I've finally finished my project to realize that when I put the volume louder, there's alot of port noise. I then realized that I made a very weird mistake calculating port size and that the ports I have used are way too small. I have a 69L enclosure with two ports for this driver. I recalculated the port sizes to have 2 three inch ports of about 12 inches long. I only want to make sure that this will actually work since I don't want to cut a hole in my box to then realize that I made a mistake...again... Enclosure has 13 inches of depth inside. Will the new ports work? Or is there not enough space between the end of the port and the rear wall? Help!!
In theory you want a 3r spacing to any boundary, so with a 3" dia. vent you ideally need at least 4.5" to any boundary to ensure it doesn't affect tuning.
Note that vents can extend out of the box somewhat, so while it doesn't look good it's a viable solution to your problem.
GM
Could you answer the above questions?
You may want to opt for an elbow and then extend the existing port.
port clearance
The poster above is correct. The idea is not to get "too close" to a boundary. When you do, the air mass in the port is sort of coupled to the air mass around the boundary, effectively increasing the length by a small percentage. In your case, if the port is flared, with 1" space between the flare opening and the wall, you probably have the bare minimum for the port to work fine, without air flow restriction. Sure more clearance would be better, but you don't have too many options.
I would install the port to its full length. Then listen at top volume for noise issues. You can always shorten the port by up to 1". Because you are near the boundary, the port is effectively longer than it would be if it terminated in free space, e.g. not near the rear wall. Make sure to shorten in small increments, because it will affect both the length of the port and the amount of the boundary effect.
In the worst case scenario, you might have to shorten the port by a couple of inches and this will increase the tuning, how much depends on the total port length to start with, e.g. the percent change. You can do some rough calculations on this first to see if it would be acceptable WRT frequency response.
There are ports tube "systems" out there that include 90 degree bends, so you could also think about using one of them if there is room inside to accommodate the bend and this would solve the problem.
Just don't make anything permanent until it has been tested and you should be able to remedy your situation one way or another.
-Charlie
The poster above is correct. The idea is not to get "too close" to a boundary. When you do, the air mass in the port is sort of coupled to the air mass around the boundary, effectively increasing the length by a small percentage. In your case, if the port is flared, with 1" space between the flare opening and the wall, you probably have the bare minimum for the port to work fine, without air flow restriction. Sure more clearance would be better, but you don't have too many options.
I would install the port to its full length. Then listen at top volume for noise issues. You can always shorten the port by up to 1". Because you are near the boundary, the port is effectively longer than it would be if it terminated in free space, e.g. not near the rear wall. Make sure to shorten in small increments, because it will affect both the length of the port and the amount of the boundary effect.
In the worst case scenario, you might have to shorten the port by a couple of inches and this will increase the tuning, how much depends on the total port length to start with, e.g. the percent change. You can do some rough calculations on this first to see if it would be acceptable WRT frequency response.
There are ports tube "systems" out there that include 90 degree bends, so you could also think about using one of them if there is room inside to accommodate the bend and this would solve the problem.
Just don't make anything permanent until it has been tested and you should be able to remedy your situation one way or another.
-Charlie
The OP stated there is 13" between the inside walls. If he is using 3/4" material, that would give 1.75" of clearance for the port end.
I ran some sims with the driver specs and it wouldn't hurt anything if the port length had a small virtual increase from boundary coupling. With 1.75" of space, I don't think it would be much though.
Don't forget, longer ports (lower tuning) = less vent velocity as well.
Fb = ~33Hz with 12" long ports.
Fb = ~30Hz with 15" long ports.
IMO you should be OK just putting in the two 3" x 12" ports.
I ran some sims with the driver specs and it wouldn't hurt anything if the port length had a small virtual increase from boundary coupling. With 1.75" of space, I don't think it would be much though.
Don't forget, longer ports (lower tuning) = less vent velocity as well.
Fb = ~33Hz with 12" long ports.
Fb = ~30Hz with 15" long ports.
IMO you should be OK just putting in the two 3" x 12" ports.
the existing ports (which are way too small...) are flared and 1.75'' at the inside end and 5'' long. I havn't closed anything permanently on my enclosure so I could still work on it. I like the bended port solution but can any bended port work if they are the right size and lenght or is there something special about what port I am supposed to use? I will check for the 3''x12'' ports to see how well that would fit.
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Have a look at these Port tubes, I think they might work out well for you.
btw - Solen, besides being in Canada, is reliable and easy to work with.
btw - Solen, besides being in Canada, is reliable and easy to work with.
cokewithlime, I wanted to buy exactly rthe same ports you have shown. I live 25mins from that company on the north shore of montreal. And also... I've talked about this with my dad (I'm only 17) and when I came back from work today.. he made some sort of port for me and had already drilled holes...... I was very mad but it ended up looking pretty good. I havn't tried them yet since he stopped drilling the 2nd hole from me being mad. I'll post a pic of what these ports look like.
it's 3'' x 10'' or 11'' and will hopefully work.. Can a port like this be ok? It's not lke I can change much because the holes are drilled, but what do you guys think?
Edit: as GM said earlier on this post, the port is 4.5'' from any wall or anything, so I'm pretty happy about that too.
Edit: as GM said earlier on this post, the port is 4.5'' from any wall or anything, so I'm pretty happy about that too.
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NOOOO!!!!! I put everything back into place.. There's still a lot of port noise.... this has me thinking that it maybe isn't the ports? I finally put the volume to the maximum and I can also see that the big 'BOOM's in the music actually feels like if the sub was just moving in free air, or that it can actually not take it which is not the case. This is just a big disaster... 
help anyone? What have I done wrong? Maybe it's the inside bracing that messes everything up? Most likely not but still.
help anyone? What have I done wrong? Maybe it's the inside bracing that messes everything up? Most likely not but still.Besides checking that everything is sealed especially around the driver, handles and plate amp you should have a back enclosure for the plate amp which will prevent air from exiting through the amp faceplate holes.
Have you put your ears right to the port to determine if it is actually port noise - like a chuffing sound - if is not a chuffing sound then there is some other cause of the noise.
For instance - the driver is exceeding it's xmaxx and bottoming out or your enclosure is resonating - or even perhaps something else in the room is resonating and you think the sound is coming from your enclosure
Just some thoughts to check,
Have you put your ears right to the port to determine if it is actually port noise - like a chuffing sound - if is not a chuffing sound then there is some other cause of the noise.
For instance - the driver is exceeding it's xmaxx and bottoming out or your enclosure is resonating - or even perhaps something else in the room is resonating and you think the sound is coming from your enclosure
Just some thoughts to check,
I did put my ear right to the ports and there is that chuffing sound. that very loud sound that's really annoying. As for the sub reaching it's Xmax (when I put it louder I think that'S what's happening), how can I remedy that? it's not like I was giving it huge power, my amp is 100W. I just don't get what went wrong!!!
Sorry but small ports do not work.
I have written it many times but it is still very popular to use a small port. A port must be at least half the area of the driver cone area to work. What will happen is you will have a lot of port noise and when real power starts to be radiated by the port the port resonator system will go into power compression and will play no louder than a fixed level. With your tuning and frequency I think power compression will set somewhere around 87-88dBa.
The best thing for you to do is to cover the port completely and listen to a sealed box.
NOOOO!!!!! I put everything back into place.. There's still a lot of port noise.... this has me thinking that it maybe isn't the ports? I finally put the volume to the maximum and I can also see that the big 'BOOM's in the music actually feels like if the sub was just moving in free air, or that it can actually not take it which is not the case. This is just a big disaster...
I have written it many times but it is still very popular to use a small port. A port must be at least half the area of the driver cone area to work. What will happen is you will have a lot of port noise and when real power starts to be radiated by the port the port resonator system will go into power compression and will play no louder than a fixed level. With your tuning and frequency I think power compression will set somewhere around 87-88dBa.
The best thing for you to do is to cover the port completely and listen to a sealed box.
I think he should stick a sock in it. Not really jammed in there, just enough to control the chuff. Works like a charm. That's why they gave it a name: Aperiodic loading.
You'll get used to a little less bass pretty quickly. If not, EQ it in.
Cheers.
big "BOOMs" = big noise
Is there a chance that you have tuned your box too high? If you are playing that dropping bass tone music, and if there is a lot of energy in the frequency range below tuning, you will have an "unloaded cone", meaning little to no SPL output but huge cone and possibly port air motion. In that case, any "noises" from the driver or the port are no longer masked by the sounds, so you hear them.
How sure are you of your design and execution of this particular speaker? Did you measure the impedance after you built it to make sure it is tuned correctly? Before building did you measure the speaker's Thiele Small parameters to make sure they are in the neighborhood of what the manufacturer listed?
If you design is way off, the response could also be.
-Charlie
Is there a chance that you have tuned your box too high? If you are playing that dropping bass tone music, and if there is a lot of energy in the frequency range below tuning, you will have an "unloaded cone", meaning little to no SPL output but huge cone and possibly port air motion. In that case, any "noises" from the driver or the port are no longer masked by the sounds, so you hear them.
How sure are you of your design and execution of this particular speaker? Did you measure the impedance after you built it to make sure it is tuned correctly? Before building did you measure the speaker's Thiele Small parameters to make sure they are in the neighborhood of what the manufacturer listed?
If you design is way off, the response could also be.
-Charlie
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