A recent small subwoofer build necessitated that the ports face out opposite sides of the enclosure. The tuning dictated ports that were too long to fit any other way. I have looked and found nothing about this type of setup. Will this be ok or did I just waste a bunch of time and need to start over with different dimensions? Each chamber will have a 5.25” driver and will port out the side opposite where the chamber is.
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If the ports are tuned relatively low this won't be a problem. Generally if the ports are tuned below 100 Hz, the sound generated becomes non-localisable so it will be difficult to distinct them as a seperate output source (assuming they're large enough not to introduce any chuffing).
If the ports are within 1/4 wavelength distance of the tuning frequency they will even sum their output. So for a 100 Hz tuning frequency they would have to be within (343 / 100 x 0.25) = 0.86 meter distance of each other.
If the ports are within 1/4 wavelength distance of the tuning frequency they will even sum their output. So for a 100 Hz tuning frequency they would have to be within (343 / 100 x 0.25) = 0.86 meter distance of each other.
The dimensions of the box from side to side is 16 inches and the tuning is 52hz so it sounds as if I should be fine. The reason they turned out so long is because I am using 1.5” PVC pipe. The drivers will be 5.25” so I wanted to use a port size big enough to reduce the potential for chuffing. I intend on using a round over bit to router each end as well which should help a bit with chuffing.
I thought the 1.5" port would be about adequate. I would have done a 2" port but that would have been over 16" long which is beyond the longest outer dimension of the box. I know that using PVC elbows is a possibility, but not sure how easy it is to calculate the length with the elbows. I'm sure I could find it somewhere in these forums. But also for 2" PVC with elbows...that would start to take up a lot of space in a small enclosure.
I am going to try these enclosures out, and if they don't really work and there is chuffing then I will make a larger enclosure to accept some 2" ports.
I am going to try these enclosures out, and if they don't really work and there is chuffing then I will make a larger enclosure to accept some 2" ports.
Uh oh. The port velocity in the model is way higher than that. I guess I will just have to finish the construction of the box and see how it actually sounds.
It just seems nearly impossible to build a ported box for this driver where a 2" or greater port would fit. Unless of course part of the port was actually on the outside of the box itself.
It just seems nearly impossible to build a ported box for this driver where a 2" or greater port would fit. Unless of course part of the port was actually on the outside of the box itself.
It's just wood, and you've already made it.
You'll also find - though perhaps you may already be aware - that the larger the box, the shorter the port gets (at the same port cross-sectional area).
I thought about making a bigger box, but when I played around in Win ISD I wasnt getting the results I wanted. I might try playing with that again. I honestly didnt even know WinISD could show port velocity and never knew to keep it to 17 or lower. I just went with the old "make the port about 1/3 the diameter of the driver" and figured 1.5" would be good enough. Live and learn I guess.
I know this won't help with my port chuffing issue, but will it mess things up to tune each chamber to a different frequency in order to get an extended response? For instance, make one of the ports longer thus tuning to a lower Fb for one driver. I would be driving the two woofers from a single signal. Would it make a difference if they were driven parallel vs series?
1) The lower Fb box would have an extended response, but would have less low output than if both were tuned low. Each box tuning would require a separate HP filter to control excursion below Fb.
2) No.
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