundown designed the box that way, I suspect they didn't put much effort into the design. Another problem with that particular design is the port has a pretty high aspect ratio (the ratio of the height to the width). At 2" x 14" thats a 7:1 aspect ratio, high aspect ratio ports are inefficient due to the large amount of internal surface area. As a general rule I like to keep ports below a 5:1 aspect ratio, and I compensate by adding more port area if its above 5:1.
As far as round ports go, they are easier to calculate the tuning, but often they are difficult to fit in smaller spaces like what you have to work with. Almost all the boxes I build use slot ports for that reason.
I tweak those values slightly based on the dimensions of the port to determine what the tuning would be. This seems to get me as close as anything. Please keep in mind that port tuning is never going to be an exact science, since changes in air temperature and pressure can shift the tuning frequency around 1 or 2 Hz anyway.
The design Sundown has on their website for a single 12" sub has 1.98 cu ft of internal volume, you need to subtract the sub displacement from that though to get net volume and net volume is the number that matters. So in your case your SA-12 displaces .14 cu ft, giving us a net volume of 1.84 cu ft. With a 2" x 14" port 37.75" long it's going to tune that box to right around 30 Hz, quite a bit lower than 35 Hz. I don't know why Sundown designed the box that way, I suspect they didn't put much effort into the design. Another problem with that particular design is the port has a pretty high aspect ratio (the ratio of the height to the width). At 2" x 14" thats a 7:1 aspect ratio, high aspect ratio ports are inefficient due to the large amount of internal surface area. As a general rule I like to keep ports below a 5:1 aspect ratio, and I compensate by adding more port area if its above 5:1.
As far as round ports go, they are easier to calculate the tuning, but often they are difficult to fit in smaller spaces like what you have to work with. Almost all the boxes I build use slot ports for that reason.
Based on the space you have available, here is what I would do:
Net volume = 1.85
Tuning = 32 Hz
Port = 2.125" x 13.875" x 33"
External dimensions = 15.375" x 13" x 31"
Net volume = 1.85
Tuning = 32 Hz
Port = 2.125" x 13.875" x 33"
External dimensions = 15.375" x 13" x 31"
Wow thank you for the thorough explanation and the suggested box. I was really trying to do a double baffle on the front (due to the added strength but mostly for the aesthetics), but I am willing to give that up for a solid functional design. I would do some tweaking here and there to get a double baffle to fit in my space but I don't know exactly how to recalculate the port length needed etc when I shift things around.
I recreated essentially what you have shown me above, I would just like to verify the design I have, could you look this over for me?
Net Box volume:
(8.625"x26.625"x13.875")+(2.875"x6.5"x13.875")-(241.92in^3(driver displacement))=3,203.6in^3 or 1.85ft^3
Vent:
2.125"x13.875"x33.125"
What do you think about bracing inside the box? I was planning on using a 1" dowel rod placed just to the right of the speaker opening running from the front panel to the vent wall and then from the vent wall to the back panel. Would that be enough bracing? And do you think I need to account for this bracing in the net volume, or is it negligible?
I recreated essentially what you have shown me above, I would just like to verify the design I have, could you look this over for me?
Net Box volume:
(8.625"x26.625"x13.875")+(2.875"x6.5"x13.875")-(241.92in^3(driver displacement))=3,203.6in^3 or 1.85ft^3
Vent:
2.125"x13.875"x33.125"
What do you think about bracing inside the box? I was planning on using a 1" dowel rod placed just to the right of the speaker opening running from the front panel to the vent wall and then from the vent wall to the back panel. Would that be enough bracing? And do you think I need to account for this bracing in the net volume, or is it negligible?
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The way you recreated the box I suggest looks correct to me.
As far as a double baffle goes, I usually like to use a double baffle, for strength and looks, but it is kind of a luxury and in your case I don't think you can afford the space it requires.
For bracing your idea of using a 1" dowel between the front panel, port panel, and back is a good idea. I generally like to brace any panel than has a 12" or greater unbraced span. Your dowel would pretty much take care of that. FYI, the best way to use dowels for bracing is to drill a hole the diameter of the dowel through all the panels (this is easiest if you do it before gluing the panels together, just stack them up and drill). You then spread some glue in the holes and on the dowel and drive it in with a mallet. You can trim the dowel flush with the outside of the box after the glue dries. If you just try to glue the end of the dowel to the panels without drilling a hole the glue joint will almost always fail due to the small amount of contact area.
If you are interested in more bracing info I put a post up on the SMD forum a while back, my name there is Triticum Agricolam. Here is the post: Implementing Bracing - Subwoofers / Enclosures - SMD Forum
Awesome read. I decided to throw in some extra bracing. Do you think this is overkill? Im not worried about overkill unless the use of the brace will negatively affect performance (due to the volume taken up inside).
Total length of bracing inside speaker volume: ~35" ~7in^3 volume
Total length of bracing in vent: ~4" ~0.8in^3 volume
Total length of bracing inside speaker volume: ~35" ~7in^3 volume
Total length of bracing in vent: ~4" ~0.8in^3 volume
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The internal volume all those braces take up is pretty insignificant, so if you want to go to the effort of including them, they aren't going to hurt anything. With that being said, I think both the braces you have between the front, port, and back panels are good, but the others probably aren't going to provide much benefit since those panels aren't very large.
Just wanted to provide an update.
Got the box all built and test fitted. Still needs some final work (rounding out the port opening, sanding) but fully functional. Sounds good so far, not tuned at all. Still need to learn how to tune the system.
Got the box all built and test fitted. Still needs some final work (rounding out the port opening, sanding) but fully functional. Sounds good so far, not tuned at all. Still need to learn how to tune the system.
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