Hi,
To make the question easier to answer, I've created two images, with each having a different area painted light red.
Please tell me which is the right way to calculate the port displacement.
In photo no. 1, the entire port and the wood panels that create it are included in the calculation.
https://s3.postimg.org/5ohgoam1v/image.jpg
In photo no. 2, only the volume of the wood panels is taken into account, and not the space between them.
https://s4.postimg.org/yqkooi3h9/image.jpg
Thanks.
To make the question easier to answer, I've created two images, with each having a different area painted light red.
Please tell me which is the right way to calculate the port displacement.
In photo no. 1, the entire port and the wood panels that create it are included in the calculation.
https://s3.postimg.org/5ohgoam1v/image.jpg
In photo no. 2, only the volume of the wood panels is taken into account, and not the space between them.
https://s4.postimg.org/yqkooi3h9/image.jpg
Thanks.
Hi YonathanZ,
Wood and air have to be subtracted from the internal volume, so Photo No.1. You are trying to determine the net internal volume of the box, so whatever you take away from the internal volume...
Regards,
Wood and air have to be subtracted from the internal volume, so Photo No.1. You are trying to determine the net internal volume of the box, so whatever you take away from the internal volume...
Regards,
So the port takes a whopping 17 litres of volume. Looks like I need to make the box even larger. :\
The volume of the box is 129, but if I deduct 17 for the port, and another 10 for the speaker and bracing, I'm left with just 102 litres. My aim was to have 115 litres of net volume.
Looks like I'll have to start it all over again. :\
just resimulate and pick a new tuning frequency with the smaller box. 10% undersize is not a big deal...
Hi JonathanZ,
It might have helped if you had stayed within your original thread? Maybe, a moderator can join these two threads for you?
Regards,
It might have helped if you had stayed within your original thread? Maybe, a moderator can join these two threads for you?
Regards,
Infinity 1260. Not sure what alignment means in this regard.
102 litres and 21hz. That moves the -3db point from 19.5hz to 20.5hz. I was hoping to have some infrasonic fun with my sub.
The other thread was about bracing, now it appears I need a new design for the box. I'm getting a headache from these calculations. 😛
I mostly just build a box in SketchUp, measure its internal volume and then re-build if I find it too small.
Multiple threads for the same design.
Hi YonathanZ,
IIRC your first thread was from 28th July, 2016:
http://www.diyaudio.com/forums/subwoofers/294814-opinions-design.html
then there is one on bracing from 13th August, 2016:
http://www.diyaudio.com/forums/subwoofers/295449-first-sub-build-not-sure-how-do-bracing.html
and finally this one from August 14, 2016:
http://www.diyaudio.com/forums/subw...-regarding-port-displacement-calculation.html
I think you could get better answers if you kept it all together. Going back to the first thread Post #3, by Planet10: "... just put the woofer into ... sealed." Again, YMMV. 🙂
Regards,
Hi YonathanZ,
IIRC your first thread was from 28th July, 2016:
http://www.diyaudio.com/forums/subwoofers/294814-opinions-design.html
then there is one on bracing from 13th August, 2016:
http://www.diyaudio.com/forums/subwoofers/295449-first-sub-build-not-sure-how-do-bracing.html
and finally this one from August 14, 2016:
http://www.diyaudio.com/forums/subw...-regarding-port-displacement-calculation.html
I think you could get better answers if you kept it all together. Going back to the first thread Post #3, by Planet10: "... just put the woofer into ... sealed." Again, YMMV. 🙂
Regards,
You're right. But apparently all of the builds don't have the net volume I am aiming, so let's stick to this thread only.
So I thought of a different box, one that has more depth than width, because of space constraints.
One option is this (external dimensions):
54 (w) x 64 (d) x 56 cm (h).
The wood thickness my carpenter works with is 1.8cm, so the internal dimensions should be like so; 50.4 x 58.6 x 52.4 cm. There's also a double baffle that's included in the calculation of the internal dimensions.
That results in a gross volume of 154.76 litres.
I deducted as follows for displacement:
speaker: 3.5 litres (though an online calculator yielded a result of 2.45, but better safe than sorry)
plate amp: 5 litres (saw someone mention this number, seems exaggerated to me)
port: 17-20 litres (last build was 17, but this one is bigger so the port might be bigger)
brace: 2-3 litres (another guesstimate)
Overall I reduced 3.5 + 5 + 18.5 + 2 = 29 litres
154.76 - 29 = 125.76 litres of net volume. Nice, right?
I'm attaching the winISD file and 3 screenshots of graphs.
Please let me know what you think. Feel free to play with the WinISD file. 🙂
Thanks.
One option is this (external dimensions):
54 (w) x 64 (d) x 56 cm (h).
The wood thickness my carpenter works with is 1.8cm, so the internal dimensions should be like so; 50.4 x 58.6 x 52.4 cm. There's also a double baffle that's included in the calculation of the internal dimensions.
That results in a gross volume of 154.76 litres.
I deducted as follows for displacement:
speaker: 3.5 litres (though an online calculator yielded a result of 2.45, but better safe than sorry)
plate amp: 5 litres (saw someone mention this number, seems exaggerated to me)
port: 17-20 litres (last build was 17, but this one is bigger so the port might be bigger)
brace: 2-3 litres (another guesstimate)
Overall I reduced 3.5 + 5 + 18.5 + 2 = 29 litres
154.76 - 29 = 125.76 litres of net volume. Nice, right?
I'm attaching the winISD file and 3 screenshots of graphs.
Please let me know what you think. Feel free to play with the WinISD file. 🙂
Thanks.
Attachments
So here's my work-in-progress sketch:
The driver is not in the middle of the front baffle, it's a bit lower. I'm worried it's too close to the port.
If I were to place it in the middle or higher, I'd need to place the brace above its current height, and so the amp plate opening will be higher too, and closer to the top panel.
I'm just not sure how much breathing room the amp needs to stay cool. It's only 300W at max power (which I'll never use), but still.
Your opinions please. 🙂
An externally hosted image should be here but it was not working when we last tested it.
The driver is not in the middle of the front baffle, it's a bit lower. I'm worried it's too close to the port.
If I were to place it in the middle or higher, I'd need to place the brace above its current height, and so the amp plate opening will be higher too, and closer to the top panel.
I'm just not sure how much breathing room the amp needs to stay cool. It's only 300W at max power (which I'll never use), but still.
Your opinions please. 🙂
The driver close to the port is fine.
Relative to your previous question, ""102 litres/21hz"" that's an alignment.😀
OK, thank you.
I still want to move the driver up for aesthetic reasons, is it OK to place the plate amp closer to the top panel? The current sketch has the top of the plate amp cutout 5.3 cm below the top panel.
Another option is to move the brace up without moving the plate amp up, but then the two will be very close.
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