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Hi everyone!
I have been playing around with Unibox and have a few questions about some port length trade-offs. First, I have actually heard this driver in the 3" port configuration, and there was not any problems with the port configuration, i.e. no port chuffing or obvious midrange SPL peak. That being said, I was looking at a lot of the general recommendations for port diameter for 10" drivers and it seems that people basically recommend the larger the better, so I decided to do some simulations with a 4" port. I will be using dual-flared ports.
Most of my simulations are at half-x_max, x_max, and x_sus, although the last simulations are really not a guiding factor in the decisions. While I understand that a lot of these comparisons should be made with a crossover slope and frequency in mind, perhaps we can leave that out of the discussion for now (if possible).
First, the resulting air speed graphs look very reasonable, so I will not post them. At x_max, the port speed is just about tangent with the 5%, .05 vent mach line with the 3" port, but this occurs under 20Hz, so I'm not so concerned. Also, the 4" port is just about tangent to .05 vent mach at x_sus. The 4" port looks even better at x_max. However, the 3" port at x_sus crosses the .05 vent mach line at 24 Hz-ish and peaks way over the .08 vent mach line at 15 Hz or so. Again, this is so far down in the noise, and plus at levels that could damage the drivers, so I'm not concerned. Does this analysis look good to you as well?
[ note: the first attachment is for the 3" port, and the other two are for the 4" port ]
So, looking at at the midrange SPL leakage in the first attached graphs, we see a a mild peak of 70 dB at 729 Hz due to port resonance and a fairly flat SPLtotal. To me, this looks great and the 3" port seems to be a good choice, with very few tradeoffs. The above doesn't change (according to Unibox) at x_sus for the 3" port.
Now, the 4" port has different results, quite possibly for the worse, which is surprising. There are two large resonance peeks at 412 Hz and 820 Hz at around 80dB and 70dB respectively. These measurements are taken at x_max (see the second graph). Also, there is some disturbance in the SPLtotal graph, as you can see. Even if we look at half-x_max (the third graph), we see the the twin resonances and the disturbance starting to form.
I guess my question is, it seems that the 3" port measures better... I find it curious that I cannot see an advantage with the 4" port, other than the air speed graphs, which seem to be so low in the frequency range (at at such high excursion levels) as they will have little effect.
Also, before someone suggests a rear or down firing port, I'd rather keep it on the front baffle to keep everything in phase and have the ability to run my speakers closer to the rear wall, if setup dictates.
Thanks for your help!
I have been playing around with Unibox and have a few questions about some port length trade-offs. First, I have actually heard this driver in the 3" port configuration, and there was not any problems with the port configuration, i.e. no port chuffing or obvious midrange SPL peak. That being said, I was looking at a lot of the general recommendations for port diameter for 10" drivers and it seems that people basically recommend the larger the better, so I decided to do some simulations with a 4" port. I will be using dual-flared ports.
Most of my simulations are at half-x_max, x_max, and x_sus, although the last simulations are really not a guiding factor in the decisions. While I understand that a lot of these comparisons should be made with a crossover slope and frequency in mind, perhaps we can leave that out of the discussion for now (if possible).
First, the resulting air speed graphs look very reasonable, so I will not post them. At x_max, the port speed is just about tangent with the 5%, .05 vent mach line with the 3" port, but this occurs under 20Hz, so I'm not so concerned. Also, the 4" port is just about tangent to .05 vent mach at x_sus. The 4" port looks even better at x_max. However, the 3" port at x_sus crosses the .05 vent mach line at 24 Hz-ish and peaks way over the .08 vent mach line at 15 Hz or so. Again, this is so far down in the noise, and plus at levels that could damage the drivers, so I'm not concerned. Does this analysis look good to you as well?
[ note: the first attachment is for the 3" port, and the other two are for the 4" port ]
So, looking at at the midrange SPL leakage in the first attached graphs, we see a a mild peak of 70 dB at 729 Hz due to port resonance and a fairly flat SPLtotal. To me, this looks great and the 3" port seems to be a good choice, with very few tradeoffs. The above doesn't change (according to Unibox) at x_sus for the 3" port.
Now, the 4" port has different results, quite possibly for the worse, which is surprising. There are two large resonance peeks at 412 Hz and 820 Hz at around 80dB and 70dB respectively. These measurements are taken at x_max (see the second graph). Also, there is some disturbance in the SPLtotal graph, as you can see. Even if we look at half-x_max (the third graph), we see the the twin resonances and the disturbance starting to form.
I guess my question is, it seems that the 3" port measures better... I find it curious that I cannot see an advantage with the 4" port, other than the air speed graphs, which seem to be so low in the frequency range (at at such high excursion levels) as they will have little effect.
Also, before someone suggests a rear or down firing port, I'd rather keep it on the front baffle to keep everything in phase and have the ability to run my speakers closer to the rear wall, if setup dictates.
Thanks for your help!
Attached Files
I've been meaning to make a post with my thoughts, but I maybe suffering a bit of design paralysis 
ops: 
Or, you know, slot port it. Nice thing about a slot port is you can in-between size it far more easily.
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