ported box volume question

I've built a few sealed boxes but never a ported one.  My question is how exact do the measurements (ft3) have to be to keep the box within the parameters of the software you designed it with.  I would like to make some FG ported pods for some adire extremis in my doors but it seems like it's going to be a huge pain so I was curious.

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

In using your design software, YOU are entering the exact net volume of the enclosure, therefore it is nothing BUT exact.  Designing and building vented boxes are much more fun than pain!  But it IS work.  Did that answer your question or do you have something more specific that I didn't read between the lines?

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

In general, sealed enclosures allow the most margin for error (at least +/- 10%.)  Vented enclosures must be more exact to achieve the modeled results.  Bass reflex (ported) can be about +/- 5% and bandpass must be more exact, like +/- 2%.  The closer you can get to modeled volume the more it will perform like the model.

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Thanks for the quick replies, you both answered my question.  I wanted to make a vented enclosure that would be 21L and tuned to 33Hz.  I started thinking about how much of a pain it is going to be to calculate the volume of the FG pods on the doors and how exact I HAVE to be to get it right.   I don't really need that low end from these because they'd be in a car and I have a sub so I wasn't sure how much the variation would change from the model.  I say its going to be a "pain" because I don't have a whole lot of free time, but I want it to be done right, and I don't feel like paying someone to do something I could.  I'm also impatient.  Thanks again.

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

Post a link to the parameters of that driver and I'll take a look at it in Unibox.  I'm thinking a higher tuning freq would make a lot more sense.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Heres the link.  I also noticed something I was doing wrong on unibox,  the port size was messing me all up. 

https://adireaudio.com/Home/ExtremisMidwoofers.htm

Correct me if I'm wrong here.  I modeled a few different sizes keeping the tuning around 33-35 and they seem like they'd be great for what I want them for.  They were all pretty flat after 70hz from 10-21L and the above tuning.  As far as 21L @ 33hz, I was just going with what the link said even though it was for a large room.  Thanks for your help.

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

Alright just one quick quesiton or 2 about ported boxes when using a program to calculate port length it says desired tuning frequency so Is this is up to you? and i was wondering about what frequency sounds really nice?

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THE DUCE

That driver looks real good tuned to 33 Hz with 21 liters until you start looking at the port diameter vs. the power input.  It needs a 3" diameter to handle 75 watts and up, but it causes a severe port resonance peak at ~300 Hz, which is going to be in it's range.  Reducing the port diameter to 2" eliminates that port resonance but the program warns of port noise at that size.  (Be sure to check the box that says "include effects of port resonance".)

vb_response_adire_extremis_6.8-33hz.gif

A compromise would be to tune the enclosure higher, resulting in a much shorter port length... to around 50 Hz   The crossover would have to be a steep one to cross this over with the sub at 60 - 80 Hz.  Looks a bit touchy.  And in neither scenario will the port actually function for (primary) sound, because the tuning frequency will be crossed into the sub's territory.

vb_response_adire_extremis_6.8-50hz.gif

Then you look at the sealed enclosure graph and it starts to look quite good for your application!  Looks like a nice crossover to the sub using an 18 db/octave slope on the crossover and no worries about ports and port resonance.  And....a much, much smaller enclosure, as I thought the vented boxes didn't look good under 19 liters.

cb_response_adire_extremis_6.8.gif

cb_response_adire_extremis_6.8tenl.gif

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Wow, thanks for the input.  I understand most of what you are talking about, except for the reason that the second ported box would need such  steep xover.  I don't know why you mean.  Thats actually cool that the sealed will work better.  I'd like to play the mids as low as I could within reason to keep the midbass up front and the reason I chose these is because of their ability to go lower than usual, so I don't have to get a 3way setup going.

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

Some of the Adire Extremis gurus might take a look at this too and let you know what they think.  The reason I thought the crossover may have to be steep is because of that peak in the response that has to crossed out with the sub.  I'd have to work with both the mid and sub using a crossover designer to get a better idea of what would happen, but right away it looked like a touchier crossover than it would be with the lower-tuned model.  But if I were to go with modeling alone without having any experience with that driver, I'd choose to go with the sealed.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Yeah, unfortuanately for me I have no one within 200 miles that sells them so I can't hear them.  I thought I'd use the 21L @33hz because if you look at the top of the page I linked earlier it says "our favorite" for that configuration.  Again though, thats for in home environment.  I'm sure sealed will be good.  That 10L sealed I think is what DYohn used when he listened to them.  He said his kicks were .3 ft3 if I'm not mistaken, and he liked them from what I gathered.

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

Look again at the graph for 21L, 33Hz.  You see that nasty port resonance?  At 300 Hz that's within the vital range of that driver, and it's a 10 db jump.  I would avoid that.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Yeah, I'm going to used the sealed for the car it's going to make my life easier.  I'd like to get these for the house though.  I'd also like the 4way for center channel  So many projects, so little time (and money!)

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

Stevdart, I hate to bug after all you've already done but check these out.  They seem to be real close (I think) to the extremis in the 10L sealed enclosure and much cheaper.  Am I right, or did I overlook something like last time?

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James

A little bit of a difference in power handling, doncha think?  This one should go vented or IB, it looks like. Fs / Qes = 66.7 EBP  Same as the Extremis in this category, IIRC, but a huge difference in Fs and not capable of the power handling (isn't the Extremis capable of 100 watts?).  I would use the vented enclosure for efficiency with this one.  Otherwise I didn't do a spec comparison because my bet is that they are not in the same boat except maybe for the XBL^2 technology.  Email Steven Kephart about this.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

thats true, i was modeling them both at 50W because of the 8ohm thing.

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"I'm Rick James bi***, enjoy yo' self Ah Ah Ah"
Dave Chappelle as Rick James